Thursday, December 20, 2012

Field Strength Calculator One

Field Strength Calculator One is a program which will calculate expected received ground wave signal strength at longwave and mediumwave frequencies.

Click image to enlarge.


To download, see the link at the top of the right sidebar under LATEST PROGRAMS. The sidebar at the top right will have the most current link in case the program is updated. The link will change in the case of an update, so I would avoid copying and pasting it into a forum or other web page. Come to the main page of this blog instead.


Being a mediumwave DXer and particularly a daytime mediumwave DXer, I wanted a way to determine a "ballpark" signal strength for various stations not only in my immediate area, but out to 100, 200, or even more miles distant. I was unhappy with virtually all the web-based signal strength calculators found on the internet, as they use the vanilla Inverse-Square-Law to calculate signal attenuation. Fine, if you are in an outer space vacuum or on a perfecting conducting surface, but not even close in accuracy for normal people here on Mother Earth.

The few stand-alone programs out there were either wildly expensive, too complicated to use, inaccessible, or plainly won't work on the Windows platform. I set out to accumulate information, formulas, and data to start writing the field strength calculator program. Investigating the history and ferreting out the pertinent information to arrive at a simplified formula that was reasonably accurate took some time.

The result was and is Field Strength Calculator One. It is based on the work of numerous engineers and mathematicians, who, starting about 1909, spent some 50 years developing the extremely complicated formulas to predict accurate signal strength at mediumwave frequencies. The basic, simplified formula has been known since the 1930s, being slightly modified by various people and agencies since then. It is accurate to within a couple of percent of the big programs that calculate field strength - those using additional input like the transmit and receive array heights above average ground, and the earth's topographic elevation changes along the signal path.

Simplified ground wave electrical field intensity calculations can be made by the introduction of a shadow or diffraction factor in the Sommerfeld-Norton planar earth expression. A mouthful! This simply means that a factor is computed and introduced to account for the additional attenuation caused by wave diffraction out beyond the radio horizon. It permits one to calculate the ground wave E (electrical) field well beyond the geometric and radio horizon, where E field values are close to the atmospheric noise level.

Be sure to read about the history of how this fascinating formula came about in the recent article on RADIO-TIMETRAVELLER: Field Strength Calculations: A History. Many of the terms used in the previous and next paragraphs are explained.

The simplified formula used by Field Strength Calculator One takes into account Sommerfeld's original plane earth theory, modified by diffraction factoring. It uses an exponential function which takes into account the spherical earth diffraction effects, and acts on the planar earth equation even before the radio horizon is reached, so the resultant E field values, as a function of distance produce a continuous curve, thus rounding-in difficult intermediate distances.

The long-accepted concept of "numerical distance" (p0) and "phase angle" (b) are used in all calculations, two variables determined by frequency, distance, and dielectric constants of the ground as a radio conductor. Numerical distance depends not only on frequency and ground constants, but also on the actual distance to the transmitter. Phase angle is the measure of the power factor angle of the earth.

Field Strength Calculator One returns expected received field strength in millivolts per meter and dBu (also known as dBµV/m), based on ground conductivity, earth dielectric and several other input constants. It also displays the distance to the radio horizon and the signal path loss in dB, along with several more technical parameters. The resulting output of Field Strength Calculator One should be accurate in most cases to a couple of percent in the longwave and mediumwave bands. It compares favorably to ITU program GRWAVE and currently available FCC Ground Wave Conductivity graphs.

Field strength calculations by Field Strength Calculator One are based on the works of A.Sommerfeld (1909), B.Rolf (1930), K.A.Norton (1936), H.Bremmer (1949, 1958), NTIA Report 86-203 (1986), ITU-R P.368-7 (1992), and NTIA Report 99-368 (1999).

For further information on how field strength is calculated see the Field Strength Calculations Series previously published on RADIO-TIMETRAVELLER.


Install is simple. Download the .zip file and unzip. Click on the FieldStrengthCalculatorOne.exe file to run. This program makes no registry changes and saves no data to your hard drive. It has been developed and tested in Windows 7. It should work fine in Windows Vista and XP environments, and Windows 8. It is written in the old standby Visual Basic 6.

Included in the .zip is a readme.txt file. Be sure to have a look.

I hope you enjoy this program and find it useful.

Potomac FIM-71 Field Strength Meter

Sunday, December 16, 2012

Field Strength Calculations: A History

A previous three-part series on RADIO-TIMETRAVELLER delved into Field Strength Calculations. It covered ground conductivity's effects on signal strength, measurements quantifying signal intensity, and how to use the FCC Groundwave Conductivity Graphs to calculate expected received signal strength. Mathematical formulas, somewhere, produced those graphs. What is their history? Might we use a simplified formula to calculate expected received signal strength for our DX purposes?

Let's continue with the story behind Field Strength Calculations and explore the 50 year quest for accuracy in calculating signal strength by mathematical formula. It is an interesting tale. We will finish with a handy field strength calculator program I wrote using a simplified formula.

When we talk about field strength, we are really talking about radio propagation - the behavior of radio waves when they are transmitted or propagated from one point on the earth to another, or into various parts of the atmosphere. In our formula quest, we will mostly be concerned with those signals that hug the ground, or "ground wave". It may surprise many who are new to the hobby of mediumwave DXing that daytime ground wave range for a mediumwave signal might extend out to as much as several hundred, and in extreme cases, nearly 1000 miles!

Accurate formulas for calculating expected signal strength at mediumwave and longwave frequencies took many years to develop. Radio originally inhabited the longwaves in its infancy. Many of Marconi's early broadcasts, including his 1905-1906 transatlantic tests, were sub-100 KHz. The trend would be decidedly upward in frequency and downward in wavelength.

At the end of World War I, a fierce battle ensued between the US government and the Department of the Navy over control of the airwaves. The Department of Commerce eventually won and became master of the air and the regulatory agency for commercial radio. They started by establishing two broadcast frequencies: 833 KHz (360 meters) and 619 KHz (485 meters). The Federal Radio Commission took charge in 1926, lasting until 1934 when the current Federal Communications Commission was formed.

Throughout the early years of radio, interest mounted to quantitatively determine the service area of broadcast stations. Engineers redoubled their efforts to derive an accurate attenuation formula. The radio world was focused on accuracy of measurements at broadcast frequencies.

"Accuracy" is the key word here. The Inverse-Square Law, as applied to physics, had been commonly known since Isaac Newton's day in the 1600s. Applied to radio, it stated that the power density of the wave is proportional to the inverse of the square of the distance from a point source. In other words, doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value. But did it apply?

"Free-space" formulas calculating signal loss in the vacuum of space or "perfectly conducting earth" using the so-called inverse-square law are indeed accurate for those environments. But the Earth is not a perfect conductor, nor does it represent perfect-world conditions. Free-space formulas alone are not usable for our purposes. You will find many of them on the web, even calculators, purporting to deliver a signal strength solution for a given transmitter-to-receiver distance. They can be ignored as inaccurate. In fact, they are not even close.

Arnold Sommerfeld, 1868-1951

Mathematicians started with a "plane earth" (flat earth) theory when they first envisioned a signal attenuation formula. Brilliant, German-born genius Arnold Sommerfeld, nominated a record 81 times for the Nobel Prize during his lifetime, solved the plane earth general problem by 1909, publishing signal attenuation graphs in 1911. Bruno Rolf, basing his work on Sommerfeld's findings, published more attenuation graphs in 1930, some 21 years later. From this information, the Federal Radio Commission compiled formulas and curves, published in 1931. They were used in hearings and allocation matters at least until 1933. It was just the beginning.

