Saturday, July 30, 2011

Mediumwave Station Reference Lists

I DX a lot outside, whether on the road in a vehicle or just to be outside and away from the extreme household noise that we find today. Whether you be a mediumwave DXer, shortwave DXer, or DXer of another kind, the problem in DXing away from home has always been the lack of ready DX reference materials nearby. You have to pack and carry all that stuff. And I like to travel light. My outdoor DXing is often casual and spur of the moment, with a ULR or portable. Who might that weak station be under KHOW-630? I need a station reference.

At minimum, a reference guide of stations helps you to know what to look for and what to expect, so it is important to have one close by. In recent years there were two common radio DXer guides in bound-book form, the World Radio TV Handbook (WRTH) and Passport to Worldband Radio. I used to buy them faithfully every year. Passport had a great radio review section, but its station reference only covered the shortwave bands. Passport also folded last year and ceased publication. It was a great shortwave guide.

WRTH covers longwave to 30 MHz and also FM and TV, listing nearly every broadcast radio and TV station a country has. Unfortunately, its US mediumwave coverage is not complete, in that it doesn't cover many lower powered and graveyard stations. The information is scant, basically only station addresses, power, and antenna type. The recent list price: $35.00 per issue, though it can be had at a discount later in the year. That's a lot of dollars for a little bit of usable information if you are just interested in mediumwave.

The National Radio Club publishes its AM Radio Log every year, and it's a winner. The current, 32nd edition of the log contains some 300 pages in 8.5 x 11 inch size, 3-hole punched, in U.S. loose leaf format. Current cost is $20 for members and $26 for non-members.

The NRC also publishes an Antenna Pattern Book, helpful in determining which direction stations are favoring in their broadcast pattern. The current, 6th edition (late 2005 data) is 238 pages containing both daytime and nightime patterns for stations in the US, Canada and parts of Mexico. It is in the same format as the AM Radio Log, and is designed to be used as a companion to it. The "book" fits in a 1 inch three ring binder. The current cost: $17 for members and $23 for non-members.

We are starting to accumulate a lot of paper (500+ pages so far). And the cost is going up. As you can see, reference guides can be expensive to buy. They also go out of date quickly. Thirdly, they can be heavy and take up a lot of space. We are back to the packing and carrying problem.

In the article, Radio Station Databases 101, we explored several countries' mediumwave databases which might help us in creating our own lists of mediumwave stations to aid us in our DX quests.

However, database information is not generally in a readable format. In most cases it is hundreds or thousands of lines of incomprehensible textual data. It is mainly useful to the software hobbyist who might want to write a database program or create an XCEL (.XLS) file to display station information in various sorted forms. This is obviously a highly technical and tedious endeavor which most people are not equipped or trained to do. My own project in this area is the Radio Data MW program. I will write more on this project at a later date.

Thankfully, a number of web sites exist which have done much of the work for us, tabulating this data and presenting it in one form or another which can be useful as a reference. These web pages, or in some cases, files, can simply be printed and placed into a binder of some sort, then used in your shack or carried to an outside DX location and used there. We have at least saved cost, though not paper.

Let's explore what's available for free on the web.

Pre-eminate in the field, the FCC maintains an AM Query web page that utilizes and searches its standard database for all US stations - AM, FM, and TV, as well as Travelers Information (TIS) stations. I have found the FCC information for US stations to be highly accurate. Be wary of Canadian and Mexican information. Much of it is either redundant or out of date. Properly used, the FCC AM Query will output a large text file of all MW stations.

Opening the web page and selecting the dropdown boxes, "Authorization type: Licensed Records Only (Daytime + Nighttime" and "Output-- AM Short List (or AM List)", then clicking the Submit Data button returns a huge list of active stations. Save this to a file, print it, and you have the entire US mediumwave listing. But it is huge, some 8 megabytes in some cases. You can also search by frequency or state, thus you can create customized lists, saving and printing them.

The FCC also makes antenna pattern plots available. Virtually all stations with multiple towers have directional patterns and the FCC makes this plot available in PDF form. Once displayed in your browser, this PDF can be saved to a file for future reference. Pull up the page for the station of interest to get to the pattern link. Example: WWKB-1520 facility and WWKB-1520 pattern., a favorite site of mine, also has an advanced station search page. Many of us think of radio-locator only as the site that shows us mediumwave antenna pattern plots. The great thing about their page is you can also plug in parameters to filter stations by frequency or state. You can even search by broadcast format. Results are returned in formatted HTML pages. Save the resultant pages to file, print them, and create your own database of stations.

As just stated, is another site which produces antenna pattern plots. These particular plots depict the expected signal coverage area of the mediumwave station over a map. The pattern plot is displayed as a GIF image. Once displayed in your browser, this GIF can be also saved to a file for future reference. Example: WWKB-1520 pattern. is a simple textual site that tallies all US stations by frequency. Canada and Mexico are also available. Pick a frequency, display the list, save it, then print it.

