SMALL - espritmodel.com SMALL - Telemetry SMALL - Radio
Reply
Thread Tools
Old Jan 26, 2013, 09:47 PM
Registered User
United States, PA, Lansdale
Joined Apr 2012
22 Posts
Question
What are the effects of changing the length of a TX's antenna??

I broke my only 433MHz antenna that I was planning on using with a OpenLRS TX module & I was wondering what might happen if I use an antenna that came with a 27MHz toy helicopter.

Basically I want to know what will (or might ) happen if I change the length of the antenna on a 433MHz 100mW transmitter?
TECH GEEK is online now Find More Posts by TECH GEEK
Reply With Quote
Sign up now
to remove ads between posts
Old Jan 26, 2013, 10:17 PM
Closed Account
Joined Aug 2007
4,497 Posts
Look around a bit.

http://www.google.com/search?q=antenna+433mhz
http://www.antenna-theory.com/basics/main.html
http://easycalculation.com/physics/e...wavelength.php

Otherwise, it's like using a coat hanger for a radio antenna.
eagle777 is offline Find More Posts by eagle777
Last edited by eagle777; Jan 27, 2013 at 12:15 AM. Reason: I should have said 'As random as a coat hanger' or something.
Reply With Quote
Old Jan 26, 2013, 10:39 PM
Registered User
United States, PA, Lansdale
Joined Apr 2012
22 Posts
One last question then...

If I hook up a wire directly into the center of a SMA connector on the 100mW UHF TX module, do I need to provide any connection to the outer connection with the threads? I remember hearing that you should never turn on your radio equipment without the antennas connected. Why should I not turn on the radio set without the antennas connected?

What can I do to make it so that I am not in any danger of burning out my transmitter module when I turn it on with a jury-rigged/homemade antenna?
TECH GEEK is online now Find More Posts by TECH GEEK
Reply With Quote
Old Jan 26, 2013, 11:02 PM
Closed Account
Joined Aug 2007
4,497 Posts
Quote:
Originally Posted by TECH GEEK View Post
One last question then...

If I hook up a wire directly into the center of a SMA connector on the 100mW UHF TX module, do I need to provide any connection to the outer connection with the threads? I remember hearing that you should never turn on your radio equipment without the antennas connected. Why should I not turn on the radio set without the antennas connected?

What can I do to make it so that I am not in any danger of burning out my transmitter module when I turn it on with a jury-rigged/homemade antenna?
I wouldn't do it myself.

http://www.w8ji.com/long_wire_antenna.htm

Check out 'How the Longwire or Random Wire Antenna Works'

'What can I do to make it so that I am not in any danger of burning out my transmitter module when I turn it on with a jury-rigged/homemade antenna?'

Simply copy your current antenna design I guess. Good luck.
eagle777 is offline Find More Posts by eagle777
Reply With Quote
Old Jan 26, 2013, 11:43 PM
KlonWarz
Joined Dec 2012
455 Posts
Quote:
Originally Posted by TECH GEEK View Post
Basically I want to know what will (or might ) happen if I change the length of the antenna on a 433MHz 100mW transmitter?
to 27mhz ant length?

Not good. :-)

You might do as the Eagle sez and read some of the antenna basics just so you can cut a short length of wire suited to your frequency.

Too short, or too long, it's all about harmonics, and RF power will reflect back into the radio output transistors if an incorrect length is used.
That will cause them to overheat quickly and fail.
Most noticeable effect of improper antenna, before failure will be short range.

There's not really any way you can practically test an antenna on one of these little units. It becomes a diminishing return.
rusty case is offline Find More Posts by rusty case
Reply With Quote
Old Jan 27, 2013, 10:46 AM
Retired in NC
Rich in ILM's Avatar
USA, NC, Wilmington
Joined Sep 2010
2,106 Posts
Quote:
Originally Posted by TECH GEEK View Post
I broke my only 433MHz antenna that I was planning on using with a OpenLRS TX module & I was wondering what might happen if I use an antenna that came with a 27MHz toy helicopter.

Basically I want to know what will (or might ) happen if I change the length of the antenna on a 433MHz 100mW transmitter?
1/4 wave at 432 is 6.5 inches. Velocity of propagation of open wire (metal shaft) is around 95%, so around 6" will be fine. The VSWR ( measure of efficent power transfer) is very broad to antenna length so it is not, terribly, critical to get it right to a very specific measurement.
Rich in ILM is offline Find More Posts by Rich in ILM
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion What characteristics minimize the wind's effect? btown2 Electric Plane Talk 47 Jan 27, 2013 03:07 PM
Discussion What are your favorite maneuver(s)? Vertigo II Classic Pattern Flying 20 Jan 26, 2013 07:55 PM
Sold Fat Shark Predator V1 Goggles + 600mw TX + CP Antenna's ukarmy04 FPV Equipment (FS/W) 4 Jan 18, 2013 12:38 PM
Discussion Boom length of a DLG - What's yours and how does it effect the plane. flyingj Hand Launch 14 Jun 08, 2010 04:56 PM
What are the effects of winding my antenna wire? ScYcS Radios 2 Jun 26, 2004 09:41 PM