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

500 MHz RF choke, DC block and bypass capacitor selection - 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

jayleung

Post subject: 500 MHz RF choke, DC block and bypass capacitor selection Posted: Sun May 13, 2007 6:14 pm

Lieutenant

Joined: Tue Apr 03, 2007 12:52 pm

Posts: 3

Hi, everyone. I have a question about a project working on around 500 MHz.

I am wondering what kind of RF choke will be suitable for this frequency range. It seems that most of the inductor-type choke Self Resonant Frequency is lower than 500MHz, and I am not sure whether I should use inductor as choke any more in this frequency range.

And the other question is that for the DC-block capacitor and RF by-pass (shunt to ground) capacitor, is 220 pF large enough?

Thanks in advance.

Top

melkhouly

Post subject: Posted: Mon May 14, 2007 8:35 am

Captain

Joined: Thu May 03, 2007 2:55 am

Posts: 8

Location: Egypt

u can use the SMT inductors in this , but be sure form SRF , and what will be the reactive part in this frequency

about the blocking capacitor in 900 MHz the 27 to 100 pF works well , u can use the 100 to 200 Pf in the 500 MHz range

_________________

Khouly

Top

IR

Post subject: Posted: Mon May 14, 2007 1:32 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hi jayleung,

As a general rule of thumb, the reactance of the RF choke should be 10 times of the characteristic impedance i.e. 500 ohm and this is for the lowest frequency of your operating BW. The RF choke should also have an SRF which is abvoe your operating frequency. A reasonable value for 500MHz would be 150nH.

DC block capacitors should have a reactacne of 3-5 ohms at the lowest operating frequency (Since the reactance is getting smaller as frequncy increases). So a reasonable value for 500MHz would be 100pF.

Top

jayleung

Post subject: Posted: Tue May 15, 2007 12:43 am

Lieutenant

Joined: Tue Apr 03, 2007 12:52 pm

Posts: 3

Hi, IR, thanks for your reply.

But since I am going to use the RF choke to feed the DC control voltage to a varactor with only a few pF capacitance, I found that with a couple hundred nH inductance will degraded the varactor capacitance to about 20% on more.

That's why I am searching for a large inductance with a few uH. But it seems the trade-off is the SRF will drop below 500MHz...

I am not quite sure what kind of RF choke is used for commercial varactor tunning in UHF range. If you have any information about that, please tell me...

Top

IR

Post subject: Posted: Tue May 15, 2007 3:45 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

Hi,

From the very few designs that I have seen by others - the type of inductors used for the tuning voltage of the varactor is chip inductors like the 0603 of coilcraft or similar.

The following series should fit your needs from SFR point of view:

http://www.coilcraft.com/0603ls.cfm

The function of the inductor is to prevent the RF frequency to reach the tuning voltage. In my previous post, the rule of thumb I mentioned is commonly used for amplifiers, but it should apply (I think) also to the particular use of the inductor for the tuning voltage of the varactor.

Hope this helps! Please update us.

Posted  11/12/2012

RF Cascade Workbook 2018 - RF Cafe
Exodus Advanced Communications Best in Class RF Amplifier SSPAs
Windfreak Technologies Frequency Synthesizers - RF Cafe
ConductRF Phased Matched RF Cables - RF Cafe
Anatech Electronics (RF Filters) - RF Cafe

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

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