Play tone or message when no tuner available for a TG

[cfc62]

SDRT does have a text message in the logs when a TG can't be followed due to no tuner being available.

However, an enhancement would be to play and/or insert a short audio indicator when this happens, so that when listening to recordings it becomes evident that there was no failure on SDRT's part, but that it was not possible to tune to the frequency called for due to SDR limitations.

It would also be helpful for troubleshooting the "I missed a transmission" situation.

Perhaps a tone like the PTT "bonk" would be appropriate.

Extending this idea, for TGs that have a mix of clear and encrypted transmissions, same idea but perhaps with a different tone/message for the encrypted transmissions.