Custom Search
Over 10000 Pages Indexed
Your Host
Click here to read about RF CafeKirt
Blattenberger

... single-
handedly
redefining
what an
engineering website
should be.

View the YouTube RF Cafe Intro Video Carpe Diem!
(Seize the Day!)

5CCG (5th MOB):
My USAF radar shop

Hobby & Fun

Airplanes and Rockets:
My personal hobby website

Equine Kingdom:
My daughter Sally's horse
riding business website -
lots of info

•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

Job Board

About RF Cafe©

RF Cafe E-Mail

Non-Reflective, High Power HF harmonic filter wanted - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.


MOSFET Blues
Post subject: Non-Reflective, High Power HF harmonic filter wanted
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 the FETs?
Thanks for any ideas!


Top


Guest
Post subject: Filter
Unread postPosted: Wed Feb 16, 2005 8:46 pm

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.

Good Luck!


Top


Guest
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







Posted  11/12/2012
A Disruptive Web Presence

Custom Search
Over 10,000 pages indexed! (none duped or pirated)

Read About RF Cafe
Webmaster: Kirt Blattenberger
    KB3UON

RF Cafe Software

RF Cascade Workbook
RF Cascade Workbook is a very extensive system cascaded component Excel workbook that includes the standard Gain, NF, IP2, IP3, Psat calculations, input & output VSWR, noise BW, min/max tolerance, DC power cauculations, graphing of all RF parameters, and has a graphical block diagram tool. An extensive User's Guide is also included. - Only $35.
RF system analysis including
frequency conversion & filters

RF & EE Symbols Word
RF Stencils for Visio

Product & Service Directory
Personally Selected Manufacturers
RF Cafe T-Shirts & Mugs

RF Cafe Software

Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel