RE: programmable crystal IC/chip
I mentioned earlier about a QST article that used one in a 30 meter Whisper transmitter. (that was the first incidence I remember hearing about them)
I have found the copy that I have. It is the January 2015 QST. pages 47-50. The schematic is on page 48.
Unless I am reading the spec sheet wrong for the current version of that chip, the pin out has changed. The schematic shows the chip to be an 8 pin device but from what I can tell the current version is a 4 pin device.
It appears the device is a programmed (by DigiKey frequency specified by purchaser) Phase Locked Loop.
It appears that it requires 10ms max to "start up" and there is an enable pin. I think, if I read it correctly, that a logic high = output on, logic low = output off
At a little over 4 dollars a unit (not including shipping) it will be worth ordering in my case and experimenting with. I would like to see if a logic low/high could be used to "key" the programmable crystal and, if so, what does the waveform look like and how would it sound as a keyed oscillator.
I see that the transmitter in this article is using a 10K resistor to reduce the output level and a .01 uf capacitor for coupling and isolation of the chip into the oscillator input of the Gilbert Cell mixer (SA612)
Sideband (double) generation is performed in the SA612 and later sent to the amplifier stages of the transmitter.
See photo of schematic included below.