In the intervening years from 1909 to 1930, four more scientists obtained independent solutions of the Sommerfeld problem which agreed with the 1909 solution. That is, except for one difference - an inverted mathematical sign. Apparently none of these authors noticed this discrepancy until the FCC's K.A. Norton, in a letter to the editor of "Nature" in 1935, pointed it out and showed that it was responsible for the anomalies in propagation predicted by the Sommerfeld-Rolf graphs. Norton in 1936 was able to construct a universal curve for prediction of field strength at relatively short distances.

Focusing on the plane earth theory, Sommerfeld expected that the surface or ground wave would be only slightly affected by the curvature of the earth since it is guided around the earth's curve in much the same manner as an electric field can follow around the bend in a wire with a comparatively small loss of energy. This explains the general success of the Sommerfeld plane earth formula at distances far beyond the line of sight. However, two major roadblocks to accuracy still existed.

The first, and most important, was "diffraction". The other, "intermediate distance".

Out beyond what is called the "radio horizon", radio signals undergo atmospheric and ionospheric diffraction, that is, refraction and scattering caused by atmospheric irregularities. This enables AM radio signals in low-noise environments to be received well after the transmitting antenna has dropped below the horizon. It has been shown theoretically that the ground wave attenuation factor at mediumwave frequencies is very little affected by diffraction at distances less than about 55 miles, the approximate "radio horizon" for mediumwave.

Norton, also in 1936, provided curves for greater distances in the diffraction region. These curves, however, were based on an incompletely developed theory. Mathematical solutions were being developed in Europe, and were two years away from completion. Europeans van der Pol and Bremmer published their paper in 1938, offering a more complete solution of the radio diffraction problem for propagation. Never-the-less, the calculation of field strength beyond the radio horizon still proved troublesome, though Norton's remarkable work clarified Sommerfeld's ground wave propagation theory.

The radio horizon at the longer wavelengths, including mediumwave, can be calculated quite simply.

For example, the radio horizon for a station transmitting on 600 KHz is about 59 miles.

By 1940 the FCC, through the work of K. A. Norton, had developed a practical method for constructing curves approximately representing the theoretical predictions. The method used the flat earth theory of Sommerfeld out to a distance of about 80 kilometers, and the diffraction theory of van der Pol and Bremmer at relatively great distances, those in excess of 200-300 kilometers depending on frequency and ground constants.

The gap in the curve was still intermediate distances. The Watson transformation, a theory originally described in 1918 by English mathematician G.N. Watson, was an attempt to connect the two. How to incorporate it into the general theory, to calculate the intermediate distances, was still the final problem. In the curves published in 1940, the gap was simply sketched in by a draftsman.

In 1952, George A. Hufford of the National Telecommunications and Information Administration provided a basis for unifying the ground wave prediction methods of Sommerfeld with Watson's diffraction transformation. It had been 43 years since Sommerfeld's 1909 thesis. There was finally light at the end of the tunnel. New curves were added in 1954 for very low conductivity. These were quite accurate, although freehand drawing was still necessary to join the Sommerfeld curve segment to the curve segment calculated for the diffraction field at relatively great distances.

Then in 1958, Hendricus Bremmer, the same Bremmer who in 1938 brought the general solution to the diffraction problem, provided correction terms which completed the search for the practical formula. Engineers could finally calculate ground wave field strength with accuracy. It had been 50 years in the making. The formula was born.

The FCC curves were considered satisfactory for regulatory purposes until it became necessary to convert to metric units toward the end of the 1970s. In a 1979 FCC report, it was recommended that a computer program be written for recalculating the curves using the methods in Bremmer's 1949 book. The program was subsequently used to produce new FCC curves in 1985 which agree within 1 to 2 decibels with the previous curves. However, the 1979 computer program was mathematically deficient in its ability to cover all the range of intermediate distances, and the great distance values it computed were shifted upward to force a match in the middle. FCC curves drawn for the X-band, 1605-1705 KHz, are the most recent. They are the result of precise calculations of field strength over the full range of distances of interest, including the previously troublesome intermediate distances.

And thus we have the short version of the history to achieve accuracy in field strength formulas. Stay tuned for the next installment, a program to calculate field strength, based on a simplified formula.

Next up: Field Strength Calculator One

Original measured vs. calculated f/s
values for KOA, Denver, 1934

Wednesday, December 12, 2012

Cross Country DX, Fall 2012

Greetings from the great southwest!

It's been awhile. Had a good trip across country during the last three weeks of October. Been busy getting life back in order the last few weeks, so apologies for no posting. Had some good DXing moments while crossing the mid-section of the country which I'd like to relate. Long distance daytime reception along the I-70 route from Columbus, OH to Denver, CO was good.

All reception on the road using 2006 Ford Ranger truck radio with 24 inch extension to whip antenna.

October 10.

WSM-650, Nashville, TN (50KW) hung in there from Ohio clear into central Missouri at mile marker 154, near Kingdom City, a distance of 346 miles. Final reception was at 13:30L. Very weak at the end, with long fades.

The next day, traveling through eastern Kansas on I-70, the following were heard with positive ID. All daylight hours, mid-morning, 9:00-10:00L. Sunrise was 06:35L.

October 11.

KOA-850, Denver, CO (50KW) at mile marker 343 (476 miles) Weak.
KKOB-770, Albuquerque, NM (50KW) at mile marker 336 (643 miles). Weak but steady.
KGAB-650, Cheyenne, WY (8.5KW) at mile marker 286 (444 miles). Very weak.
KHOW-630, Denver, CO (5KW) at mile marker 272 (416 miles). Weak.

KKOB-770, Albuquerque was the real surprise, with exceptional distance for the time of day.

More coming soon! An article on field strength calculations is in the works, plus a field strength calculator program for mediumwave. Stay tuned.

Wednesday, October 3, 2012

Tower Talk

WSM-650 tower, Nashville, TN, 1943

Let's take another look at towers in the mediumwave band across the U.S. I did a previous series on RADIO-TIMETRAVELLER entitled Mediumwave Oddities in which one installment covered tower oddities. Oddities turned out to be fairly popular judging from the number of hits.

I've always been interested in towers, and specifically mediumwave towers. Recently I've been in touch with Dan Goldfarb, owner of the Yahoo group MW Masts, and we have been exchanging information on mediumwave towers in the U.S. Dan is attempting to document every mediumwave tower in the world, and has made great progress to that end. Be sure to check out the MW Masts group. You will find interesting discussion and informative files available for download.

As I drive around the country, it occurs to me that there is a lot of mediumwave metal up in the air. I wondered how much? A few code tweaks to my Radio Data MW program gave me the answer, supplying a comprehensive and interesting fact list of tower info. We'll get into the statistics toward the end of the article.

But first let's talk about the different types of mediumwave masts in the U.S. A tower is a tower, right? Not necessarily so. There are four different types, and actually five counting the odd Franklin antenna which I'll describe shortly. Officially, the FCC defines tower types by numbers - 0, 1, 2-9 and A-Z. Sounds like a lot of varieties, but it's really not. In practice Types 0, 1, and 2 designators are used, in which Type 2 can be one or several kinds of sectionalized antenna. So there are basically three tower varieties plus the Franklin, which the FCC lumps into the Type 2 category.

