[Boatanchors] "Sweep" techniques

Fri Jan 7 22:16:43 EST 2011

Use a DC Block or you'll wipe out the SA input mixer!!! You should
probably also use an attenuator/matching pad.

-John

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

> The Tektronix 7000 series scopes I use provide a buffered
> output from the selected vertical amp, I often use this to feed a
> frequency counter.  I imagine you could also use this output to feed a
> spectrum analyzer so the circuit loading would be that of the vertical
> plug-in and probe (either 1 or 10 meg).  I wouldn't try to use this
> technique at VHF/UHF or with pulse waveforms but it should be fine for
> looking at fairly low frequency IF strips and filters.
>
> Rodger WQ9E
>
> ----------------------------------------
> From: "Carl" <km1h at jeremy.mv.com>
> Sent: Friday, January 07, 2011 9:00 PM
> To: "Al Klase" <al at ar88.net>, <boatanchors at mailman.qth.net>
> Subject: Re: [Boatanchors] "Sweep" techniques
>
> 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"
> To:
> 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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