Spring 2011 DX Notes - Phoenix To Denver

A trip across the country is always an enjoyable experience for a mediumwave radio DXer if he has a radio along. While on the road, traveling coast-to-coast presents many different DXing situations and opportunities to observe interesting propagation conditions.

Never being much of a nighttime driver, about 95% of my traveling is during daylight hours. This works out well for me since my particular radio passion is long distance daytime DXing. Cruising along at 70mph in a 2006 Ford Ranger pickup, radio on, tuning up and down the dial searching for weak stations at the lower end of the broadcast band where signals seem to propagate better - life is good.

I stewed about what route to take. Early April weather can be unpredictable and nasty in the high Rockies of Colorado. A trip through this area at this time of year can be tricky. This year I elected to avoid the possibility of extreme weather and travel the I-10 corridor from southwestern Arizona to Denver by way of Phoenix, Tucson, skirt along the Mexican border to Deming and Las Cruces, New Mexico, then parallel the front range of the Rockies northward by following I-25 via Albuquerque and Las Vegas, NM on in to Denver. This leg of the trip back to New York will cover some 1100 miles.

Wednesday April 6

Phoenix is a curious mediumwave city for its size. An unknown fact to many people, Phoenix is currently the 6th largest city in terms of population across the United States. In recent years it has regularly traded places with Philadelphia for positions five and six. As big as it is, both in population and physical area (a huge 517 square miles, 60+ miles across), Phoenix has only two 50,000 watt AM stations within a 25 mile radius of its center, and these are not even in Phoenix proper but in suburban Glendale and Tempe.

So, heading south on I-10 out of Phoenix, the lower powered Phoenix stations fade quickly. Tempe's 50KW powerhouse KMIK-1580 Radio Disney outlet seems to hold in there the longest. Approaching the north side of Tucson, some 100 miles distant, I start to hear some competition from another station on channel. They are broadcasting the Rush Limbaugh program. Confused I am, as my guide shows no other station on 1580 KHz near enough to cause interference. At the top of the noon hour when I hear the ID, the station turns out to be Tucson's conservative voice KNST-790 (5KW), being received strongly on its second harmonic of 1580 KHz! KNST's harmonic hangs in there all the way to the southern extent of Tucson, 20 miles from the transmitter site. I press onward towards the New Mexico border via Benson (north of Tombstone) and Willcox, through the lands of Cochise and the old Chiricahua Nation.

KFI-640 (50KW), Los Angeles is a mainstay of mine in southwestern Arizona during the winter. It is usually on at home or in the truck if I'm out running around. At 217 miles distant, it cannot be considered a local. But its signal is always there, and at good strength. I once heard KFI in mid-afternoon on this same truck radio from the Utah ghost town of Cisco, not far from Grand Junction, Colorado, some 594 miles distant! KFI gets out. Now at 1330L, cruising along I-10 in eastern Arizona and just east of Benson at mile marker 316, I tune for KFI. There it is, still in there but very weak. This, at a distance of 477 miles. KFI fades by mile marker 345, some 506 miles at this point, just past Willcox and only 50 miles shy of the New Mexico border. KFI transmits an omnidirectional signal with a single tower.

Perhaps the most remarkable station to put a daytime signal into southwestern Arizona during my winter stay is North Salt Lake City's sports-talk KALL-700 (50KW). It is receivable on this same truck radio during daytime hours with a weak to medium strength signal all day long. We are talking about a distance of 517 miles here, consistently. Between Benson and Willcox at 1334L, at mile marker 321 I tune for KALL. There it is at 617 miles, though very weak. I am only some 20 degrees off its four tower main lobe of 190 degrees. Understand, at this point, I am perhaps 40 miles north of the Mexican border hearing KALL's Salt Lake City, Utah signal. And during mid-day! KALL fades as I enter the western reaches of New Mexico.

At mile marker 352, ESPN's El Paso, TX station KROD-600 (5KW) is heard at 1405L with a respectable signal. This at a distance of 194 miles.

Crossing the border into New Mexico at 1445L, I tune to 850 KHz looking for powerhouse KOA (50KW) out of Denver. There it is, extremely weak and barely copyable. I have heard Denver radio twice during the daylight hours in southwestern Arizona in the form of KKZN-760 and KLTT-670 at extreme distances of nearly 700 miles, but never KOA. KOA makes the grade here at 554 miles.

