Delay TX to RX

Forum for discussion about the Langstone Microwave Transceiver that shares some features with the Portsdown. Wiki: https://wiki.microwavers.org.uk/Langstone_Project
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CU2ED
Posts: 23
Joined: Thu Jan 17, 2019 11:30 am

Delay TX to RX

Post by CU2ED » Wed May 19, 2021 10:03 am

Hello all,

I have used my Langstone SDR transceiver in QO100 but I do short QSO's, now that I use also in local contacts, and this means a long time (can be up to 10min) QSO, and I detected that after a while I do have a delay on the transition from TX to RX and will cut 1 second or more of my last transmission (when I turn off the PTT switch from my hand microphone).

Is this normal ??? anyone also have this problem? and if you have found a solution, can you share it?


Regards

Jacinto
cu2ed

g4eml
Posts: 708
Joined: Thu Apr 26, 2018 9:36 am

Re: Delay TX to RX

Post by g4eml » Wed May 19, 2021 10:14 am

The delay is caused by small differences in the sample rates of the sound device and the Pluto. This is because they both have their own clock oscillators which both have small errors. As you say, for short overs this is barely noticeable but for long transmissions the delay begins to build up.

I have not yet found a way to prevent this. It seems to be inherent in the way GNURadio works.

Colin.

CU2ED
Posts: 23
Joined: Thu Jan 17, 2019 11:30 am

Re: Delay TX to RX

Post by CU2ED » Wed May 19, 2021 10:18 am

Hi Colin,

thank you for the reply and to clarify the situation ...

but as a workaround, what is the best position on the Langstone C file to increase the time before its switches to RX?

Jacinto
cu2ed

g4eml
Posts: 708
Joined: Thu Apr 26, 2018 9:36 am

Re: Delay TX to RX

Post by g4eml » Wed May 19, 2021 10:23 am

It would be difficult to add anything to Langstone.c because the amount of delay is variable.

The function setTx() handles the switching so you could add a delay in there before going back to receive but it would not be a neat solution.

PE1JXI
Posts: 1
Joined: Mon Jan 29, 2024 10:17 pm

Re: Delay TX to RX

Post by PE1JXI » Thu Jun 13, 2024 8:24 pm

I have a 22uf electrolytes capacitor between PTT and ground so the delay is automatic

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