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Coax Jumpers
- Thread starter Mr Clean
- Start date
it isn't that important which type of coax you use for jumpers if they are used indoors just about any decent coax will suffice,its a good idea to keep them very short (under 3 or 4 inches) or 1/2 wavelength long not forgetting the velocity factor of whichever coax you use otherwise with standing waves on the transmission line you may see inaccurate swr readings at the radio end,although it won't change the swr at the antenna in any way.
As they are very short in comparison too your main coax runs the losses will be insignificant by comparison even with rg58c/u.As long as they are up too handling whatever power you put through them you will be fine.
if using an rg type cable,ensure it has a mil-c-17e or mil-c-17f or M17 (with M17 being the latest spec and mil-c-17e being a number of years old and nearing the end of its shelf life) marking on it,if it hasn't its probably cheap imported junk being passed off as better quality cable which is very very common nowadays and usually the cause of many an unsuspecting buyers problems involving coax.
B
BOOTY MONSTER
Guest
as long as its quality coax with quality pl-259's thats assembled properly and will handle the power there shouldnt be any issue .
Same goes for quality pl 259's as does for coax,there is many sellers out there trying to pass off fake amphenol 83-1sp plugs (the original and best pl259),amphenol has a list of all the companies it supplies and their stock levels.its worth checking their website out before you spend those hard earned dollars on pl plugs that may cause problems.
very interesting reading !!
A story about a fishman, a shark and Amphenol # 83-1SP-1050 connectors
"its a good idea to keep them very short (under 3 or 4 inches) or 1/2 wavelength long not forgetting the velocity factor"
I must be misunderstanding what you said! The length of a typical 'jumper' should be long enough to reach from here to there, and that's about it. Length just doesn't matter as long as the characteristic impedance is right (50 ohms normally), and there isn't a lot of losses in whatever kind of coax you used.
Because of how and where they are typically used, a 'jumper' that's sort of flexible is nice.
I honestly can't think of anything that can use a 'jumper' of only 3 or 4 inches length. I'm sure there certainly can be, but I've never run into one yet. And as for an 'electrical' 1/2 wave 'jumper', I can just see several 60 feet long 80 meter 'jumpers' piled up behind my desk. Or maybe 130 foot 'jumpers' for 160 meters? That's just not necessary, and kind'a silly, isn't it? I change bands fairly often, and never change the length of the 'jumpers'. Hasn't seemed to make any difference so far.
- 'Doc
I must be misunderstanding what you said! The length of a typical 'jumper' should be long enough to reach from here to there, and that's about it. Length just doesn't matter as long as the characteristic impedance is right (50 ohms normally), and there isn't a lot of losses in whatever kind of coax you used.
Because of how and where they are typically used, a 'jumper' that's sort of flexible is nice.
I honestly can't think of anything that can use a 'jumper' of only 3 or 4 inches length. I'm sure there certainly can be, but I've never run into one yet. And as for an 'electrical' 1/2 wave 'jumper', I can just see several 60 feet long 80 meter 'jumpers' piled up behind my desk. Or maybe 130 foot 'jumpers' for 160 meters? That's just not necessary, and kind'a silly, isn't it? I change bands fairly often, and never change the length of the 'jumpers'. Hasn't seemed to make any difference so far.
- 'Doc
Doc any self respecting ham uses one of those hose reel thingys to wind up there extra coax when switching bands.
maybe if you'd read the whole sentence instead of jumping in with 2 feet whilst trying to rewrite the laws of physics "AGAIN" you would understand.
"its a good idea to keep them very short (under 3 or 4 inches) or 1/2 wavelength long not forgetting the velocity factor of whichever coax you use otherwise with standing waves on the transmission line you may see inaccurate swr readings at the radio end,although it won't change the swr at the antenna in any way."
if you can't grasp pretty straightforward transmission line theory (which is pretty well documented all over this forum) then i certainly ain't going to get into an argument with you about it.
just to clear things up for you,as cb antennas are generally used over broadbandwidths these days then there WILL be standing waves on the line.Unless of course your using a magical A99 (dummy load/cloud heater) with shite coax (very lossy).
the reason for using a halfwave repeater isn't really worth explaining to you as in another thread you have proven beyond reasonable doubt you don't understand how a swr meter works,despite the fact you are willing to argue with others who do.
