Post
by Albert H » Sun Apr 10, 2022 3:49 am
Nice job Sinus! Have you tried AFC on your receiver? It keeps the receiver locked to the transmitter, so that any drift is automatically corrected for - the receiver "follows" the transmitter.
The other option (obviously) is to use a PLL. At Band I you can use the 74HC4024 as a "prescaler" to divide the carrier frequency by either 4 or 8. I then use a diode-programmed 74HC4040 to select frequency. The reference is (usually) a 4MHz crystal and a diode-programmed 74HC4060. The phase comparator is a 4046 (or a 7046).
You can use the same type of PLL circuit for both the transmitter and for the receiver Local Oscillator (obviously programming the Receiver LO for 10.7 MHz away from the transmit frequency).
LB has just made some PLL boards with surface-mounted logic. The "prescaler" IC in his case is a 74F160 dividing by 10 - it works all the way through Band I and Band II. He used a 74HC74 and a 74HC00 for his phase comparator, which gives a very clean control voltage when filtered by a dual op-amp circuit. It also gives accurate locked / unlocked indication. His board is double-sided, and the programming is done by linking tracks with solder blobs. We're looking into getting these made in quantity (with the components loaded), since the parts are cheaply available in the Far East, and many of the firms over there are crying out for assembly work at the moment, because there are no microprocessors available anywhere right now, and all those factories are idle.
"Why is my rig humming?"
"Because it doesn't know the words!" 
