As it is generally practiced, ham radio is a little like going to the grocery store and striking up a conversation with everyone you bump into as you ply the aisles. Except that the grocery store is the size of the planet, and everyone brings their own shopping cart, some of which are highly modified and really expensive. And pretty much every conversation is about said carts, or about the grocery store itself.
With that admittedly iffy analogy in mind, if you’re not the kind of person who would normally strike up a conversation with someone while shopping, you might think that you’d be a poor fit for amateur radio. But just because that’s the way that most people exercise their ham radio privileges doesn’t mean it’s the only way. Exploring a few of the more popular ways to leverage the high-frequency (HF) bands and see what can be done on a limited budget, in terms of both cost of equipment as well as the amount of power used, is the focus of this installment of The $50 Ham. Welcome to the world of microphone-optional ham radio: weak-signal digital modes.
Just a Regular Joe
First things first, let me make it clear that there are a ton of modes available to amateur radio service licensees that don’t require talking into a microphone, going right back to the beginning of radio with continuous wave (CW) modes. Banging out dits and dahs with a straight key is perhaps the original digital mode, if we stretch the meaning of the term just a wee bit from its current modern connotation of transmitting and receiving encoded messages using computers, either built into the radio or attached as a separate component. I’ll use that as my definition of “digital mode” for the purposes of this article.
But even with that stricter definition, there is still a huge ecosystem of digital modes that have cropped up over the history of ham radio; the desire for communications without the need to be a conversationalist goes way back, it seems. But for this article, I’ll be focusing on a couple of modes within the “weak signals” family of modes, mainly because I find them fascinating and incredibly useful, and I get a real kick out of seeing what kinds of contacts are possible using less power than it takes to light up an LED light bulb.
When you get into the weak-signal space, one name keeps popping up: Joe Taylor (K1JT). Joe is a ham based in New Jersey, and when you first start hearing about him, you figure he’s just a, well, regular Joe, an old school ham who has come up with some clever software to make low-power signals easier to pull out of a high-noise environment. And while that’s certainly true, it quickly becomes apparent that Joe is a lot more than that. Joseph Hooton Taylor, Jr. earned his Ph.D. in astronomy from Harvard in 1968. He joined the physics faculty at Princeton in 1980, and has won pretty much every major prize in physics and mathematics, including the Draper Medal, the Wolf Prize, and in 1993, the Nobel Prize in Physics.
The Magic of WSJT-X
For all these lofty achievements, in many ways Joe is very much a “ham’s ham”, and since his retirement in 2006 he has turned his considerable experience in digital signal processing toward an all-encompassing weak-signals package called “WSJT“, for “weak signals, Joe Taylor.” Actually first written in 2001, the program has undergone nearly constant revision and updating by Joe and a cadre of digital-modes enthusiasts, with the latest incarnation, WSJT-X, which implements ten different weak-signal digital modes.
We’ll skip a deep dive into the DSP techniques underpinning WSJT-X — although it’s fascinating stuff and probably worthy of an article all by itself — and suffice it to say that the package implements various multiple frequency-shift keying (MFSK) modulation methods, each of which is optimized to work under different propagation conditions. The ten modes currently implemented cover everything from high-noise ionospheric propagation to tropospheric scatter, with modes that support bouncing signals off meteor ionization trails or even listening to your own signals bouncing off the Moon.
Even though WSJT-X modes are separated into broad “fast” and “slow” categories, by modern networking standards, they’re all pretty slow. Typical bit-rates range from a dozen characters per second to 400 baud or so. The low-throughput nature of these modes is entirely by design; by not attempting to achieve blazing speeds, WSJT-X makes very efficient use of the spectrum. Some modes only need a few hertz of bandwidth, with the tradeoff being that even very short messages can take multiple minutes to transmit.
The mode that I’ve been playing with most lately, FT8, is a relatively recent addition to the WSJT-X suite. FT8 was written by Joe Taylor and Steve Franke (K9AN), hence the “FT” in the moniker. The “8” refers to “8-FSK”, which means that the modulation scheme uses eight different tones spaced 6.25 Hz apart. Each FT8 signal therefore occupies 50 Hz, a huge chunk of bandwidth when compared to other weak-signal modes, but still pretty compact. All that extra bandwidth means that FT8 transmissions can be much shorter than, say, a 30-minute transmission on JT9. That makes FT8 suitable for quick QSOs and contesting, which is sort of the contact sport of amateur radio.
