| Author |
Message |
    
Joe Hounschell
| | Posted on Saturday, January 26, 2002 - 9:52 am: | 
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I am trying to hook a 57 inch (i think) moble magnetic mount antenna to my cobra 148. I am trying to mount on a ford explorer, my coax is 18 feet, radio and antenna are both brand new, and the antenna is base loaded. my problem is, I cant get my swr below 4.1 and it is like that all through the band (11 meters). I have tried raising and lowereing the hieght of the whip, moving the antenna around in different locations on top of the roof, and nothing. I know for a fact the meter works because i used it on by base station 5 min before i tried this moble radio. I just dont know where to go from here. do big vehicles like mine cause this problem? is it possible that i would need a no ground antenna? If so, are they any good, and can they handle a couple hundred watts or so (no more than 200) if i ever decide to put an amp with it? Thank you for your time. I am very excited to get this hooked up. any help would be greatly appretiated. once again, thank you.
Joe |
bruce
| | Posted on Saturday, January 26, 2002 - 8:41 pm: |
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mag mounts are bad news at 10 meters they work at 2 and up but i have not found any that work well on 10 or cb. the problem os a lack of ground plain since all you have is the mag coupling / cap as your ground return my motorola clones outright tell you not to use a mag mount |
ChillyDog
| | Posted on Saturday, January 26, 2002 - 9:33 pm: |
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Joe,
I wish I had a definitive answer for you, but I don't. Still, there are plenty of knowledgeable people on this forum who can help.
A couple of questions: first, what antenna are you trying to use? Next, how are you checking SWR; are you using the radio's meter or an external meter? Finally, is there any (however slight) difference between the SWR at channel 40 compared to channel 1?
Now a comment or two. In my experience, magnetic antennas on larger vehicles work fine. The larger the ride the better! Just find the approximate center of the roof and plant the antenna there (but not too close to any roof rack), at least while you are figuring things out. With an Explorer you don't need a no ground antenna. Do not worry about amps until you get a good antenna match.
Like I said, this message doesn't provide any answers, but the answers to the questions may help solve the problem!
bob |
Tech181
| | Posted on Saturday, January 26, 2002 - 11:51 pm: |
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Joe,
What type of antenna is it that you are using? Also has the antenna or coax been modified or is everything stock?
Steve
Tech181
Tech181@copperelectronics.com |
Bigbob
| | Posted on Sunday, January 27, 2002 - 8:28 am: |
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Joe,if a roof rack is up there ground it to the roof ,check for kinks in coax,look for seperations in the sheild,make sure there is a snug fit between the center pin and socket of couplers. |
Joe Hounschell
| | Posted on Sunday, January 27, 2002 - 10:26 am: |
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Thanks for the reply everyone.I am not sure on the brand of the antenna. i bout it at radio shack for 30 dollers. Everything on the antenna is stock, only a week old. The coax came pre-wired to the antenna so all i had to do is plug it into the back of my radio. I am using the built in swr meter in the radio to tune it, and i get a slight veriation in swr between 1 and 40. I dont know exactly how much it is fluctuating between 1 and 40 as far as numbers go because the meter only goes to 3 and then there is about an inch of red from 3 all the way to the right. I am figuring it is at about 4. The way I can tell that there is a difference is the needle is between the "a" and the "L" in "cal" (calibrate), on chan. 1 and it is in the middle of the "a" in "cal" on chan. 40. I will keep trying in the mean time. thanks guys.
Joe |
Doug
| | Posted on Sunday, January 27, 2002 - 1:51 pm: |
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sounds like a coax problem. |
Biged
| | Posted on Sunday, January 27, 2002 - 7:09 pm: |
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Joe,
You have probably answered your own question when you told us what kind of antenna.Radio Shack does not sell an antenna that would be good enough for my use.However, your swr's should still be ok with that antenna unless there is something wrong with it.The first thing I would check would be the connector on the back of the radio.Does it fit snug?Cheap antennas usually use cheap coax.It is probably thinner.Therefor the center conductor may be too small for the radio.Second of all,dont put too much faith in the swr meter that is built into the radio.They are not usually very accurate.Hope this helps...Eddie |
Bigbob
| | Posted on Sunday, January 27, 2002 - 10:32 pm: |
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If this ant. has a large exposed coil it is a VALOR.I had one it was a base load it sucked,the radio shack version is slightly better in that it has a tapped inductor in mag. base.The big coil is just for looks,12ga.while inductor is 18 ga.And the quality of their ants. is not as good as it was 10yrs.ago.Still have a deluxe mag.mount would handle 100watts with 1.1 swr on ch.1 and ch.40 |
ChillyDog
| | Posted on Tuesday, January 29, 2002 - 10:16 am: |
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Joe,
Biged has a good point; there is a Radio Shack antenna that has a connector that sometimes doesn't fit tight enough. I've seen this with two antennas bought in two states.
This antenna is a mag mount, and the "stinger" (whip) is black fiberglas with a metal connector at the bottom. There is a fitting on the loaded base where the metal part of the antenna whip inserts and is tightened to the base by a finger screw.
The coax connector on this antenna is such that even if you tighten the connector screw barrel all the way the center part of the connector still can rotate. Guaranteed bad SWR!
If you're using this antenna I'd suggest either replacing the coax connector or getting another antenna altogether. I'd lean toward getting another antenna. Even a "Little Will" from a truck stop is better than this antenna!
Good Luck
Bob |
Chris Leggett
| | Posted on Tuesday, January 29, 2002 - 12:36 pm: |
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Seems every Radio Shack antenna I have messed with needed to be shortened a lot.I had to cut about 6 inches off of one of there bottom loaded antennas.Maybe you need to shorten yours too? |
Bigbob
| | Posted on Tuesday, January 29, 2002 - 8:45 pm: |
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MY OPINION,forget radio junk.You've got questions they got an answer"I don't know".that's a answer ain't it.miserable^%$#@&*!!!! |
bruce
| | Posted on Tuesday, January 29, 2002 - 9:20 pm: |
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all my antennas for the 28 mge range have instructions stating that a mag mount will cause measurements to be diffrent however the radio shack i have which is a mag mount is dead on still with the lack of a good ground if becomes prone to coax feedback and being unstable when my rf prosser is on. if you can try another mount. |
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