| Author |
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Bulldog
| | Posted on Monday, October 14, 2002 - 12:24 pm: | 
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I'm getting tired (old maybe) of climbing my tower, has anybody had any experances with ground mounted vertical antennas? I been looking at GAP and a few other companies that build them, trying to get an idea on what works and what does not work. Has anybody built one that works? I know it's not gonna work like a moonraker at 50ft. Just something I want to try and easy to get at! |
bruce
| | Posted on Monday, October 14, 2002 - 12:41 pm: |
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bulldog I had a mfj it worked VERY well as far as SWR and DX and did it from 40-6 meters without a tunner. It should work fine for local stuff too... maby not as good at the 80 foot high vertical. |
Phineas
| | Posted on Monday, October 14, 2002 - 2:17 pm: |
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BD
Ground mounted antennas work great for DX, but may effect your local communications depending on the freq band. The key is all in the grounding systemRadials over or underground are the key to making them work. Chicken wire also works well as a ground radial. An easy rule of thumb is 6 wires just a little longer than the height of your antenna in all directions. The purpose of the radials is more for recieve purposes than transmit. The more ground the better. If you use chicken wire, Then for 2 ft of height, you put down 1 sqr/ft of chicken wire. Any vertical will work on the ground, or close to it under the right conditions. This information is from my experience experimenting.
In general, the lower the Frequency, the less a ground mounted antenna is a factor for local talk. 27mhz does not have a robust ground wave.
I hope this helps.
Phineas |
Tech833
| | Posted on Wednesday, October 16, 2002 - 7:46 pm: |
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If you are ground mounting, be sure and choose an antenna that is not end fed. The GAP Titan DX works extremely well regardless of elevation above ground. For CB, the closest thing to the GAP antennas would be the CTE Top One. As an alternative, the Shakespeare ABS would work well at ground level also.
Make sure and ground it well! The more ground you get under the antenna, the better your ground wave signal will be. |
HoosierCardinal
| | Posted on Friday, October 18, 2002 - 8:34 pm: |
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Im curious about the CTE Top one. Is it like the astroplane in reagrds to construction and quality? |
Tech833
| | Posted on Saturday, October 19, 2002 - 11:57 am: |
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Construction, yes. Quality, no.
If you install a Top One, I suggest that you buy a couple cans of spray foam with minimum expansion and fill the aluminum elements with it. Then, buy a spray can of auto primer and coat all the plastic parts with at least 3 thin coats. Then, use marine grade silicone sealant around the elements on the mounting foot. Last, but not least, use Penetrox (available from Tessco) on all the threads. As a preventative course, I replaced all the hardware on my Top One with marine stainless hardware.
The performance is the same. |
Bulldog
| | Posted on Saturday, October 19, 2002 - 7:50 pm: |
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Thanks for all the info, I think I will try the chicken wire for the grounding. And see want happens... |
mike
| | Posted on Thursday, October 24, 2002 - 4:02 pm: |
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Tech 833 I have a novice question..How is a magnetic base antenna grounded as compared to a co-ax shield ground antenna? |
bruce
| | Posted on Thursday, October 24, 2002 - 6:40 pm: |
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mike for what ? a car i guess is a 48 inch mag mounted vers the same antenna grounded to the car is going to be down one s unit thats been what ive found
bruce |
Tech833
| | Posted on Thursday, October 24, 2002 - 11:01 pm: |
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A magnet mount doesn't exactly 'ground' to the vehicle. It is capacitively coupled to the vehicle at best.
A basic capacitor is formed by two 'plates' and a electrolytic material in between them. In this case, the magnet is one 'plate', the paint of the vehicle is the electrolytic and the vehicle metal body is the other 'plate'. Since RF can pass through capacitors of higher than xx value for given frequency, the magnet mount 'looks' like a ground path to the vehicle body for the RF (although slightly poor). There is no actual DC ground in a magnet mount. |
mike
| | Posted on Thursday, October 24, 2002 - 11:42 pm: |
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To Bruce: I have a '92 f-350, 4x4. Planning on Mounting a 102" whip on (small truck box) rail behind the rear window. Will drill, mount a bracket and whip. I know that this will put me directly to electrical ground. Will the open space of the truck box behind the whip affect anything? I don't understand how a magnetic base will ground...paint,etc. Is the magnet base completing a ground curcuit magnetically? I have used a top cab magnetic mount...I am confused as to how it really grounds.....want to improve overall. Using a Cobra 25 NWST Thanks for any advice and info. I have been comparing prices between copper and others..Can't beat copper . |
mike
| | Posted on Thursday, October 24, 2002 - 11:55 pm: |
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Thanks TEch 833 For the Information on magnetic grounded antennas. Makes lot of sense on the way you explained it. ....3's |
mike
| | Posted on Friday, October 25, 2002 - 12:00 am: |
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Bruce,,,,Thanks for the info about one s unit difference between magnetic and dc ground on a 48". I will probably stay with dc ground antenna. |
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