VHF/AIS cable for refit

[jssailem]

I'm re-rigging my mast so while down, replacing wiring and lighting. I have removed the VHF coax and thinking of replacement. I am installing a AIS transponder and will be splitting the antenna with the VHF radio. The cable that is coming off the mast was split at the mast base and is from 1974. I intend to run a continuous lead from antenna to radio (like the radar cable).

I received 100 ft of RG213/U cable in lightly used condition from a HAM radio operator. I have a run from the mast head to the radio of about 75-85 feet depending on routing in the boat.

Wondering if the gift cable would be serviceable?
Or should I purchase some LMR400Ultra Flex for the job?

Appreciate your experience with cables and the effect on reliable VHF transmission.

 

[Bill Roosa]

RG8 is the cable you want. Yes it is larger and there is a reason for that. 213 is for higher frequencies and will give more loss per foot.

 

[Bill Roosa]

also if you have an AIS TRANSCEVER (transmitter and reciever) you need a speerate antenna or you will be dumping RF power into the VHF radio that will most likly be in receive mode. They are not designed to take that kind of wattage while receiving. The wattage in a coax while receiving is measured in miliwatts (.001) You would be dumping like 5 watts (5000 times what it is designed for) into the VHF receiver. The same idea for the AIS reciever also but most have a dedicated receive and transmit antenna port. Read the instruction manual

 

[jssailem]

Thank you Bill.
I am using a splitter developed by Vesper Marine for there AIS transponder and the tuned antenna. The splitter is configured to VHF primary - default use. When VHF not in use the AIS system sends a burst transmit and then passive receive. The RG8 and 213 specs look similar. Issue is I have been led to believe that RG8 is not being made. RG8/X is available but has twice the level of attenuation at 100 feet in the 150 MGhz band where VHF and AIS exist.

Not sure in "at sea situation" if the lower loss difference between the LMR400 and RG213/U will be of significance.

 

[Fred Villiard]

Use the LMR400UF, not only lower loss but it will not wick moisture. If you go to the ham radio thread here I had a post about Belden 213 and moisture it makes a good dummy load.

 

[bgary]

I'm doing the same thing (VHF+AIS, Vesper splitter at the nav station and Vesper dual-purpose antenna at the masthead).

I originally planned to do this with LMR-400UF, primarily because I want to have the best (low-loss) configuration in order to ensure the AIS transponder gets as much signal as possible.

Due to the bulk of the cable, though, I decided to go smaller. LMR-240UF is the same size (0.240") as RG-8X, but significantly less loss. Better specs, very flexible, and it is better protected against the elements, both moisture and UV.

If you have the room for LMR-400UF, it's the best choice (IMHO). If you need less bulk, LMR-240UF is much better than the other small-diameter choices.
$.02

 

[jssailem]

Thanks for sharing Bgary. I have the room in my 42 ft mast. It is more like a telephone pole than a modern mast extrusion. My total run is about 75 ft. The VSRM and dB specs favor the LMR-400UF cable at that length in the AIS/VHF frequency range. I found it for about $1.47 a foot. The experts say I will not be able to tell anything less than 3dB difference. So it came down to the rebate I got is paying the difference in cable cost.

I did find an 87 foot length of lightly used RG213U cable from a HAM operator that is available to some one if interested. FV wrote some history of use that suggested an issue with water intrusion. The RG213U cable I have is from CableExperts and says it is for "Direct Burial". From what I could understand the leak FV reported on the forum may have been associated with an exposed connection. I figured if a leak could happen, the top of my mast was a likely spot. Got some "Coaxwrap" to seal the connection on the mast. It is a tape that sticks to it self, non-adhesive wrap that is said to seal out air and moisture. 5 year reported shelf life. Going to give it a try. Vendor said it is used by Coast Guard to seal connections on their sea buoys. What a sales pitch.

 

[Fred Villiard]

The LMR240 is also good. My back ground is in the cable business, I ran the test lab at Amphenol in Endicott for 14+ years, now working as test engineer for mil spec cables, and the military is just about completely over to the LMR coax.

My headache with the 213 this time, it was buried and a stone punctured the jacket, twice, years ago I had squirrels chew the jacket on my dipoles and got water in using 213, that was before LMR was developed.