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 Coil or not to coil coax

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Javelin Jim
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Call Sign : 26-CT-3427
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Equipment Used : Intek H520 Plus using an Albrecht CL27 TNC Rubber Duck (Not ideal

Coil or not to coil coax Empty
PostSubject: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeMon Apr 13, 2020 12:41 pm

Hi,
I’ve another question about setting up a Silver Rod.
I’m mounting it temporarily in my garden on a six foot pole with view to permanently concreting a longer support pole in the future, subject to the neighbours and ‘er indoors permitting.
With this in mind, I was considering making the coax run to the length where I finally want to mount the antenna.
Would coiling the excess length (approx 3-4m)at the antenna end affect the performance?
I could cut it to the length I need now then extend using connectors when I do need the extra length.
What do you guys think?
Cheers Jim
26 CT 3427
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BigTone
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Equipment Used : CRT 9900, Yaesu FT817, Kenwood TS570, Icom 910
Age : 65

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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeMon Apr 13, 2020 6:59 pm

Nope, shouldn't do.
Connectors out there are a point where moisture can get in and ruin your coax
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NUBSTER
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Call Sign : 26 CT050 26 FB080 26 WT105 26 TE171
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QTH or Location : NORTH LONDON
Equipment Used : original President Lincoln, Midland 8001XT, President Teddy , Silver Eagle microphones , Gainmaster antenna, use a AMP ofcourse I do sometimes
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeMon Apr 13, 2020 7:24 pm

Do not coil it up either that will effect SWR of the antenna, connectors are alright if you dont use loads and if you insulate them properly with proper water proofing there ok,I have one connector in my run of coax to the antenna to the shack I had no choice as I move my shack from a room in the house to a purpose built one in my garden and it was too much trouble and not cost effective to go and buy a whole new length of coax when I had some extra and a connector mines been up over 8 years never had a problem with water leaking.
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Cozzmik
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Apr 14, 2020 8:09 am

While i have no idea if it affects Swr coiling my coax was necessary one time as i wanted to do a similar thing to you..

Swr was fine but i had no idea if it could of been affected coiling it as i had no reference point to check..



Try and see is always my advice....
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NUBSTER
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Call Sign : 26 CT050 26 FB080 26 WT105 26 TE171
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QTH or Location : NORTH LONDON
Equipment Used : original President Lincoln, Midland 8001XT, President Teddy , Silver Eagle microphones , Gainmaster antenna, use a AMP ofcourse I do sometimes
Age : 62

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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Apr 14, 2020 9:19 am

Sorry mate I forgot to give the reason of not coiling, way back in the early AM illegal days when I first start we was all new to CB and learning,anyway we was told when you put up the homebase antenna the coax had to be cut to certain lengths because of the wavelength and to get a perfect SWR (which I did and found out it was bit of a myth doing this) so that's what I did, trouble was I ended up with loads of coax all around my bedroom which was in the way and my mum said clear all this bloody cable up (still young  and living at home) so I naturally wound it up,  only to be told by a family friend who in to radio communications who saw my coil of coax one day and asked why have you done that ,so I told him the story and his answer was dont coil it up like that because it will he started to explain but I switch off he got too technical lol all I know I couldn't get my SWR to go under 2.5 loose on the floor  to 3.0 when wound up ,but also I found out that you dont need the so called magic length of coax for the perfect SWR you just need the amount of coax needed from your radio equipment to reach the antenna which is what I did in the end and my SWR dropped straight down to 1.3 across the 40ch (only had a 40 ch when first started) after I cut my coax to the length I needed so on the advise from the family friend so I never coiled up my coax or cut it to magic lengths lol
Sorry  it was a long winded post
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Javelin Jim
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Coil or not to coil coax Empty
PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Apr 14, 2020 10:29 am

Hi,
I love waffle...! Waffle is good, I am also a huge waffler...😊
Thanks for the advice guys.
Cheers
Jim
26 CT 3427

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NUBSTER
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Call Sign : 26 CT050 26 FB080 26 WT105 26 TE171
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QTH or Location : NORTH LONDON
Equipment Used : original President Lincoln, Midland 8001XT, President Teddy , Silver Eagle microphones , Gainmaster antenna, use a AMP ofcourse I do sometimes
Age : 62

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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Apr 14, 2020 12:01 pm

The only thing is Jim , that when people say there making a balun to go under the antenna now that is coiled coax of a certain number of turns around a piece of tubing I think about 6inch in diameter it's to help stop RF  somebody on here hopefully can explain in better detail that me , but what I'm get at it does contradict the coiling of coax thing ,like I said perhaps someone who can explain it better will post the answer.
I might have been around CB for many many years but dont claim to know it all but I know enough lol
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BigTone
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Apr 14, 2020 1:41 pm

The choke is to stop RF on the OUTSIDE of the braid (Common mode current)
RF travels on the surface of a conductor and on coax, there are 3 surfaces.
(1) The core (the centre conductor)
(2) The inside of the braid
(3) The outside of the braid

Common mode current (mainly) is a pain but there is a use, the lower leg of a coaxial dipole (T2LT) The choke defines the length.
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Northern Crusader
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Apr 14, 2020 8:38 pm

NUBSTER wrote:
Do not coil it up either that will effect SWR of the antenna

Sorry but that is wrong and your entire post explaining it all is wrong. If it does alter the SWR it is because you've a poor RF ground so your coax was forming part of the antenna system.

