As nearly as I can tell, 13 people participated, and many had something positive to say about the experience, including they would like to do it again.
I say “as nearly as I can tell” with regard to the number of participants because some people posted the same thing multiple times . . . and there is a simple reason why. When someone posts a comment for the first time, or posts a comment for the first time with a new email address (which is one of the required fields when you post a comment), that comment is sent to moderation for approval before it is posted . . . which causes a delay. Thinking it didn’t work the first time, the commenter reposts again (and perhaps again and again) and after a while, all the posts appear, which confuses the counting process.
A variety of equipment was used: 4 GE Superadios, 2 Belka radios, a Yaesu FT950, an AirSpy SDR, a single-transistor regenerative radio, and a Sangean ATS 909-X2. Some ran barefoot (using internal antennas), some employed loops, dipoles, and even an AFA-200 from Icom.
In terms of station count, Tom Laskowski, in a neighborhood park in South Bend, Indiana, absolutely killed it with a GE Superadio, logging 69 stations with lots of colorful detail. Clearly he was enjoying himself. The total mileage of his top five stations was 1230 miles. He qualified for Chuck Rippel’s generous offer of a Superadio refurb.
13dka “informally reported” his results in miles, furlongs, and attoparsecs. From a dike at the German North Sea Coast (Riddle of the Sands?), his farthest station was 677 miles away and his top five total was 2748 miles . . . that’s 21,968.5 furlongs in case you were wondering. He used a Belka 2022 in combination with an AFA-200 active ferrite antenna (his ultra portable MW rig).
David Mappin in Filey, UK, managed to hear a station in Solt, Hungary, at a distance of 987 miles. His top five total mileage was 1965 miles. He used a Sangean ATS 909X2 with a Cross Country Wireless (CCW) Loop Antenna Amplifier with a one-meter loop made out of coax.
Everyone seemed to have a good time, even those to whom “life happened,” and could only get on for a few minutes.
So, therefore, you are all sentenced to more DX challenges in the future!
My operatives (the upstate irregulars) deep in the underground bunker at El Rancho Elliott tell me that some of the names of future challenges might include “The Midnight Ramble” and “The Grayline Sprint” . . . but these sources are unreliable.
In the meantime, thanks to all for participating, and I am glad you had fun.
PS – Some have suggested that taking station transmit power into account when figuring out scoring might be a thing to do. If you have practical ideas for doing this, post them, with examples in the comments section below. Bear in mind that any calculation of “difficulty factor” will fall on the folks recording their logs.
First a word of acknowledgement and thanks: it was Chuck Rippel who said (in part) — in response to this post — “We could make this interesting by restricting listening to the period 10AM – 2PM maybe 3PM.” And that got me to thinking that maybe a daylight DXing challenge might be fun.
It was Bill Hemphill, who said, responding to the same blog post:
“Every year the New Jersey Antique Radio Club has a BCB DX contest for its club members. The main purpose is to encourage the members to put into operation some of the many old am radios that they own. This year’s contest was just completed this past Sunday. For any 24 hour period, using the same radio, you attempt to log the most distant stations. The contest score is the total mileage of the ten stations that are most distant.”
Reading that, I rather liked the idea of using mileage as one way to keep score.
Combining the two ideas, the result is The Great Medium Wave Daylight DX Challenge.
Here are the rules:
Frequency rang is the medium wave band: 520-1710 kHz
10 am to 2 pm your local time on the Saturday after the post appears (Saturday, March 11, 2023).
Any radio with any antenna, but must be the radio at your location (no using remote internet radios)
The listener must hear the signal in real time
The stations must be ID’ed by listening to the signal.
Your report should include:
Your name (or Internet handle)
Your receiver and antenna (stay with the same setup from beginning to end; if you use multiple setups, provide a separate report for each).
The time, the frequency, and the ID of each station heard
The total mileage of your top five most distant stations.
A final point: this is not a contest; it is a challenge. The reward for every participant will be fun and fellowship.
The radio man listening to the world from the Arctic
Mika Mäkeläinen is a radio enthusiast who listens to stations from around the world in a remote corner of Lapland, 400km north of the Arctic Circle.
He and a group of fellow hobbyists have set up 14 wire antennas in the forest to capture weak signals from low-power stations, thousands of kilometres away. Mika explains why Lapland is a perfect place for listening to distant radio stations and how his hobby continues to inspire him 40 years after first discovering it as a child.
Many thanks to SWLing Post contributor, Paul Walker, who has kindly allowed me to published some notes he recently shared among MW DXers about DXing in McGrath, Alaska, USA: During a Zoom hang out with a bunch of Pacific NW DXers, one of the things that come up was why my DXing in Alaska is beyond amazing, and we’ve come to a few conclusions.
