The RTL SDR sticks as mentioned seem to have delays when changing frequency that cause lost calls in trunking mode. I've added a new feature (updated in git branch max-trunking-update2 and in the wiki) which uses a software Local Oscillator instead of hardware retuning which essentially makes tuning instantaneous. There is a restriction that all of the channels to be tuned including the trunk CC must fall inside the tuning passband (whose width is equal to the sampling rate). See the SignalScope wiki page for more information.
Outside of this, LSM trunking works very well now with RTL SDR
Max
Hi Max, thanks for the update.
Unfortunately, the higher sample rate is chocking my CPU. It isn't usable for me at this point. I gotta figure something else out here...
-Scott
I got to thinking about this last night, and found that the freq_xlating_fir_filter is the bottle-neck I'm having the most trouble with.
This is going to be a silly question because I don't know any better. Is there a way to pull 25k out of the spectrum and filter that, rather then the whole spectrum buffer? It seems rather silly to me to process all that data when only a maximum of 12.5k is needed. We'd obviously need to have the offset tuning capabilities too. Is there a block to do that??
-Scott
Not at all a silly question (there is no such thing, for the most part - there are silly questioners, but this is not an example of that).
So I think there's another method that uses a PFB (polyphase filter bank) instead of the frequency translating FIR filter. I'll experiment with that ... All in all there's no substitute for a nice beefy CPU : )
Max
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