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a problem with the coax going through the hach

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#1
This is on a 2008 Pontiac Torrent SUV. I have the 2m/440 magmount antenna on the roof. Right now the RG58U coax runs under the lip of the back hatch. Every time the hatch is opened the hatch rubs on the coax. The hatch over time will rub through the coax and short it out. I am looking for other ideas of running the coax short of drilling holes. I got this SUV on a fluke. It just got released from Big Toe's police impound lot to be put up for sale the day that I had my 2000 Windstar towed back in for a trade because of instrument cluster problems. The 2008 Pontiac is the newest rig that I have ever owned. Heck this is my 1st car ever with built in Onstar. period. I would like to avoid drilling any more holes in it then is already done. I mounted the 102" 10m whip on the drivers rear 1/4 panel. I need some ideas please. The rear windows on each side just forward of the hatch don't open. Question. Could I splice some Ladder Line into the coax to feed the line back through the hatch? The hatch won't rub on the Ladder Line.

Steve
 

jwt873

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#2
Ladder line won't work. It will be affected by the proximity to the metal parts of the SUV. Plus... ladder line impedances are typically 300 or 400 ohms and your radio and antenna are 50 Ohm. You might try a thinner coax such as RG-174. Run it from the antenna to inside the vehicle. (I'm guessing that will be about 4 feet). Then run RG-58 from there to your radio up front.
 

jaspence

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#3
Splicing coax is a guaranteed path to disaster for the finals in the radio. You might try an on glass mount antenna if the back window does not have defroster wires or tinting. I use a hatch lip mount on my C-Max, and it works very well with the wire going in at the side of the hatch lid.
 
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#4
No go on the ladder line for several reasons. First, it is the wrong impedance (300-450Ω rather than 50Ω) so SWR will be a minimum of terrible and you may fry your radio if you transmit. Second, running ladder line next to metal causes issues because the ladder line is not shielded. You'll have even worse impedance mismatch issues, plus significant power loss due to RF currents being induced in the steel of the hatch and frame next to the ladder line. And then you have the whole balanced vs unbalanced feedline issue.

Your only real options are to use a glass mount on the hatch window, which may not work if the vehicle has low-E coated glass or defroster wires, or drill a hole and put in a NMO mount (definitely best performance). Or live with what you've got.
 

jwt873

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#5
Splicing coax is a guaranteed path to disaster for the finals in the radio.
I guess I should have explained more... I didn't mean splice.

The proper way would be to take the base of the antenna apart. Unsolder the RG-58 and then solder on the RG-174 in its place. On the other end of the RG-174 run, install an SO-239 socket. (see image below). The radio would connect to the SO-239 socket using RG-58 with PL-259's on each ends.

The cable in the image below is mine. I just took the shot on my desk. I have an SMA connector on one side and the SO-239 on the other. I use it from time to time when I want to connect one of my HT radios to my dual band vertical on top of my 40 foot tower. The cable works well.
.
 

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#6
Coax going through the hatch

In most vehicles there are some kind of rubber plug on the underside that can be removed, replaced, cut a small hole in to allow coax to run in to the body of the car. You may have to put some kind of extension on the existing antenna coax to make up for the longer run.

In my truck there was a rubber plug (grommet) on the bottom of the firewall that already had some wires running through it. I managed to pass RG58 through the same grommet and then up to my radio.

Take a few minutes and look under you vehicle around the trunk area. There is likely a rubber grommet of some kind there. Other than that, leave it as is. Sure the coax may eventually rub through but it will take many many many cycles of opening and closing the hatch.
 
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#8
Long term, running cable through weather seals is going to result in damage to the cable and eventually, failure.

Glass mounts can work, but they will never compare to permanent or even mag mount antennas. Since glass mount antennas don't have a ground plane, they are usually a half wave design. Without the ground plane, half wave antennas are 0dB of gain, so not doing yourself any favors there. As stated, tinted glass can be an issue for these.

Finding another way to get coax outside the vehicle would be a good idea. Maybe a bracket mount off the fender. While still not ideal, it's probably the better option.

I understand your concern about the permanent mounts, but in 30 years of doing this and a lot of vehicles done (including about 40 at work running around right now), I've never had one leak.
In the long run, it's often the better solution. Mag mounts will damage the paint. Bracket mounts have drawbacks due to lopsided ground planes and coax routing. Glass mounts I covered above.
The benefit to the permanent mount antenna is you can get the antenna mounted right in the center of the roof, which gives the ideal ground plane. You don't have to worry about coax routing. It'll work better. It'll look better.

