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Probably dumb question, high SWR

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Rochester
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Probably dumb question, high SWR

#253706

Post by Rochester »

Hi, I need some help getting my base CB up and running properly.
I have a Royce radio and a Solarcon antenna. I mounted the antenna about halfway up the tower that holds my TV antenna (one of those three-sided towers that comes together right at the top). It wouldn't quite fit right against the tower itself, so I attached some brackets to the tower to attach another vertical metal pipe about four feet long, this pipe is held a few inches away from the tower, and the antenna is mounted to the top of this extra pipe.
The ground plane kit that came with the antenna is four rods angled downward attached to a metal collar. Because the antenna is attached halfway up the tower, two of these rods are within a few inches of the tower at closest approach. One of the rods is about a foot above the roof. The manual said that ideally the rods should be several feet above the roof, but I had to fudge on that one because the very top of the antenna is now just a few inches below the TV antenna that is at the very top of the tower. If I raise the CB antenna up the antennas will be going through each other.
It might be possible to mount the CB antenna at the very top of the tower, above the TV antenna, but it would be difficult and dangerous and the ground plane rods might hit the TV antenna, so I would prefer to hold this course of action except as a last resort.
The first piece of coax is 50 feet, too long really, (but the extra length will be needed if I do have to move the antenna to the very top), so I ran it up and down the tower taking care not to coil it anywhere. The other end of the coax attaches to a grounding block, in case of lightning (grounded to a chain link fence nearby), then to a female-female adapter, then to a 3-foot coax which goes through the wall. Inside there's another female-female adapter (I might replace this with a filter if I get interference problems later), then another 50-foot coax through the cellar, then another grounding block (grounded to the incoming water pipe), another adapter, then an 18-foot coax that comes up through the floor and finally to the radio.
I grounded it twice because when I installed my TV antenna, I could still feel static electricity after grounding that once so I grounded the TV coax twice and more or less copied that setup.
So I set up the SWR meter at the radio, calibrated it, and tested it. I redlined it immediately. Something's not right here.
I disconnected the radio and took it and the SWR meter down to the cellar where I disconnected the adapter that was just inside the wall and put the radio and SWR meter there instead (using 53 feet of coax instead of 121 feet). There was an improvement, I didn't redline the SWR meter, but it showed just under 3:1, I can do better than that and I will need the extra length anyways if I don't want to go to the cellar every time I want to use the radio. I examined the second length of coax, but I did not see anything obviously wrong with it. It was unavoidable that the second long coax passed some power cables, but I made sure that it crossed the cables at close to right angles and didn't run parallel to them for any significant distance.
I tested the SWR meter by hooking it up to the radio in the car, I got about 1.8:1 so I guess it works.
So my dumb questions are...
Did I do something obviously wrong?
What can I do to fix my apparently botched installation?
Am I trying to use too much coax?
Would it help to move the antenna higher up the tower (even though to do so would run it through the TV antenna)?
Would it help to move it to the very top, above the TV antenna?
Any further suggestions?
Thanks for your input.
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231

Re: Probably dumb question, high SWR

#253708

Post by 231 »

Your antenna is too close to the tower. Do a support arm that moves it horizontally away from the tower at least a few feet if not more.

Frankly, I'd be more inclined to put your TV antenna on the support arm and the CB antenna on the top. But that's just me. The vertical element on the CB antenna is your primary radiating element and is too close to the tower. The further away from the tower you can get it, the better. The ground plane radials aren't as important. Inches from the tower shouldn't hurt, but the main vertical it's a big deal.

Also, at 100' + of coax, you'd be doing yourself a big favor making sure you run decent coax like RG-213 or LMR-400. Using RG8x (aka "mini-8") there is quite a bit of loss...more than you might think. If you've already done that, disregard.

Good luck.
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Rochester
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Re: Probably dumb question, high SWR

#253760

Post by Rochester »

Ah, thanks for the information. I was afraid of that.
If I put a pole in the ground on the side of the house, I could take the CB antenna off the tower entirely, and shorten the length of the coax needed to reach the radio. I wonder if that would work!
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'Doc

Re: Probably dumb question, high SWR

#253764

Post by 'Doc »

I think that separate pole and away from the where it is on the tower will give you a big increase in performance and SWR. That pole should either put the antenna above the roof line, or be a ways from the house. Everything near that antenna will affect it's tuning and performance.

The length of feed line isn't that much of a biggy. Shortening it by half will make some difference, but don't expect 'daylight/dark' differences. Doesn't really make that much difference no matter what kind of coax you use.

Something you didn't mention (or I missed) is if you tuned that Solarcon antenna? If it's the 'A99', has the 'rings' on it, it can certainly be tuned and perform better.
Have fun.
- 'Doc

(The only really 'dumb' question is the one you don't ask.)
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Rochester
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Re: Probably dumb question, high SWR

#254102

Post by Rochester »

Wow! Thanks, guys! It worked!
I removed the antenna from the tower and set up a tripod on top of the roof, about 10-12 feet from the tower, and set up the antenna again. This time I got an SWR of below 1.1 using only half of the coax!
I hooked up the rest of the coax again and tested it and it redlined again, so I guess besides being too close to the tower before, I had a bad coax or a bad connector. I have more coax laying around, so I can improvise somehow.
I hadn't done anything with the rings, having intended to leave the fine tuning until I got the other issues solved. If I can keep that 1.1 when I finish setting up, I might not have to do anything to them.
Wish me luck finishing the setup!
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'Doc

Re: Probably dumb question, high SWR

#254116

Post by 'Doc »

You got all the good luck I can spare. Sometimes, I need it more than other people, so I may ask for it back.
- 'Doc
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Re: Probably dumb question, high SWR

#261219

Post by Rochester »

wow, time really got away from me.. anyways, I used another piece of coax and attached it to the bottom of the joists down in the cellar to keep it out of the way, and it works great. I still have that <1.1 SWR. Thanks for everyone's help :)
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