Spent the night in Deming, NM, 30 miles north of the Mexican border. Tiny Columbus, NM, right on the border and just south of here, is the site of the famous Pancho Villa raid on the United States in 1916. Excepting the 9-11 attack, it is the only time the continental U.S. has been invaded by a foreign power.

Thursday April 7

Out of Deming the next morning I elect to take the shortcut around Las Cruces. State highway 26 juts off to the northeast, bringing me out to Hatch, NM, and I-25 about 40 miles north of Las Cruces. I am now heading northbound. Approaching Truth or Consequences, the only town named for a TV game show, I hear XEJUA-640, Milenio Radio, Juarez, Mexico, advertized at 500 watts and with a good signal. Juarez is just across the border from El Paso, TX, and due south of me right now at a distance of about 105 miles.

Albuquerque flies by with hardly a blink. Notable and famous in this part of the country is The Talk Monster, KKOB-770 (50KW). With a passive loop assist, it is weakly receivable in southwestern Arizona at 446 miles. For some reason, during daylight hours it seems to propagate better to the west than other directions, as this station basically disappears off the dial in Denver and points north and east. It seems odd that an omnidirectional tower would propagate differently in different directions. KKOB does run two towers at night, with its main lobe to the southwest at 248 degrees. Interestingly, KKOB is one of those rare stations running a synchronized repeater station for signal "fill in". The repeater, also using call letters KKOB, is in Santa Fe, NM, the next fair-sized town just north of Albuquerque. However, the distance between the repeater station up in Santa Fe and KKOB-Albuquerque is only 48.9 miles. Odd, it seems to me, that they need a repeater to fill in at such a close distance, considering KKOB's 50,000 watt signal blankets such a wide area around Albuquerque. I cannot detect KKOB's 230 watt repeater signal as I go by Santa Fe. As far as I know, I am still locked on to the main signal out of Albuquerque.

Proceeding north, at 1429L and 40 miles south of Las Vegas, NM, I find Denver's KHOW-630 (5KW) with weak signal strength at 304 miles. I am only about 12 degrees off of KHOW's main lobe at 200 degrees.

All the way from Deming, through Albuquerque, right up to Las Vegas I have been following El Paso's KTSM-690 (10KW) with good signal strength. At 1501L, arriving at Las Vegas, KTSM's strength at 258 miles is starting to fade. No matter, Las Vegas's own KNMX-540 (5KW) is overloading my radio. The station sits just east of I-25 with a two tower array. The main lobe pushes the power towards 341 degrees, across I-25 and over the north part of the town. Time to rest for the night.

Friday April 8

KNMX-540's overload lessens as I leave Las Vegas, and KTSM-690, El Paso, TX fades out totally a few more miles north, giving way to an unidentified oldies station which grows stronger as I near the Colorado state line at Raton, NM. This undoubtedly is Pueblo, Colorado station KWRP-690 which does run the oldies format. A remarkable signal for a distance of 190 miles, KWRP runs only 250 watts during the daytime. KHOW-630 still at 299 miles and KOA-850 at 272 miles continue to improve as I approach Denver.

The southwest is a wonderful place to DX on the radio. Wide, open spaces with few stations assure excellent long distance DX, even in the daytime. If you're ever crossing the country at some time, give it a try. There is no special equipment needed but an in-car radio.

Eastward Bound Once Again

It's that time of year again. Winter is over and it's time to vacate Arizona's deserts and head back to New York for the summer. The projected route is Phoenix-Tucson-Deming-Las Cruces-Albuquerque-Denver - then points east - probably via I-70 or I-80. Will try to do some DXing along the way. No, of course I will do some DXing!

I apologize that a solid month has elapsed without an article. Life and work sometimes get in the way. Though no posts, I have been busy with radio endeavors. In my spare time I've been working on the Radio Data MW program some. Several articles are in various stages of completion and will be published soon. More in the Signal Patterns series are coming. An article on loop inductance calculations is in the works. I'm also working on an article on how multi-towered antenna array signal patterns are computed. Stay tuned.

Happy DXing!

