VHS and AIS Antennas ? Difference ?

[Red Sky]

You should have done what A64pilot (and myself) did. KISS & lighter.

[PassePort III]

Hi.
Speaking of cable, would it worth to use LMR 400 for vhf?? Cable run from the top of the mast to the radio= 65'

[Gypsyjon]

Originally Posted by tek-noid

Not an expert, but maybe find a Ham with an antenna analyzer and they should be able to tell you the resonant frequency. MFJ Enterprises Inc.

That antenna analyzer will NOT work for VHF radio nor AIS.

It covers 1 through 60 Mhz. That is the 160 Meter band through the 6 Meter band.

VHF radios operate in the 156 through about 162 Mhz range which is much closer to the ham 2 meter and 1.25 Meter bands.

You might find an antenna analyzer for the 2 meter ham band that would go up to 162Mhz or so. Nonetheless, that analyzer is for what we hams call HF bands. High frequencies.

[stormalong]

The post about mounting position is very important. If the two antennas are mounted at the same height a 25 watt transmission on VHF could fry the AIS receiver.

As for using LMR400 for marine VHF - not a good idea. LMR400 uses aluminum conductors and a solid wire center conductor. Neither is good for a marine environment. You could use Superflex 400 but I think the braid on that is also aluminum. The foil wrap on the braid is definitely aluminum. Marine grade rg-213 is the best choice. It should have tinned braid and center conductor. You can buy it at Davis RF for a lot less than at West Marine.

[Dockhead]

Originally Posted by PassePort III

Hi.
Speaking of cable, would it worth to use LMR 400 for vhf?? Cable run from the top of the mast to the radio= 65'

There are different opinions on this, but I personally wouldn't use foam insulator coax for VHF. Too easy to kink it and ruin everything, or water can get into it. And you don't need the small improvement in attenuation, at VHF frequencies. I do use it for ham UHF, though.

[hellosailor]

Unless the antenna cables are both junk, you will see tiny print repeated every foot or so along the cable, saying what cable type it is and who the maker is. "Quirky Cable Company RG-58" or something similar. Unless you bought them both from the same maker, there's a good chance they will be different and the antenna makers can tell you which coax cable they each use, so you can sort them out that way.

Otherwise? The only practical and inexpensive thing to do is buy a decent SWR meter for your radio. Leave it installed, since any sudden change can warn you of a failure aloft. But for now, transmit on the different VHF channels (at low power) and see what the SWR is. On the VHF antenna it "should" be lowest on Ch. 16. And the SWR on any/all channels should be lower with the VHF antenna than it is with the AIS antenna.

Similarly, if your AIS is a transceiver/transmitter? The SWR will be lowest when the AID antenna is being used.

Antennas are subject to a number of "should" factors, depending on how well they are made and tuned, effects from being located next to other metal, the coax cable itself, so they're often not exactly as they "should" be. But an SWR test is about the only practical way you're going to tell them apart, unless the cables have different printing on them.

And if the SWR test doesn't show any difference? Then it "shouldn't" really matter much. Try them one way, then the other way, use whichever seems better to you. As long as the SWR is similarly low you won't damage anything.

[Jim Cate]

Well, despite the worries posted above, I use a standard VHF whip at the masthead fed with RG213 and a Vesper splitter. The SWR analyzer in the Vesper Vision reports that the SWR it is seeing is <1.5:1 most of the time. For unknown reasons, it sometimes rises to around 2:1. None the less, I routinely see ships at >35 miles, and have had others (sailing vessels) see ours at 12 miles.

This is good enough for me. Perhaps you are overthinking the situation.

Jim

[Squanderbucks]

Take One if the cables off the antena end attach a wire to the center wire with something like an alligator clip and run the temporary wire to the other end. Attach your meter to the two wire D’s and check for continuity. If no continuity then check the other cable and that is the one you have determined.

[El Pinguino]

Originally Posted by Jim Cate

Well, despite the worries posted above, I use a standard VHF whip at the masthead fed with RG213 and a Vesper splitter. The SWR analyzer in the Vesper Vision reports that the SWR it is seeing is <1.5:1 most of the time. For unknown reasons, it sometimes rises to around 2:1. None the less, I routinely see ships at >35 miles, and have had others (sailing vessels) see ours at 12 miles.

This is good enough for me. Perhaps you are overthinking the situation.

Jim

Ed Zackery.... anyone using a splitter is using a standard VHF ant for AIS.

I use a dedicated ant but it is just a standard VHF marine band one... works good.

However.... having paid for a dedicated AIS ant I would be wanting to use it.. I think someone needs to go up the mast again....

[Squanderbucks]

Or you could take meter with you to the antenna along with the test wire already attached to the free end Run the continuity test and then hook back up without having to climb again.

[hellosailor]

Jim-
"For unknown reasons, it sometimes rises to around 2:1."
That could be a sign of moisture in the coax, or in the antenna's base coil, if there is one.
Moisture will change SWR, but since it may be absorbing power, it could just as well seem to reduce SWR. And moisture will vary with when it last rained, or whether you've been transmitting (drying it out) or the heat of the day (baking it out) etcetera. And then of course if anything is moving or swaying...
But it does mean something is not right, worth looking into before it gets "worser".

[AlanR]

If the two antennas are at the same height, and less than four or five metres apart, the 25 Watt output from the VHF transmitter could fry the input of the AIS receiver.

I use a conventional VHF antenna on the stern rail, about six feet above sea level, and can receive AIS signals from ships up to 20 miles away. Much more than I need. The Antenna on the stern rail will also serve as an emergeny one for communications, should the masthead one fail. And no interference

[Navi2016]

Originally Posted by Paul L

Is the AIS antenna a generic VHF antenna or one that is specifically tuned to AIS channels? A generic VHF can be used for AIS.

How close a part did you mount these?

The VHF is mounted at the top of the mizzen, the AIS is mounted at the spreader.. enough separation to prevent the spill over ( I hope )

[Navi2016]

Originally Posted by DotDun

An ohm meter will work, but you need a bosun's chair too.

Yes you are correct, I was trying to avoid going up

[Navi2016]

Originally Posted by El Pinguino

Ed Zackery.... anyone using a splitter is using a standard VHF ant for AIS.

I use a dedicated ant but it is just a standard VHF marine band one... works good.

However.... having paid for a dedicated AIS ant I would be wanting to use it.. I think someone needs to go up the mast again....

Yes...... its up the mast for me. Where did I put that harness

Thank you everyone for you comments.

Cheers, Navi