The extended darkness. Sunrise in the middle of winter here is 3+ hours later than the west coast, so once their Skywave burns off, I’m left with darkness over the pole and to my west.
There’re no operating AM stations within just under 200 miles from me which is a big help. I have heard distant signals on the same channel as “semi locals” such as 780 and 1080.
And I’m pretty sure there’s something to the fact I’m close to the North Pole. Still far, but closer than most.
Interesting to note though: pre sunset DX isn’t a thing there. What I’ve unscientifically discovered is it seems to be that the entire Pacific has to be dark for DX to be worthwhile for me in the evening … despite my evening DX being Canada and the lower 48 US States.
What most everyone else hears at night, such as the transpacific signals from Japan, China, Australia etc…, I hear in the morning. Hearing anything from Asia or the Pacific at night is EXTREMELY rare.
[Since I’m DXing outdoors in extremely cold conditions] I’m getting extra batteries, extra audio cables (to go between the recorder and the radio), another radio, and another recorder. Oh and some hot hands hand warmers. Also have some extra gloves and hats ordered too.. getting prepped for winter DXing well ahead of time!
The hand warmers are as much for my gloves as they are for my digital recorder… AA batteries don’t last long during continuous use in extreme cold.
i also have a portable battery and extra cable so I can use it for my phone. Those lithium ion batteries hate cold even more than aa alkaline batteries–they will shut off in the cold. In fact, you have to not only warm it up but charge it. The cold causes it to think tis dead…. and even warming it up won’t work.
Many thanks to SWLing Post contributor, 13dka, who shares the following guest post:
Dipping my toes into transatlantic MW DX
Most of my SWLing life I wanted to dig into MW DX but never managed to make that really happen for some reason. Then last November, I fetched my first transatlantic station while I wasn’t even trying, in a rather surprising setting:
I have to explain that my home and neighborhood got so infested with a multitude of QRM sources that I did not put my outdoor antennas back up after a storm blew them out of the trees in winter 2018/19. I just used an ML-200 loop indoors, which also has to put up with my own additional QRM sources in my den, consisting of 3 computers running 24/7 and a couple of switching power supplies, a TV, LED lighting… allowing for very basic reception as long as my neighbors don’t watch TV or use the internet. On top of that, medium wave is badly beaten by a mowing robot’s boundary wire here, making reception on several portions of the band completely impossible.
I never expected receiving any US stations on MW in that noise, but I couldn’t sleep that night and scanned the bands a bit with the IC-705 hooked up to my new YouLoop hanging over my bed for testing. I had seen the characteristic transatlantic carriers on MW many times before on my SDRs, but for some reason I never picked up anything intelligible on them in any winter season, now a lot of these carriers were there again but on 1130 there was actually modulation and it wasn’t the only station!
Small bedside loop: SWL’s dreamcatcher!
Bloomberg Radio 1130 came in with almost enjoyable quality at times, but Bloomberg is also kind of a surefire station for MW DX over here. I also picked up a station on 1120 and another one on 880 which was briefly so strong that it surmounted the strong interference from BBC Radio Wales on 882 kHz. 1120 was confirmed the next night to be KMOX in St. Louis, 880 kHz was *not* KCBS in NY – I checked that immediately, I have a KiwiSDR set to that frequency booknarked on my cellphone in case I have a craving for the 1-877-Kars-4-Kids commercial. Powerwise likely candidates for that would be CHQT (50kW) in Edmonton, CKLQ (10kW) in Manitoba or KRVN in Nebraska (50kW class B station) but this may be hard to verify due to the dominance of the BBC on that frequency. Anyway, KMOX wasn’t a bad catch for a small, passive indoor loop, that’s 7,150km or 4,440 miles from here!
Bloomberg Radio on the YouLoop:
This was A) quite encouraging for nighttime DXpeditions to the dike (brrr…cold!), B) a testimony for the YouLoop’s good performance on MW and C) a testimony for the IC-705 having pretty much all one could wish for in a capable MW DX radio – notch filter, passband tuning on AM, stable ECSS, waterfall display to detect stations and last but not least loads of sensitivity to make the most out of low-output antennas down on MW.