The AM Logbook by Lee Freshwater is another interesting site that lists stations in a myriad of ways. Frequency, call sign, state, city, sites (transmitter), slogan, etc. Again, select your preference, display the list, save it, then print it. US and Canadian stations are represented.

AM Logbook also provides its current AM database in spreadsheet (XCEL) format. You must of course have an XCEL (.XLS) viewer. You'll find the link on the Updates page.

Topaz Designs is a basic textual site with search box, returning results by frequency, state, power cutoff (100W), and broadcast format. US and Canadian stations are represented.

Mediumwave List is a comprehensive site that offers a lot of information, including transmitter mapping, logbooks of users, and station news. Worldwide mediumwave stations are represented, including of course North America - Canada, Mexico, Cuba, the Caribbean, etc. To create your station list, login if you are a member or click "Continue as guest". This site will also allow you to download files from their huge database of stations, by region or country. The output is in PDF form. Registration is required for certain information beyond the basic.

Outside of the US, the Mexican government provides a very nice list of their mediumwave service in PDF form. Australia provides a list of their mediumwave service in XCEL form. Using the Industry Canada site, you can search the Canadian mediumwave service and create various lists in text, HTML, and XCEL form.

Note that most of these sites return station lists in a web page (HTML format) versus a simple text page. Lists can be saved as a web page by the Save As function in your browser. But there is also another way. It is possible to select the important data on the web page, copy it to the Windows clipboard (CTRL+C), then paste it into a text editor (CTRL-V). The text can then be saved as a text file, which may require a little editing. Sometimes it is easier to read this way. If you go this route, be sure to use a text editor that supports Unicode text format, like Window's Wordpad, Notepad++, etc. Window's Notepad does not, and you may get a jumble of text with no line breaks.

So, we have several options available for saving and/or printing station lists. We have two options available for saving and/or printing antenna pattern plots. If you choose to print some or all of these and place the pages in a binder of some sort, all well and good. But a comprehensive list of the entire US database is still a lot of paper to store, pack, and carry around. Of course we could just save all these files to a laptop and take the laptop with us. There is also one another option.

Next up: Mediumwave DX Meets the eReader

Also see: Mediumwave DX Meets The Tablet Computer

Friday, July 22, 2011

The Field Strength Machine

What do professional broadcasters and the FCC use to measure the field strength of a mediumwave station? Let me assure you they don't use charts and graphs like we hobbyists do. Let's find out.

What appears to be the premium device on the market today for field strength measuring is the Potomac Instruments PI-4100 Medium Wave Field Strength Meter, available from Potomac Instruments of Frederick, MD, and shown in the photo just above. It is Potomac's "third generation of precision survey instrumentation intended for the direct measurement of electromagnetic field strength in the 520 KHz to 5.1 MHz frequency spectrum."

This meter has a laboratory quality radio frequency voltmeter, a calibrated, Balanced Loop antenna, an internal GPS receiver, an internal calibration source, and data acquisition hardware and software. The unit weighs in at about 5.5 lbs. It is the successor to the previous industry standard, the FIM-41 meter, also by Potomac.

Also included in the 4100 is a spectrum display. Sensitivity is phenomenal, from 22 µV/m (microvolts per meter) to 50,000 mV/m (millivolts per meter). And there is no "meter" as with old units; everything is indicated digitally and calibrated automatically. The on-board GPS indicates your current coordinates as well as the distance and bearing to the station. It even includes a "wet" compass. For more information, see the Radio World product survey.

Oh, what I wouldn't give to spend a day with one of these. What is the price, you ask?

A cool $14,975. You can pick up a used one for about $13,000. Or, you might be able to buy a second-hand FIM-41 for about $5,000, or rent such an older unit for $595 per week. I can only dream.

The older, Potomac Industries FIM-41 unit:

Monday, July 11, 2011

The Perfectly-Spaced Passive Loop

Let's build a passive loop with perfectly spaced coil turns.

One of the problems I've always encountered in constructing passive loops is keeping the coil turns evenly spaced and perfectly parallel to each other. Regardless if you form a loop support in the form of a cross or a square, you must devise a way to space the turns evenly at each corner. Traditionally I would make the support of wood (usually 1 x 2 lumber) and file notches in the corners for the wire to sit into, or pound many tiny nails in a row to hold the wire apart. It's tough to file evenly-spaced notches very close together and tedious to pound a lot of tiny nails.

I tend to use light gauge insulated, solid copper wire for my loops. Stripped-out four conductor telephone wire is cheap and easy, usually running about 24 gauge. It's nice and light, flexible, and holds its shape. Have a walk around a hardware store and you will find many other items that might be used in the construction of antenna devices. One day, I came across some short plastic pipe nipples, generally used in sprinkling system work. These were 3/4 inch pipe size (3/4 inside diameter) and 1.5 inches long. They are threaded the entire way across, with thread spacing at 14 threads per inch (0.0714") apart - perfect thread spacing for this sized wire. The thread notch is just deep enough to accommodate most small sized wire. It would be difficult to file notches or drive tiny nails this precisely together. 1/2 inch diameter pipe nipples could also be used, as the thread spacing is the same.

