[Boatanchors] "Sweep" techniques

[Al Klase]

Ron,

A couple of observations from a non-expert:

Sweeping TV and FM IF's is relative easy because their bandwidths are 
wide, 100 of KHz or more.  The primary problem with sweeping the narrow 
IF's in communications equipment is that the sweep rate has to be 
drastically reduced to accurately represent the shape of the filter.  
We're probably talking 100's of milliseconds if not whole seconds.  So, 
you either need a storage scope or a vivid imagination to actually see 
what going on.

The classic test equipment for doing this is a "spectrum analyzer" with 
a "tracking generator."  I use an HP 141T (8556A and 8552B plugins) with 
an 8443A TG.  The 141T is equipped with a storage CRT.  More modern 
equipment uses digital storage, and is capable of printing out the 
results.  The other advantage of this sort of a spectrum analyzer is 
that it offers 2dB-per-division and 10dB-per-division vertical response 
in addition to the linear response available in the usual oscilloscope.  
The 10dB/div gives you pictures like you see in the text books, allowing 
you to reckon things like the 6/60dB shape factor of a filter.

Hope that helps a little,
Al

On 1/7/2011 3:09 PM, bonddaleena at aol.com wrote:
>
>
> 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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