[Amps] T networks and harmonics

[carl s.]

   Jim: I certainly appreciate your response to my msg. Back when I was a
"novice" we didn't have the equipment we have today , but we did the best we
could with what we had.!!!  However: : As I said,  how many of us today have
the expertise and/ or the equipment to Evaluate  our H/B amps for the
"required" output purity??
  I have also noted , In the "handbooks" , Very little info relative to
actually "tuning' a PI-L output ckt.!! In particular the L section , for
max. "purity" output.!! Or any output for that matter.!!!
    If you or anyone on this reflector can elaborate on this I'd appreciate
it.
   I've seen a number of designs of pi- L but very little , if any info on
actually tuning the "L" section.!!!!
     carl / kz5ca
----- Original Message ----- 
From: "Jim Kearman" <jkearman at att.net>
To: "Amps" <amps at contesting.com>
Sent: Monday, February 06, 2006 7:04 PM
Subject: Re: [Amps] T networks and harmonics


> From: "Gary Schafer" <garyschafer at comcast.net>
>
> > I guess this was in response to your response to someone that said that
"a T
> > network tuner after the amp would not help reduce harmonics as it was
> > basically a high pass filter". You said that "it would help some".
>
> Of course, this is beyond the scope of my original post about the need for
pi-L output tanks to meet current FCC requirements, but thanks for the
backup. The Regs require spurious emissions be below a certain level _at the
output of the transmitter_, which would imply the output of the amplifier
used in conjunction with a transmitter or transceiver. Not the output of the
antenna tuner unless it is integrated into the amp/transmitter.
>
> Also, while a T-network _may_ attenuate harmonics sufficiently so that the
total system meets the spirit of the Regs, it's hard to know the effect of
any combination of antenna and tuner settings. If the second harmonic at the
amp output is -35 dB and the tuner adds another 8 dB, you have the -43 dB
required by the Regs, though not in the right place. Yes, I doubt FCC is
going to come knocking, but we want to build according to the best Amateur
standards.
>
> So I think we can draw two conclusions: A pi network is inadequate, and a
t-network antenna tuner is neither a legal nor a necessarily adequate
solution.
>
> In case the Commission is reading this, I assure them my pi-net amplifier
was "installed" prior to 1978!
>
> 73,
>
> Jim, KR1S
> http://kr1s.kearman.com/
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