Speed Dating for Hams
While FT8 is fast, the tradeoff is message length. Each FT8 transmission encodes only 75 bits, with a 12-bit cyclic-redundancy check (CRC). That and the rapid turnaround time means that most operators rely on automation built into WSJT-X, as well as standardized messages, to make their FT8 contacts.
Setting up WSJT-X and getting a transceiver ready for FT8 is highly dependent on your computer and your radio. In my case, I built a dedicated Raspberry Pi 4 to run my ham radio operation, using the excellent Ham Pi image by Dave Slotter (W3DJS). I also attempted to use KM4ACK’s equally excellent Build-a-Pi image, but I had trouble getting my Icom IC-7200 transceiver talking to WSJT-X, and rather than devote a lot of time to troubleshooting I just tried the Ham Pi build. Both images have outstanding communities that will help you get spun up, as does WSJT-X, which has a forum where you’ll often see Joe Taylor pop in to answer questions. A community that has a Nobel laureate as a frequent contributor is a strong community indeed.
The video above shows why I call FT8 “the speed dating of ham radio.” The waterfall display at the top shows about 2,500 Hz of passband — the transceiver must be set up to allow as wide a possible band of frequencies through to WSJT-X (tip o’ the hat to Josh KI6NAZ for the help getting that right.) The FT8 algorithm decodes every 50-Hz wide FT8 signal in the passband at once; that along with the fact that each transmission is 15 seconds long followed by 15 seconds idle results in the characteristic checkerboard appearance on the waterfall display.
Decoded messages are displayed in the left window of WSJT-X, with operators generally looking for stations calling CQ. Clicking on an entry in the Band Activity window starts a series of automatic messages, with WSJT-X keying up the transmitter and sending a minimal QSO — basically just the two call signs, a grid square locator, and the received signal strength. It’s important to note that the two sides of the conversation don’t have to be, and in fact shouldn’t be, on the same frequency — the other operator’s copy of WSJT-X will decode the entire passband if it can. Once the acknowledgment of the CQ is received by the other station, the exchange of messages is entirely automatic, until the final 73s are sent and WSJT-X gives both sides a chance to log the QSO.
Since I’ve set up my end-fed half-wave antenna for the HF bands and gotten WSJT-X installed, I’ve made quite a few contacts. Most of them have been in the continental US and Canada, but I did manage to bag Japan on 30 meters last week, which was a treat. The fact that I could do all of this without once picking up the microphone, struggling to think of something to say, is a godsend to me, and the fact that WSJT-X is able to decode signals that are so far down into the noise floor is an intoxicating technical feat. It’s also really nice to sit down for a half-hour or so before dinner and bang out a couple of low-effort QSOs without having to invest too much in the process.
As mentioned, FT8 isn’t the only weak-signal mode that Joe Taylor and his collaborators built into WSJT-X. Next time on The $50 Ham, we’ll look at the equally addictive WSPR mode, and see how you can actually work HF bands for far less than $50, transmitter included.
This is a really great series and I am enjoying it a lot. The content and writing are both really good. Thank you.
The analogies I think got the message across loud and clear.
This is the great thing about Amateur Radio is there is so many ways to send a signal from here to there.
tsss tsss, once they get more intimate they also talk about their respective weather or health
Check out http://js8call.com/ for another interesting option.
There are a couple of lots available to do FT8 at QRP levels for under $100. I don’t have any personal experience, so I can’t attest to their quality, but worth mentioning for a $50 ham.
Please, not another “it’s some crazy amount below the noise floor”. Shannon can guarantee it’s not more than 1.6 dB below the noise floor.
Au contraire, mon ami – Shannon puts no such limit. He *did* limit the data rate given the signal to noise ratio and bandwidth, however. For example, the digital modes mentioned here have very narrow bandwidths, far less than any receiver’s audio or IF filters. So the signals can be well below the total noise received without being below the actual bandwidth of the signals themselves. The digital signal processing in the WSJT software can then filter out the vast majority of the noise and, using correlation techniques and optimizing modulation and such, approach the Shannon limit of data rate with the resulting signal to noise ratio.
So, theoretically, you can approach any desired data rate provided you have a sufficiently high signal to noise ratio. And by the same token, you can pull data out of any signal despite the noise provided you accept a sufficiently slow data rate and use techniques designed to do so. All of which is how the Deep Space Network can still receive data from the Voyager spacecraft: QRP at over 12E9 kilometers!
That’s the point, the bandwidth is the bandwidth of the signal (say 50 Hz), not an arbitrary bandwidth of the baseband or IF. Sure if you choose an arbitrary 2.5 kHz for an SSB receiver, then drop the SNR an additional 17 dB. I can come along and say the BW is 250 kHz (the highest decimation in my SDR), so now it’s 37 dB lower. Look, I’m detecting at -37 dB SNR, amazing! The point is you are not getting error free communication below -1.6 dB Eb/N0.
