National NC-300 question

Ray Robinson robinson at SHLRC.MQ.EDU.AU
Thu Feb 23 22:52:41 EST 2006

Hi Alfred,

> I recently bought an NC-300, and have restored it so it is working pretty
> well and calibrated, but I'm not sure if the crystal filter is aligned
> correctly or working exactly the way it is supposed to. 
I didn't see anyone answer this.
I have aligned crystal filters in other radios, but not the NC-300.
The main thing to remember with a phasing crystal filter,
is that the phasing knob controls a "notch", not the bandwidth.
The easiest way to align this filter is with a sweep generator (wobbultor).
Set it up to sweep the IF frequency, switch the crstal filter in and out,
and you should see the passband narrow (when switched in), it doesn't matter
if the gain cahnges a little. When doing this, check that the IF passband
and the crsytal filter passband coincide.
The phasing control, moves the notch through the passband,
and is designed to reject any interferring signal, "you phase it out". 
So the passband will look asymetrical, and will change as you turn the knob.
Adjust the knob and capacitor position, to suit the passband.

I've seen this written up somewhere, but I can't remember where.
Is it in Terman?

Ray vk2ilv

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