VHF - Transmitting Issue (?)

[Cpt Pat]

Originally Posted by boat driver

if moisture has found its way into the coax- it will short.

In reference to splitters and AIS in a vhf masthead antenna- this is an example of safety being seriously compromised by combining two independent communication systems into one antenna- if anything happens like this- both are down.

Water intrusion into the coax is unlikely to show a "short" circuit. Pure water isn't conductive, and seawater isn't very conductive (place your ohmmeter probes in seawater and see for yourself). But, if seawater has intruded into the coax center conductor insulation (AKA: the dielectric), you will see some conductance. Any reading less than a few kiloohms across an open-circuit coax cable is a bad sign. A "short circuit" reading (only a few ohms) is likely a shorted coax cable (replace the lousy solderless PL-259 connectors per my post above). The biggest problem with water intrusion into coax is the alteration of its characteristic impedance such that it no longer matches either the radio or the antenna. It only takes a little seawater to cause that problem. If that is the issue, you'll see some reflected power when the coax is connected to a 50 ohm dummy load -- and unfortunately, your only option is will be to replace the coax.

The expensive LMR coax products with a foam dielectric (center conductor insulation) have lower loss than cheaper ordinary coax. That's good. The foam dielectric however is porous and absorbs water. That's bad. It gradually deteriorates in a seawater environment. If you are using LMR cable, you need to be super diligent at keeping a water-tight seal between the connectors and the outer coax sheath. As we all know, it's nearly impossible to keep seawater out of something forever. It'll only buy you time. I just use the cheap stuff and accept the extra dB or so of attenuation loss.

I completely agree that combining the VHF and AIS radios into one antenna is a very bad idea (and also violates the AIS specifications - if you really care). You've created a single-point-of-failure for two critical services, the splitter will probably cost more than two antennas and coax cables (you're only saving masthead space usage and a little weight aloft), and I believe I've tested every splitter on the market (including Vesper's) and found all of them to malfunction under some circumstances. Your AIS antenna doesn't have to be at your masthead. It's nice to see vessels 30 miles away (and sometimes 300 miles away), but do you really need to?

I have both my VHS and AIS antennas at the masthead, but it required weeks of planning, experimentation and hoisting my tabernacled mast up and down a dozen times to get it right. I'm a Ham, I enjoy that stuff. I maintain a marinetraffic.com volunteer receiving station (https://www.marinetraffic.com/ais/details/stations/595) so range matters to me. I presume you have better things to do, so I suggest considering placement of your AIS antenna on a side rail instead.

[Paul Howard]

I had the same problem with a VHF, could receive just fine, but would not transmit.
I eventually tracked it to a weak connection in the power supply to the radio.
Receiving takes little power, transmitting takes much more. The weak power connection would not support the power needed to transmit.

[ranger58sb]

Nil heard today from Sea Tow's radio check system on Channel 27 in Annapolis. Two different radios, both of which heard traffic on Channels 16, 13, and 09. I didn't ask for a radio check on a different channel, though...

-Chris

[JoeDoc]

Chris - thanks for confirming that 27 might be down!

I will be back at the boat on Wednesday afternoon this week and will test SWR and report back to this thread.

- Joe

[RhythmDoctor]

Originally Posted by ranger42c

I can check for the automated Annapolis Sea Tow (Ch 27) response when I'm next at the boat, probably tomorrow.

-Chris

Did you (or anyone near Annapolis) do this check the past couple of months? My VHF seems to work OK, but no automated response on 27. Also, I left it on 27 for a few hours and did not hear any other radio checks on that channel. I’d expect to at least hear Sea Tow’s responses.

Meanwhile, last weekend I was hearing constant radio checks on 16, with appropriate scolding from USCG and others. It seems much more than last year, and if Sea Tow’s service is broken, maybe that’s why.

[JoeDoc]

27 has been down all season. Not sure what's up but yeah the radio checks (and requisite scoldings) have been fast and furious. I do my RC's on 9 and usually get a response. If not, I try 68 or 72. Haven't yet had to RC on 16.

[RhythmDoctor]

Originally Posted by JoeDoc

27 has been down all season. Not sure what's up but yeah the radio checks (and requisite scoldings) have been fast and furious. I do my RC's on 9 and usually get a response. If not, I try 68 or 72. Haven't yet had to RC on 16.

It would be nice if Sea Tow would at least put a notice on their website. There’s an awful lot of people who could be wasting time and money fixing problems that don’t exist.

[ranger58sb]

Originally Posted by RhythmDoctor

Did you (or anyone near Annapolis) do this check the past couple of months? My VHF seems to work OK, but no automated response on 27. Also, I left it on 27 for a few hours and did not hear any other radio checks on that channel. I’d expect to at least hear Sea Tow’s responses.

Meanwhile, last weekend I was hearing constant radio checks on 16, with appropriate scolding from USCG and others. It seems much more than last year, and if Sea Tow’s service is broken, maybe that’s why.

Ah. I did, but then forgot to report back; sorry. 27 wasn't responding.

-Chris

[TBW]

I can hear everything on all channels. I cannot get a radio check lately (27 down) on 68. I am in St Michaels so there are a lot of people who should hear me. If I take a handheld VHF up to the house I can communicate both ways from the boat to the hand held units; about 150 yards. Everything is ICOM. The only thing I can remotely think of is that I have short range broadcasting but not long range. I am a Trawler with the top of the antenna at 29 feet.