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Re: [TowerTalk] Motor Driven vac used in 40M DE?

To: "Richard \(Rick\) Karlquist" <>, "Jim Thomson" <>
Subject: Re: [TowerTalk] Motor Driven vac used in 40M DE?
From: "Gene Fuller" <>
Date: Wed, 30 Dec 2009 11:56:59 -0500
List-post: <">>
Hi Rick -
Measuring speaker voltage is an easy idea that could be refined by changing 
the sig gen  output by known amounts to get a "calibration" curve or, more 
conveniently, put sig gen directly into the rx, at greatly reduced level, to 
give the same audio output level, to get "calibration" curve.
Gene / W2LU

----- Original Message ----- 
From: "Richard (Rick) Karlquist" <>
To: "Jim Thomson" <>
Cc: "Gene Fuller" <>; "Jim Walker" 
<>; <>
Sent: Wednesday, December 30, 2009 10:03 AM
Subject: Re: [TowerTalk] Motor Driven vac used in 40M DE?

> Jim Thomson wrote:
>> ###  OK.   The consensus is the  F/B  will  degrade  when trying to cover 
>> a major portion of the band.
>>   But what about the forward gain ??     Does it degrade greatly... or 
>> just a little bit ?????
>> IOW..  I can live with  greatly degraded FB...  but if the  forward  gain 
>> falls off over the cliff,  that's  unacceptable.
>> Does the F/S  degrade as well ???     F/S  at this location is MUCH more 
>> important than  F/B
> My MonstIR experience is only a guide, since "YMMV" as they say.
> However, I found that I lost 2 dB of forward gain by being off by 100 kHz 
> on the parasitic elements.  It was quite a bit worse at 200 kHz off.
> There was a difference between being too high in frequency and being
> too low in frequency by the same amount, but I don't remember which
> degraded faster.  In any event, you need to test your own beam to see
> what it does.
> To do these tests, set up a sig gen as far away as you can from the
> beam, and listen to it with your receiver's AGC off and RF gain adjusted
> appropriately.  Tune in a nice CW tone, and connect an AC voltmeter
> to the speaker terminals.  Now you can measure AF voltage as the
> antenna rotates.  Since you are operating the receiver linearly,
> the AF voltage will track the RF voltage.  dB is 20 LOG V1/V2 as
> we all know, etc.  Some voltmeters can read directly in dB,
> such as the better HP models.  There is a computer program (somewhere in
> cyberspace :-) that uses your sound card as a voltmeter and gives
> a nice plot if your rotator speed is uniform.
> Rick N6RK 


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