[Amps] Pi-L Network

[James Joyce]

The Commander, Ameritron and QRO series all use a 4to1 transformer in
the Pi-L network. The ARRL handbook also has some amp projects that use
the same type of circuit.               73, Jim K2ZO 


-----Original Message-----
From: Bill Fuqua [mailto:wlfuqu00 at uky.edu] 
Sent: Monday, March 26, 2007 11:06 AM
To: James Joyce
Subject: Re: [Amps] Pi-L Network

James,
Can you provide  a schematic of such an amp?
I am not familiar with this.

73
Bill wa4lav


At 10:39 AM 3/26/2007 -0400, you wrote:
>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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