JT65: Slow and steady wins the race

You're tuning the HF ham bands, and come across the sound of musical notes - what could it be? A kid with a Casio keyboard? The soundtrack from “Close Encounters?” Most likely it's JT65, one of ham radio's most popular digital modes for the shortwave spectrum.

Steve Ford explaining JT65 at the
Nutmeg Ham Convention.

JT65 works with very low power and small antennas, allowing worldwide contacts that might not otherwise be possible. Basically, it’s a sound card mode that uses 65 different tones to send short messages through a process called "FEC" - forward error correction. The downside is transmissions take 47 seconds each, with a maximum of 13 characters per transmission – not well suited for casual chatting.

Because it works so well under marginal band conditions, JT65 has been catching on with dxers and award chasers. Software is free and easy to install, but is more finicky than other digital modes, says ARRL QST editor Steve Ford, who led a seminar on the topic at the 2016 Connecticut Nutmeg Ham Convention this month.

Although JT65 is soundcard based and works on a waterfall display, it needs an accurate computer clock and a transceiver that doesn’t drift in frequency, Ford said. JT65 signals lock onto each other via a “pilot” tone (1270.5 Hz) and the 64 other tones deliver the information. Using low power is especially important to avoid interference, and so is keeping an eye on your ALC meter, which shouldn’t move at all.

JT65 software running on my computer.

Stations take turns transmitting, depending on whether it is an “even” or “odd” minute, and transmissions begin at one second past the minute. On the software display, stations calling CQ show up in green, and you need only double click on their call sign to answer a CQ. In contrast, stations calling you show up in red.

The latest JT65HF download can be found here.

 I wouldn't be a responsible blogger if I didn't try it myself. From the sourceforge.net site, I installed version 3.5 on my laptop, set the parameters (my call sign, location and grid square) and then tuned to the 20 meter frequency of 14276 kHz, USB mode.

The waterfall showed at least a half dozen active signals, and within a few minutes there were stations in my receive box, mostly from South America, the Caribbean and the American mid-west. I made a few attempts to answer CQ calls, but for some reason, I didn't connect on these attempts. Am I off frequency, too weak, or making some other technical error? This is still to be determined - but hey, Rome wasn't built in a day, right?

A short and to-the-point primer on JT65 can be found here, courtesy of Tomas Hood, NW7US.

Update

A full week has gone by since I wrote this article, and I have devoted many hours trying to figure out why my configuration wasn't working correctly. After my initial attempt, I could no longer receive any JT65 decodes on the software, even though I could clearly see strong signals on the waterfall.

After playing "isolate the variable" it turned out my old HP laptop, running Windows XP, just won't run the software. The solution? I installed the same version 3.5 software on a newer machine (a Dell Latitude) running Windows 10. Presto! It decodes like crazy - sometimes eight or 10 messages in a single receive cycle. The only shortcoming is that the computer has no mic input, so I have to place a speaker near the laptop's built-in mic for the audio to be heard and decoded.
This doesn't bother me, but my wife - who is not a ham and not into hobby radio - says the tones sound like an evil, demented ice cream truck. Touche.