E32-200 VHF Radio Antenna Problem

[dmoore]

I was wondering if anyone has encountered a similar situation. I bought my boat last year, and over the winter I had the mast unstepped. This season, when the mast was restepped, all electrical systems seem to be working fine, with the annoying exception of the VHF radio, which is now intermittent. The antenna is on top of the mast, of course, and the radio seemed to work fine last season.

Removing the antenna wire from the back of the radio indicates that there appears to be a short somewhere. What happens if I re-insert the wire partially, before the attachment ring touches, the reception is good. The reception disappears when I try to screw down the attachment ring. If I stick a length of wire down into the connector on the back of the radio, I get reception.

The antenna wire to the back of the radio is coax, but I didn't find any coax cable coming from the mast, when I reconnected everything. My radio reception is now either scratchy or non-existent most of the time, but seems to be clear once in awhile. Any ideas? Can someone perhaps tell me, at least, where I should look for the antenna wire coming out of the mast?

 

[Loren Beach]

The coax path from the top of our mast is:
Screw-on connector at the antenna base at the top,
Continuous coax down and thru the exit in the spar that is below the housetop but just above the headliner.
There is another screw-together connector adjacent to the mast exit that is also out of sight above the headliner. There is zipper access in the headliner beside the spar that allows access to that along with the terminal block for the multi-wire cable also coming in there from the wind instrument transducer.
Then the coax continues down a passage under a cabin side teak trim piece to get it under the side deck and back to the screw-on coax connector on the vhf radio.

I hope that the yard replaced the ancient coax when the spar was down. Our wiring was all replaced, along with the mast lighting fixtures, the coax run, and the antenna.... when we had the rig down in '02.
(Original wires in our '88 boat were "Ancor" brand but were not tinned, and coax does not age well, either.)

Hope you track down the path from the mast and find the open circuit.

Regards,
Loren

 

[Guy Stevens]

The Antenna Apears as a short

The antenna has a matching coil in the bottom of it. That is why there is that fat part. It appears as a short when it is hooked up. So just measuring it at the back of the radio is not a conclusive troubleshooting step, unless you have the antenna unscrewed from the top of the mast.

Most likely the problem is that the antenna has had water get into that very same matching coil, and it is no longer the correct inductance / Reactance for a 50ohm load.

Since the radio is transmitting into a mismatched antenna, it is going to power down on transmit to protect the final RF amplification circuit from overheating and being damaged.

Where to start in the troubleshooting:
1> Send someone up the mast, disconnect the antenna from the coax at the top of the mast.
2> Disconnect the antenna lead from the radio
3> Now put an ohm meter on the antenna lead at the back of the radio, and see what you get.
3a> You should get an open circuit.
3b> If you get a shorted circuit, then it is the coax most likely pinched when the mast was restepped,
3c> If Open, then you need to replace the antenna.

(About 90% of the time it is a bad antenna.) (As a matter of fact, I would sent the aloft person up there with a replacement, or have one ready to unpack, and send aloft, as it really is likely the bad component in the system)

Note the insulation quality of the Coaxial cable going up the mast does degrade with time. This does cause increasingly more signal loss as time goes on. This loss coupled with corrosion on the terminals can lead to a situation with an open, or mismatched antenna system, however that NORMALLY appears as an open, when tested with a ohm Meter.

If it turns out to be the cable, then I would try this next.
Verify that there are no cable splices in the bilge. (If there are replace all of the splice fittings, the 2 male pl359's and the Male to Male Barrel connector) If there are no splices (Rare) continue
If that does not solve the issue, then replace the top pl259 connector with a Shakespeare non solder pl259 connector. (It is too hard for most people to solder at the top of the mast).
Check again.
If not fixed, then replace the one at the back of the radio.
If that did not fix it, then you have an internal short in the coax cable (Very Rare, but possible with rough handeling during a downrig, and rerig. The cable will have to be replaced, which is difficult but doable. I have some tricks for that too, so if we get to that point, post again and I will share them.

Most likely however is that this is that antenna.



Guy

 

[dmoore]

Thank you!

Thank you immensely for both replies! I will check it all out and let you know what happens!

 

[Loren Beach]

Antenna Notes

Speaking of the antenna...
I found a picture on the net of one that is fairly typical of the ones we have at the mast head.
In the past, after about a decade of service, I have had one of these get water down inside around the potting that is suppose to protect the coil from rain, etc. The rubber part that seals the top had cracked from UV exposure and the inside top of the potting plastic had cracks in it.
Another one, years later, had issues with the coax connector on the bottom. Note that the part of the coax that comes out of the spar is subject to a lot of UV degradation, as well.

Regards,
Loren

 

[dmoore]

Thanks again, Loren. That looks exactly like my antenna.

 

[dmoore]

Radio Fixed!!!!

Thanks to the help I got here, I managed to fix the radio. The problem was, to coin a John Kennedy Toole phrase, "A Confederacy of Dunces."

Dunce No. 1 was the idiot who disconnected the wires when the mast was unstepped. Rather than search for the coax connector in the headliner, he simply decided to snip the wire. Then the moron compounded the problem by trimming back the outer covering of the coax on both ends, snipping the central wire and insulation, and twisting together the copper shield so that it looked like a single wire connection, not a coax connection.

Dunce No. 2 was me. Failing to recognize a coax cable, I took the two twisted ends of the shield and connected them together with a heat-shrink connector. No wonder the darn radio wasn't getting a signal.

Anyway, I undid the connection, put a new coax connector on the spar end, connected it to the already-installed coax connector that was hiding in the headliner, and the radio works great now.

Thanks again for your help!