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swr problem


 
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el_dubya
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Joined: 20 Sep 2005

PostPosted: Mon Jan 16, 2006 3:40 pm    Post subject: swr problem Reply with quote

I'm helping a buddy put a cb in his 87 cherokee. He is using his dads old 23 channel midland. When we checked swr's they were higher on 23 than on 1, indicating short antenna. We made it as long as we could and still no change. From 1-16 it is above 3, and 16-23 is barely below 3. He has probably a 15" antenna. I am guessing it is the antenna's fault, although the coax is old and needs replaced. Like everybody else my age, he has champaign eyes and a cheap beer wallet. So, any suggestions? I am thinking new antenna and coax. I also thought about running a wire from the mount to the frame somewhere to make sure the ground is good? It shouldnt be ground plane cause we mounted it on the roof, plenty of metal up there to bounce off. Thanks guys.
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Dub

'98 TJ SE
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IBTJn
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Joined: 31 Dec 2004
Location: Just Outside of Portland, OR

PostPosted: Mon Jan 16, 2006 4:34 pm    Post subject: Reply with quote

Lower SWR on channel 1 indicates the antenna is too long...not to short. What kind of antenna is this...magnet mount with a center load? It's aweful short. That means it's going to be VERY touchy to tune...and probably not perform too well. Try shortening the antenna. If you need to trim the stinger at the top, then do so very little at a time.

Wink
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el_dubya
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Joined: 20 Sep 2005

PostPosted: Mon Jan 16, 2006 6:33 pm    Post subject: Reply with quote

Yeah sorry, got that backwards. The swr's are higher on channel 1 than on 23. So that means short right?
I'm not sure what kind of antenna it is, I tried to convince him to buy a new one but to no avail. It is like a wire whip, only short. It looks to me to be center load. It has a spring at the bottom and is on a swivel base. I think it was supposed to be mounted on the "rain gutter" on the side of the roof but we bent it around and mounted it on the roof. Think we could find a longer metal peice to put in the top to make it longer? I'll try to find a pic of one so ya'll know what I'm talking about.
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Dub

'98 TJ SE
15x7 ProComp Series 51 Rock Crawler Wheels
31x10.50 General Grabber AT2's
Taurus Fan
Uniden PC68 Elite CB
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el_dubya
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Joined: 20 Sep 2005

PostPosted: Mon Jan 16, 2006 6:47 pm    Post subject: Reply with quote

Ok, heres the closest thing I could find. This one says it is 55 inches where as his is only 15 or so. Looks the same otherwise besides the mount and his has the spring at the bottom. http://www.walcottcb.com/catalog/product_info.php?cPath=28_93&products_id=401
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Dub

'98 TJ SE
15x7 ProComp Series 51 Rock Crawler Wheels
31x10.50 General Grabber AT2's
Taurus Fan
Uniden PC68 Elite CB
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IBTJn
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Joined: 31 Dec 2004
Location: Just Outside of Portland, OR

PostPosted: Mon Jan 16, 2006 7:00 pm    Post subject: Reply with quote

Yes, attach a small (short 2"? ) piece of wire to the stinger (adjustment tip). Trim it back from there as needed. It's okay if it dangles a little bit too. But don't allow it to drape all the way back to the down 180*. It's going to be very tight...so once you get it close, that'll probably be all you get. Tape up the wire and go beat the crap out of your friend. Tell him to buy a real antenna and quit being a cheap bastid like TheMajor is!

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el_dubya
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Joined: 20 Sep 2005

PostPosted: Tue Jan 17, 2006 9:01 am    Post subject: Reply with quote

How do you reccommend attaching the wire? What kind of wire? I have some electric fence wire that would be rigid, I think it would work well... but how to attach it? Yes, the beatings will commence. rofl Thanks.
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Dub

'98 TJ SE
15x7 ProComp Series 51 Rock Crawler Wheels
31x10.50 General Grabber AT2's
Taurus Fan
Uniden PC68 Elite CB
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IBTJn
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Joined: 31 Dec 2004
Location: Just Outside of Portland, OR

PostPosted: Tue Jan 17, 2006 12:03 pm    Post subject: Reply with quote

Heck, I'd just throw a piece of scrap anything you have...even 24 guage phone wire, wrapping it a couple of times on the tip (after stripping the plastic jacket making it metal to metal). I'd probably start by making sure the stinger is extended as far out as it can be without losing it...tighten the set screw and check SWR's again on 1 & 40. Then I'd put a 2" (after wrapping it on the very tip a few turns) and let it dangle.

If it wants to slide down the stinger, throw some electrical tape on it to hold it. Check SWR's and see if it made any difference. If it did and your SWR comes down some, trim off about 1/4" and check the SWR's again. If it continues to drop, continue trimming or adjust the stinger down some. If it goes up, then put a longer piece of wire one...maybe 3"

The problem with those short antennas is they are extremely narrow banded...which means they are very very touchy to tune. If you can't get the SWR's adjusted or it makes little difference, the center loading coil is probably bad or broken. Might as well throw the antenna away at that point...as they aren't worth fixing.

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SnaFu2
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Joined: 01 Apr 2006
Location: Middletown, N.J.

PostPosted: Wed May 03, 2006 2:03 am    Post subject: Reply with quote

el_dubya wrote:
Ok, heres the closest thing I could find. This one says it is 55 inches where as his is only 15 or so. Looks the same otherwise besides the mount and his has the spring at the bottom. http://www.walcottcb.com/catalog/product_info.php?cPath=28_93&products_id=401


Sounds like the antenna is way too short. A 2 meter (144.00 to 147.00 MHZ) antenna is only 19" if i remember right. u want to operate somewhere above 28.000 MHZ.
tell ur friend to pry open his wallet and buy a new antenna before he ruins his xceiver.

Just another thought. Some Antennas have traps (coils) that allow them to work at frequencies that would normally require a much longer antenna. Overall lenght would be much shorter then just a peice of wire cut to a 1/4 wavelenght.
Rule of thumb is the higher the freq. the shorter the antenna.

SnaFu
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