Going to the dike
Of course I just had to put on some long johns and drive to the dike around 3:00am local a few nights later, to try my luck with my ML-200 (lacking a better idea) with an 80cm diameter rigid loop. I was mildly surprised that reception wasn’t that much better than with the YouLoop at home. The overall yield wasn’t exactly outstanding compared to other people’s logs but a lot of stations were hidden in the frequency ranges that are submerged in QRM at home. My log has US/Canadian stations on 20+ different frequencies, unfortunately most of them UNID. Here are some recordings I made that night, hunting for unambiguous station IDs from North American broadcasters:
ML-200, Nov. 16th, 2020
1130 Bloomberg Radio on the ML-200:
Presumedly WABC 770 in NYC: In MW DX, never think you ID’d something properly just because you heard a city name and the frequency has a clear-channel station located there!
This is more unambiguously 1010 WINS in NYC (with a twist described later)
1030 WBZ Boston, MA – the first part of the clip is showing how it sounds when the signal is good, the second part demonstrates how reliably propagation is taking a rest while a station identifies itself.
The grandpa of AM broadcasting, 1020 KDKA:
Moving away from the east coast, this is WHAS 840 in Louisville, KY:
760 WJR Detroit, MI
Here’s a tough one, the religious content I heard with a great signal before doesn’t warrant a proper ID alone, and as per usual the station ID’d while fading out. I could ID this only with a set of big, closed headphones, which is a mandatory accessory for all extreme DX (CHRB 1140 in High River, Alberta):
Of course I was occasionally checking other bands too and got some serviceable signals from Brazil:
Clube do Para on 4885 kHz:
VOA Pinheiro from Belem, Brazil on 4960:
Going to another dike, this time it’s personal!
Time to try something completely different: A ~1,000m/3,000′ straight (and preliminary considered continuous) stretch of mesh fence along the dike heading ~345° (NNW), pointing roughly to mid-/western mainland North America. I had briefly tried its aptitude for being a “natural” Beverage antenna before – with mixed but encouraging results: Due to the fence not being terminated at the far end it may be kind of bidirectional, and according to my latest insights a Beverage style antenna doesn’t work well over very good (conductive) ground, probably even less so close (maybe 200′) to the ocean. Also, I forgot to pack the 9:1 balun I prepared for that purpose, so I just had some wire with alligator clip to connect the fence to the radio. Boo.
Accordingly, what I saw on the waterfall display didn’t look so much different than what I got from the ML-200 before – there were clearly more stations visible (as a carrier line on the waterfall) but nothing was really booming in. However, I managed to log a few more stations, such as WRKO in Boston and (the highlight of the night) 1650 KCNZ “The Fan” in Cedar Falls, IA which has only 1kW to boot at night to make the 6,940 km/4,312 mi to my dike. This may or may not be an indication that the “Beverage sheep fence” isn’t so bad after all!
“Fence”- reception, Nov. 18th, 2020:
VOCM 590, St. Johns, New Foundland, Canada’s easternmost blowtorch is like Bloomberg an indicator station for European MW DXers:
680 WRKO, Boston, MA:
1040 kHz, presumed to be WHO, Des Moines, IA: No ID, only a matching frequency and a commercial for “Jethro BBQ”, which has locations only in and around Des Moines:
Here’s 1650 KCNZ, Cedar Falls, IA with 1KW:
To put that into some relation, this is what 1KW sounds like on a very quiet 40m band in SSB (K1KW from Massachusetts on 7156 kHz producing a 9+20 signal that morning on the “Fence antenna”):
BTW, interesting bycatch – not the first time I caught WWV and WWVH on the same frequency but that morning was the first time I could hear both on 5 MHz:
So where have you been all my life, American AM stations?
A question remains – how could I miss the existence of these stations forever, then in modern SDR times see the carriers on the spectrum scope and still miss the modulation on these carriers? Or the other way around – why did I hear them now?
To begin with, when I started out with the radio hobby many decades ago, the reason for the occasional whine and whistle on some stations (particularly past midnight) wasn’t obvious to me: The last thing I suspected was that this could be interference from across the pond, with the pitch of the whine (or “het”) having a direct relation to the 9kHz vs 10kHz difference in channel spacing. Of course these stations were there all my life! Then, with just some regular radio you’d have to pick one of very few frequencies where a strong station from across the pond coincides with a nice silent gap in the local channel allocation. But until this millennium, European medium waves had no such gaps and a lot more local blowtorches.
Since that time many MW stations were turned off and demolished and whole countries abandoned MW here in Europe, so we’re in a much better spot now for transatlantic DX. Unfortunately the opposite is true for listeners on the left side of the pond, you guys still have a very crowded AM band but less potential DX targets in Europe. On the bright side, the remaining European stations are often not restricted to 50kW and you have another ocean with very distant and rewarding DX stations that are very, very hard to catch in Europe!
