[Hammarlund] AADE DFD1 for SP-600 question

[James A. (Andy) Moorer]

That is the correct place to tap the local oscillator - just on the wire 
that comes out of the RF deck and goes to the FCU.

It WILL change the frequency of oscillation! Rather than using a capacitor, 
I would just take an insulated wire from your preamplifier and twist it 
around the wire from the VFO. That makes a 1-2 pf joint. You will need to 
touch up the calibration of the VFO after you do this.

On the lower bands (500 kHz to maybe 8 MHz), the VFO output has all kinds of 
harmonics. The VFO signal on the broadcast band is a mess. There is not much 
you can do about it - no amount of changing the 6C4 oscillator will help. 
The only thing that would help would be another tank circuit.

That's all I know about it. I don't know what the AADE uses as its input 
stage. Best I can suggest is to put some high-frequency rolloff on the 
preamplifier and see if that helps.

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

----- Original Message ----- 
>
> 1.  FIRST I tried tapping the plate circuit of the oscillator, first at 
> the plate of the tube itself, and then at the wire that comes out to the 
> VFO/Xtal oscillator switch.  Various capacitors from 1pF to 5pF were 
> tried. Tapping the signal at either of those points seemed to produce the 
> same results.  A usable display up to about 43MC.  HOWEVER, the two lowest 
> bands read accurately at the low end of the dial, but by about midscale 
> (900KC on band 1) the readout suddenly jumped to a high reading and it 
> appeared that it was actually reading the 2nd harmonic of the LO!
>