[Amps] Pi-L Network

[James Joyce]

Hi Peter, Most of the ham amps now use a 4to1 step down transformer in
place of the switched L coil. Does this provide the same reduction of
harmonics? 
                                            Regards, Jim K2ZO 
 
-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
On Behalf Of Peter Chadwick
Sent: Monday, March 26, 2007 8:39 AM
To: Steve Flood; amps at contesting.com
Subject: Re: [Amps] Tank Coil spacing
 
Steve asked:
>It seems most of the homebrew and Handbook amps I see are Pi tanks.  Is

>the Pi-L really necessary?<
To meet the current requirements of the FCC and the Radio Regulations on
spurious emissions, yes. The Class AB stage produces a harmonic content
in the plate current that is 6 dB down on the second harmonic, and if
you do the sums, getting down the extrs 37dB to meet FCC or 44dB to meet
the Radio Regs limits is pretty darn difficult in just a pi network- in
fact, I reckon impossible, although there may be somebody who can come
up with values that in a particular case manage to do it, at least in
theory. It can even be a bit difficult in a Pi-L under some
circumstances. 
However, using a pi and an external low pass filter selected by band, or
a tuner,  is another approach
 
73
Peter G3RZP
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