wythall radio club

having fun with RF

Digital Mode – JT65 HF

December 16, 2011 By: M0MCX Category: Fun

I’m very pleased to report that I have just completed my first QSO on the HF bands using JT65-HF, a mode that was designed for very weak signal EME work but is now in use across the HF bands. If you have an RF isolated sound card you can be in business inside 10 minutes. You don’t even need a COM port for PTT, it will work with VOX. I downloaded my version here here but I believe there are other decoders out there.

In a nutshell, this is the most quirky and strange mode I have ever used but certainly fun. Calling CQ and answering CQ can only happen at the top of the minute. Each “over” takes 48 seconds and therefore you have 12 seconds to make up your mind what to do about the next over. On top of that, the protocol only allows for an exchange of 13 characters. However, it is highly tolerant of interference, fading and other nasties – ideal for EME as it seems (and also for bands that are apparently “closed”). There’s a fabulous paper written here which I recommend to all readers. Of interest, the character strings that are transmitted are not sent one at a time, like CW but as a scrunched up packet. Decoding these messages are a mathematician’s dream!

Click the thumbnail for a full-sized screenshot of my first QSO – and let me know if you have a go.