# New vhf antenna cable



## jay2k (Dec 21, 2005)

Has anyone replaced this before? I know different cables are available. Wondering if it's an easy install or just shell out the money for new antenna.


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## KaGee (Sep 8, 2006)

New antenna. That coax is a precise length. Don't mess with it. Ya, I know, it sucks. But when you need your radio, you need it. Don't mess around with safety.


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## erie mako (Jan 22, 2013)

Co-ax can be replaced but it isn't easy to do...

When did the precise length stuff happen?
That is a new one to me...


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## jay2k (Dec 21, 2005)

It didn't. West marine sells it by the foot. Seen some copper showing through the insulation so I figure sooner rather than later something will need addressed.


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## Gottagofishn (Nov 18, 2009)

I believe KaGee is spot on. I am not an electronics wiz by any means but what I found from my research and info from my son (who is an electronics wiz) would be that length matters....
Here is one of the articles I looked at when doing my research. Down about the third paragraph it starts discussing antenna length. It's a pretty easy read, pics included.

http://www.boat-project.com/tutorials/vhfant.htm


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## rockytop (Mar 19, 2008)

If it's fraying near the radio, just keep splicing. The main thing is a good soldering job,don't use those screw together fittings.


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## erie mako (Jan 22, 2013)

Cable length or antenna length...two different subjects...lets not confuse topics!


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## Gottagofishn (Nov 18, 2009)

It seems that cable length doesn't matter too much, but it appears it does matter.... here is an excerpt from the above mentioned article. As stated above, I really don't know what I am talking about (as my wife would assure you) these are just someone else's quotes.

*Coax Cable length*. It is permissible to cut coax if it is too long, however, you must make sure the antenna is at least 3ft from the radio. This is an almost universal requirement from most radio manufacturers. At any rate, you probably won't want the antenna that close to you when you transmit. If you decide not to cut the coax, you can loosely wrap up any excess into a large coil if you wish. Coax cable does present some signal loss, and that loss is greater the longer the coax is, so you can improve the performance of your system by ensuring you do not have excessive cable. This loss is highly dependent on the coax type being used, but a good rule-of-thumb for the RG-58 coax that is commonly used by antenna manufacturers is about -3dB loss for every 50ft.

If you have not figured it out by now, a -3dB loss halves the signal. Therefore, 50ft of coax would present a halving of the signal, and if connected to a +3dB gain antenna - doubling the signal's ERP, and the result would be 0dB, or unity gain. However, the -3dB loss along the coax is a true loss in signal strength, while the +3dB gain is only an increase in ERP. Therefore, you must pay some attention to the interconnection of the antenna to the radio. Some antennas come with lower loss coax, such as RG-8X, so if you have a long cable run, such as in a sailboat mast, you may wish to consider low-loss cable.

And, here is someone else's thought's on splicing, connectors and length..... theory says that it depends on how the matching is done.
If the impedance at the antenna terminals is matched to the cable, and the radio device is matched to the cable, cable length is not relevant.
On the other hand, if the something is not matched, impedance will vary according to the Smith diagram along the cable length, so you must choose the right length or add some matching network...

Well then, I should actually do some work here.... I'm not sure the boss would appreciate my new found interest in VHF antenna's and see the value added to this restaurant franchise's home office operation.


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