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Old 05-04-2019, 05:27   #1
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VHF - Transmitting Issue (?)

Hello from Back Creek in Annapolis.

During spring commissioning last weekend, I noticed that I wasn't getting my traditional radio check response from Sea Tow on 27. I tried a radio check on 68 and 72 as well but came up with nothing. Had a friend show me how to use a multimeter to check for resistance (great lesson) and he said there was an issue and it was probably at the top of the mast (45').

I took a day off work yesterday and climbed the mast (my first time up) with a spare antenna (just in case). The connector screw on the wire was very loose (which could have been the problem) but the antenna looked original to the boat and quite worn so I decided to just install the new one.

I descended and tried 27 and still got nothing. I (reluctantly) hailed on 16 and got no response. But my friend went over to his boat about 50 yards away - and I hailed him on several different channels and he came back loud and clear every time. He said I was coming in loud and clear every time as well on his radio. Note that I had my VHF set on 25W for all above referenced radio checks.

Could the automated radio check on 27 be down (and just early season quiet on the other channels) and I'm fine - or might I have an issue where my VHF is only transmitting very short distances? Any help, advice or guidance would be appreciated.

Joe
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Old 05-04-2019, 06:09   #2
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Re: VHF - Transmitting Issue (?)

Hello Joe,


If the masthead connector was loose (and therefore not weather-sealed), there is an excellent chance that the coax has filled up with water, which will make it extremely lossy for radio frequency energy. This will affect both transmit and receive - have you tried tuning the various weather channels to see if you can hear the same (hopefully distant) ones your neighbors are? Are you hearing the USCG broadcasts on 16 and 22A? In Annapolis, I seem to remember that the USCG prattle was pretty continuous (at least on weekends).

If not, I would look at replacing the cabling.



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Old 05-04-2019, 06:20   #3
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Re: VHF - Transmitting Issue (?)

Thanks Hartley. Yes, I am receiving just fine. Weather channels come in as previous and I can hear the regular chatter on 16 and the bridge to bridge traffic on 13 just fine as well.

Great point about the exposure to the elements and the coax. Though I'm hoping that my RX quality means that the line is not totally gone.

I'm currently reading all about Antenna Radio Testers and specifically VSWR which may help me continue to diagnose.

Trying to do as much as I can at deck level before having to go up the mast again! Thanks again for your reply and clues, much appreciated.

Joe
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Old 05-04-2019, 06:25   #4
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Re: VHF - Transmitting Issue (?)

G'day Joe,
a couple of things I found when I had a similar problem but I discovered when my AIS was working intermitantly. We actually had several issues which made trouble shooting the problem just that little bit trickier. The things we found that contributed to the overall problem were as follows.
1) The outer copper shielding was badly corroded where it was exposed to the sea air. We cut away the bad sheilding and put in a new peice of cable.
2) The connector where the aerial cable from the mast entered the boat was badly corroded. Removed the connector and corroded cable and replaced. Improved Connectivity substantially .
3) Our AIS splitter was also faulty which caused issues with the VHF radio. Had to replace the splitter and now all the issues have been rectified.

Not fun having more than one problem but that was me


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Old 05-04-2019, 06:35   #5
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Re: VHF - Transmitting Issue (?)

Hopefully not but transmissions without a load (antenna) can blow or damage the finals. Thatís the last amplifier in the radio transmit circuit.
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Old 05-04-2019, 06:35   #6
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Re: VHF - Transmitting Issue (?)

Our local Sea Tow auto radio check isn't working either. We use channel 28.

I don't believe it's worked since late last year.
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Old 05-04-2019, 06:39   #7
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Re: VHF - Transmitting Issue (?)

Hi Again Joe,


The fact that you're hearing things is a good sign One thing that will degrade transmit but not so much receive is if the ground/shield side of the coax is open - either thru corrosion or mechanical breakage - this will raise the SWR and cause your transmitter to go to low power (to protect itself) but won't significantly cut back your receiving ability.

I'm 110% in favor of SWR testers on every boat - they aren't expensive, and will make a very good initial troubleshooting step - and will tell you if your transmitter has pooped out, etc.. Once you get everything sorted, note your readings in the log and compare if poor performance is suspected in the future. You can also spot gradual degradation in time to arrest it.


Good Luck!


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Old 05-04-2019, 06:42   #8
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Re: VHF - Transmitting Issue (?)

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

-Chris
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Old 05-04-2019, 07:00   #9
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Re: VHF - Transmitting Issue (?)

Quote:
Originally Posted by Hartleyg View Post
I'm 110% in favor of SWR testers on every boat - they aren't expensive, and will make a very good initial troubleshooting step - and will tell you if your transmitter has pooped out, etc.. Once you get everything sorted, note your readings in the log and compare if poor performance is suspected in the future. You can also spot gradual degradation in time to arrest it.
Will pick one up this week and log readings over time as suggested. Great tip and thanks.

