locked JT9G (FAST) Experimentation #JT9


Dave Moore
 

I do MSK144 meteor scatter on 6m and 2m and have always been interested in trying it on 10/12/15, mainly due to N0AN's past posts on the subject.

This morning, I tried using JT9G(fast) with a friend 6 miles away using low power on 28.145. I am using WSJT-X 2.5.2 and he was using 2.5.3. We both observed this:

1. QSO's are manually invoked by double clicking an incoming message - (No "Call 1st" function). OK, I can live with that. That's how WSJT-X handled the old modes, like JT-65.
2. Auto Sequence doesn't. Each message (TX2, TX3, TX4...) must be manually selected to make the QSO progress.
3. With decent S/N ratio, the incoming signal is not decoded every time (I could copy him at 500mW, then not get a decode when he went up to 5W or 10W).

Auto Sequence is the biggest issue, but not sure I trust the decoder at this point. Or maybe I need to change a radio setting somewhere.

Would like to hear from others who have used this mode... Thanks.

Dave N7RF


Reino Talarmo
 

Hi Dave,

Perhaps this extract from User Guide explains a bit:

7.3. Auto-Sequencing
The T/R cycles of many WSJT-X modes allow only a few seconds to inspect decoded messages and decide how to reply. Often this is not enough time, so for FST4, FT4, FT8, MSK144, and Q65 the program offers a basic auto-sequencing feature.

73, Reino OH3mA


Amos Sobel 4X4MF
 

Dave

Years ago I did use JT9 a lot. It was better then JT65 but less popular.
In time FT8 became very popular and did replace all other modes.
What do you mean by JT9G(Fast)? Why?
Auto Sequencing came much later. I was not aware that it does not work with JT9.
What is the motivation behind your interest in using JT9? Do you suggest to use few modes on the same frequency such as 50.303 Mhz?

Amos 4X4MF

-----Original Message-----
From: main@WSJTX.groups.io <main@WSJTX.groups.io> On Behalf Of Dave Moore
Sent: Saturday, December 18, 2021 17:00
To: main@WSJTX.groups.io
Subject: [WSJTX] JT9G (FAST) Experimentation #JT9

I do MSK144 meteor scatter on 6m and 2m and have always been interested in trying it on 10/12/15, mainly due to N0AN's past posts on the subject.

This morning, I tried using JT9G(fast) with a friend 6 miles away using low power on 28.145. I am using WSJT-X 2.5.2 and he was using 2.5.3. We both observed this:

1. QSO's are manually invoked by double clicking an incoming message - (No "Call 1st" function). OK, I can live with that. That's how WSJT-X handled the old modes, like JT-65.
2. Auto Sequence doesn't. Each message (TX2, TX3, TX4...) must be manually selected to make the QSO progress.
3. With decent S/N ratio, the incoming signal is not decoded every time (I could copy him at 500mW, then not get a decode when he went up to 5W or 10W).

Auto Sequence is the biggest issue, but not sure I trust the decoder at this point. Or maybe I need to change a radio setting somewhere.

Would like to hear from others who have used this mode... Thanks.

Dave N7RF


Dave Moore
 

***What is the motivation behind your interest in using JT9? Do you suggest to use few modes on the same frequency such as 50.303 Mhz?

Amos 4X4MF***

Good question, Amos. Don’t know about your local regulations, but JT9 Fast mode is permissible to use here on HF because it occupies less than maximum FCC allowed 1kHz FSK bandwidth (JT9F is 900 Hz wide) and is therefore the fastest digital mode you can use for meteor scatter in this regulatory jurisdiction (USA) below 39 MHz. The cyclical JT9 frame rate is .85 seconds (whereas MSK144 used on VHF is .072 seconds). Since meteor bursts lengthen as the frequency is decreased, this works well enough at HF for meteor scatter QSOs as many bursts exceed seconds long on 10m.

SETUP JT9G paraphrased from earlier posts: also shown in WSJT-X user manual:

In Settings > General, select the box that says “VHF modes” and hit OK. Select JT9 mode on main screen mode pull down. A JT9 submodes selector will now appear on the main screen (select A through H) and choose “G” ( do not use the faster mode H because its BW exceeds 1KHz). Then there is another box to check called FAST.

