Have you ever received a reference signal on a shortwave radio? These signals are very helpful for testing the transmission status of a short-wave band, debugging antennas and repairing radios, evaluating and comparing actual sensitivity and noise, with the popularity of SDR equipment, you can also test the reception performance of different devices according to the waveform pattern of the signal, today and the radio uncle BG5WKP to read this article, the test part of the content has been abridged!
<h1 class="pgc-h-arrow-right" data-track="3" > looking for a reference signal: the International Beacon Project</h1>
Text: 13dka
If you really like tossing around antenna and radio repairs to get the most out of these faulty radios, you probably have your own set of reference beacon stations. If this is a new concept for you, then a reference beacon station is any station that you think is easy to check the spread, the general function of the radio, try to improve the reception or comparison of the radio ... Ideally, they are always on when you need them and receive signals from beacon stations around the world in a variety of ways to determine the transmission advantages and distances of several shortwave bands. The traditional sources are, of course, time-timing stations and VOLMET stations on the HF shortwave band, even though the latter only gives you two 5-minute hours per hour to test reception from a particular region.
A reliable reference weak signal source is especially ideal for me because I like to prove and compare the actual performance of radio receivers outdoors, a QRM-free place on the German North Sea coast. Finding reference stations with "grassroots" signal levels is a different challenge than in the past, in the absence of anthropogenic noise and an increase in 10dB antenna gain, finding reference stations with slightly larger antennas tends to be loud there, even in baseline ionospheric conditions under the least active spotless sun. In short, my old reference station wasn't that good anymore and I had to look for something new.
<h1 class="pgc-h-arrow-right" data-track="85" > International Beacon Project (IBP</h1>).
You've probably heard of the International Beacon project before, or seen it on KiwiSDR (they preset the IBP frequency in the Band drop-down list), and how the OpenWebRX client shows you the beacons you're currently using. I have to admit that until recently I completely ignored the existence of IBPs, perhaps because I rarely hear any of them when trying Kiwis. I then stored 5 frequencies in my little Icom to check how I heard them outdoors, and only then did I fully realize they were exactly what I was looking for. When I started working with radio recordings at home, I began to understand how amazing they could be!
<h1 class="pgc-h-arrow-right" data-track="86" > how this works</h1>
Unlike classic low-power propagation beacons, which are scattered across frequencies, IBPs consist of 18 beacons with common properties and common transmission formats, distributed across (almost) all continents, filling each band with only one frequency schedule in a precise, synchronized 3 minutes. Here is a list of stations with a 20m/14100 kHz transmission schedule:
Each beacon has a 10s time slot in a 3-minute cycle, and after completing the transmission on one band, it will jump to the next band until it reaches the 10m band. This means that each station will start at 20m (14100 kHz), 17m (18110 kHz) after 10 seconds, 15m (21150 kHz) after 20 seconds, 12m (24930 kHz) after 30 seconds, and 40 seconds later (2820 kHz). It will then wait for its turn again on 20m in a 3-minute cycle.
It also means you don't need to learn the code that identifies the beacon: all you need is a brand-new synchronized clock on your wrist, computer or smartphone, and the website provides you with a real-time update schedule and a list of all the apps platform and device.
<h1 class="pgc-h-arrow-right" data-track="87" > interesting beeps and whistles</h1>
Each beacon itself is a very challenging DX target, and IBP beacons come with a built-in scoring system! Each beacon sends its call sign and a 1-second 100-watt (which is a lot for beacons) plus 3 consecutive dashes of 10W, 1W, and 0.1W:
If you can hear a call sign or the first dash, you know there is a path to the continent, and the 2nd through 4th dashes tell you how good the path is right now – a great tool for assessing practical, practical, global communication conditions. 3 minutes per band. If you're wondering what the bands (at least the upper bands) are looking like right now on your own radio, that's certainly better than staring at the abstract ionospheric exponent.
What's more, these 4 dashes immediately challenged me to hear as many of them as I could! Sorry to have done the following ostentation, but I find myself overly obsessed with 1W and 100mW signals: it's not really comparable, but imagine how much light a 1W bulb would emit (that's half of a classic bike bulb) and how far the light could travel, not to mention how far 100 milliwatts (1/7 of a vintage radio dial bulb) would glow, but in the form of an HF, this power can reach an astonishing range:
This is a 4U1UN beacon on top of the United Nations Headquarters building in New York, nearly 6,000 kilometers or 3,730 miles across the Atlantic Ocean, three times in a row, the first two clips were recorded on July 2 and July 4 at 20m, and the third one (0:18s) was in the 17m band, also on July 4:
YV5B (8,135 km/5,055 miles) in Caracas, Venezuela, first at 14,100 kHz (July 2, 0:29 a.m.) and then at 21,150 kHz (July 3, 20:38 UTC):
This is the California W6WX (8816 km/5478 miles) with a frequency of 14 MHz, recorded before sunrise (2:57 a.m. UTC), 0:09 a.m. timestamp after sunrise (4:36 a.m. UTC), and unexpectedly at 18 MHz (timestamp 0: 19s, only 3 dashes):
Bragging about it, once my excitement subsided a bit, I realized how useful it was:
<h1 class="pgc-h-arrow-right" data-track="88" > world signal generator</h1>
IBP beacons are of course always there unless they encounter some sort of problem (Hawaii, Sri Lanka, and Kenya are currently offline), so they should receive one beacon at least every 3 minutes at any time of the day. In addition to indicating propagation, they provide weak signals from all important compass orientations throughout the day, and even if some of them are very strong, 3 weaker dashes can still be used. These dashes are useful for 10dB power steppings making IBPs a unique and meaningful signal source for evaluating and comparing receiver sensitivity or more generally overall receiver system performance as well as optimizing antennas for specific target areas, etc. – you can also get signals from countries where there are currently no other or reliable indication stations.
