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Coiling the coax cable causing problems....a myth or fact?
- Thread starter Turbo T
- Start date
Clockwise North of the Equator, counter (or anti) clockwise South of the Equator.
Booty, I am ashamed of you! I thought everyone knew that.
Booty, I am ashamed of you! I thought everyone knew that.
Clockwise North of the Equator, counter (or anti) clockwise South of the Equator.
Booty, I am ashamed of you! I thought everyone knew that.
works even better if you paint the coil in tartan paint.
B
BOOTY MONSTER
Guest
RatsoW8
Supporting Member, W9WDX ARC Member - WD8T
Coiling excess coax is not the the same as winding a wire choke. Makes no difference if you coil up the excess. Many have said it...just not so tight that yoiu damage the center conductor if it's solid.
If the antennas is matched to the coax 50 ohm impedance and there is a valid ground plane in place to effect that match, then
under these conditions there will be no 'common mode' outer shield current to have any effect by coiling the coax.
You need to understand that in a closed system like coax, the RF currents stay 'Inside the coax' not on the outside.
One parameter to this is how 'good' the outer shield is in the coax.
If it is junk and there is a missmatch then some outer current may be allowed to leak and flow.
These CB myths die hard because no body wants to look at known performance theory and just keep repeating hear-say.
For those who still don't believe, look it up and find out.
Coiling in a 'matched' system has no effect.
under these conditions there will be no 'common mode' outer shield current to have any effect by coiling the coax.
You need to understand that in a closed system like coax, the RF currents stay 'Inside the coax' not on the outside.
One parameter to this is how 'good' the outer shield is in the coax.
If it is junk and there is a missmatch then some outer current may be allowed to leak and flow.
These CB myths die hard because no body wants to look at known performance theory and just keep repeating hear-say.
For those who still don't believe, look it up and find out.
Coiling in a 'matched' system has no effect.
Exactly. To add further proof that this is true I offer a real example. I used to be in commercial broadcasting and one of my stations was a three tower array on 1350 KHz. The center tower was just outside the TX house. Program material was relayed to the TX from the studio via a VHF radio link called an STL which is short for studio-transmitter link. The STL receiver antenna was mounted on the center tower of the AM array. This meant that the STL antenna and it's coax cable were in effect directly connected to the output of the AM transmitter. Just inside the TX house the coax from the STL antenna was wound on a PVC form to make a nice neat coil of about two dozen turns or so. A tuning capacitor was connected across this coil and connected to the coax shield on either end of the coil. This made a parallel tuned circuit with the shield and was tuned to 1350 KHz. This allowed the circuit to reject any RF on 1350 KHz that was present on the coax shield and allowed it to be grounded on the STL receiver end with actually grounding out the AM array. In this case the parallel tuned circuit was isolating the AM array from the VHF antenna system and vice versa. There was no effect whatsoever to the VHF radio receiver that had the coax coiled up. Remembering that a given inductance has a greater effect the higher the frequency goes, it can be seen that if it had no effect on 164.940 MHz then it would certainly have no effect on 27 MHz.
Try checking swr with the coax straight, and the coiled. Just for kicks. That way, you know for sure what happens, or what does not happen. Just a suggestion.:bdh:
And that is only on the OUTSIDE surface of the shield.
As far as the diameter for winding coax, I figure 4" diameter (not radius) for RG58, 5" for RG8X, RG6, RG59, etc., and 8" for RG8, RG213 and LMR400. Those are figured using 10 times the cable O.D. for radius, and then multiplying by 2. I guess you could just use 20 times the O.D.
.That's the way we figured it in the Navy, only they use a factor of 13 rather than 10.
yes... but it can also help on some antenna systems...
I had an A-99 that had major issues, like 1.6-2 swr in the CB band...
I did a 4.25" diameter coil with 5 turns of coax at the a99's feedpoint, and isolated the antenna from the mast, as well as adding a home mad e GPK, FLAT SWRs and quieter receive (ie less static)
I think that something that people are 'missing' is that choke, that coil of feed line, only affects what's on the outside of that feed line, not what's on the inside of that feed line. The only significant affect a choke has on any feed line is that it adds some length to it. That can mean some loss because of resistance, but for the lengths commonly used to make up that choke, that resistance amounts to very, very little. Notice that I said 'resistance', not impedance. If the impedance of the -system- is changed because of that added length, then the antenna (load) on the end of that feed line is incorrectly tuned. Meaning that it is not the same impedance as the feed line and the transmitter. That holds true for any transfer of AC energy no matter it's frequency, 27 Mhz or 60 Hertz, or audio frequencies, anything AC.
- 'Doc
- 'Doc
do a 1-2 loops for a chock..
if you still have more left over..
cut it away and attach as needed a new connector..
Pretty much end of story..
if you still have more left over..
cut it away and attach as needed a new connector..
Pretty much end of story..
I have to wonder if people actually read the entire thread when they dig up older ones like this. Maybe they just read the last post or two and then comment without looking at everything that was posted before. I also wonder how many listen to myth and conjecture rather than proof and experience. :headbang :bdh: :bdh: