Testing - 4th Session
4m Conversion
The final task was to try and get the "Robin" radio (with the motorola PLL chip) active on the 4m Band
The first thing to do was to replace the original Eprom and test that the radio was working (see note below)
Then, as suggested, and after a bit of research, we set up the low-Band radio to operate on the 4m band, on the sixteen channels from 70.3MHz to 70.4875Mhz, by re-progemming the Eeprom.
Then for testing.
Tx first
The PLL locked and it transmittied, as far as we could tell from the SDR, and frequency meter. The channels could be seen switching on the SDR, as the selector turned on the front panel of the radio.
Then for receive.
The VCO was programmed via the Eeprom to run at 21.6Mz below the desired frequency, but the PLL would just not lock.
Then, remembering previous comments on the UK Vintage Radio forum regarding high-side injection into the first IF mixer, we re-did all the calculations and set to RX VCO to run at 21.6 above the desired frequency. The VCO could now lock - across all 16 channels.
Here is a chart of the Eeprom programming need to achieve this:
So, overall, a success, but we can’t try a test QSO yet on 4m, until I build or obtain a proper antenna.
One last problem seems to be that the radio is intermittent on transmit. After some fiddling this indicates a possibly a dodgy connection on the “TX Driver and APC Board"
[A final note : this card is labelled as part 8308-4-4A, which is not shown as any of the options in any manuals. !]