By far the most common tower out there is the FCC Type 0 (some 93%), a normal mast without any frills. It is simply a standard tower almost always insulated at its base. Stations strive to erect a tower at least one-quarter wavelength tall for the frequency at which they broadcast. At the low end of the mediumwave band this can be a tall tower - a quarter wave at 540 KHz is some 455 feet tall. At the high end of the band, in the western hemisphere at least, 1700 KHz, the quarter wave mast height would be only 144 feet tall.

The aim in all cases is to push as much RF energy across the ground as possible in order to get the best signal out to the target audience. Gone are the days when stations prided themselves in a nearly cross-country audience (during darkness hours of course). It's all about local and regional target audience now, as that's where the ratings, and thus the money, comes from.

So the object is to transmit as much signal near 0 degrees elevation (the ground) as possible, known as the "elevation angle" of the signal. The quarter wave vertical mast does a pretty good job, however by extending its length a little it gets even better. Excepting the Franklin type, a mast 5/8 wavelength tall does the best job, producing the strongest signal at the lowest angle. Only some 90 towers out of more than 7000 have heights in the range of 5/8 wavelength or taller. Few stations can afford this height, or may be prohibited from erecting such a tall tower due to various restrictions. Stations strive for at least a quarter wave for efficiency's sake.

To the rescue came an old electrical innovation called top-loading, discovered by Thomas Edison and put into first practical use in 1905 and 1906 by Fessenden and Marconi in their transatlantic tests on 82 KHz. A simple flat-top method of top loading creates the necessary capacitive effect to electrically extend the length of the mast. The resultant antenna is sometimes known as an umbrella antenna, top loaded with a "capacitance hat" looking like an umbrella. Some 550 towers (a mere 7%) use the top-loaded scheme. The top-loaded tower is the FCC's Type 1 tower.

A fine example of a mediumwave top-load "hat" is that of Australia's 3WV, 594 KHz, in Western Victoria, pictured just below.

So what is a Type 2 tower, you ask? The answer is a sectionalized tower, which is a tower having insulated sections stacked atop one another.

A scant 10 towers across the U.S. are sectionalized, an idea adapted for radio during World War I by Arthur O. Austin who already held the patent on sectionalized power transmission towers. The war ended, and Austin's sectionalized tower scheme was temporarily forgotten. Then station WHK, Cleveland, Ohio's pioneer broadcaster, erected a sectionalized tower. Though hampered by a power restriction of 1000 watts and a shorter wavelength, the station was suddenly being heard in faraway Honolulu, New Zealand, and all over the United States, achieving distances comparable to its super-power brothers.

With a sectionalized tower, high angle radiation can be minimized to give better ground wave performance than is possible with a simple vertical radiator. Calculations for a 120 degree (one third wavelength) sectionalized tower versus a standard 120 degree tower show the unwanted high-angle radiation at 60 degrees above the horizon to be nearly 2.5 times more for the standard, non-sectionalized tower. So why aren't sectionalized towers more commonly used today? Probably cost, and the fact that super long distance reception is irrelevant in today's markets. It's an idea relegated to the past as far as mediumwave broadcasting goes.

There are several variations of sectionalized towers within this type. The two main varieties are non top-loaded and top-loaded, both falling into the Type 2 designation. They may be fed at the bottom or the center of the tower depending on whether the tower is grounded at the base or not. Top-loading on a sectionalized tower has the same effect as the standard tower - increasing the effective electrical height without building a taller tower.

KNBC top-loaded Franklin tower, 1949
Now we have come to the Franklin antenna, actually a variation of the sectionalized tower and another Type 2 variety. One of the drawbacks to the efficient 5/8 wavelength tower described above is an unfortunate lobe of power pushed skyward at an approximate angle of 60 degrees. During daylight hours this hardly matters as it is absorbed in the atmosphere. At nighttime this skywave reflection can cause the station to interfere with itself out at certain critical distances within the broadcast target area.

The true Franklin antenna is composed of two half wave radiators mounted one above the other and insulated from each other. The tower base is insulated in the usual way. The difficulty is that the feed is in the middle of the tower instead of at the bottom. Feed line is run up inside the lower section, and a phasing network is used to feed both sections so that the currents in each are in phase, and the efficiency of two half-wave radiators is realized in terms of increased ground wave and decreased high angle signals. Thus, we have the Franklin antenna, a skyscraping one wavelength tall.

Several stations claim to be using Franklin antennas. There is one true Franklin antenna array in the U.S., that of California's KFBK-1530 in Sacramento. It consists of two towers, each a full wavelength in height, each fed in the middle. The claim is that 50KW daytime KFBK-1530 has the highest published millivolt per meter level of any station in the FCC AM system - an average of 3545.89 mV/m at 1 kilometer distance. It is the highest figure found in the FCC's database, at least.

Little known is that one other station, KSTP-1500, St. Paul, Minnesota, misses the perfect Franklin definition only by a hair, being just shy of a perfect full wavelength. Its single tower is comprised of two stacked 0.498 wavelength sections, making 0.996 wavelength height in all. It's computed (not FCC figure) millivolt per meter level is actually higher than KFBK's - 3618.76 mV/m. The difference is that the FCC publishes 1 kilometer field strength values for single towers based on a standard 1KW output, only 511.77 for KSTP. In actuality, 50KW KSTP-1500 is the champion.

The WHO-1040 tower (50 KW) out of Des Moines, Iowa,, a Type 2 center fed shortened "Franklin" is grounded at the base and fed at the center with only the top section excited. It is also top-loaded. It's curious omni-directional pattern pushes a mammoth 15.8 dB gain lobe out at 41 degrees elevation to the horizon, probably the highest gain lobe of any station in the U.S. The effective radiated power (ERP) in that lobe is some 2.1 million watts! There we have the high angle lobe described in paragraphs above. The single hop bounce off the ionosphere at this angle illuminates mid-America farm country with two million watts in a perfect ring around Des Moines ranging from about 150-350 miles out. Surprisingly, distant DX from WHO is not as good as it might seem, and in fact worse than the usual 50 KW monopole.

So, what does analyzing the FCC's tower data tell us? Here are the results.

Data has been compiled from the 09-26-2012 FCC database. 4744 station facilities are represented. Since the ASRN (Antenna Structure Registration Record) is not recorded in many cases, tower heights in this list are necessarily based on the FCC's figure of radiating height of the tower, which is always indicated. In almost all cases it comes very close to actual tower height, the difference being the base insulator and top lighting.


4740 stations are on the air during daylight hours (99 listed as silent). 7176 towers are transmitting some 27,782,249 watts. How about that for an electric bill?

6666 are normal masted towers, that is, without top loading. 500 are top loaded. 10 are sectionalized.

The tallest daytime tower belongs to WKY-930, Oklahoma City, OK at 951 feet tall (290 meters). Interestingly, the older WKY tower collapsed in a freak tornado back in June of 1998, and there is video of its collapse taken from an adjacent tower cam during the storm.

There are 5 towers exceeding 750 ft. in height. They belong to WNAX-570, KMJ-580, WSM-650, WKY-930, WHO-1040.

The shortest daytime tower belongs to KJNT-1490, Jackson, WY (listed as silent at the moment), a mere 50 feet tall (15 meters). The next shortest belongs to KBZY-1490, Salem, OR, at 52.8 feet tall. It is a top-loaded affair, the top-loading upping its effective height to a perfect quarter wavelength!

In all, there are 12 towers shorter than 75 feet. They belong to KYPA-1230, KCFM-1250, WKCY-1300, KFJL-1400, WLUX-1450, WEEO-1480, WIRB-1490, KBZY-1490, KLZN-1490, KJNT-1490, KVOG-1530, WPDC-1600.

