Triad RF Systems
LadyBug Technologies LB480A RF Power Sensor Connectors - RF Cafe

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!
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

Winding ratio in IF transformer - 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: Winding ratio in IF transformer Posted: Sun Aug 05, 2007 3:42 pm


Joined: Fri May 19, 2006 5:01 am
Posts: 25
Location: Netherlands
Hello everybody,

In building a radio, I am wondering: why do all IF transformers I see have a near 1:1 winding ratio? This goes for both single-tuned and doubled-tuned transformers. Couldn't they get more gain by using say a 1:2 ratio? I could only see one objection: more windings -> more self-capacitance -> self-resonance may get too near operating frequency. Why don't they use more secondary windings?

Thanks in advance,


Post subject: Posted: Mon Aug 06, 2007 1:35 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello Charl,

I guess that the reasons for that could be:

1. Maintaing the same impedance along the IF chain.
2. 1:1 Transformers have the widest BW available.


Post subject: Posted: Mon Aug 06, 2007 2:12 pm


Joined: Fri May 19, 2006 5:01 am
Posts: 25
Location: Netherlands
Hello IR,

Thanks for your reply. I really want to make sure I understand this, so I hope you don't mind this follow-up.

1) How can you talk of impedance when either side of the transformer is an LC tank?
2) What is the reason for this? (if this is textbook material, please refer me to a good textbook :) )

Kind regards,


Post subject: Posted: Mon Aug 06, 2007 4:13 pm

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello Charl,

Transformers are located not only between resonance tanks but also between filters and amplifiers to maintain the charactieristic impedance (1:1) or to perform impedance transformation.

There are very good application notes in RF Cafe elaborating about transformers design.

In general, if you increase the number of turns or the frequency of operation in transformer you reduce the flux. Therfore, reducing the number of turns will give you a wider BW.


Post subject: Posted: Tue Aug 07, 2007 3:20 am


Joined: Fri Feb 17, 2006 12:07 pm
Posts: 218
Location: London UK
Hi Charl et al
A good exposition on resonant single and coupled circuits, ie tuned transformers, is given in Terman "Radio Engineering" Chapter 3.
If 2 windings are resonant and the number of turns is in a reasoanable ratio, say 3 to 1, then the Q is approx the same. The dynamic impedance of each side at resoance is 2*pi*f*L*Q
If Q is roughly equal on each side, then the impedance ratio is the same as the inductance ratio, which is the square of the turns ratio. This simplistic argument does not take account of coupling coefficient, but this is fully shown in the Terman textbook. If therefore the number of turns on the secondary is increased, the load impedance will have to be very high for maximum power transfer. Whilst the resistive part of many solid state device impedances is high (IGFETs for example) the capacitive reactance is very low at high frequencies. Thus the resonant secondary will be dominated by high and temperature variable capacitance of the following stage input load.


Post subject: Impedance of parallel RLC circuitPosted: Tue Jan 13, 2009 3:14 pm


Joined: Tue Jan 13, 2009 3:06 pm
Posts: 1
can you tell me how to calculate impedance of parallel RLC circuit? if I have a L=1.2uH, C=72p, R=1.2k in parallel what will be the Impedance?[/quote]

RF circuit Design

Posted  11/12/2012
RF Cascade Workbook 2018 - RF Cafe
Werbel Microwave - RF Cafe

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

These Are Available for Free