I would hope no one flames you for wanting to design your own digital repeater - that's in the spirit of amateur radio and repeater-building.
I don't think the Motorola manuals will be much help since all the 'heavy-lifiting' is done in software inside of DSP chips. Some products from other vendors might be more useful. IIRC there were some hams - maybe in Colorado - that created a P25 repeater using EFJ logic and MastrII RF. Also, you could look up this thesis as a starting point: A SOFTWARE BASED APCO PROJECT 25 DATA TRANSMISSION BASE STATION FOR LOCAL POLICE HEADQUARTERS BY ERIC RENÉ RAMSEY ------------------------------------------------------------------- --- In [email protected], "kt...@..." <kt...@...> wrote: I'm wondering if anyone has thought about or attempted to modify an analog repeater to regenerate P25 signalling (C4FM)? I know the easy way would be to buy a Quantar or similar box, or tying two mobiles back-to-back for flat-audio passthru. I want to find a way to recover the phase-modulated signalling, passing it to a homebrew "logic" board. This board would stream the bits into memory and if the NAC is valid, then regenerate the similiar stream out the transmitter. You could also store-and-forward this "audio" to other systems or for playback. So I either need to buy a manual to read the theory or ask here if anyone has tinkered with this. Maybe I'm missing something here, but isn't phase-modulation not quite the same as our VCO-modulated direct FM? P25 as I understand it, either shifts the phase 600Hz or 1800Hz plus or minus, and based on this generates a two-bit "symbol" at 9600 baud. So please don't flame and say "Go buy a Quantar" because if this could be done, many surplus systems could be modified for new digital modes. Any help with schematic scans or what part numbers for Astro/Quantar style unit manuals would be welcomed. Thanks! Tony