Quote :
anyway we was told when you put up the homebase antenna the coax had to be cut to certain lengths because of the wavelength and to get a perfect SWR

....because the coax was making up for the missing ground plane so altering its length either by cutting it or coiling it up thereby creating a RF choke affected the tuning. Unfortunately next to no CBers understood this so it became an old wives tale you had to have it a certain length for low SWR.

If changing the length or coiling the coax alters the tuning of the antenna then it's telling you you've got a problem with your RF ground at the antenna.


Last edited by Northern Crusader on Tue Apr 14, 2020 8:44 pm; edited 2 times in total
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Northern Crusader
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Apr 14, 2020 8:40 pm

Javelin Jim wrote:

Would coiling the excess length (approx 3-4m)at the antenna end affect the performance?
I could cut it to the length I need now then extend using connectors when I do need the extra length.
What do you guys think?
Cheers Jim
26 CT 3427

No it shouldn't do but you can put that extra length to use. Find something that's 110mm/4.25" in diameter (ground waste pipe is spot on) and wrap 5 turns of the coax round it as near to the end that goes into the antenna as possible. This will create a RF choke for 11m which will help reduce the risk of common mode RFI which causes interference on received signals, distortion on transmitted ones and the dreaded TVI.

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NUBSTER
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Call Sign : 26 CT050 26 FB080 26 WT105 26 TE171
Posts : 553
Times Thanked : 39
Join date : 2019-06-27
QTH or Location : NORTH LONDON
Equipment Used : original President Lincoln, Midland 8001XT, President Teddy , Silver Eagle microphones , Gainmaster antenna, use a AMP ofcourse I do sometimes
Age : 62

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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeWed Apr 15, 2020 7:16 am

I said someone would come along and explain it, and thankyou Conner for trying to make me look stupid as you always do to people who make mistakes ,I did say I didnt know much about it back when I first started cb, in 1975 I was a 15/16 year old just wanting  to talk on the radio and TBH I don't know much more now but I know enough, but people like you who have the knowledge should be more helpful and not a sarcastic git ,but anyway thanks for info

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26TC62
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeWed Apr 15, 2020 8:15 am

Buy the full length of coax now and coil it up. The reason for not coiling up coax used to be that most people were using horrible RG58 with thin braid which had all sorts of consequences for the behaviour of the current in the coax. One of the effects was that the inner core of the coax started to behave like the turns of an ordinary coil inductor and screw the SWR. Properly screened coax can be coiled, because the inner core is properly screened from the inner core in the next turn of coil and it doesn't "know" it is coiled up.

If you're using a run long enough to go into a garden you probably want to think about RG213 as a minimum anyway, because it is lower loss and much nicer than even the good RG58 some dealers sell now (there is still horrible stuff available -watch out for Ebay etc). You can coil RG213 up happily but try to keep the turns above 8" diameter unless you are making a coil out of it which you never intend to unwind and re-route. You can fix RG213 in turns with a couple of inches radius for permanent fixing.

Avoid in-line connectors and extension pieces if you can - better to overbuy the coax and coil it in the long run than have PL259s and back-to-back SO239s because they are a point of mechanical and electrical failure.
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Javelin Jim
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeWed Apr 15, 2020 10:58 am

Thanks for all the advice guys.
Really useful information.
I’m expecting the delivery later today of my gear, so the fun will start, so expect more questions...!
I plan to use around 27.500 to take SWR readings. If I get can that low, I’ll write out a frequency/SWR chart to see how the SWR changes above and below 27.500.
Cheers
Jim
26 CT 3427
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Northern Crusader
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Call Sign : M0GVZ / 26CT1760
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Equipment Used : Icom 7300, TS480, President McKinley, Albrecht AE6110, CRT Mike
Age : 50

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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeThu Apr 16, 2020 8:53 pm

Depending on how enthusiastic and how much you want to learn about antennas and experimenting have a look at the nanoVNA analysers on Amazon. They're about £30 and are much more useful than a SWR meter especially when you put up an antenna and its low SWR point is outside the CB bands. With a normal CB SWR meter you'd only be able to test within the range of the CB it's hooked up to so you could see high SWR on every channel and assume the antenna was broken when in fact it wasn't, it was just tuned outside the CB band.

An example is my mobile installs. I have a very good RF ground but unfortunately manufacturers make mobile antennas assuming there won't be a good one which means they need to be made longer. Adjusting the antenna throughout all its adjustment from shortest to longest you'd see the SWR into the red using just a SWR meter. Using the antenna analyser allowed me to see it was actually resonant about 1MHz below the CB band. 3" lopped off with a dremel and it was 1.0:1 right where I wanted it on Ch19.

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43CT016
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PostSubject: Re: Coil or not to coil coax   Coil or not to coil coax Icon_minitimeTue Jun 09, 2020 12:20 pm

Talking of chokes, probably one of the best articles out there is this one:

http://www.karinya.net/g3txq/chokes/

You’ll see from his graphs why the 5 turns of RG213 on 4” pipe is always cited, and if you can wade through all the complex impedance theory, there’s a good explanation of why co-ax chokes can bite you, having a predominantly reactive impedance.

I run his “designs” on all my HF antennas, usually using either 240-31 or 240-43 cores and LMR200 or RG400 depending on what antenna they’re on.

With regards to the OP, I’d echo the answers above and not cut the coax....just coil it loosely out of the way. The old wives tales from the early CB days will never leave us, I feel.

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