Post subject: Non-Reflective, High Power HF harmonic
Unread postPosted: Sun Feb 13, 2005 10:34 pm
Using MRF154 x2 in a 3-50Mhz, 1KW HF amp. Currently using
7 pole Butterworth LC filters. The reflections, harmonics, from
this type of filter slowly smokes the highpower FETs (MRF154). Any
ideas on a filter that would block these reflected harmonics from
Thanks for any ideas!
Post subject: Filter
Unread postPosted: Wed Feb 16, 2005
If I understand you correctly, what you need is
what's variously called a "branching" filter, a "complementary"
filter, or a "dissipative filter". The power that doesn't go out
the output port has to go somewhere. Right now, it's reflected back
and absorbed by your output stage transistors. The only other place
it could go is into a resistive load.
There's a discussion
of this kind of filter in the book by Anatol Zverev, "Handbook of
Filter Synthesis". It's kind of pricy, but a nearby university library
may have it. What you need is only a few pages.
Post subject: mrf154 filters
Unread postPosted: Wed Mar 16, 2005 9:01 pm
Hi--I am using
7 section, eliptical filters with my mrf154's with no problems.
The steeper roll off of the eliptical allows you to move the corner
frequency further from the operating frequency and thereby allows
you to look into a better impedance at the operating frequency.
My 2nd harmonic was down about 55 db and the 3rd was down 15 db
with a matched pair of mrf154's without the filters. This allows
you to move the corner out even further.
I hope this helps