[R-390] Re: Spurious Resonances

[Tony Casorso]

Hi Bob,

I'm not sure what you are getting at. I used a 10x scope probe connected to 
the Grid of the RF stage. I want to measure the response of the preselector. 
I do not want to swamp anything. The two pictures show a sharp response from 
the preselector in one case, and a not so sharp response in the other case. 
The only difference is the impedance of the signal source connected to the 
antenna.

Tony
----- Original Message ----- 
From: "Bob Camp" <ham at cq.nu>
To: "Tony Casorso" <canthony15 at msn.com>
Cc: <r-390 at mailman.qth.net>
Sent: Saturday, October 27, 2007 9:04 AM
Subject: Re: [R-390] Re: Spurious Resonances


> Hi
>
> What are you picking off the output with?
>
> Picking off at the plate would be a *much* better idea if you are  trying 
> to measure the input circuit. You will have far less impact  from the 
> probe that way. If you want to suppress the effect of the  output tank, 
> swamp it with a low probe impedance.
>
> Bob
>
>
> On Oct 27, 2007, at 10:35 AM, Tony Casorso wrote:
>
>> How lucky can I get? I posted a set of images this morning that had  a 
>> "spurious response" in it. It turns out it was cause by the  settings on 
>> my sweeper (DC Offset was cranked over to one side for  some reason). The 
>> mailer wus unable to post it for some reason so I  get to try again with 
>> good pictures.
>>
>> Here are links to couple of pictures. I am sweeping the preselector  in 
>> my R-390a. The left edge of the sweep is 1.5MHz. The right edge  is 
>> 4.5MHz. The center is approximately 3MHz. The receiver is tuned  to 
>> 3.00MHz and the power is off. I am measuring the response at the  grid of 
>> the RF stage.
>>
>> The broader response picture is with the 25 Ohm (gen with 50 Ohm 
>> rterminator) sweep gen directly connected to the balanced input. The 
>> sharper response is with a 2.2K resistor in series with one side of  the 
>> balanced input.
>>
>> It looks like I was right that low source impedance broadens the 
>> frontend response.
>>
>> http://i25.photobucket.com/albums/c90/tonysradios/IMG_0825.jpg
>>
>> http://i25.photobucket.com/albums/c90/tonysradios/IMG_0826.jpg
>>
>> Tony
>>
>> ----- Original Message ----- From: "Tony Casorso" <canthony15 at msn.com>
>> To: <r-390 at mailman.qth.net>
>> Sent: Saturday, October 27, 2007 8:09 AM
>> Subject: [R-390] Re: Spurious Resonances
>>
>>
>> I should havethought about it for a few more minutes.
>>
>> Maybe the sweeper has a strong second harmonic that is visible near  1.5.
>>
>> Tony
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>