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Mobil install..Coax length??

I have to say that I used the same length coax for the wilson when I replaced it, which was 17ft 4in. Don't know if it made a difference or not, with my sirio pl5000, I used 20-22 ft of coax as it's what I really needed to reach where I have my equipment mounted. Swr reading never changed though from switching the factory coax out. If it was longer I would have used it. But with several 50ft and 25ft lengths of lmr240 I possess, I ran that instead. Does the job well and I know I have some quality coax as well. Like posted, there are several different ways that people try to interpret what coax length they need. As long as it is 50ohm coax it should work no matter the length. We don't do this with radio base station equipment (cell site), all coax jumpers are cut to whatever reaches. But never had anyone ever tell me that the coax had to be a certain length unless it specifically calls for it. Like posted above, use what reaches.
 
What it amounts to is that there's no 'magic' lengths. Use the length that will reach from here to there and then tune the antenna so that it has a good match. That's not a simple thingy, there are a lot of factors in it that you have to account for. The 'myth' that there's a 'magic' length that will make everything 'right' is so much 'el-torro-poo-poo'. Do it right and you don't have to worry about it.
- 'Doc
 
As said the correct length is the shortest length from antenna to radio.

I use a screwdriver antenna on my car. It does all frequencies from 3.500MHz through to 29.700MHz. If the length mattered what length do I use on that?
 
If you were selling coax, what would you recomend?

Changing the leght of the coax has no effect on swr. If it does you have a problem and in most cases of pickup trucks it's does to the location and mounting of the antenna/bracket.
I would recomend a lenth long enough to do the job, with out any coils or kinks.
Set the stinger of the antenna according to manufacture.
 
If I were selling coax and my conscience wouldn't bother me, I would recommend the most expensive stuff I had. But, I would recommend using a cable with minimum losses at the frequency range you were going to use it in. For there to be a notioceable difference because of that loss, there would have to be a huge difference in the published ratings. For HF stuff, almost anything from RG-58 to 6" hard line will do just fine. That 6" hard line is quite a stretch, you know, so forget that (unless you just wanna throw money away). There's nothing wrong with using something like LMR-400, but there's really no benefit at HF. AT VHF or higher, you bet, that's what I use too. Fractions of a dB in loss is meaningless unless you have a huge number of them.
I don't sell coax...
- 'Doc
 
Actually,you should go back and reread the previous comments as to why some entity such as Wilson would recommend using a certain length coax for their product. I was referring to forum members and guests. I too had at one time been brainwashed by the cb community about using certain lengths of coax myself until I saw the light. I have a Sirio Performer PL5000 w/magmount. It's got a 12 or 13 foot coax attached to it. Some months back I emailed Sirio headquarters in Italy asking why they've settled in that length of coax. Their reply was simply to provide just enough coax to track the furtherest antenna location providing that I'm using the vehicle as the so called ground plane and not the coax itself.
In a nutshell,I was thinking about that if the forum provided a database with links to radio,antenna,and coax "real" information and not myths that would make it easier for noobs and the (want to learn) misinformed get the info they need to make right decisions on their projects.
Some time back,some local wanted to argue with me on the air with him admandantly declaring that he's used that coax length formula(9' lengths'for thirty years. He didn't want to learn and thought I was the crazy one even though I told him I fought the real facts about coax length on the radio forum I frequent.
I do like sacred cow tipping. :D
 
Lil'Yeshua,
One site that does give 'real' information about antenna systems is 'K0BG's. It isn't the only one by any means, but it does tell you how and why things happen. A lot of the information there is going to seem 'wrong' for a number of reasons, but you really can take it as 'gospel'. It's not a matter of 'faith', it deals with measured results.
- 'Doc
 
Lil'Yeshua said:
In a nutshell,I was thinking about that if the forum provided a database with links to radio,antenna,and coax "real" information and not myths that would make it easier for noobs and the (want to learn) misinformed get the info they need to make right decisions on their projects.
Click to expand...

Sadly it never works out like that because they always listen to the idiot who claims he's been using the 9' formula for 30 years and its always worked so it must be right.
 
Only the ones who would rather resist change,clinging to ignorance while proudly keeping their traditions intact. There are those who want to enrich their lives. I found the real facts but I still have to watch myself among the ignorant and proud.

Some people will go on believing that the gold painted turd that was sold to them is really a lump of gold. :D


P.S. That's why there are forums. People seeking knowledge that they need to make an informed decision. Forums are very useful. I have a issue with a defunct rear window defrost switch on a car I recently bought. I found out that some of the manufactured parts for that car sourced out for money reasons and not for quality. I found a homebrew fix for it that only involved wiring a good momentary switch in parallel,desoldering the bad switch from the circuit board and finding an switch or I could pay $154 for the whole control unit that would probably fail again after a few months.
 
Lil'Yeshua said:
Only the ones who would rather resist change,clinging to ignorance while proudly keeping their traditions intact. There are those who want to enrich their lives. I found the real facts but I still have to watch myself among the ignorant and proud.

Some people will go on believing that the gold painted turd that was sold to them is really a lump of gold. :D


P.S. That's why there are forums. People seeking knowledge that they need to make an informed decision. Forums are very useful. I have a issue with a defunct rear window defrost switch on a car I recently bought. I found out that some of the manufactured parts for that car sourced out for money reasons and not for quality. I found a homebrew fix for it that only involved wiring a good momentary switch in parallel,desoldering the bad switch from the circuit board and finding an switch or I could pay $154 for the whole control unit that would probably fail again after a few months.
Click to expand...
Gold turds, Enriching their lives, The ignorant??? Wow this stuff seems to have hit the heart and sole for you!? Hey what do you think about base antenna coax it seems that ONLY 10 foot sections should be used !!!!
 
hammer0630 said:
Hey what do you think about base antenna coax it seems that ONLY 10 foot sections should be used !!!!
Click to expand...

That's a load of crap too.

Basically the length people are saying you have to use are multiples of a quarter wave. I run a Hexbeam. It works on 6m, 10m, 12m, 15m, 17m and 20m bands. How long should I make my coax? I actually don't have a clue how long my coax is. Its merely the length needed to get from the radio to the antenna when the mast is up at its highest plus a length for the rotator loop. SWR is 1:1 on all of the bands.

The only time that you need to use odd multiples of a quarter wave of coax is when the antenna design is using the coax as the other half of the antenna or you've done such as piss poor job of installing the antenna that it has to use the coax as a counterpoise. And this is where this old wives tale of needing to use 9ft of coax has come from - loads of people who have done piss poor antenna installations and found by using 9/18/27/36ft of coax that they can get a low SWR. The myth is therefore in their minds confirmed and they assume it must be true because they don't have the knowledge to understand why it isn't and why they're seeing the results they are.
 

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