Out of 4740 daytime stations, 3554 have omni-directional patterns, or a single tower. 1214 have shaped patterns using multiple towers.

The total height of all towers broadcasting during daylight hours is 1,775,871 feet (541,286 meters), or 336 miles (541 kilometers) of metal antenna structure up in the air!

Again, the highest daytime published millivolt per meter level goes to KFBK-1530 of Sacramento, CA with 3545.89 mV/m. KSTP-1500's actual calculated level is higher at 3618.76 mV/m.

The lowest daytime published (and actual) millivolt per meter level goes to two-tower, 250 watt WCTA-810 of Alamo, TN with 140.82 mV/m.


4158 stations are on the air during nighttime hours (81 listed as silent). 7689 towers are transmitting some 10,956,214 watts. Quite a drop in power.

7,335 are normal masted towers, that is, without top loading. 525 are top loaded. 9 are sectionalized.

The tallest tower "in use" day or night goes to nightime WRDT-560, Monroe, MI at 992 feet (302 meters). An interesting situation, as daytime and nighttime services transmit from different locations. WRDT-560 daytime service of 500 watts transmits from Monroe, MI (near Detroit) on 4 "short" towers of the same height (each 410 ft.). Nighttime service (a puny 14 watts) transmits from the huge 992 ft. Detroit Metro Media Center tower in suburban Oak Park. FCC records show WRDT uses the entire length of the tower to radiate its 14 watts. Even at the operating frequency of 560 KHz, the 992 ft. tower is still just 0.565 wavelength. The media tower is obviously used for multiple purposes.

There are 6 towers exceeding 750 ft. in height. They belong to WRDT-560, WNAX-570, KMJ-580, WSM-650, WKY-930, WHO-1040.

The shortest tower belongs to the nighttime operation of WSIV-1540, E. Syracuse, NY at 31.9 feet (10 meters) which appears to be operating out of a house in a residential neighborhood. It is not top-loaded either, transmitting a signal of 57 watts into a 0.050 wavelength radiator. It appears that nighttime WSIV-1540 takes the prize for the shortest wavelength antenna too.

There are 13 towers shorter than 75 feet. They belong to KYPA-1230, KCFM-1250, WKCY-1300, KFJL-1400, WLUX-1450, WEEO-1480, WIRB-1490, KLZN-1490, KBZY-1490, KJNT-1490, KVOG-1530, WSIV-1540, WPDC-1600.

Out of 4158 nighttime stations, 2530 have omni-directional patterns, or a single tower. 1655 have shaped patterns using multiple towers.

The total height of all towers broadcasting during nighttime hours is 1,965,079 feet (598,956 meters), or 372 miles (599 kilometers) of metal antenna structure up in the air! Nighttime wins over daytime with an extra 36 miles of antenna tower.

Wrap Up

Several things are apparent from these statistics. Fewer stations (582 fewer) are on the air during nighttime hours, but they use 513 more towers than the daytime group. This is because of the need for signal directivity to avoid interference.

The total power output of the nighttime group is only 39% of the daytime group, again for the same reason.

Nighttime KFBK-1530 of Sacramento, CA this time has the absolute claim to the highest computed millivolt per meter level: 3126.79 mV/m. KSTP-1500 switches to a 3 tower array at night and loses its place.

The lowest nighttime published (and actual) millivolt per meter level goes to two-tower, 1 watt WZRK-1550 of Lake Geneva, WI with a micro field strength of only 9.11 mV/m. WZRK takes the overall prize in this category.

The next time you take a drive, look for mediumwave towers. They are an interesting subject! More from the west coast. I am headed across country soon.

A nice shot of the WSM-650 tower as it appears today.

Thursday, August 30, 2012

Using Arbitron To Determine Station Format

When DXing, it's often helpful to know the broadcast format of stations on frequency for identification purposes. I recently had the case where I was DXing at a remote site on 1470 KHz up along the Canadian border. Two stations were down at the noise level, one slightly above the other. The stronger one was broadcasting in country music format, the other undetermined. I couldn't quite catch a call sign.

When I got home it was a simple matter to check the Arbitron data on the two possibilities and determine which one I heard. It turned out it was WPDM-1470, out of Potsdam, NY. The weaker station was WNYY-1470 out of Ithaca, NY. The Potsdam catch was the better of the two, and at lower power too. I would not have been able to determine this without the ability to check station formats.

I've covered the availability of station lists for mediumwave DXers in two previous articles on RADIO-TIMETRAVELLER, Mediumwave Station Reference Lists and Mediumwave DX Meets The Tablet Computer. Many of these lists don't document station formats. Those that do may be out of date, or incomplete. And that's just for US data - information for Canada is even more suspect. This is not surprising considering the frequency at which stations change formats.

Those lists that do document station formats are Lee Freshwater's AM Logbook (perhaps the most complete), Topaz Designs, and presumedly the National Radio Club's AM Radio Log (though at a steep price - currently $28.95 for non-members and out of print). radio-locator - technically not a list site, but you can generate a list from this link using search parameters - will also provide a nice custom list of stations which includes format information. It seems fairly complete.

Virtually all US and Canadian stations subscribe to Arbitron. Arbitron, of Columbia, MD, is an international media and marketing research firm serving all types of media — radio, television, cable, etc. It is Arbitron's business to measure network and local market radio audiences across the United States, survey the retail, media and product patterns of U.S. consumers, and provide measurement and analytics. This includes, of course, what formats stations are using. It is probably the most up-to-date format reference of all.

The Arbitron Radio Station Information Profiles (SIPs) contain information about all radio stations in the United States: current addresses, station names (including call letters), frequencies and formats. Many if not virtually all Canadian stations are also represented in the profiles.

So how do we use Arbitron to identify station formats? Though the Station Information Profile used to be made directly available on their web site, lately the link has been moved to a members only site, My Arbitron. However, still buried deep within the Arbitron's main web site are a couple of links which can get us our needed information.

Stations are asked to update their Arbitron reference data four times per year. This goes into a seasonal "survey". We must take an educated guess of the current season on file that we wish to extract information from. Survey codes are:

  • WI (winter)
  • SP (spring)
  • SU (summer), noted as SU12 in the example (12 = current year, 2012)
  • FA (fall)

Using the call letters of the station, compose a link for the AM broadcast service as such:

Note the use of the surveyID=SU12 (summer of 2012), and callLetter=WHAM fields. You can also check FM stations by substituting the band=fm field.

A station search page is accessible as well, if you know the current survey season and date:

Old surveys do not seem to be accessible. Use the current season and year, or sometimes the season just past if the current season is not yet up for inspection.

Keep trying with your link until you have success. I have found the Arbitron site to be quite busy at times. During busy periods, it also may return a "survey not found" message. Persistence is good.

Thursday, August 2, 2012

The Silicon Labs 477x Chip - A New DSP DX Champ?

Silicon Labs recently released a new "high performance" consumer electronics broadcast radio receiver DSP chip, the Si4770/77 A20 (477x) series. What makes this chip special or any better than the familiar Si4734 chip used in the Tecsun PL-380, PL-310, and other consumer DSP-based receivers? I recently downloaded the spec and programming sheets on the new Si477x series and had a look. This chip set has some interesting new features.

