Saturday, June 10, 2017

Better Know a Mode: JT65 and JT9 Part 1/x

JT65 and JT9 are new modes made possible by computers. Back in the halcyon days of the late 90s, the preferred weak signal communication mode was CW. Now, the new JT modes are a popular way to get your Worked All States or at least build a healthy QSL card collection. What's better is that the mode works so well, it's possible to use compromise, HOA-friendly antennas and work the world. Next, if you're an introvert then you'll love this mode. There's nothing to talk about other than the bare basics.

WSJT-X waterfall and JTAlertX showing activity on 40 meters at 0102Z on May 6, 2017

There are compromises for any weak-signal mode, and the JT modes are no exception. They are slow. Transmission cycles run in 1 minute intervals. The messages you can send are limited as well. You're not going to be racking up major contest points using this mode, however for casual operation it is fantastic.

The JT modes were created by Joseph Hootoon Taylor, Jr., Ph.D. Joe is an astrophysicist by trade, and has used binary pulsars to make high-precision tests of general relativity, and has bagged a Nobel for his efforts. He's also an avid amateur radio operator, and created the JT modes as a means of facilitating Earth-Moon-Earth contacts. [1] With JT9 and JT65, you can now work these modes with a modest antenna [2] and patience.

It turns out that weak-signal work is good for traditional HF frequencies too. We'll talk about some of the intricacies o, followed by some details of how to use this fun mode.

The algorithm uses a small shifting tone, that is then used with a Hamming-tree to decode messages. There are many different versions of software out there, and I use WSJT-X. Looking at the source code, there's a lot of Fortran, it's written in C++ with the QT GUI subsystem. It's not easy to read code, either. There are various other versions of implementations of the modes, but these are almost all minor GUI tweaks.

Good Mode For:
  • Ham's who have young children, that cannot go for more than 30 seconds without some sort of interaction. The 1-minute intervals are enough time to change a diaper, make a sandwich, refill a juice box, extract a marble from a nose, etc.
  • Compromise antenna situations, such as a station in an HOA. I use a 350' Horizontal loop fed with an LDG-600 remote tuner, which I'll talk about in a later post.
  • Those who have a hard time figuring out what to talk to other ham's about.
  • Working the world on 5 watts and a mattress bed-spring
Not a Good Mode For:
  • Rag chewing
  • Making more than one contact in 4 minutes
  • Any message requiring more than 13 characters.
Future posts will include details on how QSOs work, what all the fiddly-bits of the GUI mean, and a general description of the software setup that works for me. I'll also delve into intricacies of getting the software working with the FlexRadio and Kenwood TS-590SG rigs.

[1] If you're not familiar with EME work, it involves sending a large and indecent amount of power at the moon, then listening for other nerds who are trying to do the same thing. In my day, EME was the coup-de-grat of the hobby. It often required massive antennas that made me wonder how many drug dealers were in our fine hobby.
[2] The joke is, "How do you know when your EME antenna isn't big enough? When it didn't blow down in the last wind storm."

No comments:

Post a Comment

Note: Only a member of this blog may post a comment.

Better Know a Mode: JT65 and JT9 Part 1/x

JT65 and JT9 are new modes made possible by computers. Back in the halcyon days of the late 90s, the preferred weak signal communication mo...