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Coax length on mag mount question

Did you cut the connector end or the antenna end. My Wilson mag ended up with a broken connection inside on the center conductor. I had to solder it back together. I have seen connections that look good on low power but show themselves on high power.
 
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Road Squawker said:
if that (the coupling) was effective, then why did you get an RF burn from the mic?

All mag mounts use the shield as part of the antenna. that shield length is calculated into the design.

Turning the amp on did not create a new problem, it was already there after you cut the coax but you didn't notice it at the lower power level.
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I am not saying it is effective, or that turning the amp on caused the problem. I think the opposite - that the problem exists regardless of the amp being on, regardless of coax length, and that it’s the shorter coax and the amplifier that makes it noticeable. But then again, if it works with factory 17’ of coax, is there problem at all?

What I was saying in response to your post is that Ive never heard that magnet mounts use the braid as half of the antenna. That is interesting. At the same time, there must be some substantial effect of the magnet via capacitance, or we wouldn’t need to mount antennas (including magnetic ones) to metal...the braid would do the work we could all just run longer coax to save our lips.

I was always of the thought that the frequency was the only factor that determined whether a capacitive coupling worked or not, and not the power level (except at the extent that the power is so great as to overcome the dielectric material). Now I am wondering if a capacitor’s effectiveness in coupling to the vehicle body decreases with greater power.

Anyway...thanks for your thoughts. Happy Thanksgiving.
 
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WINKDOGG said:
Im sure I will get some boo's here but I cut my coax to needed length for any particular install ;) never get out a calculator or a tape-measure . Never been a big problem...
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I am in total agreement. I didn’t expect to see any issues with shortening the coax in this case.

As far as the coax on Wilson’s, the RG8X on the 5000 is actually pretty good stuff, and in reality, more than enough for my little set up. I do like larger coax in vehicles also, but more for the durability than the performance.

Shadetree Mechanic said:
Did you cut the connector end or the antenna end. My Wilson mag ended up with a broken connection inside on the center conductor. I had to solder it back together. I have seen connections that look good on low power but show themselves on high power.
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I cut it at the connector end. I agree on connections that pop up at higher power, I have seen that also. I tend to think I ruled that out when I added a jumper in and everything went back to normal.

Have a Happy Thanksgiving!
 
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fourstringburn said:
Makes a good case to do a permanent install with a puck mount.

Drill that hole!
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Agreed. I plan to take license with the OPs story (as my old man said, no story so good a coat of varnish won’t help) and turn that RF burn into an arc weld teaching moment. Wanna run powah?!

Drill. Car has dozens of holes already. Buy a cell antenna mount to fit it you remove the real radio years from now.

.
 
Ok, so you guys think I should drill it?

lol...you guys kill me.

It’s always been the plan to drill a hole. I dropped the headliner and drilled 15 holes in the roof the day after I bought it...in other words, I don’t need persuasion to drill a hole in a work truck.

As mentioned in the first post, I wanted to have an understanding of why this issue popped up with shorter coax, not find a solution around it.
 
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dledinger said:
Ok, so you guys think I should drill it?

lol...you guys kill me.

It’s always been the plan to drill a hole. I dropped the headliner and drilled 15 holes in the roof the day after I bought it...in other words, I don’t need persuasion to drill a hole in a work truck.

As mentioned in the first post, I wanted to have an understanding of why this issue popped up with shorter coax, not find a solution around it.
Click to expand...

DRILL, DRILL, DRILL.......maybe frack that mutha. Drill baby, drill! LOL
 
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dledinger said:
As mentioned in the first post, I wanted to have an understanding of why this issue popped up with shorter coax, not find a solution around it.
Click to expand...
Mag mounts do not properly "couple" the shield of your coax to the vehicle body. The vehicle body is the OTHER HALF of your antenna and only "minimal capacitive coupling" to the body occurs with your mag mount. Your coax shield needs to be solidly connected to your vehicles body. Shortening your coax threw your antenna balance out. You have a common mode current problem and they are using nearby conductive objects to attempt to "balance" the current flow on your antenna so BOTH sides are equal (Kirchholff's current law) that is WHY your experiencing RF burn and OTHER erratic behaviour with other equipment in your truck. You need to increase the "counterpoise area" so you have a BALANCE. Getting one of those ground plane Wilson kits that screw on between the coil and mag base will also help you out, improve balance and reduce RFI.
-73's from the Bam brother.
 

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