Wrong time, wrong place
Another bunch of factors are – of course – propagation, season and location/latitude. The MW DX season is roughly fall to spring nights (when TX and RX are in the dark) with a period of increased absorption in the middle (the “mid-winter anomaly”), signals are potentially stronger at lower latitudes and weaker at higher ones but the distance to the noisy equator and a lack of stations interfering from the N can be a huge advantage for using over-the-pole paths on higher latitudes. The big showstopper is solar activity: Good condx on shortwave can be rather bad for skywave propagation on medium wave, so a solar minimum is the long-term hotspot for (transatlantic) medium wave DX.
I’m glad that I learned how intense that relationship is right away: When I discovered that Bloomberg is pretty good on my indoor YouLoop at home, condx were pretty down with SFI in the low 70s and very little excitement of the auroral zones. 2 weeks later the SFI was only slightly higher in the 80s-100, many of the carriers were missing on the waterfall and Bloomberg could be heard only in much bigger intervals.
Speaking of which – even with favorable condx, a proper radio and a half-proper antenna, patience is key! In my very fresh experience the fading cycles on those over-the-pond signals are long! So far I have seen everything fading in and out over the course of a few minutes to half hours or more, with less favorable conditions or a worse antenna it may take much longer until it sticks out of the noise for a while. So you may have to park on a frequency for a long time to not miss the station coming up so much that it becomes readable at the right time to ID it. Multiple DX stations on the same channel can make identification difficult unless one station really dominates the other and that all may take hours or days until it happens. Here’s a lucky example on 1010 kHz:
Lucky because in this case one station is already known – it’s WINS but it often has another station underneath and I was curious what that station might be. On this occasion, the station ID’d itself as “Newstalk 1010” (which is CFRB in Toronto, 0:05 in the clip) just in a short talking break on WINS. Again, this can’t be heard on my laptop speakers but on headphones:
Waiting for a moment like this to happen isn’t exactly fun, that’s why spectrum recordings are incredibly valuable particularly on MW – you won’t miss a possible station ID on frequency A because you were listening to frequency B, but a part of me thinks this is taking a bit of the challenge away, like blast fishing. 🙂
The IC-705 fits snuggly-wuggly into my steering wheel for extra-comfy tuning!
Fun fact: While Bloomberg NY on 1130 was (kind of) booming in at home so I knew for sure it was there, I could hear it even on the XHDAtA D-808 with its tiny loopstick and only average sensitivity on the AM band! So for “easy”, loud and undisturbed stations some persistence and a simple portable radio may suffice to catch some transatlantic DX. But most of the stations will be hit by interference from closer stations, then the radio needs at least to be capable of stable sideband reception, with a corresponding narrow filter and proper suppression of the unwanted sideband – luckily this isn’t an unusual feature on inexpensive portables anymore. So if you already have an SSB capable radio that’s all you need to address the most common issue with transatlantic DX, US and EU stations being too close in frequency. Of course passband tuning and notch filters are most helpful assets in a radio for this, rescuing reception in even more severe interference situations and the spectrum/waterfall display on an SDR helps a lot with finding the carriers and SDRs also have all the nice tools but with some more patience you may find stations with many conventional receivers.
Of course antennas are the crucial component again: If conditions are excellent, even a loopstick may bring the first stations into the log, some small magnetic (wideband) loop could dig up some more stations, from there it’s quickly going a bit esoteric – AFAIK there are no commercial offers for multi-turn (tuned) loop antennas nor are FSL antennas easy to come by, you can’t buy EWE et al antennas either and Beverage antennas for MW are quite a project – not that hard to get a kilometer of wire and there are even kits to buy but it could be much harder to find a place to roll it out in the direction you’re interested in, in an area that doesn’t have electric fences or high voltage power lines within a radius of at least several miles. I guess once you become addicted, you’ll stop asking yourself whether or not it’s worth the effort.
So it’s pretty clear what happened: For catching TA DX stations, the ionospheric conditions must be good, to receive that with a loopstick they must be ideal and that’s what they are currently – it’s winter in what’s still a deep solar minimum and on top of that, some of my radios are very apt for MX DX and I was lucky to listen on the right time on the right frequency. When I started writing this article, my enthusiastic bottom line was supposed to be something like “MW DX isn’t rocket science”, which is certainly true but I think my history with it shows that it’s not exactly trivial either. Maybe that’s why it’s so rewarding, it sure is some hardcore DX challenge that complements the shortwave activity quite nicely and may give you something to look forward to when solar activity is down.
Many thanks to SWLing Post contributor, Nick Hall-Patch, for sharing the following guest post:
Using Carrier Sleuth to Find the Fine Details of DX
by Nick Hall-Patch
Medium wave DXers are not all technical experts, but most of us understand that the amplitude modulated signals that we listen to are defined by a strong carrier frequency, surrounded on either side by a band of mirror image sideband frequencies, containing the audio information in the broadcast.