What's more, because they are CW signals, the recorded audio signals and their waveform plots directly reflect the SNR (at least when they're weak, so AGC doesn't work), so if the recording gain level is always the same (e.g. in the IC-705's recorder), recordings at different times can be compared and correlated with each other – even visually:
A practical example is to record, for example, several 3-minute loops before. Connect radial or lift wire supports and then record a few more cycles after the change. If the differences are small, you can use recordings to analyze and verify more subtle differences, and if you don't bring a computer to experiment on site, you may be able to experiment later in a quiet home. Beat listen to a radio station, rush out and make changes, and then listen to the station again a few minutes later when you forget the previous sound.
By importing all recordings into the same project into the multitrack editor, as shown in the image above, I can keep a complete history of the recordings and compare them to new ones, such as verifying the feeling of blurring, proving that the perceived improvements are not just flukes by making enough recordings so that I can average daily or hourly changes. Of course, it's best to track conditions at logging time to include them in any consideration:
<h1 class="pgc-h-arrow-right" data-track="89" > proof of concept</h1>
Maybe you can understand my keenness to try this out in some actual receiver testing. I also took the opportunity to try out my now slightly improved receiver comparison setup (pictured below): The signal from the regular antenna (a simple vertical wire on a 33 ft./10 m fiberglass rod, as shown at the top of the article) goes into the diamond-shaped SS-500 splitter box (not visible), from there to the two receivers to be compared, recording their audio signals via the line output into a small digital field recorder.
Because it was the only other receiver I had the right CW filter, and the only one I could handle all the voltages my favorite outdoor antenna could provide, I had to use my little Belka DSP against the high-priced 10dB IC-705. It's not exactly an Apple-to-Apple comparison: Belka's antenna input is designed to match well with its short whip, so what makes this radio so good in this role may mean less than ideal or at least a different match (passive!). External antenna, depending on frequency. That's why I'm not entirely sure how much of the difference is due to impedance issues. I should also say that I couldn't reverse that test and pit Icom against Belka on Belka's turf: on a 26-inch short antenna, Belka would push Icom to the ground and rub it.
Back to IBP beacons: In order to level the field, I had to take Belka's 300 Hz CW bandwidth on Icom, otherwise I would set it to 100 Hz to get a better SNR on those beacons (the example you bragged about in section above). After loading the recorded file into my home DAW, the SNR difference between the radios looks significant:
The top Icom, the second waveform below is the Belka DSP.
<h1 class="pgc-h-arrow-right" data-track="90" > the W6WX beacon disc antenna on Umonhon Hill</h1>
The method certainly has some limitations: first, receiving these very weak signals is indeed a challenge, for example, in the noise of my house, I can hardly receive one of them. If the radio does not have a CW, an SSB filter must be used, and then the frequency neighborhood may become a problem and may not work properly on race weekends, at least not at 20m. It also doesn't say anything about filter shape or sound quality, SSB clarity, or AM performance, but that's where other reference stations (shown above) complete the World Signal Toolbox.
W6WX beacon disc antenna on Mount Umunhon
<h1 class="pgc-h-arrow-right" data-track="91" > conclusion:</h1>
This "IBP" approach seems to be a very meaningful way to assess or compare actual sensitivity and noise. Again, the importance of a QRM-free environment is emphasized: Thanks to the dashed 10dB power stepping, I can safely say that anthropogenic noise of only 10dB (and possibly even less) at the top will make both receivers look exactly the same. Instead, it allowed me to give me a rough idea of how big the difference between the two receivers is.
The CW nature of the reference signals makes their recordings a useful, even visual tool, for short- and long-term comparisons and experiments with my toys, which is a surprising finding for me. I haven't proven its practical usefulness yet, but I'm pretty sure it will help, for example, a practical evaluation of antenna concepts, and perhaps something I haven't thought of yet.
Here comes the uncle:
So what are your "benchmark" and "reference" stations? Welcome to review!