Seriously, if you drove around with a 102" whip flying off your fender, an NMO mount on the roof is going to be insignificant.

All my personal vehicles and all my work trucks have permanent mount antennas, and I don't regret it for one moment.
 
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#9
I'd either look for an existing hole and run your coax through it or seriously consider creating your own. An NMO mount is clean and trouble free when done properly. I sympathize with not wanting to put too many holes in your car but it is 10 years old.
 

chief21

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#10
One of the Diamond NMO mounts on my SUV uses a special cable with a section of very thin coax (RG-174??) where it passes through the rear hatch and gasket (the RG58 transitions to the thinner coax before it gets to the NMO mount). It's been there for four years and no apparent issues as yet. I think that the cable only might be available separately without the mount.

- John AC4JK
 
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#12
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#13
There is a reason you should use a ball mount and the largest you can find, it spreads out the load over a larger area of the car body. I remember people who used small footprint mounts like the one you got on 1970s vintage cars with much thicker body metal and they still warped and bent the car body from the 9ft whip moving around.
prcguy


I didn't use the big ball mount for the 102" whip. I got the following mount from eBay https://www.ebay.com/itm/Workman-PS...121063&hash=item568d385780:g:sS0AAOSwYIxX2J-Q this mount doesn't stand out as much and it doesn't need the center hole and the 3 smaller mounting holes.
 
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#14
Thanks for the tip. I still have the large ball mount sitting in my shack. I took the ball mount off the Chry
Town & Country mini van when I traded it in. So far the body hasn't warped from 2 road trips and banging on tree limbs. I also have the matching loading spring installed. But I will change the mount out if you think it is best. I also figured out how to run the coax for the magmount antenna. By the way I use the magmount antenna because when I am carrying a roof load I need to move the antenna out of the way. Anyways in order to mount the 102" whip mount I had to take the twisty jack and it's mount out and remove some of the insulation to get at the inside part of the fender wall. I can make a small hole next to the ball mount for a UHF female feed through connector.


There is a reason you should use a ball mount and the largest you can find, it spreads out the load over a larger area of the car body. I remember people who used small footprint mounts like the one you got on 1970s vintage cars with much thicker body metal and they still warped and bent the car body from the 9ft whip moving around.
prcguy
 
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#15
If you buy a hatch back mount or trunk lip mount, they are designed to
enable you to close the hatch ot trunk lid without damaging the coax.
 
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#16
I found a 2' chunk of the RG-174 with a female SO-239 on each end on eBay. I cut the RG-58U coax and put and I put 2 male PL-259 connectors on each side of the cut in the RG58U and put it all together. It works great. The SWR hasn't chaged at all. The RG-174 coax is small enough in dia that the hatch doesn't rube on the coax. I checked the antenna with my antenna analyzer. I even made a 10m contact, I had a 5 by 9 report come back to me.

I guess I should have explained more... I didn't mean splice.

The proper way would be to take the base of the antenna apart. Unsolder the RG-58 and then solder on the RG-174 in its place. On the other end of the RG-174 run, install an SO-239 socket. (see image below). The radio would connect to the SO-239 socket using RG-58 with PL-259's on each ends.

The cable in the image below is mine. I just took the shot on my desk. I have an SMA connector on one side and the SO-239 on the other. I use it from time to time when I want to connect one of my HT radios to my dual band vertical on top of my 40 foot tower. The cable works well.
.
 
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#17
Prcguy I changed the mount for the 102" whip to the large ball mount that I have. I saw the (cheap) plastic seal on the small footprint mount wasn't staying in place and the top insulated feed through screw (there is 2 screws on the small mount) that connects to the whip it self was coming lose from the wind wiggling the antenna while I drive. The bottom screw holds the mount in place.With that plastic seal coming lose. The 1st hard, rain, down poor would have shorted out the antenna and let rain leak inside the drivers side 1/4 panel. As an added precaution I added a ring of clear silicone sealer on both sides of the 1/4 panel before bolting the mount together. I did the same thing when the ball mount was on the town & country minvan and there was never a leak. .

Originally Posted by prcguy View Post
There is a reason you should use a ball mount and the largest you can find, it spreads out the load over a larger area of the car body. I remember people who used small footprint mounts like the one you got on 1970s vintage cars with much thicker body metal and they still warped and bent the car body from the 9ft whip moving around.
prcguy
 
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