VOX tail for packet mode

[W3RED]

Hi Folks:

I know HTs don’t make the best choice for digital packet communication, but that doesn’t mean we can’t play around with it. I also know I could buy or build a true PTT for TNC use versus using VOX.

The lowest setting for VOX Tail is 0.5 seconds. Unfortunately, that’s too long for two-way packet communications. The HT is still transmitting while the remote station is trying to respond.

Can VOX Tail be made any shorter, or does anyone have any other ideas for using OpenGD77 for packet?

On a related note, can the radio be used for packet via the USB cable, similar to how it runs as a MMDVM for DMR?

Thanks,

Scott
W3RED

[VK3KYY]

Vox was not designed for packet use, however it may be possible to modify the firmware to have an option to have less VOX tail than 0.5 secs. Specifically for packet use.

What are you using as the TNC

[F1RMB]

Hi,

@Roger: I think he's using a kind of sound modem.

Vox is not the best option for such usage, as by design it gives operator time to breath, add space between words, etc.
Don't expect the VOX to switch back to RX once the 1200/2200 Hz are silent.
If, like I think, you're using a sound modem software, I'm sure there is a PTT driving option, using some serial pin. Better off using that kind of solution to have full control of the beginning/ending of transmission. I can't imagine the TXDELAY you currently have.


Cheers.
---
Daniel

[N1LSJ]

Vox was not designed for packet use, however it may be possible to modify the firmware to have an option to have less VOX tail than 0.5 secs. Specifically for packet use.

I've read that it needs to be at or under 250MS, with 50MS being ideal.

[F1RMB]

Again, if you want to use it for packet, you have to control the PTT pin.

[N1LSJ]

So, the open firmware for the $20 UV-K5 claims to have their VOX adjustable now down to 128ms or even 0ms but I can't get that to work - I think they are adjusting something different LOL.
In any case I'd sure like to see OpenGD77 adjustable down as far as the hardware allows to see if we can have a simple and cheap I/F between a RT3S and an Android phone or a Windows laptop. The ARES national network uses WinLink as their primary emergency comm method and I'm pretty sure we can get a writeup in QST magazine if this can be made to work - I live near ARRL headquarters and know a couple former staffers .

Pretty please?

[VK3KYY]

So, the open firmware for the $20 UV-K5 claims to have their VOX adjustable now down to 128ms or even 0ms but I can't get that to work - I think they are adjusting something different LOL.
In any case I'd sure like to see OpenGD77 adjustable down as far as the hardware allows to see if we can have a simple and cheap I/F between a RT3S and an Android phone or a Windows laptop. The ARES national network uses WinLink as their primary emergency comm method and I'm pretty sure we can get a writeup in QST magazine if this can be made to work - I live near ARRL headquarters and know a couple former staffers .

Pretty please?

The source code for all hardware platforms was released last week, you can download the source code and recompile it for your own radio and experiment with shorter vox tail settings

We are unlikely include a setting of less than 0.5 seconds as its likely to be unreliable, and generally unusable and would result in the radio constantly switching between Tx and Rx

[M0GZP]

The source code for all hardware platforms was released last week, you can download the source code and recompile it for your own radio and experiment with shorter vox tail settings

We are unlikely include a setting of less than 0.5 seconds as its likely to be unreliable, and generally unusable and would result in the radio constantly switching between Tx and Rx

Done, and it works well for packet. Would you consider a submission to have this as an option -- turn on "packet mode", and when that is on you expect the VOX to only be used for packet transmissions so can configure it below the current setting?

[VK3KYY]

The source code for all hardware platforms was released last week, you can download the source code and recompile it for your own radio and experiment with shorter vox tail settings

We are unlikely include a setting of less than 0.5 seconds as its likely to be unreliable, and generally unusable and would result in the radio constantly switching between Tx and Rx

Done, and it works well for packet. Would you consider a submission to have this as an option -- turn on "packet mode", and when that is on you expect the VOX to only be used for packet transmissions so can configure it below the current setting?

Can you let us know what you changed to make VOX work for packet.

i.e I presume a very short start and end delays ?

[M0GZP]

Sure. In summary:

- Disable the VOX pre-triggering timer
- Remove the check for AUDIO_AMP_MODE_RF when doing getAudioAmpStatus() to allow VOX to transmit with an open squelch
- Change the VOX tail time to a 10ms stepping (though in practice, the SNR threshold has some hold which means values below 100ms only work sometimes, not consistently)