I am working on a simple RTL-SDR based way of receiving slow scan TV transmissions on 145.8 MHz from the International Space Station. The aim is that it's easy enough for secondary school teachers to follow and implement in class.
I'm having a few problems with hearing ground based voice transmissions that cover the ISS signal when it's passing over. Apparently there's a repeater on 145.7875 MHz, only 12 KHz away, and I hear them instead of the ISS.
Here's an example of the audio I'm getting;
https://soundcloud.com/user-135945298/i ... 90605-1356
I use rtl_fm on Linux (Raspbian on Raspberry Pi) to demodulate the FM with the following parameters;
Code: Select all
rtl_fm -M fm -f 145.8M -s 48k | play -r 48k -t raw -e s -b 16 -c 1 -V1 -
My idea is that the FM bandwidth rtl_fm is listening to needs to be narrowed to exclude the repeater frequency from being processed. I'm currently not doing any Doppler correction because QSSTV can track the centre frequency of the tones and compensate automatically. I do have a python script that will do this though.
So if I can narrow the bandwidth rtl_fm is processing and do Doppler correction then I should be sorted right?
Trouble is, I am not sure how to do this with rtl_fm - is it possible? How do I do this?
Many thanks in advance