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 Build Your Own Antenna - Discuss topics for building your own antenna.

07-14-2017, 2:30 PM
 Member Join Date: Jun 2017 Location: WV Posts: 10
size of elements

Will using a different circumference change the length of the element you use. In other words the elements that I am using are about 3/8". For the 150 - 155 Mhz the elements would be normally 18". So would the length still be 18" if I used elements the size of a coat hanger?
07-14-2017, 3:44 PM
 Member Premium Subscriber Join Date: Jul 2014 Location: PA Posts: 6,780

Element diameter affects length and resonant bandwidth. There are any number of online calculators that demonstrate the effect of element diameter on antenna design.
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07-14-2017, 5:42 PM
 Member Join Date: Jun 2017 Location: WV Posts: 10

I just got a headache at looking at different calculators and still don't know what I want to know. Sorry but I am new at this and don't know the language. Can you point me to one online calculator that is simple as I am.
07-14-2017, 6:26 PM
 Member Join Date: Jul 2005 Location: WTVLCA01DS0 Posts: 8,535

Diameter doesn't change the length for making an antenna resonate. It does change it's bandwidth (good thing)

A 3/8" diameter element at 18 inches would be just fine for what you are doing. If it's just for receiving, it's even less important. A coat hanger will work just fine, but on the transmit side will have slightly less bandwidth.

Use what you've got. Cut it to the suggested length, and you'll be OK.
07-14-2017, 6:28 PM
 Member Amateur Radio Join Date: Jan 2009 Location: Gettysburg, Pa Posts: 579

I'm sorry it's not a simple process. Many variables effect
antennas. Every antenna can be reduced to a math equation
which will provide answers required to construct a functional
unit. The math computations can be rather complex thus
most folks utilize computer software to design their antenna.
Some things to consider

Diameter of elements effect resonate frequency and pattern
of the antenna.

Boom size and material effect the design. If the boom is
metallic, are the elements insulated or in contact with the
boom. It makes a big difference.
Insulated booms can be used, (wood/PVC),with good looks results
but it effects the required element length.
Type of driven element feed can effect performance. May common
antennas use gamma matches and "T" matches. There are others
types that can be used. It's important that the feed line be properly
matched to the antenna.
These are only some of the problems that can make construction
difficult. The list gets even more complex deceideing if the antenna
needs to provide maximum gain or you require a very clean radiation
pattern when trying to null out unwanted sites in a multi site system.
I don't mean to discourage you from building your own. If your
perplexed with antenna design software, try to find a design
someone has provided but make sure you use exactly the same
material and measurements.
Good luck...
07-14-2017, 6:37 PM
 Member Join Date: Jun 2006 Posts: 6,551

Diameter does change the length but there are many variables. Small changes in dia like going from 1/4 dia to 3/8" dia may go unnoticed. If you have a thin 6" long whip that resonates around 460MHz and you make it 2" dia, the length will change drastically and it may end up being only 4" long. If you do the same thing at 7Mhz it will be hard to tell the resonant frequency changed.
prcguy

Quote:
 Originally Posted by mmckenna Diameter doesn't change the length for making an antenna resonate. It does change it's bandwidth (good thing) A 3/8" diameter element at 18 inches would be just fine for what you are doing. If it's just for receiving, it's even less important. A coat hanger will work just fine, but on the transmit side will have slightly less bandwidth. Use what you've got. Cut it to the suggested length, and you'll be OK.
07-14-2017, 7:32 PM
 Member Join Date: Jul 2005 Location: WTVLCA01DS0 Posts: 8,535

Understood, and I over generalized in my comment. I was attempting to keep it simple for the guy with only 8 posts.

For 3/8" on VHF, I doubt he's going to have an issue. Since this was in the scanner, receivers and related equipment forum, it's probably safe to say he's going to be OK and reflected transmitter power won't be an issue.

I appreciate the correction, but I don't understand the purpose of providing over complicated answers to new guys when they ask a simple question. We shouldn't be trying to impress him with knowledge, just provide a simple, easy to understand answer.
07-14-2017, 7:41 PM
 Member Premium Subscriber Amateur Radio Join Date: Dec 2009 Location: Michigan Posts: 210

Quote:
 Originally Posted by mmckenna Understood, and I over generalized in my comment. I was attempting to keep it simple for the guy with only 8 posts. For 3/8" on VHF, I doubt he's going to have an issue. Since this was in the scanner, receivers and related equipment forum, it's probably safe to say he's going to be OK and reflected transmitter power won't be an issue. I appreciate the correction, but I don't understand the purpose of providing over complicated answers to new guys when they ask a simple question. We shouldn't be trying to impress him with knowledge, just provide a simple, easy to understand answer.
Because you did the OP a dis-service by providing incorrect information. If you would have qualified the first statement instead of making a matter-of-fact statement, that would be a different story.

Please don't get me wrong on this. I have read may of your posts and you are usually spot on with your information, but, this one was different.
07-14-2017, 8:05 PM
 Member Join Date: Jul 2005 Location: WTVLCA01DS0 Posts: 8,535

Did you read the second line?
07-14-2017, 8:39 PM
 Member Premium Subscriber Amateur Radio Join Date: Dec 2009 Location: Michigan Posts: 210

Yes. My statement stands.
07-15-2017, 9:54 AM
 Member Join Date: Jun 2017 Location: WV Posts: 10