Most DXers’ traditional experience of carriers has been in using the BFO of a receiver, using USB or LSB mode, and hearing the decreasing audio tone approaching “zero beat” of the receiver’s internal carrier compared with the DX’s carrier frequency as one tuned past it. This was often used as a way of detecting that a signal was on the channel, but otherwise wasn’t strong enough to deliver audio. Subaudible heterodynes, regular pulsations imposed on the received audio from a DX station, could indicate that there was a second station hiding there, with a slightly different carrier frequency, And, complex pulsations, or even outright low-pitched tones could indicate three or more stations potentially available on a single channel.
With the advent of software defined radio (SDR) within the last 10 years or so, the DXer has also been able to see a graphical representation of the frequency spectrum of the carrier and its associated sidebands. (Figure 1) Note that the carrier usually remains stable in amplitude and frequency, unless there are variations introduced by propagation, but that the sidebands are extremely variable.
In addition, by looking at a finer resolution of the SDR’s waterfall display, one might see additional carriers on a channel that are producing heterodynes (audible or sub-audible) in the received audio (Figure 2). Generally speaking, a DX signal with a stronger carrier will be more likely to produce readable audio, although there are exceptions to that rule.
Initially, DXers wanted to discover the exact frequency of their DX, accurate to the nearest Hertz. Although only a small group of enthusiasts were interested, they have produced a number of IRCA Reprints (https://www.ircaonline.org and click the “Free IRCA Reprints” button) over the years under the topic of “precision frequency measurement” (e.g. T-005, T-027, T-031, T-079, T-090) describing their use of some reasonably sophisticated equipment for the day, such as frequency counters.
So, why would this information be at all important? In effect, the knowledge of the exact frequency of a carrier was used to provide a fingerprint for a specific radio station. Usually, this detail was used by DXers who were trying to track down new DX, and wanted to determine whether a noisy signal was actually something that had been heard before, so would not waste any more time with it. The process of finding this exact frequency has since been made much easier by being able to view the carrier graphically in SDR software, assuming that the SDR has been calibrated before being used to listen to and record the DX. Playing back the recorded files will also contain the details of the exact frequency observed at the time of recording. And, because the exact frequency of DX has become much easier to determine using SDRs, more and more DXers seem to be using this technique.
At present, Jaguar software for Perseus is the one being used by many to determine frequency resolution down to 0.1Hz, both in receiving and in playback. But, if you have recorded SDR files from hardware other than Perseus, it is possible to get that resolution also, using software called Carrier Sleuth, from Black Cat Systems, available for both Mac and Windows, at a cost of US$20.
This software will presently take as input, sets of RF I/Q files generated by SpectraVue, SdrDx, Perseus (which includes files recorded by Jaguar), Studio One / SDRUno, Elad, SDR Console, and HDSDR. It then outputs a single file with a .fft extension, that provides the user with a set of waterfalls, similar to those displayed by SDR programs. The user decides ahead of time which frequency or set of frequencies (including all 9kHz or all 10kHz channels) will be output, and these will be displayed as individual waterfalls. one for each chosen frequency. These waterfalls can be stepped through from low frequency to high frequency, or chosen individually from a drop down menu.
Let’s start by looking at a couple of output waterfalls and work out what can be done with them, then step back to find out how to generate them, and what other data is available from them. Finally, we’ll do a quick comparison with two other programs that can produce similar output, and discuss the limitations in all three programs.
Example outputs from Carrier Sleuth
An example showing the original intent of Carrier Sleuth, determining precise carrier frequencies, is shown in Figure 3, a waterfall from 1287kHz on the morning of 28 November 2020. At 1524UT, a woman mentions “HBC” and “Hokkaido” in the original recording, so, it’s JOHR, Sapporo. Although there are a number of vertical lines representing carriers in this graphic, only one has a strong coloration, indicating at least 25dB more strength than any other carrier at the time of the ID, and about 50dB more than the background level. The absolute values of time, signal strength, and carrier frequency precise to 0.1Hz, can be found by mousing over the desired point in the waterfall and then reading the numbers in the upper right corner of the display, (encircled in Figure 3). In this case, the receiver’s reference oscillator had been locked to an accurate 10MHz clock, disciplined by GPS, so the frequency indicated in the software is not just precise, but should also be accurate. Similar accuracy could be obtainable by the traditional method of calibrating the SDR to WWV on 10 or 15MHz.
