On Fri, 9 Apr 2004 22:06:47 +0200, "Helmut Sennewald"
wrote:

You are wrong here. I assume that the book doesn't claim to do an
impedance match to 50 Ohm input resistance for max. output power.
It's just designed as a passive lowpass filter with different source
and load resistor having a flat amplitude response. Nothing more.
The input resistance of this filter is for example 5 Ohm at f=12MHz.
According to the seven reactive parts, it has 3 notches and 3 resonances
for the input resistance over the frequency band from 0 to 200Mhz and
an additional zero at infinity frequency.

Thanks, Helmut (and others)
You're right as usual. I'd carried out my checks at 35Mhz which is of
course the cut-off frequency. I'd forgot I was dealing with a LPF and
had proceeded on the basis that 35Mhz was the centre frequency of a
BPF. D'oh!
Sometimes I'm amazed by my own carelessness. No doubt my regular
admirers won't be, though. :-(
I'll do another series of plots for 20, 10 and 5 Mhz later and expect
to see the input impedance point shift accordingly.
Thanks for your sterling efforts, BTW.
p.