[Boatanchors] "Sweep" techniques

[Carl]

The problem with an SA is that its 50 Ohms and would seriously load down an 
IF strip or xtal filter.A sweeper and storage scope is more realistic since 
the sweeper is designed for the job and the scope wont load down the 
circuit.

Johns explanation was the way I first did it, in the early 60's. Tedious but 
thats how everything was then.

For a good description of the old way see the WW2 Super Pro manual. It also 
covers IF alignment without the test equipment and IMO its mandatory reading 
before doing any of the early HQ series. IMHO I can do a better job faster 
with a sig gen, meter and ear on a HQ.

Another good read is the HRO-60 manual.

Many users want to either narrow or widen the factory selectivity if they 
are dedicated CW or AM operators. This can be done by peaking, stagger 
tuning, loading or unloading the IF circuit with a resistor (increasing or 
removing the transformer swamping resistor for some Collins for AM), 
regeneration, and more. Not all are very good or limit the sets usefulness. 
These days its easier to add a Kiwa AM filter than try to custom tune the 
IF's.

To keep in the BA spirit I use a GR-1025A sweeper which still has the 
National Radio inventory tag. The scope is a lot more modern. I also have 
several HP items for when the spirit or the job moves me.

Carl
KM1H


----- Original Message ----- 
From: "Al Klase" <al at ar88.net>
To: <boatanchors at mailman.qth.net>
Sent: Friday, January 07, 2011 4:06 PM
Subject: Re: [Boatanchors] "Sweep" techniques


> 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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