[Amps] 200-ohm tank and "un-un" in HF amp design

[Jim Thomson]

Date: Tue, 22 Oct 2013 19:26:50 +0200
From: peter chadwick <g8on at fsmail.net>
To: Jim Thomson <jim.thom at telus.net>, amps at contesting.com
Subject: Re: [Amps] ?200-ohm tank and "un-un" in HF amp design


##  I checked..and cant find any reference to  minimum  harmonic suppression  requirements anywhere......so far. 
If you manage to find out..... pse let me know.   

Jim  VE7RF




Jim,

The regulations state in level in the feedline. However, I could ask one of my friends at Industry Canada what they think.....

73

Peter G3RZP


========================================
Message Received: Oct 22 2013, 03:06 PM
From: "Jim Thomson" <jim.thom at telus.net>
To: amps at contesting.com
Cc: 
Subject: [Amps] ?200-ohm tank and "un-un" in HF amp design
 
Date: Mon, 21 Oct 2013 10:32:27 +0200
From: peter chadwick <g8on at fsmail.net>
To: amps at contesting.com
Subject: Re: [Amps] ?200-ohm tank and "un-un" in HF amp design?
 
>The touted higher harmonic suppression of a PI-L is mainly a myth.....a plane jane PI  is more than ample for harmonic suppression.<
 
As a Class AB stage has a second harmonic component of plate current only 6dB down on the fundamental, what sort of Q do you run in the pi network to get the extra 37dB of suppression needed to meet the FCC regulations or the extra 44dB needed elsewhere?
 
73
 
Peter G3RZP
 
##  ameritron uses a simple PI net on 40-10m on their bigger amps...and it easily meets the 44 db down FCC requirements.  Ameritron uses a PI-L  on 160+80m..but that?s so a smaller load cap can be used. 
My ants all exhibit sky high swr on their harmonics..including the 3rd...so whats the problem ?   Me,  I could care less  about harmonic suppression  since the amp kills most of it..and  the ants kill the rest.   My  F12  40m yagi barely resonates just a bit below the
12m band...and not at all on 15m.     Optibeam uses linear decoupling stubs on their 40m yagis  so they wont resonate on  15m.      I enter a  Q of 8-10 on  the GM3SEK  spreadsheet  for all my hb amps.  30-36 db of 2nd harmonic suppression 
is plenty  imo..... from any amp.   With 1 kw out....and  36 db down.... that means   1/4 watt on the 2nd harmonic.   .25 watt  into a sky high swr isnt gonna  bother anybody anytime soon.  
 
 
Jim   VE7RF