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Langstone Update
Posted: Mon Aug 03, 2020 9:34 pm
by g4eml
Update to improve FM Transmission.
Added deviation limiter.
Corrected Pre-Emhasis.
Adjusted Mic Gain and deviation.
Transmitted FM audio now sounds much crisper and does not over deviate.
Colin G4EML
Re: Langstone Update
Posted: Tue Aug 04, 2020 5:53 am
by DL5BCA
Hello Collin,
Thank you for the Update.
I update my system.
I tested over our city repeater.
With my Equipment (2headset, 1 Tablemicro) the sound is to low. Compared to a normal Tranceiver...
I will look for a microphone preamplifier.
Thank you for your effort.
73 Thomas DL5BCA
Re: Langstone Update
Posted: Tue Aug 04, 2020 10:00 am
by g4eml
The low level might also be caused by the low voltage supplied by the USB audio dongle. Some microphones need a higher voltage to work correctly. Those designed for Icom radios need about 8V, they do still work with the lower voltage but the output is greatly reduced.
A simple one transistor preamp would probably be sufficient.
Re: Langstone Update
Posted: Tue Aug 04, 2020 1:42 pm
by DL5BCA
Hallo Collin,
thank you for your answer and help.
All 3 tested microphones are computer microphones. Extra for a sound card input.
The dongle is especially for the Raspberry, this one:
https://www.rasppishop.de/USB-Soundkarte-Soundadapter
I'll try a mic preamp.
73 Thomas DL5BCA
Re: Langstone Update
Posted: Tue Aug 04, 2020 8:23 pm
by G8GKQ
We have discovered in the last few days that all the audio levels on the latest Raspios build on the RPi 4 are initially set a lot lower than is sensible. Use of 'alsamixer' at the command line has been able to resolve these issues in Portsdown.
I hope to set the initial levels to something more sensible by default in a future Portsdown build (which will work on co-hosted Langstones), but need to do a bit of testing and experimentation before pushing the update.
Dave, G8GKQ