A handful of Motorola K1003A Receive Channel Elements arrived from eBay:
Having three 13466.666 kHz candidates, two with gold labels (2 ppm tempco) I disemboweled a silver-label (5 ppm) victim:
They’re well-studied, with readily available schematics:
For lack of anything smarter, I put a 1 kΩ resistor from RF Out to Ground to get some DC current going, then used a 470 nF cap and 47 Ω resistor as an AC load:
Which oscillated around a mid-scale DC bias, but looked ugly:
Perusing some receiver schematics suggested a heavier DC load, so I swapped in a 470 Ω resistor:
It’s now running around 3 V bias with fewer harmonics; the scope’s frequency display in the upper right corner seems happier, too.
The receiver will run that through a filter to wipe off the harmonics, then multiply the frequency by three to get the mixer LO.
There are many, many different Channel Elements out there, in receive and transmit flavors, but at least I have some idea what’s going on inside.
