VHF Coax Cable

[Doug Fallin]

I have my mast down and will be installing a VHF antenna. I have found a variety of coaxial cabling on the market with varying prices from $1.19 to $.16 per foot. What should I look for when buying coax?

[Richard Bell]

With the mast down this is the time to go quality. Insure you use a good Marine grade cable. You can find it at any good marine store.

I believe of the top of my head it is called RG-58 or 59. (a little help here from the board) Either way the marine grade is tinned to lesson corroision and improve conductivity to avoid signal loss.

Rick

[Carter Brey]

http://www.westmarine.com/webapp/wcs/st ... xcable.htm

[Rollergirl]

a 3 db decrease in signal strength means the power is 1/2 of its' previous value. 50' of Rg-58 will cut your 25 watt signal to 12.5 watts.

This is informative: http://www.geocities.com/rf-man/db.html

Given the overall mast weight, and the amount of junk that crusers pile on up there (radar, wind indicators, lighting, et al) I would consider the cable weight to be a minor factor.

Go big, go loud.

Bill

[Andy Denmark]

The $$$ invested in a VHF transceiver can be totally wasted by using poor quality coax. In a nutshell, "marine grade coax" from your local marine supply store is probably questionable at best.

Without going into a lot of whys and wherefores about antenna and feedline theory, look for these characteristics: at least 95% outer braid, get the largest size you can physically use (RG-8, RG-213) and if you need to go smaller use RG-8X Mini. Remember that each connector you put in the line reduces power by -3 db so minimize the number of these (one at each end is the best you can do unless it's already terminated at the antenna then there's only one). Use the standard PL-259 UHF connectors with appropriate bushings. Under no circumstances use the "no solder" connectors -- these are short-lived and very lossy. High grade PL-259's and adapters are available at most electronic supply houses at a fraction of the "marine store" price. I like the Mil-spec ones that have the dull silver plating as they are easiest to solder.

For all outside connections use a silicon grease on the inside of the connector and a 100% covering of Coax Seal (or equivalent) to seal out moisture. Be sure to use some sort of strain relief at the top of the mast so the coax isn't just hanging on its connections. Don't crimp the coax anywhere along its length and make the overall length as short as possible (but leave enough slack to work with it).

While all this sounds complicated it's really fairly straightforward for those of us who regularly make antennas (ham radio nuts, boatyards, etc.) The net result is a good peforming and long-lasting communications system that works at max efficiency. After all, it is an electronic lifeline so treat it as such.

Hope this helps
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Winning

[bottomscraper]

Although electrically RG-8X is not as good as RG-8U it is significantly smaller in diameter. You will want tinned wire rather than the bare copper stuff you will get a Radio Shack.

Here is a link to the Ancor web site. It has more information.


http://www.ancorproducts.com/Products/W ... _pag27.pdf

[Doug Fallin]

Thank you for all the advice. I found a good electronic/radio shop that specializes in marine applications. He made up a length of RG-8U with one of the silver ends mentioned by Andy. I will install the other after the mast is up. He also convinced me to go with a Morad antenna instead of the Shakespeare sold at WM. It was about twice the price, but he assured me the difference will be impressive. Does anyone have a comment about either antenna?

[Andy Denmark]

This is my personal favorite for a masthead antenna. It is rugged and simple and also works on 2-meters with a VSWR of <1.5 (on the local repeater frequency anyway).
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TEEN VID