A Sensitivity Boost

One thing was immediately apparent: the new chip has received a sensitivity boost. Where the old Si4734 chip's AM sensitivity was pegged at 25µV (27.9dBµV), the Si477x's comes in at 14µV (22.9dBµV). AM adjacent channel (±9 KHz) rejection for the new chip is 62dB, alternate channel (±18 KHz) is 62dB. AM image rejection is 72dB. Impressive figures for a chip radio.

FM sensitivity has also improved from 1.1µV (Si4734) to 0.66µV (-3.5 dBµV, Si477x). Selectivity is pegged at 65dB at ±100 KHz and 72dB at ±200 KHz frequency offset.

Bandwidth Options Galore

The old Si4734 chip had 7 programmable bandwidth options, the ability to set AM IF bandwidth at various widths from 1 - 6 KHz. Five AM bandwidths were implemented in the Tecsun PL-380: 1, 2, 3, 4, and 6 KHz. The Si477x chip enters with what Silicon Labs is calling "Dynamic AM/FM channel bandwidth control". The AM and FM IF channel bandwidths are dynamically optimized according to the on-channel RSSI (signal strength), and with the ability to further refine bandwidth by detection of the adjacent and alternate channel RSSI. Channel filter bandwidth is programmatically settable from 0 Hz to 15 KHz in 100 Hz steps for both AM and FM. Further, automatic bandwidth selection can be triggered not only by RSSI, but by signal to noise ratio. It can also be hard set to a fixed width by software. This could present some interesting possibilities if full user control is ever implemented in a consumer device.

Uh-oh, Soft Mute Again

Once again, programmable audio soft mute is implemented in the new chip. Soft-mute, a further lowering of the audio level of the received signal when it drops below a prescribed strength, is undoubtedly meant to provide a more comfortable listening experience for the casual listener and not the DXer. The idea is to relieve the listener from all that nasty low level "static" and "interference", or as Silicon Labs states: " attenuate the audio outputs and minimize audible noise in compromised signal conditions." Soft mute attenuation in the Si477x is available in 0-31dB steps (default is 12dB of attenuation, unfortunately twice the amount of the Si4734), and can be triggered at a pre-programmed S/N ratio (default is 8dB, the Si4734 was 3dB).

New Audio Bandpass Filters

Silicon Labs has deemed these "Hi-cut" and "Lo-cut" filters. The AM hi-cut control is employed on AM audio outputs having degradation of signal quality. Signal strength and signal-to-noise ratio thresholds can be programmatically set to activate the filters. The Hi-cut filter can be disabled by setting the Hi-cut filter  margin to the default audio bandwidth for AM. AM Lo-cut is employed on audio outputs for rejection of power-supply 50/60 Hz interference. AM Lo-cut is a high pass filter, and is enabled by default and can be disabled by programming. Note that the Lo-cut filter is not available for FM.

HD Radio

For HD Radio (IBOC) buffs, the Si4777 model of this chip series has AM/FM HD Radio capabilities. Additionally, an interesting innovation has been added called "IBOC Blend". This feature supports the ability to blend between analog and digital audio. When the bit error rate of the HD Radio digital signal falls below a predefined threshold and the digital audio fades out, the analog audio is blended in. This prevents the received audio from muting when the digital signal is lost. The audio will "blend to digital" upon reacquisition of the digital signal.

It will be interesting to see if the HD version of the Si477x chip is incorporated in any new, portable consumer electronics device. Car radio seems to be the only outlet anymore for HD Radio, which may die on the vine in the end anyway.

Improved Inductance Handling

Usable antenna inductance has expanded somewhat from 180-450µH to 180-540µH, though the documentation does show the chip capable of maintaining tuning up to a 688µH inductor. Again, like the Si4734, the chip is adaptable to an external air loop antenna if a ferrite rod is not used. An air loop antenna is supported by using a transformer to increase the effective inductance of the air loop. Using a 1:5 turn ratio inductor, the inductance is increased by 25 times and easily supports all typical AM air loop antennas which generally vary between 10 and 20µH.

Frequency Coverage Suffers

Unfortunately, shortwave and longwave band coverage are not available, unlike the Si4734. FM range is 64 MHz - 108 MHz. AM range is 520 KHz - 1710 KHz, at 9 or 10 KHz channel spacing.


The Si477x is Silicon Labs' cutting edge consumer electronics broadcast AM/FM receiver radio chip. It brings us higher sensitivity for both AM and FM. IF Bandwidth is now dynamically set dependent on signal conditions, using primary, adjacent, and alternate channel signal information. Soft mute is still in force, and is even more heavy handed when left to its default settings. New high and low audio bandpass filters shape the audio signal and are dynamically set by signal conditions. HD Radio for both AM and FM is made available in one version of the chip series. Finally, ferrite loopstick inductance range is expanded.

It is likely that consumer grade AM/FM radios using this chip will stick with default settings for bandwidth and soft mute, basically rendering the increased sensitivity and enhanced DX capability of this radio chip nearly moot. Opening up the myriad bandwidth options to manual selection, allowing soft mute to be manually controlled, and further, allowing the audio bandpass filters to be manually controlled would render this a nice DX machine for both AM and FM.

Market Watch Report

Tuesday, June 12, 2012


1 Watt At Night - U.S.

1 Watt At Night - U.S.

The ultimate DX. How good (or lucky) a DXer are you? Have you ever tried for extremely low power AM stations at night?

Every night, 15 stations across the U.S. transmit with an output power of only one watt. How far does one watt travel normally, let's say under static conditions during the daytime? I'm glad you asked.

One watt into an omni-directional antenna (1 tower), over medium ground conductivity (8 mS/m), will get you out 10 miles, at which point the signal enters the "fringe" area of reception (0.15 mV/m and less). A good receiver will hear somewhat farther than that. At night, and using a directional pattern, who knows how far that signal will travel? All things are possible.

CallSign       Freq    Power Class Location                     
WCKB            780        1    D  Dunn, NC                     
WRFM            990        1    D  Muncie, IN                   
WHFB           1060        1    D  Benton Harbor-St. Jo, MI     
KLEY           1130        1    D  Wellington, KS               
WGAB           1180        1    D  Newburgh, IN                 
WSQR           1180        1    D  Sycamore, IL                 
WPGR           1510        1    D  Monroeville, PA              
WENG           1530        1    D  Englewood, FL                
WJJT           1540        1    D  Jellico, TN                  
KBOA           1540        1    D  Kennett, MO                  
WBNL           1540        1    D  Boonville, IN                
KLKC           1540        1    D  Parsons, KS                  
KDYN           1540        1    D  Ozark, AR                    
WZRK           1550        1    D  Lake Geneva, WI              
WSRY           1550        1    D  Elkton, MD

Here's some statistics for our 15 one watt stations, taken from the 5-27-12 FCC database:

All 15 are Class D.

12 are located east of St. Louis, 3 are west of St. Louis.

KLEY-1130, Wellington, Kansas, is the most westerly, leaving no 1 watt stations from there all the way to the west coast.

11 are "W" callsigns. 4 are "K" callsigns.

The 15 stations broadcast using 24 towers.

11 stations broadcast an omni-directional pattern (single tower). 4 broadcast a directional pattern (multi-tower).

1 station is on the FCC "Silent" list: WZRK-1550.

Interesting to note: 5 of the 15 are on the same frequency - 1540 KHz.

The lowest powered daytime station in the FCC's database broadcasts with 135 watts.

The most interesting broadcast pattern is that of WRFM-990, Muncie, Indiana. This station broadcasts using 6 towers. Its pattern projects generally to the north, covering Muncie and Delaware County as shown in the radio-locator graphic. WRFM-990's daytime power is 250 watts.