I built a square frame for this loop, 24 inches on a side, again out of 1 x 2 inch wood, commonly called "furring strip". At each corner and at the center of each side I screwed a 2 inch screw (8 screws total) to hang the plastic pipe nipples on. One could probably use wooden pegs to avoid the metal screws being near the loop wires, but I have not found it a problem as it's a small amount of metal, and at 90 degrees to the wires. I placed a plastic nipple on each screw. The screws don't actually fasten the nipples down, but the nipples sort of pivot on each screw and move with the wire, settling where they need and taking up the wire tension. Use a screw with a wide enough head to capture the nipple so it doesn't slip off the screw.

The loop requires about 90 feet of wire, 11 full turns in all. I mounted a 365pf variable capacitor for tuning near one corner. Drive two very small nails into the frame at the same corner as the variable capacitor to secure the start and end of the coil. Fasten the wire to start and begin winding the loop, making sure the wire sits into each nipple thread from the thread closest to the frame and working towards the outside. Run the last leg of the final coil turn back to the ending nail and fasten there. Solder the start and end of the loop to the capacitor. Install a knob on the capacitor and you are done. This loop tunes precisely between 530 KHz and 1700 KHz.

PVC could be adapted to use as a frame, and I considered this before using the wood. A 3-legged, 3/4 inch PVC corner tee is available which has a female pipe thread at the center leg. The nipples would be screwed into this leg of each tee to form the corners of the loop like we did with the wooden frame. A PVC frame would be totally portable, as it could be disassembled very easily.

I find a loop with perfectly spaced turns to have sharper nulls and more precise (sharper) tuning. Try this loop sometime.

Tuesday, July 5, 2011

Silicon Labs Si4831 Chip and the Tecsun R-2010

Many of us are anticipating the arrival of the new Tecsun R-2010 DSP radio. This radio will use the Silicon Labs Si4831/35-B30 chip, developed for consumer AM/SW and FM operation. This second generation mechanically-tuned digital CMOS AM/FM/SW radio receiver IC integrates the complete receiver function from antenna input to audio output into one chip, like the Tecsun PL-380's Si4734 digital chip did. The difference: this chip is analog-tuned.

Band coverage of the new chip is 504 KHz to 1750 KHz in the mediumwave band, 5.6 MHz to 22.0 MHz in the shortwave band, and 64 MHz to 109 MHz in the FM band. Note that the 120, 90, and 60 meter tropical bands are not available. Also note that the longwave band is not supported.

AM sensitivity is comparable to the Si4734 chip, at 30µV input for 26dB (S+N)/N (signal plus noise to noise). The PL-380's Si4734 chip had a typical 25µV (S+N)/N sensitivity.

The receiver IC has very low power consumption and runs off of two AAA batteries. Typical supply current at 2.7 to 3.6 volts input is 17ma. Shutdown mode (power off) requires an insignificant 10µa.

The main external components required are a 100K ohm tuning pot, LED tuning and power indicators, a ferrite loopstick antenna for mediumwave reception and telescoping whip for shortwave and FM. Again, similar to the Si4734 chip, the antenna ferrite inductance required will be 180-450 µH. The Si4831 also supports an air loop antenna for AM. Air core loop support is suggested through an external 1:5 transformer, raising the input inductance 25 times, allowing for an actual air loop inductance between 10 and 20µH. The PL-380's Si4734 chip also supported the air core loop in the same way.

No mention of soft-muting or user-selectable bandwidth filtering is found in the currently available Si4831 documentation. Surely this chip would have the capability of multiple bandwidths. In the documentation they describe "....patented architecture allows for high-precision filtering, offering excellent selectivity and SNR with minimum variation across the AM band." Selection of bandwidths on the Tecsun PL-380's chip was done by program code. Let's hope this one has the ability.

Frequency drift tests show perfection compared to a traditionally capacitance-tuned radio like the Sony ICF-C218 clock radio. Hot and cold tests performed (room temperature to 45C and room temperature to -10C) resulted in virtually zero drift.

As an added bonus, use of a mechanical resistive tuning pot allows the frequency to be displayed in a linear format on the dial, so frequencies at the high end of the band are not crammed together as with capacitive tuning.

The size of this unit is unknown to me, although it looks similar in format to the Tecsun R-9012 or the Kaito WRX911. Both of these units are cigarette pack-sized.

Silicon Labs recently reached a major milestone in the broadcast audio market, announcing that it has shipped its one billionth broadcast radio IC. Silicon Labs’ digital CMOS broadcast radios are widely used in handsets, portable media players (PMPs), personal navigation devices (PNDs), automotive infotainment systems, tabletop and bedside radios, portable radios, boom boxes and numerous other consumer electronics products.

Silicon Labs introduced the industry’s first single-chip FM receiver in 2005, the Si4700 IC. As the industry’s smallest, highest performance and most integrated FM broadcast radio IC, the Si4700 redefined how FM tuners were designed into consumer electronics products.

I eagerly await the introduction of the Tecsun R-2010.