Project #7 A narrow bandwidth 12.8 MHz PLL

My station receiver NRD525 uses an internal 12.8 MHz reference oscillator for it’s synthesizer.

I added a SMB o/p connector to output this frequency for my 144 MHz and 432 MHz converter.

I noticed that after division and subsequent multiplication in the converters’ PLL the frequency offset was already a few kHz on 432 MHz.

After finding a 12.8 MHz VC-TCXO-38C5 of KSS Japan at a flea-market it was rather simple to extend my ZDF locked source to output a accurate 12.8 MHz aswell. Even for an 1152 MHz LO for 23cms this is a neat frequency (90^th harmonic)

Operation is straight forward, the 12.8 MHz oscillator is divided by 256 using a 74HC40103.

The reference frequency comes from the 1 MHz of my ZDF locked source, divided by 20, using the internal divider of the HEF4750.

No active loop filter amplifier is used. Due to the limited tuning range of the TCXO, the time constant of the loop-filter is rather large and so the bandwidth of the PLL is small.