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 Engineering Event Calendar RF Engineering Quizzes USAF radar shop Notable Quotes App Notes Calculators Education Engineering Magazines Engineering magazine articles Engineering software Engineering smorgasbord RF Cafe Archives RF Cascade Workbook 2018 RF Stencils for Visio RF & EE Shapes for Word Advertising RF Cafe Homepage Sudoku puzzles Thank you for visiting RF Cafe!
Exodus Advanced Communications

72MHZ Model Aircraft Antenna Design Question - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues - primarily having to spend time purging garbage posts from the board. At some point I might start the RF Cafe Forums again if the phpBB software gets better at filtering spam.

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: 72MHZ Model Aircraft Antenna Design Question
Posted: Thu Jan 26, 2006 12:49 am 

Joined: Thu Jan 26, 2006 12:37 am
Posts: 2
I am working on the front end of a 72MHZ receiver project for model aircraft.
Most model airplane receivers use a monopole antenna consisting of a single 1/4 wavelength long wire . However I have yet to find an antenna design book or reference that does not analyze a monopole antenna without referring to a "good ground". Obviously a large metal sheet acting as a counterpoise is not possible for this project, and I do not want to use a dipole antenna.

What is the radiation impedance of a 1/4 wavelength wire far from any metal ?

I am trying to determine the impedance matching for this type of antenna.

 Post subject
Posted: Sun Mar 05, 2006 6:05 pm 

Joined: Tue Dec 27, 2005 1:51 pm
Posts: 8
When you say far from any metal you think "without any ground plane"??

I think the ground plane even if very small is mandatory because without it there isn't any return and then the impedance becomes very high. Of course ground proximity can act as a return but in a plane it may be very far from ground.

At 72 MHz your 1/4 wave length antenna will be 105cm long. Is it not too much?

 Post subject
Posted: Sun Mar 05, 2006 9:21 pm 

Joined: Thu Jan 26, 2006 12:37 am
Posts: 2
Yes, when I say far from metal I mean without a ground plane.

The pcb does have a ground plane but the area of the entire pcb is about 2cm x 5 cm. My understanding is that since these dimensions are much smaller than the wavelength of the received signal, the small ground plane on the pcb will be essentially invisible to the wave, and the standard monopole method of antenna impedance calculation will be invalid.

The simplest way to approach this problem might be just to build the circuit and measure the antenna impedance.

I am not sure what you mean when you write "return" as in "there won't be any return".

105cm is indeed too long, but what I am looking for is a method to analyze a monopole antenna with a very small (or non-existent) ground plane. Then I can determine what the impedance of a shorter antenna will be.

 Post subject: 72 MHz antenna
Posted: Thu Mar 23, 2006 8:31 pm 
User avatar

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104

One antenna type that does not need a "good ground plane" is the "slim jim". Here's a link: http://www.hamuniverse.com/slimjim.html

It's an antenna that in effect provides its own return.

Although probably too big for you, a "J-Pole" is also a no-ground-plane antenna.

Google is your friend.

Good Luck!

Posted  11/12/2012
Windfreak Technologies
Res-Net Microwave - RF Cafe Berkeley Nucleonics Webinar Buying Signal Generator - 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 typing 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


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

These Are Available for Free