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Old 10-02-2017, 2:03 AM
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Question Will this homade antenna work?

I put a mag antenna on to of an umbrella stand. Then grounded the thing to the roof.
This is probably a stupid build, I have 0% spending money and had to use what I had around the house.
I haven't tested the SWR yet (can't find the meter) and haven't transmitted yet (don't want to risk anything).
My friend drove to the end of the road (about a block down) and I was able to hear him fine.
Any suggestions would be nice. And yes, I would rather use a proper antenna, but, I am broke.
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Old 10-02-2017, 8:53 AM
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I would say it would work better if the ground plane was at the base of the antenna.
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Old 10-02-2017, 9:15 AM
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It appears it is shorted to the mast.
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Old 10-02-2017, 9:55 AM
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Quote:
Originally Posted by WA0CBW View Post
I would say it would work better if the ground plane was at the base of the antenna.
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Yes.. The stand won't really do that much.

If the plate is ferrous, I'd just stick the mag mount directly to it. If it's not ferrous, you can pick up a sheet of galvanized steel that size at places like Canadian Tire.
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Old 10-02-2017, 10:38 AM
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I would be concerned about the heavy umbrella stand falling off the roof and hitting someone. The extra height above the roof will make no difference as short as that stand is.

Those extra ground plane legs will also not likely make any difference. I would suggest just setting the mag mount directly on that sheet of metal.

What frequency or band is this antenna for?
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Old 10-02-2017, 11:26 AM
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Quote:
Originally Posted by KD4UXQ View Post
I would be concerned about the heavy umbrella stand falling off the roof and hitting someone. The extra height above the roof will make no difference as short as that stand is.

Those extra ground plane legs will also not likely make any difference. I would suggest just setting the mag mount directly on that sheet of metal.

What frequency or band is this antenna for?
27MHz
The reason I didn't just set the mag right on the sheet was because the the wire isn't long enough to make it through my window, I had to use an L bracket one because the coax cable was longer.
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Old 10-03-2017, 4:52 PM
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The bracket explains it. Couldn't see that in the photo.

For that base loaded antenna, the best ground plane would be at least 3 x 1/4 wavelength radials pointed about 45 degrees down from horizontal to get a 50 ohm match provided the antenna itself is properly adjusted. Not very practical for what you hope to do. That would be the most efficient, but not required to work reasonably well.

I am not sure what materials you have available, but if you can fashion some other L bracket to mount that bracket directly to the the largest sheet of metal you can place on the roof would work best, but use what you have and see what you get on a SWR meter. Center placement is best, but off center can work. You can adjust the antenna length to offset the impedance mismatch of the flat ground plane. A long time ago I used a 3 foot by 3 foot piece of sheet metal with a mag mount on it for CB and it worked just fine. I don't remember the SWR, but I remember it was pretty good after adjusting the antenna length and range was pretty reasonable.

SWR only needs to be below 3:1 to be effective and keep too much power from being reflected back at the transmitter. Anything below 2.5:1 is most desirable and below 2:1 is very good.

SWR table for reference.
SWR POWER LOSS TABLE


You can also consider making an inverted V out of any available wire. These work quite well and very easy to make. At 4 watts on 27 MHz don't worry about the 1:1 balun you see in most examples.
Inverted V antennas are omnidirectional and very efficient.

Use the below online calculators for 27 MHz. 27.195 is middle band. Best results using 45 degrees down angle for each leg. One attached to the center of coax and the other the shield.

https://m0ukd.com/calculators/inverted-vee-antenna/

Martin E. Meserve - K7MEM - Inverted-V Antenna Calculator

Last edited by KD4UXQ; 10-03-2017 at 4:57 PM..
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