I am glad you asked. Looks like the software has bugs. I ran this with SPICE just now and the results do not match the filter program.
I have had this filter designer laying around for a long time. It is AADE version 4.42. Yes, you can design filters and alter values etc. But it seems to be somewhat limited. From a design flexibility point of view ELSIE is better (IMHO) but both suffer from
awkward user interfaces.
Spice gives a better results (about 4 ohms at 42 MHz) (attached). I guess it is time to look for an update to AADE or ditch it altogether.
ony
toggle quoted message
Show quoted text
Tony, what software is that? Does it design any filter functions? Does it simulate the filter property when you manually override the values? If it runs on Mac or Linux I'll modernize my filter design technique...
Is that impedance peak at 21MHz to block 2nd harmonic of 10.1MHz or 3rd harmonic of 7MHz? That is contributing to the high impedance at 42MHz.
A typical approach is to add series resonance to shunt out the harmonics. That'll "push back" the unwanted energy to the RFC and can get used for the fundamental. However, that'll be a trade-off with the circuit complexity especially in a multiband rig.
Another way to possibly improve efficiency is to use a bifilar RFC to supply the final transistors so that the same phases (DC, some harmonics) see no reactance but opposite phases (fundamentals) see a large reactance. It may or may not be useful depending
on the circuit and construction (two separate RFCs are just fine if the LPF works well enough) but cancelling DC flux alone is an advantage in constructing a small ferrite choke that works well.