The Vertically-Challenged Ferrite Loopstick

As we saw in a previous article, An Unassuming Antenna, The Ferrite Loopstick, the groundwave signal decreases in strength when tilting the radio (and thus the ferrite antenna) towards vertical. This effects not just the station tuned to, but all signals across the mediumwave band because the pickup of the magnetic component is lessened when the ferrite rod or bar is rotated away from horizontal. During reception of nighttime, skywave signals, the effect is often less pronounced depending on atmospheric bending of the wave. So, how much is a signal reduced?

I decided to perform a static test. At mid-day I tuned my Sony 2010 to station KBLU-560 (1KW, omnidirectional) out of Yuma, AZ, 69.6 miles distant on a bearing of 200 degrees. KBLU is not a powerhouse here at this distance, but does present a lower-medium strength signal to a sensitive receiver. KBLU was arriving with a respectable 6-7 leds lit (out of 10) on the Sony. Rotating the 2010 to vertical reduced the signal to barely 2 leds. It was weak, but still copyable.

Next I fired up the Tecsun PL-380. Now, the PL-380 is an interesting receiver because it has a direct signal strength readout. KBLU, not as strong on this ULR, peaked at a strength of 25,07 (25 dBµV, 7 dB signal to noise ratio) during normal reception. Rotating the PL-380 to vertical reduced the signal to below the noise level at 15,00. There was no trace of KBLU in the headphones.

Another local, somewhat stronger station is KLPZ-1380 (2.5KW, omnidirectional) out of Parker, AZ, 33.5 miles distant on a bearing of 354 degrees. It registers 31,25 (31 dBµV, 25 dB signal to noise ratio) on the PL-380 during normal, peaked reception. Rotating the PL-380 to vertical reduced KLPZ's signal to a level of 16,06. It was still copyable, though very weak and just above the noise level.

On the Sony 2010, KLPZ registered a solid 7 leds when peaked in the normal horizontal position. However, when tilted vertically, the signal reduced to only a strong 2-3 leds. It was easily copyable. Overall, the Sony 2010 does not seem to do as good a nulling job as the PL-380 in the vertical position.

Similar results were had for the Sony SRF-M37V and Tecsun PL-600.

It was interesting to note that while in a vertical attitude, each radio could be spun about the vertical axis to a certain position causing a marginal improvement in the station's signal strength. This, proving some possible interaction with the radio's circuitry and the ferrite loopstick, or imbalance in the ferrite loopstick itself, causing some pattern skewing.

That the radio receives any signal at all while in the vertical position is interesting. At 90 degrees to the magnetic component there should be no magnetic component to receive on a local, groundwave signal! Again, skewing of the ferrite's receiving pattern might cause this, or perhaps a little magnetic component sneaking through due to path shift of the signal. Or perhaps the cause may be a curious effect usually attributed to open loop antennas known as "antenna effect", where the loop, if unbalanced, does in fact respond to and receive a small amount of the transmitted signal's electrical, or vertical component.

Nighttime reception using this technique is a mixed bag. Although mediumwave DXers routinely use tilting of a radio from horizontal towards vertical to help null distant pest stations at night, using the vertical technique to generally reduce the strength of all signals works erratically at best. Example: powerhouse KOA-850, Denver, CO was actually equal strength at times the other night in both the horizontal and vertical positions, at the same time! With skywave signals booming in from all directions and at many different angles due to atmospheric distortion of the wave polarization, you have your answer as to why.

Could this odd way of nulling signals be used to the benefit of the mediumwave DXer? Maybe at least during the daytime for those of us who are daytime DXers, when conditions are stable?

I set to wondering if it would be possible to nullify the radio loopstick's direct reception of signals while at the same time coupling a passive, external antenna device to the radio - all without tearing into the radio. This sounds counter-intuitive. Why would we want to reduce signal pickup of a radio's ferrite loopstick?

Passive antenna devices like loops and QStick-like devices are routinely used by mediumwave DXers to enhance signal pickup. The problem, and what bothers me the most about using these devices, is that the radio's own ferrite loopstick is still receiving contrary signals of its own at the same time, degrading the effect of the passive device. Further degradation may come from the radio's loopstick having poor nulling ability or an overly wide broadside peak, also compromising the purity of the passive antenna. The radio also might be positioned somewhat differently than the passive device, causing unwanted signals to interfere with the natural peak and null of the passive device.

