When I first started my AM DX journey back in 1993, one of the things I loved experiencing the most were DX Tests.
I have always been a bit of a night owl, anyway, so the thought of staying up until the wee hours of the morning in order to snag a new station, a new state or even a new country was hardly a deterrent.
I have fantastic memories from those early DX Tests that I took advantage of: KWCO-1560 in Chickasha, OK, KERR-750 in Polson, Montana (that night, I was joined by my mother, W4GVH, in the shack to snag my first Montana station) and WVWI-1000 / Radio One in the Virgin Islands (a new country for me). There were a lot of swings and misses during that time as well. Lots of "I think that is morse code, maybe?" Those were missed opportunities of stations that didn't make it into the log book.
For the unfamiliar, a DX Test is a special broadcast by a radio station that is coordinated by volunteers or the DX Clubs (such as the National Radio Club [NRC] or the International Radio Club of America [IRCA]) in an effort to provide rare DX opportunities to DXers. These are usually difficult to hear stations in rare states or countries that are not commonly heard out of certain locations. The stations volunteer to conduct these test as they can often use the opportunity to calibrate and adjust their transmitter for better operation.
DX Tests usually consist of very unique programming, designed to purposely 'cut through' a frequency and stand out. Things such as morse code IDs, various tones and unique sounds, marching band music, etc. Anything that will allow the signal to stand out and also be a bit easier to recognize from deep in the noise floor.
After those early 90s DX Tests, I hadn't participated in listening for a DX Test in.....decades. Then, earlier this month, it was announced there would be a DX Test at KJJR in Whitefish, Montana. I was transported back to the energetic, young DXer, giddly contemplating coloring in a new state on my "states heard in Charleston" map.
Further, I was very excited as this would be my first DX Test using SDR technology. In those years past, I as completely reliant on my ears, and only my ears, to pull out the sounds of the test. I would often record the DX Test so I could play it back later, but even then, all I could rely on was my ears.
One added benefit for many of the SDR as it relates to DX Tests, no more late nights! Set up a schedule to record during the DX test, and while you slumber away, your SDR and software are capturing all of the audio and data needed for you to review when you are much more awake!
Also with SDRs, we now have visual clues as well to aid in knowing when a signal is coming in. Morse code and other tones stand out very clearly on an SDR waterfall. And if you can see it visually occurring, you know better when to listen closely for the audio. Perhaps some of those missed opportunities I mentioned earlier could have made it into the logbook had I been able to visually see clues of the test and then line that up with received audio?
In review of the video playback of the audio I received from the KJJR DX test, it is easy to see where the morse code and tones were coming through. Starting with the first screenshot, below, we see the morse code ID appearing on the SDR waterfall during a fade of dominant WCBS - New York.
As we look closer, we can identify very clearly the tell-tale markers of the CW signal on both sidebands. As they are tones in an amplitude modulation signal, they will appear off frequency from the main carrier frequency, and in both sidebands, making them easier to spot. This is the same concept we see in amateur radio digital modes, where the individual tones appear on the waterfall of our digital mode programs as individual blips. I have zoomed in for the screenshot below, you can clearly see the actual CW dots and dashes. Even if you do not know CW, you could record on the SDR, and use the visual clue to then pull up a list of CW letters/numbers and VISUALLY decode them. Here we see the unmistakeable DAH-DIT-DAH of the K and the DIT-DAH-DAH-DAH of the first J in KJJR. We also see the peaks on the spectrum analyzer that coincide with the CW signal.
As a DXer, if I am listening for a DX Test that I know is transmitting morse code, and I see what looks like morse code on my SDR waterfall, this is a visual clue that I need to listen closely to see if any audio is making it through. Mind you, if there is a station (or more than one) on frequency they might not stand out this easily. Especially if the station(s) are especially strong. However, fading happens and if you are lucky, that fade will line up with a period of easily identifiable signals, such as these!
In the KJJR DX test, another thing that was transmitted was "tone sweeps". these are tones that start at a low frequency and then will "sweep' up to a higher frequency (they can also go the other way). These are usually very easy to hear, but they can also be incredibly easy to catch on an SDR waterfall.
The screenshot below shows a tone sweep being received by my SDR. Do you see it?
If you spotted the diagonal lines that start at the center carrier frequency and then shoot outward on both sidebands, then you found them! The below screenshot points them out.
Further, do you notice how the upper sideband has a longer tone sweep than the lower? That is partly because of adjacent channel interference from a Cuban station on 870 kHz. Because there was less interference on the upper side band side of the AM signal, the USB tone sweep is able to continue to be seen in the higher frequencies. The LSB portion of the sweep cuts off when it hits the interference.
Finally, another element to the DX Test were 1kHz tones. Any DXer that has ever tried to pull in a Trans-Atlantic signal and when hunting for Hets knows this sound and what to look for all too well.
Do you see the tones in the screenshot below?
If you spotted the solid lines at 881 and 879 kHz, good job!
These are super easy to identify as they maintain as a solid line on the waterfall. Even with a strong station on frequency, during slight pauses in programming, breaths, etc. you would be able to easily see and hear these tones. Even as weak as these were, they were audible and visible! It is important to note that had these been 2 kHz tones, they would have been found at 882 and 878 kHz. So, if you know what kind of tones are being broadcast, that makes it easier to know what to look for!
Now that you have trained your eyes on what to look for, try watching the video below that contains all of the samples received here in Charleston from the Montana DX Test. See if you are able to notice the audio a bit more now as well!
With the advent of SDR technology DX Tests, while they still can be challenging, are something that even more DXers can now enjoy and have.a greater rate of success in receiving them. So keep a look out here on DX Central for announcements of upcoming DX Tests and get those SDRs ready to put some great DX in your logbook!
73 and best of DX,
Loyd
W4LVH