Windfreak Technologies Frequency Synthesizers - RF Cafe
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024
    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

My Hobby Website:

Electronics World articles Popular Electronics articles QST articles Radio & TV News articles Radio-Craft articles Radio-Electronics articles Short Wave Craft articles Wireless World articles Google Search of RF Cafe website Sitemap Electronics Equations Mathematics Equations Equations physics Manufacturers & distributors Engineer Jobs LinkedIn Crosswords Engineering Humor Kirt's Cogitations RF Engineering Quizzes Notable Quotes App Notes Calculators Education Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Homepage Thank you for visiting RF Cafe!
Innovative Power Products Combiners / Dividers

LC duplexer - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2010, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. If the folks at phpBB would release a version with integrated sign-in from the major social media platforms, I would resurrect the RF Cafe Forums, but until then it is probably not worth the effort. Regardless, there are still lots of great posts in the archive that ware worth looking at.

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

-- Amateur Radio
-- Anecdotes, Gripes & Humor
-- Antennas
-- CAE, CAD, & Software
-- Circuits & Components
-- Employment & Interviews
-- Miscellany
-- Swap Shop
-- Systems
-- Test & Measurement
-- Webmaster

Post subject: LC duplexer Posted: Sun Aug 07, 2005 9:22 am
i would like to design LC duplxers consist of HPF and LPF
in an eagleware software i got influence between the two filters and i dont get the needed performance when combining the filters

i would like to know the right way to design it, or to model it in eagleware or an application note regarding the subject

thank you


Kirt Blattenberger
Post subject: Posted: Wed Aug 10, 2005 1:04 pm

Site Admin

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings shai_s:

It has been a while since I have designed a diplexer, but if memory serves me correctly, the way to go about a LP/HP combination is to design with an input impedance of 1 ohm and an output impedance of whatever you system impedance is (50 ohms?). Then, tie the two 1 ohm inputs together as the common input.

The theory behind it is that between the LP and HP filters, the input will "see" the system impedance spanning in frequency across both filters. At least that's the way I remember it.

- Kirt Blattenberger
RF Cafe Progenitor & Webmaster


Post subject: LC DiplexerPosted: Wed Aug 10, 2005 5:55 pm
In designing an LC Diplexer, it's important to have the right kind of filters for the HP and LP filters. Neither should start with a shunt element. (Use Tee filter sections instead of Pi sections for the first stage).

Otherwise, each filter will "short out" the signal in its stopband, with disastrous results.

If I remember correctly, you design both filters at the system characteristic impedance (usually 50 Ohms). That way, the return loss stays (more or less) constant over both bands.

Good Luck!

Posted  11/12/2012
Werbel Microwave - RF Cafe
Amplifier Solutions Corporation (ASC) - RF Cafe

Please Support RF Cafe by purchasing my  ridiculously low−priced products, all of which I created.

These Are Available for Free