Imax 2k and coax ?...

[Oatmeal]

I had a forrest fire here about 3 weeks ago, and the fire burnt up about 300ft of hardline wire I was using going up the mountain, and this wire does lay on the ground...

And back there where I had my antenna the wire and where the coax was spliced into the wire it too was on the ground, oh and this coax is 24ft long and I was using LMR 400...

So, the fire burnt low on the ground, and it did burn the coax, the coax was black inside on the center wire it burnt a few inches that I saw, but too that is as far as I checked on it....my ground wire, the center wire also burnt inside it..

Ok, the mast pipe is 21ft tall, in which as you no this is where my antenna is on this mast pipe, and when the fire took places the antenna was 21ft off the ground...

Ok, what Id like to know, can the heat from the fire travel the length of the coax which was 24ft up the center wire to the base of the antenna which was 21ft, off the ground and damage the base of the Imax ?.....

Reason asking, since this has happened, I had to move my antenna down the mountain about 200ft from the top, and I had to replace the wire I had laying on the ground, and I replaced the coax with 24ft of RG 213 coax, and replaced the ground wire with 10ga house wire I had left over from a job, and my swr is still a 3 and on up into the red....I have the antenna hooked up now and have been listening to the locals talk on it....but havent talked on the radio do to the swr been like it is...

So, hoping you guys can give me some info where to go from here....

I was going to go up there today, and take the antenna down, and check the swr in just the antenna, just to see if the antenna is in deed ok, just from looking at it, it looks to be ok...but after the fire, I didnt check the swr or anything in the antenna, since the rings, and the antenna all looks ok...

But I dont no if the heat from the fire could travel up inside the coax and do anything to the insides of the Imax....could this happen and not show any damage to the antenna from the outside ?.....

Really dont no where to go from here, so I sure could use some good advise..

 

[W5LZ]

The first part, I very much doubt that any heat would propagate very far in coax. That would be a matter of inches, not feet. So, I wouldn't worry about that.
If there's any obvious damage from heat then I would have to suspect that the cable which has that damage is unusable. If there are undamaged lengths they should still be usable.
Why is the antenna not showing a decent SWR since it was moved? The first reason is that it isn't in the same place it was, that certainly will change it's electrical characteristics. The quick'n'dirty 'cure' for that is to re-tune the thing. That's absolutely normal when any antenna is moved significantly.
All of the coax cables you've mentioned are 50 ohms characteristic impedance. Swapping from one size to another shouldn't make any differences there. The only time it would make a difference is if that particular cable was used for impedance matching, and then length changes certainly could make a difference. I don't think that was done so it wouldn't be a factor.
- 'Doc

 

[Oatmeal]

10-4, I didnt think moving it from one place to another would have any affect on the antenna....

But I took the antenna and mast pipe all down, and Ill check the swr in the antenna and see if its changed somehow from when I tuned it a few years ago...

Ive never had this kinda problems out of that hardline, but its never been on fire either.....but Ill check the swr in the antenna and go from there, thanks...

 

[hotrod]

10-4, I didnt think moving it from one place to another would have any affect on the antenna....

But I took the antenna and mast pipe all down, and Ill check the swr in the antenna and see if its changed somehow from when I tuned it a few years ago...

Ive never had this kinda problems out of that hardline, but its never been on fire either.....but Ill check the swr in the antenna and go from there, thanks...

yes moving your antenna can change your swr. my guess is up on the mountain top
it was above houses/buildings,ect.i could be wrong but that be my guess. try mounting higher
once you get everything checked over

 

[Oatmeal]

Here a update...

I ended up having to put the Imax 2k up at the shack, have it in the corner of my back porch....I used a couple good metal clamps on it and its up 21ft off the ground to where the antenna is on the mast pipe......I have a 10ga grd wire under the bottom U bolt and it comes down the mast pipe to the bottom where I have a 4ft copper pipe in the grd and used a clamp for the wire here..

Also went from the bottom of the mast pipe over to the 5/8s solid grd rod, with a 3 wire and it too is grd using a clamp here...

Im using the RG 213 coax, have about 60ft going to the shack....swr is 1.1 and less around the band..with the box on its a 1.2...in which havent used it much yet..I dont mess anything up in the house except for something in my son's room and it dont have a speaker in it, dont no how its coming through it, but thats what he tells me..

I dont have a choke on it yet, not sure what length to go with, I know they call for 18-21ft, not sure what to go with and what diameter I need to make the wraps...

This isnt pretty, but I live in a trailer park and also have one across the road..

Need some good advice on what length I need to go on a choke and what diameter is the best to go with....

Probably would hurt even if it was over kill, long as it worked....

 

[Robb]

I dont have a choke on it yet, not sure what length to go with, I know they call for 18-21ft, not sure what to go with and what diameter I need to make the wraps...

Ummm . . . no.
A choke for this will only need five close wraps on a ~4" plastic coil form and placed just below the feedpoint of the antenna. That works out to be only ~5ft length or less. More is NOT better; it must be done exactly as mentioned for the CB band. Different bands have different amounts of coils. It isn't that hard.

You might also consider putting four 1/4 wave length radials on the antenna too (about ~104" each).

 

[Oatmeal]

10-4, Ive been reading in some of the threads here to use 6-8 turns of coax, and then 5 wraps of coax, but these have been using a 4" form,...

Even read somewhere if your not going to use 20ft of coax for a choke, thers no use to make it....

Guess Ive did so much research on this stuff its all got me confused...

 

[Robb]

10-4, Ive been reading in some of the threads here to use 6-8 turns of coax, and then 5 wraps of coax, but these have been using a 4" form,...

Even read somewhere if your not going to use 20ft of coax for a choke, thers no use to make it....

Guess Ive did so much research on this stuff its all got me confused...

If you find the chart that shows the requirements to get the choke tuned for the 11m/CB band, you will see that claim is wrong.

Do some more homework; you will see . . .

Look at the last bar on the bottom of this graph. You will see that the green band offers the highest resistance to common mode current when 5 turns are used on a 4.25" coil form @ 27mhz (the CB band). See it?

 

[Oatmeal]

10-4, I see it....

So, 5 wraps is on the 4 1/4 coil form would it be 5ft of RG 213 coax ?....

Does this stuff really work ?..

Id never saw that graph before...

 

[Beetle]

I'd never bend RG-213 or any other coax cable that size on a 4-1/4" form - unless that was the radius. 8" diameter is about the smallest safe bend for this size cable.