A further operating courtesy is not use the normal 28.080 MHz frequency used for JT9/JT65 on 10m but add 28.185 MHz to your frequency list. Many use JT9F mode experimentally on tbis frequency.

I read some posts in earlier threads that suggest not using JT9F when F2 or Es skip is open. I can’t see a reason to not do this as long as you’re not bothering the normal FT8/JS8/JT9/FT65 channels.

Lastly, when you invoke JT9F, the FT8-style waterfall display is replaced with an MSK144-style display with time being the X-axis and Y-frequency axis fixed at approx 0-1500 Hz for visualizing meteor bursts in the 15-second frame as they occur. The default audio carrier that WSJT-X sets is 700Hz (can be changed on main screen). Further, you can now decrease the RX bandwidth on your HF radio to 1500 Hz or less to improve S/N sensitivty (assuming it had been set to 2500-3000 Hz fo FT8 mode).

Hope this helps.

Dave N7RF
EL09os


Joe Subich, W4TV
 

On 2021-12-19 7:09 AM, Dave Moore wrote:
Don’t know about your local regulations, but JT9 Fast mode is permissible to use here on HF because it occupies less than maximum FCC allowed 1kHz FSK bandwidth (JT9F is 900 Hz wide) and is therefore
the fastest digital mode you can use for meteor scatter in this
regulatory jurisdiction (USA) below 39 MHz.
There are two limiting factors *maximum shift* and *BAUD (SYMBOL) RATE*.
The 1000 Hz shift and/or 1200 baud below *29 MHz*. JT9G and JT9H are
both less than 1200 baud but the maximum shift for JT9G is only 800
while JT9F has a maximum shift of 1600 Hz.

Note: JT9F is 50 baud with 400 Hz shift.

MSK144 is not allowed below 29 MHz because it is 2000 baud.

See:

<https://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-2.5.2.html#FAST_MODES>

<https://www.ecfr.gov/current/title-47/chapter-I/subchapter-D/part-97>

73,

... Joe, W4TV


On 2021-12-19 7:09 AM, Dave Moore wrote:
***What is the motivation behind your interest in using JT9? Do you suggest to use few modes on the same frequency such as 50.303 Mhz?
Amos 4X4MF***
Good question, Amos. Don’t know about your local regulations, but JT9 Fast mode is permissible to use here on HF because it occupies less than maximum FCC allowed 1kHz FSK bandwidth (JT9F is 900 Hz wide) and is therefore the fastest digital mode you can use for meteor scatter in this regulatory jurisdiction (USA) below 39 MHz. The cyclical JT9 frame rate is .85 seconds (whereas MSK144 used on VHF is .072 seconds). Since meteor bursts lengthen as the frequency is decreased, this works well enough at HF for meteor scatter QSOs as many bursts exceed seconds long on 10m.
SETUP JT9G paraphrased from earlier posts: also shown in WSJT-X user manual:
In Settings > General, select the box that says “VHF modes” and hit OK. Select JT9 mode on main screen mode pull down. A JT9 submodes selector will now appear on the main screen (select A through H) and choose “G” ( do not use the faster mode H because its BW exceeds 1KHz). Then there is another box to check called FAST.
A further operating courtesy is not use the normal 28.080 MHz frequency used for JT9/JT65 on 10m but add 28.185 MHz to your frequency list. Many use JT9F mode experimentally on tbis frequency.
I read some posts in earlier threads that suggest not using JT9F when F2 or Es skip is open. I can’t see a reason to not do this as long as you’re not bothering the normal FT8/JS8/JT9/FT65 channels.
Lastly, when you invoke JT9F, the FT8-style waterfall display is replaced with an MSK144-style display with time being the X-axis and Y-frequency axis fixed at approx 0-1500 Hz for visualizing meteor bursts in the 15-second frame as they occur. The default audio carrier that WSJT-X sets is 700Hz (can be changed on main screen). Further, you can now decrease the RX bandwidth on your HF radio to 1500 Hz or less to improve S/N sensitivty (assuming it had been set to 2500-3000 Hz fo FT8 mode).
Hope this helps.
Dave N7RF
EL09os