[Boatanchors] "Sweep" techniques

Fri Jan 7 22:38:59 EST 2011

I forgot to mention the HP FET probe. - Al

On 1/7/2011 10:16 PM, J. Forster wrote:
> 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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>>>>          
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