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Subject: [AMPS] IMD
From: (2)
Date: Tue, 18 Sep 2001 06:47:38 -0700
>> As evidenced by the published test figures on, for example,  the
>> TS2000. Interesting, since modern MOSFET PA's are supposedly very
>> linear.
>The TS2000 is not a good example. It is exceptionally poor. It is 
>one step removed from class C performance. 
>We have to remember a two-tone test does not show IMD caused 
>by poor dynamic power supply regulation.
//  Amen to that.  

>Also AB1 or 2 tetrodes get nasty FAST compared to a GG triode 
>when overdriven or misadjusted.

//  True enough, however, I have heard some over-driven G-G amplifers 
that would have been exceedingly hard to beat in a feculence race.   
>> If the linear at full rated power is capable of -30dB rel PEP IMD
>> products, then the total IMD power is likely to be (neglecting phasing
>> and compensating distortion effects) 27dB down on PEP.
>That's right, IMD can add. So the PA must be many times cleaner 
>than the exciter to not make things worse.  

//  If the amplifier was but 5db less feculent than the transceiver,  
virtually no humanoid could detect the difference.  
>> case the transceiver) needs to be a lot better. That suggests that
>> either it needs to run at a lower power output, demanding more gain
>> from the amplifier, or needs to be 10 to 20dB better on IMD at the
>> rated output. Many transceivers probably need to run around the 25
>> watt level rather than the 100 watt level for acceptable overall IMD.
>> However, Part 97.317 (a) 3 of the the FCC rules gives us a problem, as
>> it requires a 50 watt (mean) drive minimum for an amplifier.
>Reducing drive power from an exciter does not always make things 
>better. Quite often it actually makes things worse.
//  Good point.
- cheers.  

>73, Tom W8JI
>FAQ on WWW:     
>Administrative requests:

-  R. L. Measures, 805.386.3734, AG6K,  

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