You are absolutely right, and this is a source of some dishonesty out there. I was just watching a video where Joe Taylor was talking about FT8, and was showing a table with the minimum usable SNR for various modes. He showed -15 dB for CW, and -21 for FT8, but I’m quite sure he was measuring both relative to the full receiver bandwidth. Patently misleading, especially since he was the co-developer of FT8 and certainly knows better – makes it look like his magic modulation is 6 dB better than CW for weak signal use. Which, spoiler alert, it’s not, since his FT8 is only looking at 1/50 of the receiver noise, giving him an artificial gain of 17 dB. But even that isn’t right – who can copy Morse at 15 dB below noise? Nobody, that’s who. Probably he was doing the same nonsesne for CW, giving it extra dBs for also using less bandwidth. Let’s see – assuming 100 Hz for CW, that would be 1/25 or -14 dB, so probably so. But again, that’s not what SNR means. So really, the actual minimum SNR for FT8 is fairly close to that of CW. But THEN you have to consider how S—L—O—W FT8 is, or it’s still apples vs. oranges.
But hey, that gives me an idea that’s probably already being done: If you take the audio output of an SSB receiver and run it through multiple DSP filters, you could decode all of the CW happening within that 2.5 or 3 kHz, simultaneously. Which means you could simultaneously have five or so simultaneous QSOs if you use the sort of pre-programmed conversations that FT8 does. Take THAT to your next contest!
Ha ha, have a look at CW skimmer; does just that. I wrote one that does that for FM:
https://github.com/madengr/ham2mon
Anyway, I think the latest coding schemes get to within a few 1/10 dB of Shannon, so there isn’t much room for improvement. What’s always room for improvement is dealing with fading, doppler, etc., and that’s where I think WJSTX is neat as it has specific formats for specific channels. But yes, I think the whole SNR thing is hogwash.
I understand, but it irks me that with all the fanfare about FT8, it’s really not significantly better than CW. This is what contests do: they reward automation more than skill.
And then there are spread spectrum modulation schemes, like the one used in GPS. Here your signal is indeed wide band and below the noise floor. Of course with low data rate. And after the despreading it has also low bandwith.
Hm. Less than $50, including a dedicated Raspberry Pi?
As I said in earlier installments, the series isn’t just about projects that can be completed on a $50 budget. The idea is that there are projects that can be done without spending a lot of money, with what you might have on hand. A lot of hams have a spare Pi lying around, or an old laptop that can host the free software, so the idea is what counts.
Seems a bit of a stretch. I mean, I _could_ have a whole shack full of equipment “just lying around”.
Most people reading this blog have a computer with a soundcard to use with FT8 or JS8Call.
It’s robust enough to use even without a digi interface, just with the built in speaker and mic in a laptop and holding the radio’s mic to the laptop speakers on transmit.
If you hold a speaker near a microphone, you risk picking up noise in the room. If it’s an SSB rig, your signal is no longer pure.
A sinewave audio signal into an SSB transmitter results in a CW signal. That’s how this and AFSK works. Put two sinewave audio signals into an SSB transmitter, suddenly you are transmitting a carrier and a sideband.
Maybe can be as simple as the Youtube channel QRQcw designs using super homebrew made modules with even more limited investment?
A pair of high level balanced modulators, fed by a quadrature signal source. No need for a string of linear amplifiers to get it up to power.
The computer provides the quadrature audio signals.
Just a variant of early SSB transmitters.
There are simple rigs designed for this sort of protocol, with crystal filters on the signal frequency. The disadvantage is they stay on one frequency, and the frequency depends on cheap available crystals.
Yes, and that would be appropriate when talking about under-$50 radios, if you’re going to talk about not including the cost of things “just lying around” in the price, then you might as well say, “hey, if you happen to have a $3,000 spectrum analyzer lying around, you can set it to zero span, wire some headphones into it, and voila!” But you’re going to piss off a few people along the way. Like, as we’ve seen a number of times in this series. So either knock off the “under $50” nonsense, or expect nasty comments. That’s all I’m saying.
