As is common practice, amateur radio is a bit like walking into a grocery store and talking to everyone you meet while walking down the aisles. Apart from the fact that the grocery store is the size of the planet and everyone brings their own shopping cart, some of which are heavily modified and very expensive. And pretty much every conversation is about the cart or the grocery store itself.

Given this admittedly dubious analogy, you might think that if you are not the kind of person who normally gets into conversation with someone while shopping, you might be poorly suited to ham radio. But just because most people exercise their ham radio privileges this way, it doesn’t mean that it is the only way. It focuses on some of the most popular ways to take advantage of the radio frequency (RF) bands and find out what can be done on a limited budget in terms of both equipment and power consumption by paying installments from The $ 50 Ham. Welcome to the world of the optional amateur radio with microphone: digital modes with weak signal.

Just a normal Joe

First, let me be clear that amateur radio licensees who do not need to speak into a microphone have a variety of modes available, dating back to the very beginning of radio with continuous wave (CW) modes. Knocking out dits and dahs with a straight key is possibly the original digital mode, if we take the meaning of the term just a little bit from its today’s modern connotation of sending and receiving encrypted messages with computers either built into the radio or being connected are stretch a separate component. I will use this as my definition of “digital mode” for the purposes of this article.

But even with this stricter definition, there is still a vast ecosystem of digital modes that have popped up throughout the history of amateur radio. The desire to communicate without the need to be an interlocutor seems to go way back. In this article, however, I’m going to focus on a few modes within the “weak signal” family, mostly because I find them fascinating, incredibly useful, and because I really enjoy seeing the types of contacts that can be made with less power than to light up an LED lightbulb.

When you get into the weak signal area, a name keeps popping up: Joe Taylor (K1JT). Joe is a New Jersey ham, and when you first hear about him you think he’s just a regular joe, old-school ham who developed clever software that makes it easier to get low-power signals can be from a noisy environment. And while that’s certainly true, it quickly becomes clear that Joe is much more than that. Joseph Hooton Taylor Jr. received his Ph.D. 1968 in astronomy at Harvard. In 1980 he moved to Princeton Faculty of Physics and won just about every major award in physics and mathematics, including the Draper Medal, the Wolf Prize, and 1993. the Nobel Prize in Physics.

The magic of WSJT-X

Despite all of these high achievements, Joe is in many ways a “bacon” and since retiring in 2006 he has had considerable experience in digital signal processing on a comprehensive package of weak signals called “WSJT“For” weak signals, Joe Taylor. “The program was first written in 2001 and has been almost constantly revised and updated by Joe and a cadre of digital modes enthusiasts with the latest incarnation. WSJT-Xwho implemented ten different digital modes with weak signal.

Joseph H. Taylor Jr. (K1JT), 1993 Nobel Prize in Physics. Source: Nobel.org.

We’re going to skip a deep dive into the DSP techniques underlying WSJT-X – though it’s fascinating and probably deserves an article in itself – and suffice it to say that the package includes a variety of Multiple Frequency Shift Keying (MFSK) modulation methods. implemented, each of which is optimized for different working conditions. The currently implemented ten modes cover everything from the noise-intensive propagation of the ionosphere to tropospheric scattering. These modes assist in bouncing signals off meteor ionization paths or even listening to your own signals bouncing off the moon.

Although the WSJT-X modes are divided into broad categories of “fast” and “slow” according to modern network standards, they are all quite slow. Typical bit rates range from a dozen characters per second to around 400 baud. The low throughput of these modes is entirely by design. WSJT-X does not try to reach blazing speeds and uses the spectrum very efficiently. Some modes only require a few Hertz of bandwidth, the disadvantage being that the transmission of even very short messages can take several minutes.

The mode I’ve been playing with lately, FT8, is a relatively new addition to the WSJT-X suite. FT8 was written by Joe Taylor and Steve Franke (K9AN), hence the “FT” in the nickname. The “8” refers to “8-FSK”, which means that the modulation scheme uses eight different tones that are 6.25 Hz apart. Each FT8 signal therefore occupies 50 Hz, a large part of the bandwidth compared to other weak signal modes, but still fairly compact. All of this additional bandwidth means that FT8 transmissions can be much shorter than, say, a 30 minute transmission on JT9. This makes FT8 suitable for quick QSOs and competitions, which is a kind of contact sport of amateur radio.

Speed ​​dating for ham

While FT8 is fast, the tradeoff is message length. Each FT8 transmission encodes only 75 bits with a 12-bit CRC (Cyclic Redundancy Check). This and the fast turnaround mean that most operators rely on the automation built into WSJT-X as well as standardized messages to establish their FT8 contacts.

Setting up WSJT-X and preparing a transceiver for FT8 will depend heavily on your computer and radio. In my case, I built a dedicated Raspberry Pi 4 to run my amateur radio operations the excellent Ham Pi picture by Dave Slotter (W3DJS). I also tried to use The equally excellent Build-a-Pi image from KM4ACKBut I was struggling to connect my Icom IC-7200 transceiver to WSJT-X and instead of spending a lot of time troubleshooting, I just tried the Ham Pi build. Both images have stellar communities to help you improve, as does WSJT-X which has a forum that Joe Taylor often stops by to answer questions. A community with a Nobel Laureate as a frequent contributor is indeed a strong community.

The video above shows why I call FT8 “Ham Radio’s Speed ​​Dating”. The waterfall display above shows a pass band of around 2,500 Hz. The transceiver must be set in such a way that the widest possible frequency band up to the WSJT-X (tip of the hat to) is possible Josh KI6NAZ for help getting this right.) The FT8 algorithm decodes any 50 Hz wide FT8 signal in the passband immediately; Coupled with the fact that each gearbox is 15 seconds long, followed by 15 seconds of idling, this gives the characteristic checkerboard appearance on the waterfall display.

The characteristic FT8 checkerboard pattern develops at the WSJT-X waterfall. The 40 meter band was pretty good tonight, but I couldn’t do any QSOs.

Decoded messages are displayed in the WSJT-X’s left window, with operators generally looking for stations calling CQ. Clicking an entry in the Tape Activity window starts a series of automatic messages, with WSJT-X keying in the transmitter and sending a minimal QSO – basically just the two callsigns, a grid square locator and the received signal strength. It is important to note that the two sides of the call need not and should not be on the same frequency – the other operator’s copy of WSJT-X will decode the entire passband if possible. As soon as the confirmation of the CQ has been received by the other station, the exchange of messages takes place fully automatically until the last 73 are sent and WSJT-X gives both sides the opportunity to log the QSO.

I’ve settled down there my end-fed half-wave antenna I made some contacts for the RF bands and the installation of WSJT-X. Most of them have been to the continental US and Canada but I managed to pack Japan at 30 meters last week which was a pleasure. The fact that I could do all of this without even picking up the microphone and bothering to say something is a godsend for me, and the fact that WSJT-X can decode signals so far lying in the noise Floor is an exhilarating technical achievement. It’s also really nice to sit down for about half an hour before dinner and pull out a few QSOs with little effort without investing too much in the process.

As mentioned earlier, FT8 isn’t the only weak signal mode that Joe Taylor and his coworkers have built into WSJT-X. Next time at The $ 50 Ham we’re going to look at the equally addicting WSPR mode and see how you can edit RF bands for far less than $ 50, including transmitters.