In DSD+ FL 2.360, using FMP24 2.76 with an RTL-SDR.com dongle, I used the "R" key to toggle recording on and off, which recorded a large .iq file (centered 600 kHz above the frequency being tuned) and a 0-length .fm file. I had it tuned to a freq with no activity, but was interested in other signals within the 2.4-MHz-wide capture in the .iq file.
When I attempt to play it back with:
When using a recording as its input in this way, is FMP24 only able to demodulate the one frequency it was tuned to (f) when the recording was made, even though the recording contains 2.4 MHz of spectrum (from f - 0.6 MHz to f + 1.8 MHz)? If so, is there another way of recording chunks of spectrum for later analysis that will properly support P25 PSK simulcast signal decoding the way it works live with FMP24 and DSD+?
It turns out that SDR# with Vasili's baseband file plugin can read the files (it asks for the sample rate = 2400000, bits = 8, and channels = 2), but unfortunately doesn't know what the center freq is, so displays 0 in the main freq display (or 0 to -1.2 MHz in the mouse cursor popup) for those below the center and 0 to 1.2 MHz for those above it. It will tune correctly, but you have to calculate the frequencies yourself. I can probably write something to solve that problem. However, because it does not have a PSK demodulator, it feeds DSD+ FM-demodulated audio, which doesn't decode well, if at all. I'd would rather use SDR# because of the time-shift plugin that lets you pause and go backward and forward, and the other decoding plugins, but don't know of a way to get it to also feed DSD+ in a way that will decode PSK. Help please?
When I attempt to play it back with:
.\FMP24 options < filename.iq
it will ignore the -f option (if present) and instead tune to the center freq of the recording minus 600 kHz (the same freq it was tuned to when recorded). Using the left/right cursor keys or clicking in the display "tries" to change the frequency – the freq in the spectrum display window's title bar changes, as does the popup associated with the redline mouse cursor – but the actual freq it's tuned to remains the same and the spectrum display itself doesn't move (i.e. active signals remain in the same place).When using a recording as its input in this way, is FMP24 only able to demodulate the one frequency it was tuned to (f) when the recording was made, even though the recording contains 2.4 MHz of spectrum (from f - 0.6 MHz to f + 1.8 MHz)? If so, is there another way of recording chunks of spectrum for later analysis that will properly support P25 PSK simulcast signal decoding the way it works live with FMP24 and DSD+?
It turns out that SDR# with Vasili's baseband file plugin can read the files (it asks for the sample rate = 2400000, bits = 8, and channels = 2), but unfortunately doesn't know what the center freq is, so displays 0 in the main freq display (or 0 to -1.2 MHz in the mouse cursor popup) for those below the center and 0 to 1.2 MHz for those above it. It will tune correctly, but you have to calculate the frequencies yourself. I can probably write something to solve that problem. However, because it does not have a PSK demodulator, it feeds DSD+ FM-demodulated audio, which doesn't decode well, if at all. I'd would rather use SDR# because of the time-shift plugin that lets you pause and go backward and forward, and the other decoding plugins, but don't know of a way to get it to also feed DSD+ in a way that will decode PSK. Help please?