Ham Radio Forms a Planet-Sized Space Weather Sensor Network
https://eos.org/features/ham-radio-forms-a-planet-sized-space-weather-sensor-network
Ham radio is currently experiencing a technical renaissance, thanks to the advent of inexpensive single-board computing platforms (a complete computer built onto a single circuit board, such as a Raspberry Pi) and open-source software. Such computer-based systems serve as virtual radio repeaters, connecting computers via the Internet to actual ham radios in the real world to enable remote control and data collection. Beyond the old-fashioned pursuit of voice communication, the lure of maker movement projects and the removal of the Morse code requirement from the amateur licensing exam have led to a greater number of licensed amateurs than ever before.
Out of this increasing technical sophistication, digital communications networks, such as the Automatic Packet Reporting System (APRS), the Weak Signal Propagation Reporter (WSPR), and the Reverse Beacon Network (RBN), enjoy wide membership and serve the amateur community while collecting propagation data at rates and resolutions that were previously impossible. The reach of these crowdsourced systems, and the support of the amateur community, offers tremendous opportunities for scientific measurements
Thank you for the article Dan. I am a 21 year old ham, and I have been reading hackaday, daily now for 8 years. Throughout my journey in electronics I have always seen ham radio as the absolute top of being a “hacker”, and that is in part thanks to hackaday articles. Operating as a general for the past 8 or 9 months, I have been loving it. Whether operating from home, setting up in the snow, parks on the air, QRP, building antennas, I love it all. Interestingly enough, I built my 49:1 antenna the day before your article came out, and today arrives all my parts for my DIY digital mode cable. I am not interested in emcomm or prepping or anything that people might associate with ham radio, I am a hacker. Thank you for your articles that keep this hobby alive. Just a note, there is a RTTY contest this weekend, hope to catch you on the air.
Ok, so I guess I’m a beginner’s beginner. This introduction to WSJT-X didn’t answer the questions I hoped it would. They are, what equipment do I need and how do I set it up to get the motley collection of parts I currently own to work? They are: Kenwood TS830s transceiver but no antenna yet due to severe space limits (a work in progress). I also have a 12 year old personal computer and a Rasp-pi4 based Ham-pi but no monitor for I-O (another work in progress). How can I get THIS equipment to work digital modes without having to replace it all and buy a new radio and new house to put it and a new shack and a normal sized antenna?
You can build an inexpensive double side band FT8 transceiver kit as well. http://www.crkits.com/
Yes, you can. For $102, including postage and handling.
I think this series needs to be renamed.
But what kind of signal does that put out?
Feed a pure audio signal into an SSB transmitter, and you get a CW signal. If you shift the frequency of that audio signal, you get Frequency Shift Keying.
But feed it into a DSB transmitter, and you get two sidebands. I’m not sure how the result is classified, but it’s not FSK. “It’s DSB”, but the intent was to send FSK.I
And on a practical level, you have the same issue as receiving DSB, you have to reinsert the carrier exactly at the point between the two sidebands. Otherwise, the two sidebands don’t translate back to the same audio frequency. The expectation is that at the other end someone has a good SSB receiver, so that turns the DSB signal into SSB inside the receiver.
Why not just build a DSB transmitter, and use voice?
While it may be technically legal to transmit signals that are double sideband where this is not necessary, these can interfere with other transmissions, and this may breach the community rules. At the very least, it should be avoided, Although it is customary to use lower sideband on frequencies below 10 MHz and upper sideband on frequencies above 10 MHz in the HF bands, it is not prohibited to transmit DSB or even AM. However, transmitting DSB will interfere with any communication being done in the frequencies occupied by that other sideband, and may not be allowed in sub-bands designated for SSB. For example, because FT8 uses up to 2 kHz of spectrum, if you are doing FT8 at 7074 kHz LSB, this would occupy the spectrum from 7072 through 7074 kHz. But if you tune a DSB transmitter to that frequency, it will occupy 2 kHz on both sides of the carrier, so 7072 through 7076 kHz. Which means that although this would work, if there was another communication happening on 7076 kHz, either SSB voice or any SSB-based digital mode, your upper sideband would talk over their portion of the spectrum. Likewise, anyone transmitting in the upper sideband of your carrier, 7074 through 7076 kHz, would interfere with your reception of FT8 tuned to 7074 kHz. I use this frequency as an example because that is the conventional frequency on which FT8 is used in the 40 meter band. But what is of special note is that 7076 kHz is the conventional carrier frequency for JT65, so if you do FT8 on 40 meters, you will be interfering with JT65 mode in that band, and vice-versa.
The reason we see a low-cost DSB transceiver is that the IF filter for DSB doesn’t have to be nearly as sharp as one required for an SSB transceiver, in order to adequately suppress the unused sideband. SSB also requires two local oscillators, compared with only one for DSB, in superheterodyne designs. This also allows for direct conversion, or “zero IF” radios, since these cannot suppress the unwanted sideband in the IF section, there being no IF section in a direct conversion radio.
