JT65 and Latency

[kansas400]

Hi - for time sensitive modes like JT65, are there certain settings in the manager software that may work to reduce latency? Seems I can make JT65 contacts fine when I'm home (no remoterig) but using remoterig, I can see all signals coming in, decodes fine, but no one hears me or responds to me, so I'm thinking maybe my buffering or latency settings may be affecting the timing?  Any thoughts?  Thanks. 

[g4swx]

I would very much doubt if latency is your problem!
I operate a lot of JT65 and FSK441 on 144MHz having had over 3,000 remote 144MHz JT65 EME QSOs in the past 4 years. I have deliberately increased the buffer size (and therefore increased latency) to between 16 and 20 to minimise lost UDP RX packets which is critical for really weak signal JT65.  I do exactly the same on TX. I also use Dimension4 to ensure correct timing of the PC. I can measure around 120-150ms total delay between the computer and final TX signal!

On TX you must ensure that you are not distorting the JT65 tones. This will cause your signal to be undecodable when weak. You should switch off any speech processor and reduce the audio level until you have a minimum amount of ALC indicated.

One word of warning:  Do not run the remote rig system with an audio quality setting which uses ALAW. Unless you understand how ALAW compression works and are very skilled at setting up the TX and RX levels at both ends ALAW will distort JT65 signals badly!!!

73
John G4SWX

[k6ufo]

John said: > Do not run the remote rig system with an audio quality setting which uses ALAW.
> ... very skilled at setting up the TX and RX levels at both ends...

Hi John, The Elecraft K3 "Twin" setup uses Audio Quality 2 – Linear 16 bits 8 kHz. Is that a good setting for digital modes, and can you briefly explain how you set the levels properly? Thanks, Mark K6UFO

[g4swx]

Mark writes:
> Hi John, The Elecraft K3 "Twin" setup uses Audio Quality 2 – Linear 16 bits 8 kHz. Is that a
> good setting for digital modes, and can you briefly explain how you set the levels properly?
> Thanks, Mark K6UFO

Audio Quality 2 is a linear transfer mode which does not employ ALAW compression and hence it is excellent for digital modes. I normally run a TS2000 on 144MHz and a K3 on HF both with this setting. My comment about setting up levels was specificaly aimed at those that use digital modes with Audio Settings that use ALAW compression.

As you are running with Audio Quality 2 careful setting of levels is not so important as the RRC 1258 has a huge amplitude range.
On RX, as I set it up running with AGC off and have set the background noise from the RX to be around 15dB above the background noise from the RRC1258 but it is not so critical.
On TX I have set the system up where there is low noise out of the TX (>45dB down on single tones) when the audio tones from the computer are off.

What is probably more important with JT65 is to set-up the transmitter so that the processor is off and there is minimum ALC.

73
John G4SWX

[k6ufo]

John, Thank you for the information. I'll review my own levels again. Mark K6UFO

[W4PFM]

I am using the K3/0=mini control and K3 remote to operate JT 65 and JT 9 on the HF bands. I have one limitation and that is bandwidth. The WSJT-X is made to display 4 KCs of the band so one can monitor JT 9 and JT65 at the same time. I am using audio quality 2. I would like to use 4 for better decoding and wider band monitoring. The problem when I use any quality above 2 I get breaks in the audio every half second. I  am using full duplex YES and RTP tx mode  Continuous in the advance settings. Does anyone have any suggestions for increasing the bandwidth? I have the K3 bandwidth opened up from.4 to 4Kc. Any way to use a higher audio quality for better decoding??

Thank you,
Paul, W4PFM

[sm2sum]

Paul
Change Bins/pixel to 5 on WSJT-X  wide graph window and you will have 4khz.
 I am using audio quality 2....... Full duplex no....... RTP tx mode normal.....
And dual rx no in radio settings
Peder sm2sum

[W4PFM]

Thank you for your reply. I reset the settings to you and the transmitter would key but would not transmit data. I reset I had to set RTP tx mode to continuous and not I can transmit data again. Re: the 4 Kc bandwidth i9n WSTJ-X, I can see the 4 Kc on the waterfall but can only decode 200 to 2500 JT 65, JT9 transmit above 2500 but it will not decode JT 9. This is with mode set to JT9 + JT 65. If I switch to JT 9 then the program sifts the frequency of the Transmitter and it decodes fine.

Do I understand you can decode both JT9 and JT 65 at the same time? I assumed that the bandwidth restriction of the remote rigs is the problem, since decoding works fine when I am at the K3. When I try and work JT9 and JT 95 from my remote location is when I have problems.
73,
Paul

[sm2sum]

Paul
I have k3 twin remote using RRC 1258 and have done some  JT65 using wsjt-x.
Have not tried JT9 yet but can decode both JT65 and JT9 at the same time up to 4 khz. I can also transmit both easy with my setup.
Push and toggle..... tx jt65¤....just under  monitor and erase buttons
Good luck
Peder