Return to KLUBNL.PL main page

[Top] [All Lists]

LF: Re: JT9-2 and JT9-5 mode application

To: "[email protected]" <[email protected]>, "[email protected]" <[email protected]>
Subject: LF: Re: JT9-2 and JT9-5 mode application
From: Rik Strobbe <[email protected]>
Date: Fri, 9 Nov 2018 09:25:25 +0000
Accept-language: nl-BE, en-GB, en-US
In-reply-to: <[email protected]>
References: <[email protected]>
Reply-to: [email protected]
Sender: [email protected]
Thread-index: AQHUd6mXGlRzs26Lqk2M7O3cP/CWt6VHKrE8
Thread-topic: JT9-2 and JT9-5 mode application

Dear all,

the first bug is discovered ;-)

I deliberately limited the maximum audio frequency to 1400Hz (as it is not a good idea to use JT9 in the WSPR band), and this is send as a parameter to the decoder executable.

But I did not keep in mind that for JT9-2 all frequencies are doubled (and x5 for JT9-5), meaning I have to set fmax to 2800Hz for JT9-2 and to 5000Hz for J9-5.

I will try to fix this today and upload the new beta version 0.9.01.

For those who want to test the current (0.9.0) version: keep the audio frequency below 700 Hz for JT9-2. For JT9-5 the upper limit would be 280Hz, but this is too low for most transmitters.

73, Rik  ON7YD - OR7T

Van: [email protected] <[email protected]> namens Rik Strobbe <[email protected]>
Verzonden: donderdag 8 november 2018 22:29
Aan: [email protected]; [email protected]
Onderwerp: LF: JT9-2 and JT9-5 mode application

Dear all,

a few months ago there was a short discussion about a "revival" of the slower JT9 modes such as JT9-2 and JT9-5.

These modes existed in early versions of WSJT-X, and had the advantage of a better S/N treshold level, at the cost of longer transmissions. But unfortunately thse modes were abandoned in later WSJT-X version.

As a result I raised this question in de WSJT-X developers group, but there was no intention do implement these modes again, as the focus was more on the (further) developing of new(er) modes.

Having a closer look at the WSJT-X source code I noticed that the JT9 decoding was done in a separate executable and with some assistance of Joe, K1JT, I managed to write an application that used this executable for decoding.

As this executable only decodes JT9 signals, not JT9-2 and JT9-5, I had to use a lttle trick: speeding up a JT9-2 recording by a factor 2 results in a JT9 signal (at the double frequency) that can be fed to the JT9 decoder. The same can be done for JT9-5 (now speeding it up 5 times).

Some tests showed that this way a JT9-2 signal could be copied at a 2.5dB better S/N treshold compared to JT9(-1). Not completely the theoretical 3dB, but 2.5dB can often be the difference between a failed or successful QSO. JT9-5 hasn't been tested yet.

All this was done "manually" and it was rather time consuming.

So I decided to write an application that I named SlowJT9. It takes care of all the conversions and frequency shifts.

Besides JT9-2 and JT9-5 it also supports JT9(-1) for convenience reasons.

Over the past weeks I tested the application in JT9 mode and after more than a dozen QSO's I feel that it now time to release a beta version.

Whoever is interested can download the SlowJT9 installation file at

For now only a Windows version of SlowJT9 is available. But as the used IDE has cross platform facilities it should be possible to support other operating systems as well in the future.

The aim of this beta version is:
- To test if the application is working properly.
- To find out if JT9-2 and/or JT9-5 have a sufficient S/N advantage over JT9(-1).
- To find out if there is sufficient interest in using these modes to continue the project.
Therefore all comments, bug reports and suggestions are most welcome via the Blacksheep RSGB LF Reflector, Yahoo RSGB LF Group or directly at [email protected]

73, Rik  ON7YD - OR7T

<Prev in Thread] Current Thread [Next in Thread>