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Paper765
New member
Username: Paper765
Post Number: 4
Registered: 12-2004
| | Posted on Thursday, December 30, 2004 - 11:57 pm: | 
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I'm in the process of making a homebrew base antenna. I've done it before, and it worked pretty well, but I wanted to make a modification on my initial creation. On the old antenna, I had a 9 ft steel whip mounted on a base plate, and 4 radial wires coming off, roughly in north/south/east/west directions. These I tied down with 60 lb test fishing line (non conductive) to the four corners give or take of the roof (of my house).
This project is different in a couple ways. First off, I don't live in the old residence, and I am putting this new antenna on top of a tower. Recycled the mounting plate, and I wanted to attach radials to it, shorter but more of them (like 8 three foot radials). Some reading I did tonight in a OLD cb book (The big dummy's guide to CB radio) gave me the impression that those ground plane radials all must be a 1/4 wavelength. That is to say, 8 short radials won't work, instead I should stick with 4 long radials (102 inch each).
Now I'm aware of the Antron and lots of other stick antennas, and they are doing a much shorter ground plane radial length, but they are also doing all sorts of coils and capacitors and nonsense I don't want in my homebrew. I want this to be an antenna based strictly on simple radio physics.
My question is, what do I need to know about the ground plane radial length. Will a number of short radials not work?
tech note
Paper765,
your on the right track,but for a question like this,you may get better response if you post it in the topic; ask the tech>>antennas area.this question is right up Tech833's ally and you cant go wrong with his advice,for it is his livleyhood!
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That Elco Guy (Unregistered Guest)
Unregistered guest
| | Posted on Friday, December 31, 2004 - 7:38 am: |
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Here is the strate stuff from the ARRL Handbook.
If you want to look it up its on pg 22.24 in diagraqm 22.46 of the latest edition of the handbook.
A traditional ground plane antenna is a quarter wave length in the vertical position serving as the antenna with four (4) radials draped at about a 30 degree angle at the feedpoint.
By draping, angling, the radials you adjust the feed point to 50 ohms and match the antenna to the coax. To tweak the antenna adjust the angle of the radials.
The purpose of radials is twofold. Tweaking the feed-point to 50 ohms and to make the antenna MORE efficient.
However remember, a quarter wave ground plane antenna does not have any built in gain unless you co-phase them into a mini-beam.
Later
That ELCO Guy |
Ferd (Unregistered Guest)
Unregistered guest
| | Posted on Tuesday, January 18, 2005 - 3:57 am: |
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i am a little late on posting ,, but .. all the ground radials should be 1/4 wave ... the more the better .. and the angle as ELCO says will make a difference in impedance {matching} {swr's} .. what you can use and is cheap , is electical or copper conduit tubing . holes drilled through and U bolts used will work , and bent down to 30deg or more to match it. like i said earlier , the more ground radials the better . i have used up to 10 radials on VHF and UHF . |
The ELCO guy (Unregistered Guest)
Unregistered guest
| | Posted on Thursday, January 20, 2005 - 8:25 am: |
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@ 765
Being as you have already built your own antenna before, why not build a 3 element beam or your own version of a PDL2.
Play with the spacings to customize your own gain and FB Ratio.
That Ol ELCO Guy |
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