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Re: [Amps] Tank Coil spacing

Subject: Re: [Amps] Tank Coil spacing
From: Ian White GM3SEK <>
Reply-to: Ian White GM3SEK <>
Date: Mon, 26 Mar 2007 17:32:23 +0100
List-post: <>
Tom W8JI wrote:
>Let's not leap to conclusions!  The answer is actually no. Most 
>amplifiers will meet the regulations easily without a pi-L, and many 
>pi-L's actually are insignificantly better on harmonics or no better at 

There are some interesting measurements on G4AXX's website, at:

For that particular amplifier, the harmonic levels on various bands 
ranged from -45dBc to undetectable. Mark found that the unexpectedly 
good results were due to VHF parallel resonances in the shorted turns of 
the tank coil, which sometimes - though purely by luck - could notch out 
the harmonics. Scroll to the bottom of the web page for details.

(Also check out the rest of Mark's site, which is full of high-quality 

Agreed that the harmonic levels into real-life antennas would be 
different again, and even harder to predict... but the regulatory tests 
into 50 ohms.


73 from Ian GM3SEK
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