Sunday, June 10, 2012

Mexican AM List Updated Once Again

Just a head's up. Mexico's Federal Telecommunications Commission "Cofetel" has published the official Mexican AM station list in .PDF form again. The list is dated May 31, 2012. This is starting to become a regular thing of late, as the last update was just two months ago. Kudos to them!

Get the list at the Cofetel site.

Don't be mislead by the 2008 date in the site link. After downloading the PDF, you can find the actual list date at the bottom of the document.

This list can be made into a nice spreadsheet form by converting the saved PDF document to an XCEL (.XLS) file. If you don't have the software to do that, a great, free online conversion site can be found at Zamzar on the web.

Viva Mexico!

Wednesday, May 23, 2012


50 Kilowatts Night - U.S.

50 Kilowatts Night - U.S.

Our next map depicts all 50 kilowatt stations broadcasting during nighttime hours in the United States. 98 stations are represented. Black flags indicate allocations in the nighttime service class, pink flags the unlimited service class (24-7). The FCC defines service classes as DAYTIME, NIGHTTIME, UNLIMITED, and CRITICAL HOURS (the first two hours of daylight after sunrise and the last two hours of daylight before sunset). Data is from the 4-24-12 FCC database.

Representative antenna pattern plots are also shown.

Here are the statistics.

59 stations are Class A. 39 are Class B. 0 are Class C. 0 are Class D.

50 are located east of St. Louis, 48 are west of St. Louis.

51 are "W" callsigns. 47 are "K" callsigns.

The 98 stations broadcast using 269 towers.

30 stations broadcast an omni-directional pattern (single tower). 68 broadcast a directional pattern (multi-tower).

1 station is on the FCC "Silent" list: WDCD-1540.

If we divide the western hemisphere MW broadcast band in half (the center is at 1115 KHz), we have an equal number of MW channels below 1115 KHz and above 1115 KHz. There are 31 nighttime 50KW stations broadcasting above 1115 KHz. 67 broadcast below 1115 KHz.

Monday, May 21, 2012

Mediumwave DX Meets The Tablet Computer

A previous series on this blog talked about the wealth of information we mediumwave DXers have for listing stations, and ways to reference it in the field. Last year about this time I bought an eReader (a Nook Color), with the idea of using it to read books and other saved documents. What I discovered was how easy it was to create customized station lists from various web sources using my laptop, then transfer them to the eReader for reference in the field when DXing. The second part in that series talked about using the eReader for displaying DX lists.

After a summer's use it became apparent that a tablet computer might be an even more usable device, as it would allow better web access, more options for file reader software, and a bigger screen (10 inch vs. 7 inch). This spring I purchased an Asus Transformer TF101 Android tablet. It has been a good choice.

As mentioned previously, typical station lists can be created in several forms using various web or other sources. Reader apps for tablet computers can handle .TXT (text) file format, .PDF (Adobe's Personal Document File) format, .HTML (web) format, and others - even .XLS (XCEL) spreadsheet files or comma-separated value text (.CSV) files.

Three favorite web sites of mine for mining mediumwave AM data are Lee Freshwater's AM Logbook, MWList, and the FCC's AM Query. Let's review what they have to offer.

AM Logbook will generate a single web page list of stations by frequency, callsign, state, city, transmitter location, and others. US and Canadian stations are represented. The page can be saved locally by your browser and transferred to your tablet through either a hard connection, WiFi, or a Cloud service like Dropbox or Box. AM Logbook also supplies its AM list in downloadable XCEL spreadsheet form.

MWList, a more complicated site, attempts to document all AM stations worldwide, by country. It encourages users to register, but its data is also available to non-registered users. MWList has the ability to create a customized country file in PDF form which is then made available for your download. This is really the way to go on this site. Enter the site, login if you are a member or click "Continue as guest", then click the "Downloads" heading tab. Check off the countries desired, then download your PDF file. Transfer to your tablet as indicated above.

MWList also outputs country data to a generated web page, like AM Logbook. Country data is initially displayed by frequency, but the data columns on the page can be click-sorted by location, callsign, state, etc. Data is presented in an HTML "frame" within a parent page, so saving the web page core data in this way is not as easily done. Sometimes it is necessary to break the frame out into its own window, and this is the technique that I use. Some browsers allow this option and present a right-click menu item to accomplish it. Firefox and Opera include this function. Once the frame is broken out into its own page it is easily saved as HTML. Text formatting is maintained this way.

Data from both AM Logbook and MWList are based on a variety of sources, one being actual reception reports. Canadian data seems accurate for both, as it is not drawn from the FCC database. Ditto Mexico and other countries for MWList.

The third option, the FCC's AM Query, can also be used to create a station reference file. US data should be highly accurate, but be suspicious of any foreign data. You would be better off with AM Logbook or MWList for Canada and Mexico or other countries. Output can be displayed as a simple web page or a text file, easily transferred to a tablet, as above.

My own Radio Data MW program has the capability of creating station list files in HTML and CSV formats. I often use its files on my tablet, as I can set them up to show expected signal strengths and sunrise/sunset times for each station, something not available with any of the other sources.

Much reader software (in the form of apps) is available for the tablet. Adobe Reader (free) and ezPDF Reader (less than $5) are good ones for displaying PDF format. Your tablet already has text reading software and an HTML browser, though many others are also available for free through the Google Play Store (previously known as Google Marketplace). Apple's iPad has similar software available at their App Store.

An advantage to staying with the HTML format for your AM list is the tablet browser's pinch-to-zoom function. With file sizes fairly large, and long line lengths, it is advantageous to be able to zoom the text smaller and larger. Most PDF readers have the pinch-to-zoom capability, but not all work as well as the web browsers. Basic text (.TXT) reader software doesn't always have an appropriate zoom capability, or may wrap long line lengths causing confusion. HTML is the better choice here.

Tablet batteries typically last 6-10 hours, more than enough for a casual afternoon or night of DXing. All tablets seem to have sound recording capability, and most have video and sound recording, both. Thus your device can also be used to create a record of your DX catch for personal record or verification purposes, an added bonus to owning a tablet.

Turn your tablet device into a mediumwave DXer's station reference!

Viewing a MW database on a tablet

Sunday, May 13, 2012


50 Kilowatts Daytime - U.S.

50 Kilowatts Daytime - U.S.

Something new here on the blog - RADIO-TIMETRAVELLER Maps. On occasion I will present a map of interest to the mediumwave DXer. Maps and charts are generated by the Radio Data MW program. Here is the first one. Data is from the 4-24-12 FCC database.

The map depicts all 50 kilowatt stations broadcasting during daytime hours in the United States. 248 stations are represented. Yellow flags indicate allocations in the daytime service class, pink flags the unlimited service class (24-7). The FCC defines service classes as DAYTIME, NIGHTTIME, UNLIMITED, and CRITICAL HOURS (the first two hours of daylight after sunrise and the last two hours of daylight before sunset).

Representative antenna pattern plots are also shown. As you can see, not all are omni-directional as might be expected for 50KW stations. Obviously due to map size constraints, a number of station flags overlap, as do their patterns. Thus, for example, you see KXEN-1010, St. Louis, MO, highly directional, sits under KMOX-1120's omni-directional pattern.

Now, some statistics.

60 stations are Class A. 157 are Class B. 0 are Class C. 31 are Class D.

134 are located east of St. Louis, 114 are west of St. Louis.