"it doesn't measure impedance."
I would imagine you also use the traditional ham secret weapon of an atu/auto atu,in which case swr will read whatever you want it to read,and you no doubt have a perfect 1.0:1 swr on every band and every frequency.
MR;Clean I would take Doc,s advise on this or any other subject, as for Jazzsinger Its like talking to a political service hot line??? Maybe he,s running for office ? I,ve bin into radios for 35 years & never used a 3 or 4 inch coax jumper on any set-up. As for mixing cable here not a problem here. Just my 2 cents! Bob "cordova lucky 13"
Mr. Clean, I can't speak for Jazzsinger, but I suspect his 3" - 4" idea simply means, if you can't use a jumper this short, then at a minimum use a tuned 1/2 wavelength line for the jumper...
What Jazzsinger tells you is good advice to consider, because he knows that your system may show a different SWR, compared to what you saw with your original feed line in use. He is suggesting, if you add length to your feed line that you might expect to see your SWR change and for sure if you have standing wave on the line. Actually the SWR at the antenna has not or will not change like he says. What happens is your resonant frequency shifts due to feed line transformation, and this can cause your SWR meter to reflect a different value of SWR.
Of course 'Doc is also correct, if you just want to talk on your radio. 'Doc just fails to inform you what likely happens if you have standing wave on your antenna system.
Good luck,
Forget all the science, and use what you have. If you order jumpers directly from Yaesu, who should want the best performance from their equipment, they send RG8X jumpers that are 6' long. Length at HF does NOT matter much, as long as you use good quality components that are assembled correctly! Heck, I am using one that is 25'. Works fine for me. Of course, when I get the station where I want it, I will use a more reasonable length. Don't get too caught up in that velocity factor crap, it will needlessly trip you up.
Ive used jumpers of all different types, lengths, brands, quality ETC aslong as you know what the coax can handle and use it in the appropriate place and its a well soldered or put together piece it will be fine.
Yes there is some coax cable better than others but sometimes you need to use what you have until you get some good stuff to replace it or if it works just leave it alone or as it is if its not of importance.
Yes there is some coax cable better than others but sometimes you need to use what you have until you get some good stuff to replace it or if it works just leave it alone or as it is if its not of importance.
Only office i'm running for is "President of cleaning up CB myth".
I love it when people quote how long they've been into radios for,
doesn't mean they ever learned anything though,does it?
"There are none so blind as those who will not see" : John Heywood 1546
As for Packrat's advice of you should be building your own jumpers,I couldn't agree more,its the only way to ensure they are quality.
I'm agreeing with everyone.
Half wave is best if you are afraid your SWR might change and want to see real readings on your meter.
3-4 inch jumpers are not long enough to go from anything to anything unless both items are sitting on top of each other.
Jumpers the length you need plus a few extra inches for movement of you equipment for cleaning is what I use. I know my SWR is set correctly with only radio and antenna in line. With everything in line I know my meter is not reading properly but it hasn't changed the SWR in any way. I'm just fooling my meter. Now I just know that what my meter is telling me is a reference now. If for some reason it goes up then there's a problem.
Make your own jumpers from good coax and good pl259's. Solder and test each one when your done.
"Set it and forget it" as the man says.
Half wave is best if you are afraid your SWR might change and want to see real readings on your meter.
3-4 inch jumpers are not long enough to go from anything to anything unless both items are sitting on top of each other.
Jumpers the length you need plus a few extra inches for movement of you equipment for cleaning is what I use. I know my SWR is set correctly with only radio and antenna in line. With everything in line I know my meter is not reading properly but it hasn't changed the SWR in any way. I'm just fooling my meter. Now I just know that what my meter is telling me is a reference now. If for some reason it goes up then there's a problem.
Make your own jumpers from good coax and good pl259's. Solder and test each one when your done.
"Set it and forget it" as the man says.