Carrier Sleuth indicates 1287.0002kHz, within 0.1Hz of that observed by a contributor to the MWoffsets list about 7 weeks earlier (https://www.mwlist.org/mwoffset.php?khz=1287). If you look closely, there is a slight wobble on the frequency, but the display is precise enough that it can indicate that, despite the wobble, JOHR does not wander away from that frequency of 1287.0002kHz.
But let’s face it, tracking carriers to such accuracy is a specialist interest (though admittedly, the medium wave DXing hobby is full of specialist interests, and this one is becoming more mainstream, at least among Jaguar users). However, if I played back a file from another morning, and found a strong carrier on a slightly different frequency from 1287.0002kHz, it might be an indication that some new Chinese DX was turning up, and that the recorded files would be worth a closer listen at that particular time.
In fact, I’ve found Carrier Sleuth to be useful in digging out long haul DX after it’s been recorded, as both trans-Arctic and trans-Pacific DX at my location in western Canada can be spotty at the best of times. This means spotty as in a “zero to zero in 60 seconds” sort of spotty, because a signal can literally fade up 10 or 15dB to a readable level in 20 seconds, perhaps with identifiable material, then disappear just as quickly. My best example so far this season was on 1593kHz, early in the UTC day of 16 November 2020, when a Romanian station on that channel paid a brief visit to my receiver in western Canada. An initial inkling of that showed up in a Carrier Sleuth waterfall, a blotch of dark red at 0358UT, and indicated by the yellow arrow in Figure 4; that caused me to go back to the recorded SDR files that had generated these traces.
The dark blotch indicates a 10dB rise and fall in signal strength including about 60 seconds of rough audio, which turned out to be the choral version of the Romanian national anthem (RCluj1593.wav). That one carrier and another one both started up at 0350UT, the listed sign-on time for Radio Cluj, which does indeed begin the broadcast day with that choral anthem. Which one of the Radio Cluj transmitters was heard is still an open question, due to the lack of carrier sleuths (computerized or otherwise) on the ground in Romania, but the more powerful one listed is a mere 15kw, so I will take either.
Finally, for those who have interest in radio propagation, the Carrier Sleuth displays can reveal some odd anomalies, for example, Figure 5 which displays both Radio Taiwan International (near 1557.000kHz on 28 November, but varies from day to day), and CNR2 (1557.004kHz) carriers as local sunrise at 1542UT approached in Victoria, BC.
The diffuseness of the carriers is striking, as is their tendency to shift higher in frequency at local sunrise. This doesn’t seem to be some strangeness in the original SDR recording, as there appear to be unaffected weak carriers on the channel. For comparison, Figure 3 shows the same recorded time and date, but on 1287kHz, and JOHR’s carrier is pretty stable, but there are others on that channel that show the shift higher in frequency around local sunrise. As one goes lower in frequency, these shifts became smaller and less common on each 9kHz channel, and disappear below about 1000kHz. On later mornings, however, the shifts could be found right down to the bottom of the MW band. Certainly, these observations are food for further thought.
Many of the parameters in Carrier Sleuth are adjustable by the user, for example, the sliders at the top of the screen can allow adjustment of the color palette to be more revealing of differences in signal strength. The passband shown is also easily changed, and in fact, setting the passband width to 400Hz, instead of my usual 50Hz , and creating another run of the program on 1557kHz, shows very clearly the sidebands of the “the Rumbler”, a possible jammer on the channel (Figure 6). Incidentally, a lot of the traces around 1557.000kHz in Figure 5 may well be part of “the Rumbler” signal as well, as filtering of the audio doesn’t seem to improve readability on the channel.
Although the examples here are taken from DXing overseas signals from western Canada, there is no reason why similar techniques may not be applied to domestic DXing, particularly during the daytime, when signals can be weak, but can fade up unpredictable for brief periods.
How to create these waterfall displays in Carrier Sleuth?
You start with a group of supported SDR data files, previously recorded, and use “Open I/Q data files” in the File drop down menu. Figure 7 shows the window that will open to allow you to choose any number of the files from your stored SDR files, by clicking the Add Files button circled in red. Then choose one of the options inside the green circle in Figure 7. They are explained in more detail in the help write up; note that the “Custom Channel” can be specified to considerably more precision than just integer kHz values, e.g. 1205.952 The rest of the settings you will probably adapt to your needs as you gain experience. Finally, set an output file name using the Set Output File button, and hit the “Process” button at the bottom of the window. There are a couple of colored bars in the upper right hand corner of the display that indicate progress, along with number of seconds left, although these are not always visible.