137 are "W" callsigns. 111 are "K" callsigns.

The 248 stations broadcast using 628 towers.

103 stations broadcast an omni-directional pattern (single tower). 145 broadcast a directional pattern (multi-tower).

4 stations are on the FCC "Silent" list: WSJC-810, KYWN-890, WQOM-1060, WDCD-1540.

If we divide the western hemisphere MW broadcast band in half (the center is at 1115 KHz), we have an equal number of MW channels below 1115 KHz and above 1115 KHz. There are 85 daytime 50KW stations broadcasting above 1115 KHz. 163 broadcast below 1115 KHz.

The last graphic is a plot centered on the geographic center of the contiguous U.S., near Lebanon, Kansas. It shows the distribution of 50KW daytime stations radiating out from this location, using a scale of 2000 miles. A vague outline of the continental US can be detected, with 4 satellite 50KW stations towards the northwest (Alaskan stations), and a solitary 50KW station to the southeast in Puerto Rico (WKVM-810).

50 Kilowatts Daytime - U.S.

Hope you enjoy the map and chart. Look for more interesting maps and statistics to come.

Sunday, May 6, 2012

Canadian AM List

Let's continue with our topic of governmental radio station databases and create a customized Canadian AM list for our mediumwave DXing use.

Dear reader, a newer list has been published in October, 2019.

Download Canadian AM List (creation date: 05-06-2012).

A previous article on RADIO-TIMETRAVELLER, Radio Station Databases 101,  discussed several governmental databases that are available online. The Canadian database is one of them. Using the Radio Data MW program, I set out to make a Canadian AM station list right from the official files.

Canada has a nice AM Query of their own, like the FCC's AM Query. But also like the FCC's, the output does not tell the entire story, leaving out detailed technical information. We are in luck, however. It turns out that Canada's AM Query searches a deeper database just like the FCC does, so much of the information is available, though hidden.

The Industry Canada engineering database houses the files we need. Links are shown just below.

Industry Canada engineering database (

Rather than simple text files, Canada has chosen a dBase file format (.DBF) for its files. Download and unzip and you will see the many files that comprise Canadian broadcast - AM, FM, and TV. Though the records are somewhat textual in nature, they are more like XCEL records and a text editor cannot be used to view them. You must use a specialized viewer in order to look inside.

CDBF for Windows by WhiteTown Software is one such viewer, which also offers file conversion utilities. A demo version is available, though it it is only usable for a short time. Other DBF file viewers with conversion abilities are also available, notably the free Exportizer.

What we need to do is convert the DBF file to a readable text file so we can process it. We will use Exportizer to open the Canadian DBF file and convert it to a comma-seperated values (.CSV) file, readable by Radio Data MW with some simple tweaking.

So which file do we use to gather information on Canadian mediumwave stations? From the Industry Canada database files, one file stands out that will give us most of the information we want: callsign, frequency, transmitter latitude and longitude, station class, and daytime and nighttime powers. That would be the AMSTATIO.DBF file.

Comparable to the FCC's facility.dat file, Canada's AMSTATIO.DBF file contains basic station information. But also like the FCC's facility.dat, it contains many stations outside Canada. The current AMSTATIO.DBF file I have (dated 4-20-12) documents some 9503 station facilities from not only Canada, but the United States and Mexico as well. We will have to strip out the unnecessary country data. Easy enough.

Now on to the results. I have created a list of the current, operational Canadian AM stations in .HTML form which will display nicely on your computer. A .CSV type file is also included which may be read into a spreadsheet form. The list contains only licensed stations. Nothing in this list has been verified on the air, though it is official and right from the Canadian governmental files. I have calculated local sunrise/sunset times for all stations for this date (5-6-12).

The Canadian AM broadcast service is comprised of 321 station facilities, transmitting in 641 services (daytime service and nighttime service), with varied station classes of A, B, C, and LP (low power).

34 class A stations, 249 class B stations, 74 class C stations, and 284 low power stations round up the list.

For those curious about output powers, 48 stations broadcast at 50KW during the daytime, 40 during nighttime hours. 8 broadcast between 10,001 watts and 49,999 watts during daytime hours, 10 during nighttime hours. 66 broadcast at the 10KW power level during daytime hours, 53 during nighttime hours. 57 broadcast at power levels between 100 watts and 9,999 watts during daytime hours, 75 during nighttime hours.

Stations broadcasting at power levels below 100 watts are considered low power facilities, and are licensed as such with the special license class of LP. There are 142 of them. CBPC-1 and CBPD-1, both out of Glacier Park, British Columbia, have the lowest power level at 5 watts, day and night.

The following frequencies are devoid of any MW broadcast activity in Canada:

550 KHz
670 KHz
700 KHz
720 KHz
780 KHz
1000 KHz
1020 KHz
1030 KHz
1080 KHz
1120 KHz
1160 KHz
1180 KHz
1300 KHz
1360 KHz
1390 KHz
1500 KHz
1520 KHz
1530 KHz
1590 KHz
1600 KHz
1620 KHz
1640 KHz
1660 KHz
1680 KHz
1700 KHz

Canada has 122 graveyard stations. 61 broadcast during daytime hours, 61 during nighttime hours.

Canada has 6 X-band stations (1610-1700 KHz).

Low power stations (99 watts or less) occur throughout the mediumwave frequency band. The following frequencies are occupied by LP stations exclusively:

650 KHz
750 KHz
830 KHz
970 KHz
1090 KHz
1100 KHz
1110 KHz
1170 KHz
1230 KHz
1340 KHz
1400 KHz
1480 KHz
1560 KHz
1630 KHz

                               Radio Data MW Program (early version).

Sunday, April 15, 2012

Analyzing The Mexican AM Radio List

After reporting on the publication of the updated Mexican AM List by Mexico's Federal Telecommunications Commission the other day, I decided to plug their current station list into my Radio Data MW program and compare it to what the FCC thinks is on the air in 'ole Mexico. The results were alarming.

Download Mexican AM List (

The accuracy of the FCC's foreign data is even worse than I thought, though not entirely their fault. The FCC obviously maintains very accurate data for US stations, however data for Mexico is in serious question. One can assume (at least I can, from previous experience) that Canada, Cuba, and other foreign countries throughout Central and Latin America are lacking as well.

By international telecommunications agreement, treaty or otherwise, border nations and others in the nearby broadcasting sphere are required to file with each other's telecommunications commissions in order to keep the resulting RF collision between countries at a minimum. From the results tallied, it seems not much inter-communication is going on. Let's have a look.

A little file gyration was necessary to put the released Mexican data (file name Infra_AM, in .PDF form) into a textual format so it could be read, analyzed, and compared by Radio Data MW. Unfortunately, the Mexican data does not include transmitter geo-coordinates, facility IDs, or engineering information like the FCC maintains, so pairing the records at the outset seemed to be a problem. Call signs can be compared, however, as these almost always remain the same, and stations do not generally move about the landscape more than a mile or two before a new facility ID and call is mandated.

One simple method to grab text from a .PDF file is to load it into Adobe Reader and select it, then paste the selected text into a text editor. Unfortunately, this method often leaves a lot of unnecessary line breaks which must then be removed. A better method is to e-mail the .PDF file to your GMail account, open it, then view it as an .HTML file. At that point, select the screen text again, copy it, then paste this into a text editor. The end formatting is a bit better with not so many false line breaks to contend with. After a bit more tweaking, I wrote a little extra code into Radio Data MW to handle the new file and merge its data with the FCC's.

