Radio antenna connector wired wrong??

[FishFinder]

Hi -- so I am attempting to hookup a new radio (Icom m422) to the antenna my boat (1980 S2), and I am having trouble getting reception. The old antenna connector was trashed so I cut the wire and have tried using several different connectors from radio shack, all of which do the same thing: I get reception only when just the tip of the connector is put into the radio. As soon as the outside (ground?) part touches the radio, reception stops. I have made sure that the braided part of the antenna wire is NOT touching any part of the main wire. And I've even tried omitting the connector altogether, and just push the bare central wire into the radio -- same thing, reception is fine but if any part of the braid touches the outside of the radio's antenna connector reception stops. Any ideas?

[mguenthe]

If you have signal with the shield disconnected but non with it connected
you probably have a short in the system. The cable, connectors (either end)
even the antenna. I would first disconnect the antenna from the cable and
check for a short or open. If the cable checks then look at the antenna

[Omatako]

Yep, I reckon it's a short between the sheild and the antenna wire. The easiest way is check it with a good ohm meter, visual inspection is probably not good enough.

Andre

[btrayfors]

Many VHF antennas will show a dead short with DC current. They are designed this way to reduce noise (they pass RF just fine). So, a simple ohmmeter test will not necessarily tell you anything.

That said, I'd agree that it sounds like something wrong in the coax, the connectors, or the antenna itself. You need to check/replace all. Relatively cheap insurance.

Bill

[Gary1]

Here's what I'd try and do:

Talk to a boater friend and see if you can hook your new radio to their antenna. If it works normally, then you're sure your antenna/coax have a problem. I know that sounds dumb, but never assume a brand new piece of electronics equipment is good straight out of the box. Since I spent 35 years working in that business, I can tell you we had more DOA circuit boards, etc., than you can imagine in your worst nightmare.

Also, most electronics devices, if they're going to fail, fail during the first 5 or 6 hours of use.

If the radio works on another boat with another antenna, you have your problem isolated to your own antenna or coax.

To isolate it further, you need to run a temporary coax from your antenna to your radio. If this is a masthead rig, I know it's a pain, but your options are a very long coax or pull the antenna down. At least you'll have separated the problem.

Long experience tells me to suspect the antenna, but you don't mention whether it was working before you changed radios, or why you changed radios. If your original radio blew up, I'd definitely suspect the antenna.

Last thing: until you've absolutely isolated the problem, don't transmit. Not even for a second, or the radio will go up in a small cloud of smoke. The transistors in the 'final' amp don't like seeing a short on them.

good luck.

Cap'n Gary

[camaraderie]

You need an emergency antenna anyway...so buy one and hook it up. If it works, you know you have a cable antenna problem.

[SEMIJim]

FishFinder,

You should have an emergency antenna aboard, anyway, so get yourself one of those with which to test your radio. They're about $50 or so.

You should have a digital multimeter aboard, anyway, so get one of those with which to test your coax. Cap'n Gary pointed out that Harbor Freight sells a pretty decent one for about $40.

Hook radio to emergency antenna and test. If the radio works: It's your coax or antenna. Doing this test first may save you an unnecessary trip up the mast.

Disconnect antenna from coax. With meter set to minimum resistance range (continuity test): Check for a short. If it shows "open," run the resistance range up, looking for a higher-resistance almost-kinda-short. It should measure "open" all the way.

Short the far end of the coax. With the meter set back down to "continuity" range: Make sure you measure an exceedingly small amount of resistance--on the order of a half an ohm or so (assuming good, solid connections at both ends--see note below). Just for s&g's, I just checked what I estimate to be about 50' of vintage Belden 8214 RG-8/U and read 0.4 ohms. Perhaps 100' of the smaller coax would measure up to an ohm or so. Sorry: Don't have that around to test.

If the coax' DC tests come out well, it's your antenna. If they don't, well, it's your coax.

A note on procedure: It can be harder than one would think to establish good connections to antenna connectors. Put both meter leads on either the outer body or center conductor part of a connector, with the meter in continuity range, and you'll see what I mean.

Jim

[sailingdog]

You should probably get an SWR meter, since they're less than $60 or so...and it will tell you a lot about your VHF antenna system. Getting the spare antenna and coax is a good idea...