[Amps] Spectrial purity and tank configuration

[Michael Tope]

Norm,

It depends on the tuner. Many commercially available tuners
are "T" networks that use two series capacitors and and shunt
inductor. This forms a hi-pass network and will not improve
harmonic rejection significantly. A pi network tuner in a low
pass configuration (series inductor and two shunt capacitors)
would improve harmonic rejection, but the degree to which it
does would depend on the loaded Q of the tuner network at
each particular setting. I am not sure that you can generalize
without looking at the specific values of reactance involved
in each case. In fact with a tuner you can oftentimes come up
with different tuning solutions which all give 1:1 VSWR for a
particular load impedance, but involve different levels of
loaded Q. Thus harmonic rejection would be dependent on
which solution you arrived at. In most cases the solution which
is arrived at involves some degree of random chance (random
knob twiddling), so unless you went thru with a spectrum
analyzer or external receiver and verified which tuner settings
produced acceptable harmonic rejection you might not get the
desired result everytime. I would want to do some analysis
before making any claims one way or the other.

BTW, with respect to IMD, I don't believe either configuration
offers any real advantage.

73 de Mike, W4EF......................................



Sent: Thursday, May 22, 2003 7:33 PM
Subject: [Amps] Spectrial purity and tank configuration


> Amp Guru's,
>
> Will I get the same results with a pi output tank and a tuner as I
> would get with a Pi-L output tank ???
>
> Norm  N8NH
>