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 Calculators Education Engineering Magazine Articles Engineering software RF Cafe Archives RF Cascade Workbook 2018 RF Symbols for Visio - Word Advertising RF Cafe Forums Magazine Sponsor RF Cafe RF Electronics Symbols for Visio RF Electronics Symbols for Office Word RF Electronics Stencils for Visio Sponsor Links Saturday Evening Post NEETS EW Radar Handbook Microwave Museum About RF Cafe Aegis Power Systems Anritsu Alliance Test Equipment Amplifier Solutions Anatech Electronics Axiom Test Equipment Berkeley Nucleonics Bittele Centric RF Conduct RF Copper Mountain Technologies Empower RF everything RF Exodus Advanced Communications Innovative Power Products ISOTEC KR Filters Lotus Systems PCB Directory Rigol RF Superstore San Francisco Circuits Reactel RFCT TotalTemp Technologies Triad RF Systems Windfreak Technologies Withwave LadyBug Technologies Wireless Telecom Group Sponsorship Rates RF Cafe Software Resources Vintage Magazines Thank you for visiting RF Cafe!
Innovative Power Products Couplers

Passing 25W DC while rejecting 4W 4-20GHz - RF Cafe Forums

RF Cafe Forums closed its virtual doors in 2010 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. 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.

NOTICE: The original RF Cafe Forum is available again for reading, and the new RF Cafe Blog is an active board.

-- Amateur Radio

-- Anecdotes, Gripes, & Humor

-- Antennas

-- CAE, CAD, & Software

-- Circuits & Components

-- Employment & Interviews

-- Miscellany

-- Swap Shop

-- Systems

-- Test & Measurement

-- Webmaster

 Post subject: Passing 25W DC while rejecting 4W 4-20GHz
Posted: Sun Sep 16, 2012 9:35 pm 

Joined: Mon Apr 20, 2009 2:04 pm

Posts: 14

I'm attempting to power some equipment in an enclosure that sets in an EMC test chamber.

My difficulty is that the customer tests up to 20 GHz for RFI and has some customers that want 20 V/m or more of signal strength, and I'm concerned that my shielded DC power cable will leak enough to interfere with my own electronics.

My first thought was to use a bias tee, but none have met the need (including cost).

My next thought was to bring power in through a back to back bulkhead connector, into a shielded chamber, and run the signal through about 10 feet of RG-174 before exiting through a bulkhead filter into the equipment chamber.

Any ideas?



 Post subject: Re: Passing 25W DC while rejecting 4W 4-20GHz
Posted: Tue Sep 25, 2012 10:45 pm 

Joined: Wed Apr 08, 2009 11:07 am

Posts: 33

That would work, assuming the lowpass filter held in there all the way up to 20 GHz.

I would be tempted to put some round ferrite toroids along the outside of the coax cable--just to keep any standing waves down. If there is a big standing wave, then you could get leakage thru the ground braid at the E field maximum points. The ferrite toroids would de-Q the outside braid so the standing wave would be small.

If you still had leakage, and needed to add another lowpass filter outside of the chamber, that is where it gets dicey. Since the lowpass filters are totally reflective, if you have two of them at either ends of the cable, you can make a resonant circuit out of the whole mess and lose your rejection. A standard fix is to add a few dB of attenuator pad at the outside LPF, but that would screw up your passing of DC.



Maguffin Microwave Consulting


Posted  11/12/2012

Windfreak Technologies SynthHD PRO - RF Cafe
Anritsu Test Equipment - RF Cafe
ConductRF Phased Matched RF Cables - RF Cafe
Berkeley Nucleonics Corporation - RF Cafe
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

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

These Are Available for Free


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: