[Boatanchors] SP600 and DDS?

[James A. (Andy) Moorer]

Sure. You have to inject it into the crystal pin that is connected to the 
grid (pin 4) of the 6AC7, and it has to be a fairly strong signal - 1V or 
so, but it will work.

Of course, if you have a SP-600JX-17, there is a SO-239 jack in the back of 
the FCU where you can directly inject a DDS signal. It was built 
specifically to accept an external oscillator there. Unfortunately, T35 is 
broken into several pieces in EVERY JX-17 I have ever worked on. Something 
about the material they used. I replace it with a hand-made transformer 
using a modern Micrometals torroid.

The frequency of the DDS has to be 455kHz (3 lower bands) or 3.955 MHz (3 
higher bands) higher than the desired frequency to offset the IF frequency.

You still have to tune the station in on the receiver to set the resonant 
frequency of the first two RF amplifiers. You will be startled at how poor 
the tracking is on most receivers (i.e., the audible peak will be occur at a 
significantly different dial reading from the actual frequency, even if the 
receiver is aligned perfectly).

James A. (Andy) Moorer
www.jamminpower.com

----- Original Message ----- 

I was reading the december issue of ER and read an interesting article about 
injecting a DDS signal into a crystal socket for a Drake 4C.  So I was 
wondering if anyone ever tried/thought of doing the same thing with an 
SP600? Would seem a logical idea. Would give high stability and direct 
frequency readout (assuming you built the readout circuitry).

Thoughts anyone?
Eugene