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Re: [TowerTalk] Are All Low-Pass Filters Alike? -

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Are All Low-Pass Filters Alike? -
From: K4SAV <RadioIR@charter.net>
Date: Tue, 16 Aug 2005 21:29:45 -0500
List-post: <mailto:towertalk@contesting.com>
I wasn't going to jump on this one, because I knew Tom would squash it, 
but seems these harmonics need more amplification.

Don wrote:
As for the statement that 'amps do not amplify harmonics' that was
posted by another submitter .. I defer to the "experts" as to why
harmonics ARE amplified by a well-designed amplifier .. a FACT that  can
be easily measured.


The "other submitter" is one of the best experts around, and he gave you 
the "straight skinny". Read it again, it's all true. 

Maybe some of the terms he used weren't simple enough.  If you clip the 
top, or bottom, of a sine wave everytime at the same point, you generate 
harmonics, not spurious frequencies.  Any amplifier that does not 
conduct over the entire 360 degrees of the sine wave, generates 
harmonics.  That's ALL amplifiers except class A amplifiers. These 
harmonics are mostly removed by the tank circuit.

If you happen to have a broad band untuned  class A amp that has gain at 
the harmonic frequencies, then the amp can amplify the harmonics.   

Jerry, K4SAV


Don Havlicek wrote:

>Correct me if I am wrong, but aren't "harmonics" exact multiples of a 
>given frequency?
>As such, they should be differentiated from the spurious frequencies 
>generated by an amplifier which usually are NOT an exact multiple of the 
>driving frequency.
>Those spurious frequencies are, correctly as stated, not filtered by a 
>LP between the Xcvr and amplifier.
>The original question I raised was concerning HARMONICS, not spurious 
>frequencies generated by the amplifier.
>Perhaps operating an amplifier ONLY within the linear portion of its 
>curve would cure most of the spurious frequencies and limit the need for 
>a LP filter post-amp.
>As for the statement that 'amps do not amplify harmonics' that was 
>posted by another submitter .. I defer to the "experts" as to why 
>harmonics ARE amplified by a well-designed amplifier .. a FACT that  can 
>be easily measured.
>Don
>N8DE
>
>Jim Lux wrote:
>  
>
>>At 01:10 PM 8/16/2005, Don Havlicek wrote:
>>
>>    
>>
>>>Why don't hams place the LP filter between the Xcvr and the Amp?  That
>>>way, the amount of harmonics reaching the Amp will be minimized,
>>>rendering their output levels relatively the same, if not lower, than if
>>>the LP filter was AFTER the Amp.
>>>BTW:  this is what I have done since the 50's.  Never blew up a LP
>>>filter yet!
>>>Don
>>>N8DE
>>>      
>>>
>>probably because the harmonics people are concerned about come from the 
>>power stage, not the exciter.   
>>
>>_______________________________________________
>>
>>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
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>>questions and ask for Sherman, W2FLA.
>>
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>>    
>>
>
>
>_______________________________________________
>
>See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any 
>questions and ask for Sherman, W2FLA.
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
>
>  
>

_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
and ask for Sherman, W2FLA.

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