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Author Topic: my antenna idea  (Read 3106 times)
N3IDG
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Posts: 118




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« on: December 27, 2015, 12:24:39 PM »

Due to living in am apartment ground leval I may put up and take down an antenna only ,not permanent. So I have started my home brew 40 ground mount verticle. A mount using a 54 inch hustler base then a shorty hamstick that I will.rewind. and a 113 inch whip on top.going to make the hamstick portion 3 inch around by adding pvc pipe. So I need to add just over 18 ft of wire to the coil. To get 1/4 on 40. Do I just get 18 ft of wire ustart winding it and try to evanlly space it on the pvc . Any ideas will be helpful. Thanks n3idg
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KH6AQ
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Posts: 7889




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« Reply #1 on: December 27, 2015, 12:29:15 PM »

A short loaded antenna cannot often be designed by making the total length (radiators + loading coil) equal to 1/4 wavelength. For your antenna (using EZNEC) the coil inductance to resonant the antenna to 7.15 MHz is 18 uH.

Given your 3" diameter form the coil can be made using insulated #18 wire and 13 turns close-spaced. This is based on a wire + insulation diameter or 0.06". Note that the total length of radiators plus wire is 16 ft.

Over perfect GND the feedpoint impedance would be 8 ohms. With coil loss and ground loss I would expect at least 25 ohms. That is for a decent ground that might consist of a dozen 15' radials on the ground. If you can have only one counterpoise wire it should be 32' 8", give or take. A 1:1 balun in the feedline will reduce feedline shield current (current on the outside of the shield). This can reduce the magnitude of the RF current induced into the apartment AC wiring. Without the balun the coax shield and the apartment AC wiring form a counterpoise. The path from the coax shield to the AC wiring is via the power supply DC terminals, through the power supply chassis, to the AC outlet GND terminal.

Here is a link to a coil calculator (I have not verified it): http://electronbunker.ca/eb/InductanceCalc.html
« Last Edit: December 27, 2015, 12:38:15 PM by WX7G » Logged
JS6TMW
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Posts: 1255




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« Reply #2 on: December 27, 2015, 02:39:20 PM »

You can also use K7MEM's calculators for a shortened dipole. http://www.k7mem.com/Electronic_Notebook/antennas/shortant.html    I have used it and attest that it works.

Steve in Okinawa

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N1RND
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Posts: 57




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« Reply #3 on: December 28, 2015, 07:43:11 AM »

Do you own a car?  If so, do you park it outside your window or entrance?

If you do, put a mobile antenna on it and run the coax into the apartment.
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KC3BBI
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Posts: 77




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« Reply #4 on: December 29, 2015, 01:01:47 AM »

I could live in an apartment, but have much more freedom with my RV. I have the ability to at least run antennas on top of the RV. I have no apartment management telling me I cant do anything.
I have a Flex 5000 running into a vertical 5BTV, and a loop 20 meter delta. I will be ordering a hexbeam next week. The ability to move and use my ham radio is so much greater freedom that living in a "compartment" as i call it. It gives me claustrophobia living in some of the apartments. I would highly recommend it to anyone living in a "compartment". Just a thought...
KC3BBI
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ONAIR
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Posts: 3735




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« Reply #5 on: December 29, 2015, 01:49:38 AM »

I could live in an apartment, but have much more freedom with my RV. I have the ability to at least run antennas on top of the RV. I have no apartment management telling me I cant do anything.
I have a Flex 5000 running into a vertical 5BTV, and a loop 20 meter delta. I will be ordering a hexbeam next week. The ability to move and use my ham radio is so much greater freedom that living in a "compartment" as i call it. It gives me claustrophobia living in some of the apartments. I would highly recommend it to anyone living in a "compartment". Just a thought...
KC3BBI
   Interesting!  Do you park the RV at a fixed location, or cruise from place to place?  Smiley
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