| Author |
Message |
    
todd
| | Posted on Tuesday, July 23, 2002 - 06:08 pm: | 
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ok,
I have a 5 ft. firestick II, 18 ft. of coax, and a radio shack cb. I pluged up a swr meter to this set up and no matter how much i move the top of the antenna, the meter reads the same. What did I do wrong? I mounted my antenna on the spare tire. I also have a spliter that lets me run my radio off the antenna along with the cb. Thanks for the help.
Todd |
Al Oliveira (Offroaddisco)
| | Posted on Tuesday, July 23, 2002 - 06:14 pm: |
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Start by removing the spliter. Then if that won't help try relocating the antenna. The spare is isn't the best location for the antenna but lots of people do it. And lastly try another SWR meter. |
Paul D. Morgan (V22guy)
| | Posted on Tuesday, July 23, 2002 - 08:12 pm: |
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Hi Todd,
#1 A splitter could result in a Dead Short which is bad in CB land.
#2 Also, you need to make sure you have good metal to metal contact between the CB antenna mount and the spare tire carrier for grounding.
#3 Another big mistake is the improper location / installation of the plastic grommet on the antenna. You will create another dead short by not isolating the antenna.
I hope the mistakes I made during my installation will help you.
Paul |
p m
| | Posted on Tuesday, July 23, 2002 - 08:23 pm: |
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Todd,
I have a radio shack SWR meter that reads the same, no matter what i do to it. Like, 0 when it's not plugged, and maxes out when a TX button is hit.
since the CB works fine, i use it as a little paper weight.
peter |
Al Oliveira (Offroaddisco)
| | Posted on Tuesday, July 23, 2002 - 09:14 pm: |
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Paul, what's the "ground" for? I don't think he's going to get much of a "ground plane" with mounting it on the spare. |
Paul D. Morgan (V22guy)
| | Posted on Wednesday, July 24, 2002 - 06:38 am: |
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Our Spare tire carrier is not properly grounded due to everything being painted. The below is a tech item from firestik which I checked out after I had CB problems.
On standard mobile antenna systems (those NOT designated as no-ground-plane), it is imperative that the antenna mount be grounded to the vehicles chassis. Ungrounded mounts will cause high SWR readings and/or low output power readings. There are three common situations when the mount may be inadvertently affixed to an ungrounded fixture.
1.Swing-away SUV spare tire racks mounted on nylon bushings.
2.Luggage racks or RV ladders mounted with rubberized bushings.
3.Mirror arms on fiberglass trucks or motorhomes.
For proper performance the mount must be grounded. It should be a standard part of the installation procedure to verify that the mount is grounded. It is an easy test to perform with either a VOM meter set in the Resistance (Ohms) mode or in the audible diode testing mode. Another method of checking is with a self-powered continuity tester. These test need to be made with the coax disconnected from the antenna mount or the radio. If the coax is fully connected and the radio is grounded you will get the false sense that you have a sufficient ground at the mount. Grounding the mount via the coax cable to the radio is not good enough. It requires a direct ground. Either the mount has a good direct chassis ground or it is grounded via the object it is mounted to.
The SWR readings on an ungrounded mount will almost always be 2.0:1 or higher on all channels. You may actually see the SWR dip during the testing procedure (i.e. 3.5:1 on channel 1, 2.5:1 on channel 20, 3.5:1 on channel 40). But, anytime it stays high you can be 90% sure that the mount is ungrounded, there is insufficient ground plane and/or you have low quality or the incorrect coax.
Also, keep this in mind. If it becomes necessary to run a ground wire or braid to a chassis ground point, use a wire of at least 12 gauge. We have reviewed installations where the installer used a small gauge wire (20ga) and when the SWR was tested it fell from over 3:1 to below 1.5:1. However, the power out put was very low due to the undersized path to ground provided by the thin wire. The path to ground must be sufficient enough to carry the power being applied to the antenna.
I sanded and treated and everything works fine.
Paul |
Greg P. (Gparrish)
| | Posted on Wednesday, July 24, 2002 - 08:21 am: |
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On this subject, does anyone know if the rear door skin is aluminum or is it sheet metal? Just wondering if I need to treat the metal around the hole I drilled for my wire to pass through. |
Magnus
| | Posted on Wednesday, July 24, 2002 - 08:35 am: |
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Try to stick a refridgerator magnet to your door, that should tell you right away what kind of metal it is.... |
Greg P. (Gparrish)
| | Posted on Wednesday, July 24, 2002 - 08:57 am: |
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Good idea Magnus,
Thanks,
Greg |
Greg P. (Gparrish)
| | Posted on Thursday, July 25, 2002 - 09:19 am: |
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Well, the magnet did not stick, so I'm guessing the outer rear door skin on my DII is aluminum. Not as much of a worry then about the hole I drilled for the coax.
Thanks,
GP |
Paul D. Morgan (V22guy)
| | Posted on Thursday, July 25, 2002 - 10:00 am: |
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Greg,
Slow down and think about this. You do not have to drill a whole into that door. Your rear window washer grommet will handle the coax cable and the washer fluid tube with a little bit of Vasoline. Get you mind out of the gutter  Just cut the connector and resplice after routing.
Paul |
Greg P. (Gparrish)
| | Posted on Thursday, July 25, 2002 - 10:20 am: |
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I didn't run a connector through the door. The new hole is very small. I decided after putting the coax through the washer grommet that I didn't want to put any additional pressure on the washer tube, so I added a second hole to the exact size of the coax using a grommet.
I did use dish soap to get the wire through the grommet and door boot.................
I didn't happen to have a half used jar of vasoline laying around.............. |
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