Homemade 1/2 wave dipole

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ChrisABQ

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Greetings everyone. I recently made my own 1/2 wave aluminum (1/2" thickness poles) dipole because most of my listening is between 150 mhz and 156 mhz public safety band on my analog scanner.

From what I've been able to find, it's best not to cut them too short, so the current length of the 1/4 poles is 19.5" which should resonate at 151.35 mhz.

My question is, would I get more range if I cut the 1/4 wave sections another half inch (both sides) to better tune them closer to the middle of the range at 153 mhz. I'm looking for more advice before I cut any more off and possibly ruin the antenna.
Thanks
 

wyShack

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If you do not have an antenna analyzer, I would just let it go. Another item to consider is orientation-most dipoles are horizontal polarization , while most users in the 150 Mhz range use vertical polarization. If you are trying to receive vertical with a horizontal antenna you will 'lose' 20 dB or more of the signal. set up the dipole in a vertical direction and they will come booming in-even if the dipole is cut a little long.

Warning -antenna building can be addicting- proof can be found on my roof and in the back yard.

Have fun and never stop learning.
 

popnokick

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Since you are building a scanner antenna, try this one. Covers much greater frequency range than the dipole (nearly all popular scanner bands) and actually exhibits some gain over the dipole you just made. The 2nd version shown (scroll down the Wiki page) is super-simple and can be put together and hung vertically in about 15 min with common home-store parts. Lots of writeups here on RR; search "OCFD" -
Homebrewed Off-Center Fed Dipole - The RadioReference Wiki
 

ChrisABQ

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Thanks for the great info, the dipole is currently vertical and receives very well, was just wondering about proper tuning. Also learning about baluns and chokes. It is quite addicting and I'm sure I will end up building the OCFD at some point.
Thanks
 

jhooten

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19.5 is 144 mhz.
18.55 is 151.35 mhz.


2808 divided by frequency in mhz equals length in inches of a quarter wave whip.
2808 divided by length of whip in inches equals frequency in mhz.
 

ChrisABQ

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Well, that explains why It's doing so good on aircraft bands as well. Would there be any good reason to cut to the 18.55" length, improved reception, distance maybe?
 

Ubbe

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Get some crocodile clips http://thumbs4.ebaystatic.com/d/l225/m/m33X_wnJ4cZDnMWUD7JSfog.jpg
and attach to the end of the dipoles and check if that makes any difference. If you do, then cut the dipoles.

A dipole usually have a bandwidth of 10% of the frequency, in your example it will be 15MHz. Cutting it an inch or two will not be noticable in reception, if you don't use a constant signal to receive and measure with an instrument that can detect 1% variations in signal.

If you have a telescope antenna to use on a scanner you can check have much you'll need to adjust the lenght to be able to tell a difference in reception, it's probably more than a 10% change in lenght.

/Ubbe
 

Golay

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Good enough

Thanks for the great info, the dipole is currently vertical and receives very well, was just wondering about proper tuning. Also learning about baluns and chokes. It is quite addicting and I'm sure I will end up building the OCFD at some point.
Thanks
I believe you said this is a receive only antenna? If so, your good. Adding or subtracting an inch or two isn't going to attenuate or bring up the gain any. I personally would ascertain if you are happy with how well it receives what you want to hear, before you entertain suggestions for other antennas.
 
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