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SWR in the red


Kylepwoods

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I installed an old cobra 19 ultra in my ranger, with a magnetic antenna in the center of the roof. The wiring is all good and dandy but I went to calibrate the antenna and it's in the red, way above 3 on both 1 and 40. I have since disconnected power so I don't fry it but I don't know how to fix this. I've seen that I should extend the antenna. I've also read that I should shorten it. Can someone please help?
 


ratdude747

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I installed an old cobra 19 ultra in my ranger, with a magnetic antenna in the center of the roof. The wiring is all good and dandy but I went to calibrate the antenna and it's in the red, way above 3 on both 1 and 40. I have since disconnected power so I don't fry it but I don't know how to fix this. I've seen that I should extend the antenna. I've also read that I should shorten it. Can someone please help?
First, make sure your mount is getting good ground (this is why I don't like magnet mounts and why my Wilson 1000 is roof mounted). Bad connections/grounds (magnet not on enough metal, bad cable, etc.) will do that. Given how high your SWR is, I'd look there first. If that's good, then continue:

If this is a new antenna, depending on what type it is (C40? Wilson 1000/5000? Cobra "celluar style?), you may need to go shorter right off the bat; they are sold long as it is obviously easier to shorten an antenna rather than make it longer (just cut it with bolt cutters in 1/4" increments until it's there). IIRC wilson whips are sold that way (at least the short load that I have in mine).

Side note- speaking of short load whips, these need to be adjusted above the center element; adjusting the section below such can and will cause headaches. As will installing one upside down; the length of the whip section going to the base and possibly orientation of the element relative to the
base is important and pre-designed and made to the correct length.

Here's the trick (and why one should use a meter, not a cal light): you need to test it right in the middle (20) and see if it gets better at all going up or down. If its better going up from there, you need to go longer, if going down helps (quit laughing, you 2nd grader!), you need to shorten the antenna. Then, adjust until tuned.

Hope this helps. (FWIW, I'm an EET who both does CB (eventually Ham) and also took a couple of college classes in this sort of thing).
 

Kylepwoods

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Thanks for the quick response!
I think you're probably right, it's most likely in the antenna. It's definitely not new.. It was up in my father in laws barn collecting dust.. So that's probably my issue. Can't blame a guy for trying though lol.
I meant to say I used a meter, I know zero CB lingo haha. I had to go to a truck stop to find one!
Do you have any recommendations on an antenna?
 

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It's possible that antenna might not even be a CB antenna, which could also explain the bad SWR (does it have a name or logo or anything on it?).

In standard base-load magnet mount antennas, I think it's hard to beat a Wilson 1000.

If you want to go to a 3/8-24 threaded antenna, the Francis CB-26 Hot Rod I think is one of the best choices out there (short of a full 102" steel whip). There are a number of 3/8-24 magnetic mounts available too, though I would suggest one that has three actual magnets such as this Tram unit (these are almost impossible for a tree branch to knock off if you have the antenna mounted on a spring).

If range is important, do not buy a CB antenna of any type that is less than 5 feet tall. Shorter antennas have very high resistive losses which greatly reduces the range of your transmit ability.

Also, be sure to place the antenna fully in the clear. Top of roof is always best, though fender or bedrail mounts can work fairly decent if the antenna is a center-load or top-load type (or is a full 102" long).
 
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Kylepwoods

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I'm sure it is a cb antenna. It's just been sitting collecting dust and corroding for years so I'm guessing I should just get a new one. I do think I should just get a mounted one, I don't mind making a hole, I know how to seal it so that's not an issue. If I did go with a whip how does the other end get tied down?? That hot rod one looks good though.
 

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Usually you just have a small clip that the end of the antenna hooks into (attached to your rain gutter, fender, etc.).

Do note that you shouldn't use your radio while the antenna is clipped down, as it not only screws the SWR up, the antenna not being vertical means your signal will not be radiated (polarized) correctly.

I'd recommend a ball mount if you go with a hard-mount.
This one includes a spring:
http://www.amazon.com/ProComm-JBC986-Heavy-Duty-3-Inch-Ball-Mount/dp/B0054HME58

W/o spring, but instead uses a conventional threaded (SO-239) connector:
http://www.amazon.com/ProComm-JBC985-3P-Heavy-SO-239-Connection/dp/B007L6X940

Hope that helps
 

Kylepwoods

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Thanks for all the help guys! Appreciate your time. That ball mount looks sweet, probably go with that and the hot rod antenna!

Thanks again guys. Cheers
 

softshellcrab

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Ground plane/grounding

There is a difference between grounding and ground plane. When using a HF frequency your transmission needs to see a ground plane in order to "bounce" up. HF frequencies actually bounce off of the atmosphere above you to the person that is tuning you in. Placing an antenna on a truck rail or a rain gutter even if it is physically grounded to the auto does not guarantee that you will be able to transmit and be heard. When I first got into CB's my first antenna was a Wilson 5000 physically attached to my roof by drilling a hole into the metal and then attaching the antenna. I had a peaked and tuned SSB Cobra at the time and was able to reach SE USA from Arkansas with 25 watt's! With that set up I rarely had any issues with being heard even under bad conditions. The other option is to add an antenna tuner to your antenna from LDG. The 100Z runs about $150 and runs off of AA cells.

There is a lot of science with mobile monitoring and many Hams have pulled their hair out trying to get a good ground plane for their radio's. HF/VHF are not affected by ground planes and that is why they are the most popular mode used for Hams.

Mike K0CCP
 

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In standard base-load magnet mount antennas, I think it's hard to beat a Wilson 1000.
The hard mounted version is pretty nifty too... the way they made the roof mount one, they made it so all the cable is internal (only seal is the antenna mount itself) and said mount is low profile (fits under headliner). Also, they made the radio end two piece, which means no horsing a big PL259 connector when routing the cable. Finally, they also include a rain cap that can be screwed on in place of the antenna to accomode parking garages, drive thru "watch out" bars (usually that's all it hits), car washes, etc.

Sure you gotta drill a hole in the roof (just smaller than 3/4", use a step drill) but magnet mounts IMHO suck (bad/inconsistant ground, external cabling, etc.) and if you're gonna leave it, what point is there? If not, I'd get a cheap cellular style mag mount to play with (and see if you really want a CB after all) and then go for a hard mount if you decide to continue. Or get the 1000 magnet mound and swap the mount later if you wish (they can be bought separatly).

About my wilson 1000 in my truck:

I mounted mine in the rear center of the roof in the 3rd tailight/cargo light bay as at least my 1995 has a welded brace that runs lengthwise down the roof that only has an opening there (this also made maintinace easy as it can be accessed by removing the tail light or dome light). From there I ran it through the sides of the roof (there is hollow bracing) and out through an extra hole near the A pillar on the passenger side which only needed a little drilling; one note, I had to push the connector from behind with pliers to make it fit through. After that, down the outside of the pillar (under the trim) and behind where '96+ has a passenger air bag (this is where I hid the bundle of extra cable) and to where the Ashtray would be, which is where I mounted my radio.

I have build pics on another forum... Maybe I ought to post them in another thread? For now, the pics in this post show what it looks like on the outside.
 

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