Author Topic: Crazy(?) VHF Antenna Design  (Read 650 times)

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GreekMan

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Crazy(?) VHF Antenna Design
« on: August 17, 2017, 12:41:32 PM »
Well, assuming a dipole has a impedance of 75Ohm and an Inverted V antenna has a 50ohm one, how about making the latter cut for the VHF and then turn it 90 degrees to achieve a vertical polarity?

I had a look at the two ARRL books and some other sources, and the closer to this idea is the inverted L antenna.
Things are a bit complicated cos the elements may be of a different length than standard dipole calculations.


« Last Edit: August 17, 2017, 12:44:48 PM by GreekMan »

Tempstar

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Re: Crazy(?) VHF Antenna Design
« Reply #1 on: August 19, 2017, 08:03:26 AM »
It's hard to beat a balanced dipole for getting the most of your power out, and this holds true in almost any configuration. Experiment! I know I have come up with stuff that shouldn't work but did, and you will too.
"Preparedness is a lot more than just buying stuff"

jdh

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Re: Crazy(?) VHF Antenna Design
« Reply #2 on: August 19, 2017, 11:28:46 AM »
My thoughts for what they are worth.

Use a PVC support instead of a metal one.  The extra metal mass will effect both the impedance and radiation pattern.  If you have to use a metal support bend the elements towards the support not away from it.

Use a straight dipole feed with surplus RG-11/59 with a 1.5 to 1 UNUN transformer at the shack end.   

GreekMan

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Re: Crazy(?) VHF Antenna Design
« Reply #3 on: August 20, 2017, 07:49:34 AM »
of course...the pic was a demo, and i had to improvise with a mop broom.
Tomorrow i will be testing the idea, using a piece of stick to keep the coax horizontal for 1/4 wavelenth or more, at the opposite side..This way i will be able to turn the antenna too, cos I cannot extrapolate the shape of its loabs

Good tip regarding elements direction on a metal support... ;)

GreekMan

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Re: Crazy(?) VHF Antenna Design
« Reply #4 on: August 23, 2017, 11:27:43 AM »
i experimented some....But I need to improve the way the elements are retained. I will try a washer and a flat face





« Last Edit: August 23, 2017, 11:35:34 AM by GreekMan »