Length of antenna cable

[bradbald]

Hi guys,

Foregive the stupid question, but:

Everyone knows the shorter the lead the better but is there and operational maximum length that could be achieved? The cables on the antennas are too short to be mounted up a small tower, however I'd like to so that I can clear some trees and gain some more height.

Also, what is the best way to join the cables if I do choose to extend them?

Currently I have a 6dB GME VHF and a Belden 21-900MHz that serves as my UHF antenna that I'd like to put at least another 10 meters of cable on the end of and just get some crimp ons to make the joins and new ends for connection into the back of the gear. They are just PL259's on the ends currently.

I've found the best antenna for my UBCT9 is a dedicated FM/UHF/VHF Clipsal TV antenna - and it works well.

Thanks.

[Comint]

Everyone knows the shorter the lead the better but is there and operational maximum length that could be achieved? The cables on the antennas are too short to be mounted up a small tower, however I'd like to so that I can clear some trees and gain some more height.

The optium length is one wavelength, or multiples thereof, at the operating frequency, which poses a problem when using it with scanners.

It also depends on the type, and quality, of cable you are using. The RG58 family is probably total 30 metres maximum (existing cable plus extension). RG213 can be longer.

Also, what is the best way to join the cables if I do choose to extend them?

Currently I have a 6dB GME VHF and a Belden 21-900MHz that serves as my UHF antenna that I'd like to put at least another 10 meters of cable on the end of and just get some crimp ons to make the joins and new ends for connection into the back of the gear. They are just PL259's on the ends currently.

You can purchase an in-line joiner that will mate with two PL259s. Just make sure the joins are waterproof, by using self-amalgamating tape, or similar.

You can also buy a line socket (inline SO239 - as shown below) that will mate with a PL259, although they are not as readily available as PL259s, or the in-line joiners.

SO-239_In-Line_Crimp.png

These are available from http://www.radiospecialists.com.au in South Australia

--
Comint

[rochedalescan]

I guess it depends what type of cable you are using for RG58 it will be absolute crap over a long distance if it's something bigger like RG213 that would work alot better, for connecting two lengths of coax which would probably be a last resort, if you can try and have just one run of coax because you will have some loss in a connector. I'm not too sure if you can get these for the thicker coax/ would be as effective over a long distance but I got like an egg shaped capsule from Jaycar it's only a few $ from memory and the plastic casing splits in the middle exposing two ends which you thread the coax through then screw the down to crimp together and then enclose in the casing.

Edit: this is what I have http://www.jaycar.com.au/productView.as ... rm=KEYWORD but it wont fit RG213, you would have to buy proper screw on connectors but I would try and just have one run not using any connectors therefore having minimum loss

[Azoic]

Depending on the cable....length is not an issue.
RG-58 C/U loses over 9Db at more than 100 foot. RG-213 loses about 3Db.
450 Ohm Ladder line loses less than 0.5 Db on runs below 500 foot.
Belden 9913 loses a whopping 17 Db at more than 110 foot runs.
RG-8 loses 4 Db over 500 foot.
The loss is both received and transmitted power loss, and is comparable to voltage loss or VSWR.
How high do you want to go with your antenna ? How much bend can your feedline cope with ? Does it require a rotator for a directional antenna ? All these and more factors determine what feedline you should run from your radio/tuner to your antenna.

The ONLY time length comes into the equation is for TUNED feed antenna's or for the patch between radio and an amplifier. For a scanner receive only antenna, the best length i found is ant + h + 15 to allow for stretch and shrink. So the antenna length plus the height + 15 foot to adjust. So for a 27 Mhz dipole at 40 foot high it would be 17.8 + 40 + 15 = 72.8 foot of co-ax. For a discone or top hat antenna, use height + 20 foot + 15 for stretch and shrink.

[Kevaclone]

limit the number of connectors so avoid the barrel connector and use a male/female so you only have one connection
Also use "N" type as they have less loss than the PL259/SO239 connectors

[RADIOHEAD]

@ azoic

I do not mean to be critical, but you have posted loss figures for coaxial cables without the appropriate frequency information. Without this, the loss figures are somewhat meaningless.

[Azoic]

I have tried for 45 minutes to post a reply and finally have given up, all i get is a time out. My post contains no explicit language, no threats, and no insulting data to other users, but it wont submit, so i gave up.

[rochedalescan]

You managed to post that one so what's the problem ? or was this at the time of your last post ? I don't think we have had issues with that sort of thing before.

Cheers Shane

[Azoic]

You managed to post that one so what's the problem ? or was this at the time of your last post ? I don't think we have had issues with that sort of thing before.

Cheers Shane

This seemed to post fine, but a longer reply just wouldnt , is there a limit on the amount of words available ?

[rochedalescan]

It was set to 60,000 characters I have set it to unlimited now so try that. Otherwise you might need to clear your cookies or something.

[Azoic]

It was set to 60,000 characters I have set it to unlimited now so try that. Otherwise you might need to clear your cookies or something.

I shall try that, i meant NO OFFENCE to the board or user's, just had no reason come to mind as to why my reply post was hung up. A single line post worked fine, but the lager one didn't post. I will try breaking it into 2 parts.

[Azoic]

It was set to 60,000 characters I have set it to unlimited now so try that. Otherwise you might need to clear your cookies or something.

Im PM'ing the message as typed to you. See if you can post it, i have run out of idea's. This is the 1st time i have had an issue on this board.

And the PM failed aswell

[Azoic]

@ azoic

I do not mean to be critical, but you have posted loss figures for coaxial cables without the appropriate frequency information. Without this, the loss figures are somewhat meaningless.

The most important part of the post i tried to add is this.....the co-ax length is not important. the resistance and inductance is, the co-ax can run any freq. over any length, but loading improper co-ax with non compatible frequencies is detrimental to an efficient feed. The inductance, minus explicit Ohms impedance is the formula. Look it up in the Antenna handbook

[stickybeak]

Best of all to avoid having any connectors at all. I was in a hurry to get my co phased 10 element 2 metre yagi's up so did a feedline out of three offcuts of cable left over from other jobs, 6 PL 259's two barrel connectors etc a few months ago I finally replaced the feedline with one length of LMR-400 and now I am hitting repeaters up to 400km away that I had never heard before.
I used to always make my feedlines in 1/2 wave length increment but saw no real advantage in it , no matter what the length of the feedline was, I never saw the swr change appreciably. Now I just put up the shortest possible length and make sure losses are kept to a minimum.

[Vkfour]

I too have had replies all typed up ready to go, press to send and they disappear into the void.