You will not find any commercial amplifiers or construction articles in the
last 20 years that use Pi only. Pi-L is the simplest way to go for new
amps. Ten-Tec uses an L-Pi-L circuit and solid state amps use bandpass
filters. Low pass filters only attenuate above 30MHz, so are not adequate
to meet the requirements on the lower bands. High power bandpass filters
are an expensive alternative.
Silver plating of the tank components will help Q and reduce losses as well.
Mike, W1NR
----- Original Message -----
From: "Jim Kearman" <jkearman@att.net>
To: "Amps" <amps@contesting.com>
Sent: Wednesday, February 01, 2006 12:15 PM
Subject: [Amps] Pi vs Pi-L
> My understanding of current FCC regs is
> * the mean power of any spurious emission from HF transmitters or
> external RF power amplifiers installed after January 1, 2003, must be at
> least 43 dB below the mean power of the fundamental emission.
> * the mean power of any spurious emission from HF transmitters or
> external RF power amplifiers installed on or before January 1, 2003, must
> not exceed 50 mW and must be at least 40 dB below the mean power of the
> fundamental emission. If the mean power output of such as transmitter is
> less than 5 W, the attenuation must be at least 30 dB.
> Still exempt from the provisions of §97.307(d) are transmitters built
> before April 15, 1977, or those first marketed before January 1, 1978.
>
> I don't believe a pi net of Qo 12-15 can achieve -43 dBc suppression of
> the second harmonic. The numbers I'm coming up with are an order of
> magnitude worse. So, shouldn't any new amplifier design include a pi-L
> tank, or external lowpass or bandpass filtering?
>
> 73,
>
> Jim, KR1S
> http://kr1s.kearman.com/
>
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