Harold E. Johnson wrote:
Then later, some rigs used PLLs. I can't remember if the Signal One
used one, but certainly in the seventies they came along. Same basic
idea as the premixer, but the PLL was the filter so the VCO directly
fed the receiver's first mixer.

Michael VE2BVW


Well the CX-7 didn't use a PLL, but the CX-11 did. It was however only for
generating a comb frequency to be used with premixing. The analog PTO's
still tuned 3.1 to 4.1 MHz.

The main problem with up conversion is the hit you take on oscillator phase
noise. These days, with the advent of the "H" mode mixer, oscillator phase
noise and birdies are THE limiting factor in receiver compromise.

W4ZCB


I've heard that DDS units do NOT have the phase noise problem that
conventional oscillators do. DDS does generate spurs, but if you can
find a DDS that will allow for a clock rate many times the desired
output frequency the spurs a far out of band. The Analog devices AD9954
family of DDS chips have a max clock rate of 400 mhz. If you do NOT use
the on board PLL multiplier and clock it externally from a good low
noise clock, you can overclock these chips to as much as 600 mhz!
So if you up convert to 70mhz you'd need a 100 mhz local oscillator at
10 meters. Thats 1/4 the clock (or 1/6 if over clocked).
With a 45 mhz first IF even better.

BTW I had an idea for a rig up converting to 6 meters as the first IF.
This would be dual conversion on the HF bands, though a crystal filter
at 6 meters for a fixed first IF would not be impossible here.