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Old 11-04-2014, 14:19   #1
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VHF Antenna Cable Question

I need to install a couple of VHF antennas, each needing about 60-75 ft. of feed wire/coax. I have the antennas, two 8 ft. Shakespeare std. quality stuff. Free stuff, in fact.
Each of these comes with about 25 ft. of RG58 on it, which comes down out of the ferrule in which the whip is epoxied. Cable comes out the side of the ferrule, through a grommeted hole.

I've done some research online and see that RG8U would be a much better match cable for runs that long. I am planning to import some, but am not clear on how to attach the new RG8 to the antenna. Do you just solder the core and braid from the RG58 to the RG8? Install some inline connector? Should I try to get the 1" aluminum ferrule off the antenna and see what kind of stubs are sticking out of the bottom of it ?
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Old 11-04-2014, 15:15   #2
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Re: vhf antenna cable question

No, don't solder, terminate with connectors. Can you describe the installation? Why such long runs?
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Old 11-04-2014, 15:18   #3
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Re: vhf antenna cable question

I'd suggest using the original oem cable to get the connector out of the weather , then use connectors to couple to the long run cable. Support the cable so that strain doesn't come on the connector.

Most antennas have the boss glued on so removing it isn't easy.

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Old 12-04-2014, 07:45   #4
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Re: vhf antenna cable question

Okay, so it sounds like I can just cut about a three inch pigtail on the attached RG58 and install a connector, which I can secure inside the mounting pipe. Thanks.

We had probably the best radio setup on the island, before lightning took it out last summer. I had an 8 ft. whip on a ten foot pole on top of a house sitting on a little hill, putting the top of the antenna about 75 ft. asl. I had just used two pieces ( 50 ft. total) of RG58 at the time, and we got a nice 50ish mile radius range. The lightning damage to the house was severe, and I am just now getting around to replacing the antenna, feed, radio, and power supply. They were all blown to smithereens. THIS time, antenna on a steel pipe that is grounded. I'm a little slow sometimes, but I do learn eventually. Two lightning strikes immediately above my head in the same year sure got my attention re VHF antenna installations. Same culprit, both times.

El Rubio, the 60 ft. run is from the tip of the mast to the radio in the helm station on a 40 ft. catamaran. The 75 ft. run is from our home office to an antenna mounted on 20 ft. of pipe attached to a porch at home. Two different installations.

It's common here to install marine VHF in homes, businesses, taxi's etc. It was the standard form of communication here until cell phones came out.
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Old 12-04-2014, 15:43   #5
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Re: vhf antenna cable question

Quote:
Originally Posted by Canibul View Post
Okay, so it sounds like I can just cut about a three inch pigtail on the attached RG58 and install a connector, which I can secure inside the mounting pipe.
A well-known corollary to Murphy's Law for electronic installation warns:

Any cable cut to length will be too short.

Leave more of the molded-in transmission line available. You will eventually need it. Make a small loop of any excess. It will act as a choke to suppress antenna current from flowing on the transmission outer shield.
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Old 12-04-2014, 16:46   #6
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Re: vhf antenna cable question

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Originally Posted by continuouswave View Post
A well-known corollary to Murphy's Law for electronic installation warns:

Any cable cut to length will be too short.

Leave more of the molded-in transmission line available. You will eventually need it. Make a small loop of any excess. It will act as a choke to suppress antenna current from flowing on the transmission outer shield.
Thanks for that reminder, and you're absolutely right. And your corollary to Murphy's law might fit in with my own observations after 40 years installing and trouble shooting systems in the subsea acoustics industry.....Rule No. 1: It's Always Connectors.
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Old 12-04-2014, 22:32   #7
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Re: vhf antenna cable question

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Originally Posted by Canibul View Post
Okay, so it sounds like I can just cut about a three inch pigtail on the attached RG58 and install a connector, which I can secure inside the mounting pipe. Thanks.



We had probably the best radio setup on the island, before lightning took it out last summer. I had an 8 ft. whip on a ten foot pole on top of a house sitting on a little hill, putting the top of the antenna about 75 ft. asl. I had just used two pieces ( 50 ft. total) of RG58 at the time, and we got a nice 50ish mile radius range. The lightning damage to the house was severe, and I am just now getting around to replacing the antenna, feed, radio, and power supply. They were all blown to smithereens. THIS time, antenna on a steel pipe that is grounded. I'm a little slow sometimes, but I do learn eventually. Two lightning strikes immediately above my head in the same year sure got my attention re VHF antenna installations. Same culprit, both times.



El Rubio, the 60 ft. run is from the tip of the mast to the radio in the helm station on a 40 ft. catamaran. The 75 ft. run is from our home office to an antenna mounted on 20 ft. of pipe attached to a porch at home. Two different installations.



It's common here to install marine VHF in homes, businesses, taxi's etc. It was the standard form of communication here until cell phones came out.
I was curious because 8' fiberglass whip is unusual on a mast. You must not worry about passing under bridges with an antenna that doesn't flex well.

You definitely don't want 75' of RG58. Cut it a few feet from the antenna and terminate with a connector. Connectors don't cause much loss or impedance bumps at 160MHz, so you can put a male to female splice, or male to female barrel to male and it won't make much difference. Weatherproof every exposed connector, even those not in direct rain.

Ideally, when grounding the new base installation, run the coax all the way down the pole or mast it's mounted on and then route into the building in an upward direction. The purpose is that a surge will not likely reverse direction and travel back up. You can increase your odds by grounding the shield of the coax before it enters the building and add a surge arrestor to divert energy on the center conductor. Also, the ground must be connected the building main ground or you could develop ground loop current or a different path for surges through your radio system.
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Old 21-04-2014, 13:50   #8
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Re: VHF Antenna Cable Question

When connecting to a standard VHF antenna you should consider the weight of a thicker cable.
Another citeria why I like the H155 cable is:
- for refit it has the3 same diameter as RB58
- the outer cable plastic is UV protected, tha will prevent the entry of moisture in medium term
You will find data to compare at:
http://www.dd1us.de/Downloads/Daten%20Koaxialkabel.pdf
Greetings, Willy
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