The generation of these waterfalls takes time. A computer with a faster CPU and more memory will speed things up. There is, however, an important limitation of the program. It is specified for 32-bit systems, and although it will run with no problem on 64-bit systems, individual input I/Q files are therefore restricted to 2GB or less. Many SDR users now choose to create larger files than this, and Carrier Sleuth will not handle them. Another possible limitation can occur when processing 32M FFTs, which are useful for delivering very fine frequency resolution of the carriers displayed. The program really requires in excess of 4GB of memory to handle the computation needed to deliver this fine a scale. Unfortunately, both the 2GB file size limitation and insufficient memory limitation deliver generic error messages, followed by program termination, which leaves the inexperienced user none the wiser about the true problem.
This might be a good place for a word about FFT size and Resolution Bandwidth (RBW). The FFT is a mathematical computation that takes as its input the samples of digital data that an SDR generates (or those samples that have been saved in recorded files), and generates a set of “bins”, which are individual numbers representing signal strength at a defined number of consecutive frequencies spaced across the full bandwidth being monitored by the SDR. You could think of these bins as a series of tiny consecutive RF filters, spread across the band, each delivering its own signal strength. As we are trying to look at fine scale differences in frequency when using a program like Carrier Sleuth, it is important that these little “RF filters”, or bins, each have a very narrow bandwidth. This value is called “Resolution Band Width” (RBW), and preferably should be a fraction of a Hertz to get displays such as those shown in Figures 3 through 5.
The “FFT Length” is the number of bins that the FFT display contains, and is equal to the number of I/Q samples (either from the SDR or recorded file) that are used for the input to its computation. The relationship between FFT Length, the bandwidth of the SDR or of the original recorded I/Q file, and the RBW is fairly simple:
Because the MW DXer is usually looking at data with 1MHz or more bandwidth, this equation tells us that to get a smaller than 1Hz RBW, we will need to have an FFT length of well over one million bins, so it would be wise to use an FFT length at least 8M(illion). If you are looking at a recorded file that is from an SDR using a lower bandwidth, then a lower FFT length will do the job to get a smaller RBW.
A downside of using a long FFT length is that the time resolution of the FFT becomes poorer, resulting in a display in Carrier Sleuth that will appear to be compressed from top to bottom compared with what was seen when recording the SDR file, and with correspondingly less response to fast changes in signal strength. However, using a 16M FFT Length on a recording of the MW band results in a time resolution of about 12 seconds, so it should not be a deal breaker for most.
Producing signal strength plots
A further specialist activity for some DXers is recording signal strength on specific channels, and then displaying the progress of signal strength versus time, often to indicate when openings have occurred in the past (say, at transmitter sunset), and perhaps allowing one to predict such openings in the future. But, the world has come a long way from the noting down of S-meter readings at regular time intervals, both in deriving signal strength and in plotting the results. Read on for an example.
Carrier Sleuth recently added the capability of creating files containing signal strength versus time for specified frequencies, and, depending on the size of RBW, to deliver that signal strength as observed in a passband as narrow as 0.05Hz, or as wide as 10Hz. The program extracts the signal strength information from one of the FFT files that it has already generated from a selection of SDR I/Q files. In Figure5, two stations’ signals, from Radio Taiwan International, and from CNR2, were featured in the display. With roughly 4Hz difference between the two signals, it is easily possible with Carrier Sleuth to derive signal strength from each one, specifying a bandwidth of, say 1.2Hz, to account for the propagation induced drifts and smearing of the carriers, not to mention any drift in either the receiver or transmitter.
The program creates a .csv file (text with comma delimiters) of signal strength versus time for all the frequencies chosen from an individual FFT file, but does not plot them. There are several programs that can create plots from CSV files For example, an Excel plot generated from Figure 5 is in Figure 8, showing peaks in those signals that occurred both before and after local sunrise at 15:42UTC. Note that the user is not restricted to the signals found on just one of the waterfalls that are found in the FFT file, but can pick and choose dozens of signals found anywhere in those waterfalls. (Note also that one can choose locations on any waterfall where there is no signal trace, in order to provide a “background level versus time” in the finished plots, if desired)
The process used to generate this CSV file involves searching through the FFT waterfalls for signal traces that are likely candidates for adding to such a file. On the first candidate found, the user right clicks the mouse on the trace, at the exact frequency desired; this will bring up an editable window. The window will show the chosen frequency as well as any subsequent ones that will be chosen, then the overall selection is saved to a text file after editing, so that the user can move on to generating the CSV file.
That file is created by going to the File drop down menu, and choosing “Generate CSV File”, where the text file produced earlier can be chosen. Once that file is selected, the CSV file is immediately generated, and can then be manipulated separately as the user chooses.
