Some of you have been following the fact that I am making in effort on converting the SEA ESP1000 repeater to amateur radio use. Finnaly got some other peoples radios off the bench and I have had the last few nights to tinker.
Progress made so far: Changed Mini-UHF jacks to BNC. Prepared RX board to accept re-synth board by removing molex connector and adding 7pin SIP socket. And changing C4 and C24 to be minirature size. Prototype resynth using ATMEGA8 instead of ATTINY45. This is being done to finalize coding as ATTINY uses all I/O pins making further programming of the chip impractical. 5 volt to 9 volt logic transposers running perfectly. Resynth is running in brute force mode with no intelegence at the moment. That means it is still clocking data to the port while the micro orders a tune to the master reference oscillator. This has the result of shifting the receive frequency around. Audio is sometimes pristine, sometimes noisy, sometimes transposed. I will have to write the code of the re-synth to be more 'Transparent'. Receiver tuned to 222.700 MHz, Best -113dBm for 12dB SINAD (Untuned). Trying to get my hands on a logic analyzer at the moment, that way I can see what is trying to do what instead of being in the dark. VCO range is unknown at the moment, I can say it will not tune to theoretical 225.0. VCO will need a tweak to run acceptably in the 222-225MHz range. To be done: Allow resynth to pass DAC information Resynth to grab commercial use PLL programing and inturpret it into the amateur range. Move Transmitter into amateur range. NBFM - Yes! 10.275MHz or 10.7MHz IF? Turn Product detector to quadrature detector, IF linear amps to become limiters. Anyone know if you can stretch the bandwidth of a crystal lattice filter by say adding a coil, capacator or resistor in parallel?
