Windfreak Technologies Frequency Synthesizers - RF Cafe
Windfreak Technologies
 

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024
Webmaster:
    Kirt Blattenberger,

    BSEE - KB3UON

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:

AirplanesAndRockets.com

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!
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

Anyone know how a coax filter works - 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

hawk
Post subject: Anyone know how a coax filter works
Unread postPosted: Fri Jul 16, 2004 4:56 pm
Offline
Lieutenant

Joined: Fri Jul 16, 2004 4:51 pm
Posts: 1
Hi,

I have a device that is a microwave filter, the manufaturer says it is a coax device. How does a coax cable get a sharp enough cutoff to be used as a filter? Does it have to do with TEM wave modes?

Thanks in advance.


Top
Profile

Guest
Post subject:
Unread postPosted: Tue Jul 20, 2004 1:38 pm

Coaxial filters are basically cascades of differing lengths of differing characteristic impedances. They're usually made up of a constant diameter outside shield and lengths of differing diameter center conductor to get the different characteristic impedances.

The (differing) lengths allow a segment of the line to appear capacitive or inductive, depending on its length and its termination. (Think Smith Chart!) The differing characteristic impedances cause the mismatch reflections which the line segment lengths then transform into capacitive or inductive reactance, out of which the filter is built.

That's a bit hand-wavy, but one of Kirt's "books of the day" a week or so ago goes into some depth if you really need to know.


Top


Guest
Post subject:
Unread postPosted: Tue Jul 20, 2004 1:51 pm

Thanks!! Where can I find Kirt's book of the day? How does coaxial compare to waveguide (interdigital) filter? I would think that a waveguide filter would have a better VSWR, loss, and steeper cutoff than a coax device.


Top


Guest
Post subject:
Unread postPosted: Tue Jul 20, 2004 4:00 pm

Thanks!! Where can I find Kirt's book of the day? How does coaxial compare to waveguide (interdigital) filter? I would think that a waveguide filter would have a better VSWR, loss, and steeper cutoff than a coax device.


Top


Kirt Blattenberger
Post subject: Coaxial Filters
Unread postPosted: Fri Jul 23, 2004 8:36 am
Offline
Site Admin
User avatar

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

I believe the book being referred to is "Theory and Design of Microwave Filters," by Ian Hunter.


When the vendor said the filter is a coaxial device, did he/she/it mean built of multiple lengths of coaxial cable, or is it a tubular filter like what K&L, Lorch, Salisbury Engineering, etc., sell?


- Kirt Blattenberger :smt024


Top
Profile

K5DVW
Post subject:
Unread postPosted: Fri Jul 23, 2004 9:41 am

A coax filter is nothing more than a filter made with series L and shunt C elements, except the elements are made with coax. Remember a low impedance coax (think fat center conductor) that is short vs a wavelength looks like a capacitor to ground and a high impedance (think skinny center conductor) piece looks like an inductor. So, in a coax low pass filter, you'd find alternating fat and skinny center conductor pieces that make up the elements. They work quite well and are super inexpensive once you get the initial design figured out. Most always they are setup to be low pass filters because of the topology C,L,C.

One drawback is a coax filter can have a pretty severe flyback area (usually about 3x the cutoff frequency) where the rejection isnt so great. Waveguide and interdigital filters dont usually have this problem, but are more expensive and harder to get built right and tuned.

Darrin


Top


Rosemary
Post subject: W6
Unread postPosted: Fri Jul 30, 2004 5:58 am

it could be whatever. Take it apart. Some filters use shiny expensive box and you will find cheap dicrete L C inside.
There are very good narrow filters made of coax.
Do you hear the BPL QRM? It jamms all bands, on 80m its peaking 59+


Posted  11/12/2012
TotalTemp Technologies (Thermal Platforms) - RF Cafe
PCB Directory (Manufacturers)
LOTUS Communications Systems Modular RF Component Building Blocks - RF Cafe
 

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

These Are Available for Free