Are there comparable programs?
Displaying waterfalls in SDR programs playing back their own files is nothing new, though not that many can do it at as fine a scale as Carrier Sleuth does, and most programs are not optimized to handle such a variety of input I/Q files.
One that does read a fair number of different kinds of SDR files is the SDR Console program; this includes Data File Analyser (64-bit only) which also can display carrier tracks to a high resolution, so let’s take a quick look at what Analyser does. If you are familiar with SDR Console, and are reasonably experienced with the way it handles your SDR or plays back files from your favored SDR software, then these online instructions https://www.sdr-radio.com/analyser will help you get started with Analyser
This program will input a group of SDR files, then display an equivalent to a single one of the waterfalls output by Carrier Sleuth, displaying the carrier traces in reverse order, with time running from bottom to top of the display. Figure 9 shows the equivalent of Carrier Sleuth’s display of the 1287kHz carrier traces shown in Figure 3. Analyser has a convenient sliding cross hair arrangement (shown in the yellow oval) to reveal time and frequency at any point in the display, but the actual signal power available at that point must be derived from the rough RGB scale along the left hand border. Analyser is apparently capable of about 0.02Hz resolution when reading from full bandwidth medium wave SDR files, but the default is to display exact frequency only to the nearest Hertz. The “Crosshairs” ribbon item has a drop down of “High-Resolution” which displays to the nearest milliHertz however, though that will be limited by the actual RBW of the generated display. The graphic display can be saved as a project after the initial generation of the signal traces, which allows the user to return to the display without having to generate it all over again, equivalent to opening one of Carrier Sleuth’s FFT files.
A useful facility in Analyser is the ability to click “Start” in the Playback segment of the ribbon above an Analyser display, then mouse over and click on a signal trace; this action will play back the audio for that channel in SDR Console, at that point in time.
It is possible to generate a signal strength plot of signal strength versus time for any individual frequency in the waterfall display, and to save that plot as a CSV file (“Signal History”). But, the signal strength is that found only in a +/- 0.5Hz passband around the chosen frequency, with no other possibilities. If you want to generate a plot for another frequency on the same waterfall, then you will need to run the process again, and if you want a plot for another frequency in the SDR files, then you need to generate another waterfall, which, depending on your computer’s capability, could take some time. On an i3 CPU-based netbook with 4GB of memory, it took 30 minutes to produce one frequency’s worth of traces from data files scanning three hours. On the same machine, Carrier Sleuth could deliver all 9kHz channels in 1hr20min from the 3 hours of files. However, it also took 1hr20min to play back just one channel in Carrier Sleuth, which is not so efficient. (further note: Nils Schiffhauer has developed a technique to speed up Data Analyser processing, by first using Console’s Data File Editor on full bandwidth MW recorded files; details will likely appear at https://dk8ok.org)
To conclude then, SDR Console’s Analyser will produce a display of a single channel faster than Carrier Sleuth will, and will play back the audio associated with that channel, while also having the capability to plot and record signal strength for a single given frequency within that display, but only on 64-bit computers. It can also handle SDR files larger than 2GB in size, and will run more quickly if a NVIDIA graphics card has been installed. Analyser is also strict about sequence of files. If there is the slightest gap between one file finishing, and the next file starting in time sequence, it regards that as a new set, that will need to be processed separately.
Where Carrier Sleuth is more useful is that once an FFT file has been generated, it is easy to quickly check multiple channels for interesting openings during the recorded time period. It can also provide very precise frequencies of carriers, and is able to generate a file of signal strengths versus time from multiple frequencies, including those frequencies that are separated by barely more than the RBW. For the MW band, that can be near 0.1Hz, often beyond the capability of transmitters to be that stable. See Figure 10, which shows signal strength traces from JOCB and HLQH both on 558kHz, and separated in frequency by 0.1Hz. At 1324UTC, JOCR dominates with men in Japanese, and at 1356UTC, the familiar woman in Korean dominates, indicating HLQH.
Incidentally, another program that seems to offer a similar functionality to Carrier Sleuth and SDR Console’s Analyser is, of course, Jaguar, which has made a point of displaying 0.1Hz readout resolution when using the Perseus SDR, and in playing back Perseus files, but…only Perseus. There is a capability called Hi-Res in Jaguar Pro that can be applied when playing back files; this also displays fine scale traces of frequency versus the passage of time. Steve VE6WZ, sent the example shown in Figure 11, zeroing in on his logging of DZAR-1026. As with Analyser, clicking on a certain point in the display plays back the audio at that time, but it is unclear at this point whether the display can be saved, or whether it is generated only for one individual channel, and then is lost.