Sending Radio Data MW off to pair the records by call sign, it then compared frequency of operation, daytime and nighttime powers, and tallied what services each station did broadcast. Annotations were made to the resulting records, and the output tabulated and printed. I have provided a link to the list (find it below) for all interested. Perhaps it will help in your mediumwave DXing.

Now on to the results. But before I get ahead of myself, let me define station "records" and station "facilities", and explain the difference between the two. It will be important in understanding the data.

  • A station "facility" refers to the singular station itself. A station facility generally has several station records.
  •  A station "record" is a single data record usually applying to one of a station's particular "services". This record is a result of a station's application to the FCC for commencement of services. 

A station service can be defined as a "Daytime" service, "Nighttime" service, "Critical Hours" service, or "Unlimited" service. If, for example, a station has both a daytime and nighttime service, at least two records are maintained in some database, somewhere, one for each service. Separate records are a must due to probable differences in daytime/nighttime power, towers used, pattern, etc. Stations must also file for such things as applications for licensing, construction permits, frequency changes, power changes, and other modifications.

The FCC's AM database is huge. Some 25,290 station records are warehoused as of this date, attempting to cover virtually all of North America, most of Central America, South America, and the Caribbean. Mexican records number 4355, not all current - and none have ever been archived when outdated. Sorting through this quagmire is not easy.

A scan of Mexico's Infra_AM file by Radio Data MW shows 855 station facilities. 759 station facilities hold licenses to broadcast and 96 are applications for license or construction permits. 1458 services, day and night, are operating under license, by their claim. AM radio is alive and well in 'ole Mexico.

Of the 1458 services actually operating under license, 1387 were found and matched in the FCC database. 71 were not found. Are they actually on the air? According to Mexico's Federal Telecommunications Commission they are. There is no evidence of them in the FCC's database.

Out of the FCC's 4355 Mexican records, nearly 3000 are impertinent - outdated data, abandoned operations, unlicensed. Many of these could and should be archived.

Furthermore, Radio Data MW discovered the following in its comparison:

  • An incredible 296 Mexican station services have changed frequency, unknown to the FCC database.
  • 624 Mexican station services have changed power, generally upwards. Again, unknown to the FCC.
  • 203 Mexican station services have changed both frequency and power, unknown to the FCC.
  • 670 Mexican station services are in full agreement with FCC records: power, frequency, and service hours.

Part of the problem is once a foreign commission files for station application to the FCC, often that's the end of the communication. Power changes may ensue, and even frequency changes. Additionally, the FCC does not maintain any official "status" of each foreign record - meaning - is it an application, construction permit, or license to broadcast? All 4355 records are lumped under the symbol: "-". Unknown!!! The best we can do under the current situation is accept the newest application ID number as the most current information and hope for the best.

I have created a list of the current licensed Mexican data in .HTML form which will display nicely on your computer. A .CSV type file is also included which may be read into a spreadsheet form. The list contains only licensed stations which have been matched to FCC records, with changes. Nothing in this list has been verified on the air. It should make for some interesting reading.

Download Mexican AM List (

Friday, March 30, 2012

Cofetel Updates Mexican AM List

Mexico's Federal Telecommunications Commission "Cofetel" has published the Mexican AM station list in .PDF form again, posted March 22, 2012. This is a rare event that seems to happen only every 6-18 months. The data is up-to-date as of February 29 (yes this is a leap year).

Get it at the Cofetel site.

No official Mexican AM database in downloadable form, like the FCC database, is evident. It would be nice to have this in readable format in order to incorporate it into a program, like my Radio Data MW program. If someone knows of a link to an official Mexican governmental source, please let me know.

The supposed "official" Mexican governmental link to the AM station list (again in .PDF form) continues to return 503 Service Temporarily Unavailable, and has done so for at least a couple of years. This, I'm sure, was simply a copy of the Federal Telecommunications Commission .PDF. Perhaps we should start recognizing Cofetel as the official source from now on.

Viva Mexico!

Friday, March 2, 2012

Loop Calculator One

Loop Calculator One is a program which will display detailed information about coils, including accurate inductance for short and long coils of many types. It is especially tailored for inductance calculations of polygonal-shaped mediumwave receiving loops.


To download, see the link at the top of the right sidebar under LATEST PROGRAMS. The sidebar at the top right will have the most current link in case the program is updated. The link will change in the case of an update, so I would avoid copying and pasting it into a forum or other web page. Come to the main page of this blog instead.

Click image to enlarge.


Being a mediumwave DXer and wanting to construct my own passive loop devices, I was unhappy with virtually all the web-based coil calculators found on the internet. They used either inaccurate formulas, or formulas that weren't even designed for large but very short polygonal coils like our passive loop, or they didn't correct for internal inductance, self-inductance, mutual inductance, or self-capacitance. The few stand-alone programs out there didn't satisfy either. I set out quite some time ago to accumulate information, formulas, and data to start writing the inductance calculator program. The going was slow. Investigating the history and ferreting out the accurate information took much more time than I thought.

The result was and is Loop Calculator One. Four main formulas (plus two extras) are presented. Two formulas build on the fact that a polygonal loop inductance can be calculated by figuring its equivalent circular size using area and perimeter equivalents, with modification, then calculating the inductance from that as if it was a circular loop. H. Nagaoka's old inductance formula and Wheeler's 1982 Continuous formula, both for circular coils, are used in this way to arrive at surprisingly accurate results. More surprising, I discovered that Nagaoka's old turn of the twentieth century formula using Lundin's formulation of Nagaoka's non-magnetic uniformity coefficiant holds amazing accuracy across a wide range of loop form factors. An excellent treatise on calculating the modified equivalent circular loop radius of a polygonal form can be found at electronbunker.

The remaining four formulas are by F. W. Grover of the NBS (National Bureau of Standards). In 1929, Grover offered two remarkable formulas for solenoid and flat spiral polygonal loops in his paper, "The Calculation of the Inductance of Single-Layer Coils and Spirals Wound with Wire of Large Cross Section", Proceedings of the Institute of Radio Engineers. His two simplified versions for polygonal loops appear in the book "Inductance Calculations: Working Formulas and Tables", (Van Nostrand, 1946 and Dover, 1962 and 2004). Loop Calulator One also presents these four formulas.

All formula results are corrected for self-inductance, mutual inductance, internal inductance at frequency of operation (which is user-definable), and self-capacitance (by check box). Much additional information is displayed about the loop or coil, including calculated tuning range from a user-defined variable capacitor, the coil's form factor, Nagaoka's constant, and more.

Wire gauge can be input directly in American Wire Gauge format, or as a user-specified diameter. R. G. Medhurst's calculated self-capacitance estimate is displayed and can be user-entered to see how it effects the tuning range of the loop.

As a side bonus, a separate formula box can calculate the actual self-capacitance of the loop using the low and high capacitor values and the actual discovered low and high tuning range by using a receiver.

Small circular "radio" (long) coils can be calculated. The Nagaoka and Wheeler formulas are used in these calculations.


Install is simple. Download the .zip file and unzip. Click on the LoopCalculatorOne.exe file to run. This program makes no registry changes and saves no data to your hard drive. It has been developed and tested in Windows 7. It should work fine in Windows Vista and XP environments, and Windows 8. It is written in the old standby Visual Basic 6.

Included in the .zip is a readme.txt file. Be sure to have a look. Also included is an American Wire Gauge chart showing wire diameters.

I hope you enjoy this program and find it useful.