Proper coax length

[RI126]

I now what a controversial subjuct this is. I have 50' of RG213 that I am going to use on my lincoln for a base station. I don't need to use all 50'. My question is... Do I need to use 50'? or can I use just what I need to go from the radio to the antenna.
Secondly, what length should the jumpers be going from the radio to the other equipment? should all the coax together equal 50'? [/b]

 

[EDUK8TR]

I now what a controversial subjuct this is.

Yes it can be.

I have 50' of RG213 that I am going to use on my lincoln for a base station. I don't need to use all 50'. My question is... Do I need to use 50'? or can I use just what I need to go from the radio to the antenna.

I have followed the following advice offered to me by a trusted technician. Mark your coax run in 9ft increments. Once you get the coax in the house and decide how much slack you want or need, cut it at one of the markings and install your Pl-259.

Secondly, what length should the jumpers be going from the radio to the other equipment? should all the coax together equal 50'? [/b]

I would use jumpers in 3, 6 or 9 ft lengths.

 

[AMPOWER]

A 50' section from antenna to the meters is just fine...
3',6' or 9' jumpers as stated above for meters to radio etc...
if 50' is too much then its better to have a little extra than not enough... unless you can get away with 21' from ant to radio??


AM POWER

 

[RI126]

I will stick to 50' and find some way to pick up slack. I will also use 3' jumpers from radio to meter, from meter to Low pass filter( which I'm not sure will work but, must try. Hopefully it will cut down on interfereing with the neighbors) and then the coax out. Thanks to all

 

[Moleculo]

Ideally, as short to the antenna as possible. Between components, you can use whatever you need. However, you may find that certain components will not be "happy" with certain lengths of coax, usually because a component's input impedence isn't right at 50 ohms. The most usual culprit is an amplifier. Also, with multiband antennas you may find certain bands that won't be able to tune with whatever length of coax you're using. In that case, adding an odd 1/4 wave length segment for the band you need can help solve that problem.

 

[RI126]

So are you telling me that I can get away with less than 50' and if so should I keep it at even footage such as 48,46,44 and so on or can it be 49,47,45 not 47-1/2 or 48-1/2. should all coax used for antenna and between equipment equal 50' or it doesn't matter By the way I saw your pics, looking good. Nice job mounting the antenna to your jeep. I have a jeep cherokee and wonder how to mount an antenna with out putting holes in the body. I was going to use a 102" whip but couldn't bring myself to cutting a hole in the body. RI126

 

[Moleculo]

Hey, thanks for the compliments on the Jeep....that took some work.

It really doesn't matter on the coax. It can total whatever length you have. The thing about "magic" lengths is that kind of advice or reasoning doesn't take into account something called velocity factor. Without getting into too much detail (unless someone wants it), different types of coax have different velocity factors, which affects how long the coax looks electrically. So 50' of one type isn't the same as 50' of another type, even if they're both 50 ohm coax.

 

[RI126]

should coax be the same as the jumpers. I'm using RG213 for the antenna. should the jumpers be the same or can I use RG8

 

[FL Native]

use what ever kind of coax you want as long as its 50 ohm coax.

so using rg8 and 213 is fine. also between your radio and antenna use what ever length you want. just keep in mind you only get an acurate reading on your swr meter with multples of 1/2 wave lengths for the freq you are listening to. other than getting an acurate reading at your radio end of the coax. the length makes no difference. so the answer your looking for is use what ever length of coax you want to go from your radio to your antenna.


hope that helps you out 8)

 

[RI126]

AAAHHH!you have to remember I am GREEN when it comes to 1/2 wave lengths and such. It has been along time since I set up a station. The last one I set up I used 50' of coax and just through it up with a Big Stick. I don't even remember having a SWR meter( I think I may have borrowed one to check SWR). It worked fine, talked all over the world. Do you think you might give it to me the Kindergarten version. I did comprehend the use of "what ever legth you want" and also the different coax.NEWBEE

 

[AMPOWER]

Ok....The RG 213U is a 66% velocity factor...
And the Mini 8 is a different velocity factor because the insulator of the coax is not the same bettween the mini 8 and the 213U...So because of this point...the lengths change...
there is a math equasion for the lengths in the ARRL handbook...
But you have to have the velocity factor,frequency,and something else...Moleculo?? im shure you know what i mean??

Ill look in the ARRL handbook i have and see what i can find on it for a reference....
(there is a difference in the lengh of the coax that you use depending on insulation type and freq use....)

Edit: (id use all the same coax type for the antenna and the jumpers)

AM POWER

 

[FL Native]

ok to get an acurate reading the proper way is to check your swr at the feed point of the antenna but since its way up in the air that is not allways easy to do.

your using a imax 2000 so do it like you did last time throw it up there use what ever length of coax you want and just ajust for lowest swr's with the coax length you have with the tuning rings on the antenna.


not dont worry if you dont get a perfect flat match cause the coax length could be giving you a false reading and changeing the coax length will just fool the meter. so just try to get even readings on channel 1 and on 40 and the lowest reading on channel 20. as long as the meter shows bellow 1.5-1 leave it be. forget about this thread and go talk.


now as far as 1/2 wave lengths..... 11meter (cb channels).
1 full wavelength is about 36 feet. so 1/2 wave length would be 18 feet. 18 X 3 = 54 so 50 foot is real close to 3 1/2 wave multiples.

 

[Peddler]

Personally I would use RG8X on the bench and for jumpers. It is smaller than the RG213 and a lot easier to handle. RG213 is really good for the antenna.

JMHO

 

[FL Native]

AM Power is right to get the right 1/2 wave length multples it does change depending on coax type cause of velocity factor freq your on and so on.

there is a web page somewere set up to tell you exacly but dont remember were it is and ya Adam it is in the arrl handbook aswell the equation for it.

 

[DXman]

Here is what you need for your VF of your coax.
http://www.signalengineering.com/ultimate/coax_basics.html
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DXman