[Boatanchors] "Sweep" techniques

[J. Forster]

Basically, it's pretty straight forward. An IF stage is little but a band
pass filter with gain.

You put in a constant amplitude, unmodulated, swept RF signal and observe
the amplituse of what comes out.

Suppose you are doing a 10.7 MHz IF.

You could do it manually with an RF generator:

1. Check your generator's output flatness by looking at the RF output on a
'scope or with a simple diode detector. It should be flat over the range
of interest, typically 10.6 to 10.8 MHz, for an IF BW of 200KHz.

2. Hook the IF amp up between the generator and then plot the measured
output v. frequency, point by point.  This is slow and a PITA, but it
shows you whatr you what to do.

3. Now change the RF generator for a sweep Gen. The RF outpot goes to the
IF as befor; the IF output to the 'scope or detector as before. Now hook
the "Sweep Out" of the SG to the 'scope horizontal input in X-Y mode.

The 'scope should now display frequency on the X-axis; Output Amplitude on
the Y-axis. This display is what you need to align IFs.

If you are going to align a full receiver, first align the IF; then retune
the SG to the receive frequency and align the RF section.

FWIW,

-John

==================




>
>
>
> Hello to all. I've been a ham for a long time and there is one area where
> not only is my knowledge severely lacking, but I seem to be unable to find
> any decent info on this technique.
>
> The subject is 'sweep alignment' of IFs and filters, etc.
> I have quite a few Tek 'scopes, and also a nice collection of MODERN
> Sweep/Function Generators. Krohn-Hite, Exact, etc. I have also purchased
> and repaired a ton of test equipment including 'scopes and TDRs, in
> addition to my boatanchor collection.
> The manuals for the Sweepers assume you know how to connect them and use
> them.
>
> A while back, I noticed that there were several articles in ER Magazine
> showing the swept response of various boatanchors, (SX-117, etc).
> Unfortunately, the authors never describe the test methodology. I have
> purchased more than a few (!!) "How to use your Sweep/Signal Generator"
> books.
> However, they are pretty old and only deal with old, tube type TVs.
> I even suggested to Ray at ER Mag that this subject would make a great
> article and he agreed, but I still haven't seen anything.
>
> So, could some of you guys with all the expertise in this area (Carl, Al)
> at least give me a shove in the right direction?
>
> Yes, I have searched the WWW extensively and no joy......
>
> Thank you!
>
> ron
> N4UE
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