So, the question remains: What if it were possible for the radio to only see the passive device as its antenna, and largely ignore directly-received signals from its own ferrite loop antenna? The vertically-held radio with its corresponding vertically-oriented ferrite loopstick seems to fill this bill. But how do we couple to it in this position?

This creates coupling problems in several respects. In the case of the external tunable ferrite loopstick or QStick device, it must be placed parallel to or off the end of the radio's own ferrite loopstick in order for it to work. That means it would be vertical too, and it wouldn't receive much signal itself, since when vertical it is 90 degrees to the magnetic component of the received wave just like the radio.

The usual passive loop, with its coil wound in a solenoid fashion on a square frame (sometimes called "depth-wound"), won't couple much signal at all to a radio held in the vertical position due to its loop being 90 degrees in relation to the radio's ferrite coil winding. If we rotate the passive loop to a horizontal position we have good inductive coupling to the radio, but then the passive loop is 90 degrees to the wave's magnetic component and signal pickup is reduced to nil. Perhaps a spiral-wound loop?

And another possibility becomes evident. Why not put the radio inside a Faraday cage, eliminating all outside signals? But then, how do we couple the passive device to it, and still not tear into the radio? All food for thought. Perhaps more in a future post.

Hope you have enjoyed this series on a most interesting device, the ferrite loopstick.

The Twin Coil Antenna Patent

Let's continue our discussion of the ferrite loopstick, a most interesting device.

A curious animal appeared on the radio scene in March of 2003. It was called the Twin Coil Antenna. Its inventor was one Christopher Justice of the C. Crane Company.

A July 2001 application for United States Patent number 6529169, "Twin Coil Antenna", shows an "antenna for a radio receiver comprising a ferrite rod; spaced coils wound about the ferrite rod; a variable capacitor element connecting each coil together; and a combiner connecting each coil together." It was a souped-up ferrite loopstick.

In analyzing the standard tuned ferrite rod utilizing a single coil, Justice determined there is a "need for improved efficiency and a higher signal-to-noise ratio antenna that does not saturate at high frequencies", and it was to these ends that his experiments were directed.

Ferrite core antennas are widely used as antennas for radio receivers, particularly for AM broadcast band radios. This is done by winding a coil or loop, generally with tightly-spaced turns over one end of a ferrite rod or bar. The ferrite has the effect of concentrating and intensifying the received magnetic field inside the loop.

Unfortunately, the ferrite core tends to absorb some of the signal power. Additionally, the combined resistance or impedance of the antenna and ferrite core is typically just a few ohms or less. In operation, the antenna must be coupled to the larger input impedance of the receiver. This is generally accomplished by adding a capacitor to tune the ferrite loop to a certain frequency, creating a resonant circuit.

When a signal enters a ferrite rod antenna that is tuned to resonance with a coil and capacitor, the magnetic lines of flux begin to saturate. When this saturation occurs, the ferrite rod antenna takes on polarity, much like a magnet does. Ferrite antennas having only one pick-up coil result in loss of efficiency and limit the signal-to-noise ratio available to the receiver.

In the words of the patent application, "The invention provides an antenna for a radio receiver that has high efficiency, high signal-to-noise ratio and that does not saturate at high frequencies. This is accomplished by an antenna structure which employs a ferrite core having two (or more) coils coupled together and located on the ferrite core such that the magnetic fields coupled to the coils induce signals which combine to produce a resulting signal level equivalent to the combined signals in the coils. The coils may be coupled through a transformer where the combined signals of the coils are received in the primary of the transformer. The transformer coupling the antenna coils can dramatically narrow the bandwidth of the received signal. In addition, the antenna coils and the transformer windings may be connected to a capacitor to form a resonant circuit. The capacitor may be variable so the resonant frequency of the antenna may be set by tuning the capacitor. This results in an increased signal level and reduced interference and noise."

Read more about this fascinating antenna device on Google Documents' Twin Coil Ferrite AM Antenna. Justice's patent was accepted and issued on March 4, 2003.

CCrane sells their version of the Twin Coil Antenna on their website.

Next up in this series: The Vertically-Challenged Ferrite Loopstick