[Hammarlund] Sweep method of alignment - Spectogram.

[Kenneth G. Gordon]

Further info on sweeping at RF.

Ken Gordon W7EKB

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One point I didn't mention about using sinusoidal sweep is that it is
NOT necessary to see the bandpass traces superimposed on each 
other.  Just open up the sweep frequency excursion and adjust the 
center frequency and the traces will appear side-by-side. That is, going 
one direction the bandpass will be swept and produce the outline 
before the trace reaches the center of the scope display, then it'll be 
swept as the trace comes back from the other end before it reaches the
center again. So the two traces will appear side-by-side and as mirror
images. 

For my home workshop, I was considering adding a varactor tuning 
diode to my RF generator so I could drive it from the scope sweep 
generator but I've found it much easier to adjust filter band passes 
using a different method that also gives me a wonderful display of the
bandpass characteristic. I use a pc-based audio spectrum analyzer 
such as Spectrogram. It gives me an amplitude-vs-frequency display 
based on the audio spectrum from a few cps to up to some tens of 
kilocycles/sec with an amplitude range that is limited only by the sound 
card: greater than 60 dB with my notebook computer. I feed the receiver 
with white noise and look at the resulting audio spectrum at the audio
output with Spectrogram and I'm looking at a perfect image of the
overall receiver bandpass. Unless I've got an audio filter switched
in, that's the I.F. bandpass. 

Ron AC7AC

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