Indeed, in the instructions that come with WSJT-X, the application commonly used to do FT8 communications, an SSB is listed as required equipment, specifically to avoid this kind of interference.
The fact that someone is selling kits to do exactly this, and in fact is not equipped to do SSB voice transmission (no “push to talk” input), indicates either that they don’t care about taking twice as much bandwidth as they ought to, or possibly that this is acceptable in the community. Does anyone know the “community” rules on this? Perhaps the phrase “we offer quality QRP radio kits directly from China” on the crkits.com website could shed some light on this. They appear to be selling this based on the reputation of a different SSB transceiver, the KN-Q7A, but this is a considerably different design.
My point is that a pure tone into an SSB transmitter isn’t sending audio, it’s CW, A1 when I was a kid. It has to be pure, or else the output is something else.
Same with AFSK, the SSB transmitter output is FSK, F1.
You can’t tell the difference between these done with audio and and keying an rf oscillator, or shifting that rf oscillator.
Audio tones work, and it’s easier than modifying the rig.
But a DSB transmitter doesn’t give you CW or FSK. I’m not sure what the result is. “It’s just the unwanted sideband”, but in this context you were never sending a “sideband” from an SSB transmitter, just FSK.That an SSB rig is used is irrelevant, the output is what matters.
People would complain about your bad signal if you were sending identical CW signals 2KHz apart.
Even before the issue of “twice the bandwidth” I think there’s a fundamental misunderstanding of how this works.
As for that DSB rig, it’s not using an IF, it’s direct to audio. In this context, the issue isn’t “selectivity” but the lack of opposite sideband (or “audio image”) rejection. You can’t get rid of that without a good filter (ie a sharp edge, rather than how wide it is) or by using the phasing method (which I hinted at earlier up). And that’s the joke, the cult of simplicity says it’s okay to build a DSB transmitter, but not build two in parallel to get SSB, because the computer to do the quadrature audio makes it complicated.
The internet age means people don’t immerse themselves, they follow what’s in front of them. So there’s no context to this, or that stupid one transistor transmitter. You trip over something in your way, and feel obligated to spread the word, without looking deeper.So tye same thibgs get passed around.
There are projects out there that are “simple” in that they are direct conversion, but have a simple crystal filter on the signal frequency. You can’t turn a dial to change frequency, and you need crystals on the needed frequency, but relatively simple. Since CW or this mode requires narrow bandwidth, that’s easier to build a simple filter compared to SSB width.I
Real change happens when people look deeper.
A) That’s mostly what I already said, and B) MY point was that using a DSB modulator instead produces the same FSK signal that you get from an SSB modulator, but ALSO the same signal with its spectrum mirrored on the other side of the transmitter’s carrier frequency, and furthermore, that in the case of the frequencies that are used for the WSJT sub-bands, using a DSB transceiver for FT8 WILL cause you to stomp heavily upon the JT65 sub-band, because if you do the math, that’s precisely where that mirrored spectrum ends up. So marketing it as a “DSB transceiver for digital modes” is dishonest.
As for “why not build a DSB transmitter and use voice?”, the main reason is that FT8 splits a 2 kHz SSB channel into a number of 50 Hz sub-channels, each of which has 1/40 of the noise of the whole channel. This allows it to receive signals 16 dB lower in signal strength than voice. Theoretically, at least.
Additionally, there seems to be an aversion these days to voice contacts, these being seen as the exclusive domain of old men talking about their medical problems. FT8 only lets you communicate in pre-programmed messages, allowing today’s hams to participate without any social interaction whatsoever. One can make “contacts” and win contests without actually having to deal with people.
yes why nor.. i enjoy these posts i hope some of you don’t get too critical .. just try to give positive comments so that the new hams get a gud feel for Amateur Radio.. Its a nice Forum here.
Ive been a ham for over 40 years and find the articles here interesting and intriguing.. K7DV
BrightBlueJim:
As a grandad who encouraged his 12 year old granddaughter to take and pass her Technician test Dec 2020, I can assure you that she does not care for the weekly usual aged-population local club “rag chew” online meetings. Even that phrase turns her off. I will try this QRP idea for her and me. This type of combining computers and Ham may save the hobby.
You may be right. FT8 and other weak signal modes seem to have provided an attraction that CW/Morse code lost a long time ago. As long as there’s a challenge in what you’re doing (but not so much that you don’t make any progresss), the hobby will survive.