Joe
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Old 05-04-2019, 07:09   #10
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Re: VHF - Transmitting Issue (?)

The problem with using a multimeter to check an antenna is not conclusive. Because you are checking DC path, not an AC path. Radio frequency transmission are AC sine wave. The multimeter will only tell you if the cable is open (broken conductor) or closed (shorted conductor).

VHF antennas usually have a coil in the circuit. Using a multimeter will show a short with some resistance. This will tell you that at least the path exist. But this is a DC path, not an AC path.

The transmitted radio wave is a AC component. It is a sine wave. So even if your have a good DC path, the AC path might be faulty. This is where you would use a SWR meter, or a power meter to test the system. An SWR meter at the radio will tell you if the antenna and cable are showing any return energy back to the radio. We want the SWR to be low like 1.1:1. If the SWR is like >2.0:1 then there might be an issue.

To check power, you can go back up the mast with a power meter and a 50Ω dummy load. First check the power at the back of the radio. Then up the mast and connect the cable to the power meter and dummy load and check the power again. This will tell you if the radio is producing the correct power output at the radio and will tell you the loss at the end of the cable. If the loss is excessive then the cable needs to be replaced.

But like you said earlier, maybe the Sea Tow system is down.

OT... why is there always a double-space after each paragraph? Very annoying.
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Old 05-04-2019, 07:16   #11
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Re: VHF - Transmitting Issue (?)

Brian - thanks for this. I was just reading up on the DC vs AC challenge and my head was spinning. Your explanation simplified it for me. Thanks.

I am getting a SWR meter ASAP. Thanks for the guidance on the readings.

Good plan on the power meter and dummy load. Chris (above) has graciously offered to check 27 (he is nearby Annapolis on Selby River). I'll wait for his update before ascending the mast again.
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Old 05-04-2019, 08:57   #12
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Re: VHF - Transmitting Issue (?)

Same problem. Same location.

I was hearing the WX channels just fine but was not communicating with other channels. The SeaTow channel worked, but we are only a 100' from their transmitter so that was not indicative of our problem. Upon checking the antenna after testing with SWR meter, we found the screw holding the wire mast was loose. Tightening did not solve our problem so we replaced the antenna and voila! Everything works great.
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Old 05-04-2019, 09:09   #13
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Re: VHF - Transmitting Issue (?)

I have an SWR meter in line with my main VHF radio at all times: https://www.mfjenterprises.com/Produ...ductid=MFJ-822. It's reassuring to see all is well, and if something does go wrong, I won't waste time before reaching for my handheld radio as a backup.

If you find you have high SWR, my first suspect would be any "solderless" PL-259 connectors. They are awful. They either come apart or eventually corrode. If you don't know how to solder a PL-259, find someone who does. If you're lucky, a bad connector isn't at the top of your mast.

PL-259 connectors are NOT waterproof. I wrap mine in rubber mastic tape to keep the water out.

Ham Radio Outlet has silver-plated PL-259s that are easily soldered. You can also get a 50 ohm "dummy" load rated at 25 watts minimum from the same source. Use that, along with a "barrel" (dual SO-238) adapter to simulate a "prefect" antenna for testing your coax. You should see no reflected power into the dummy load. If possible, wiggle the coax at the connectors while transmitting to detect intermittent connections.

If you have an amateur radio club nearby, you'll have no trouble getting someone out to your boat who will help you troubleshoot the problem for free (you may have a dozen people show up.) We do that stuff for fun.

And in the future, avoid solderless PL-259s like the plague. Antenna manufacturers often include them with antennas, and I wish they didn't because it's a real disservice to the user.


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Old 05-04-2019, 09:35   #14
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Re: VHF - Transmitting Issue (?)

a quick diagnosis at this point in time-
take you spare antenna and a jumper wire and hook it int the back of the radio.
If everything works (three-four miles) then radio transmitter fine.
then begin looking at mast.
disconnect the mast antenna and measure wire-(radio also disconnected on other end)
if moisture has found its way into the coax- it will short.

From the sound of talking close by with friend I would lean towards a cable problem.

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.
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Old 05-04-2019, 10:10   #15
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Re: VHF - Transmitting Issue (?)

Quote:
Originally Posted by Hartleyg View Post
Hello Joe,


If the masthead connector was loose (and therefore not weather-sealed), there is an excellent chance that the coax has filled up with water, which will make it extremely lossy for radio frequency energy.
This! Water intrusion in the coax at the top of the mast is virtually guaranteed. You may have to pull new coax since you don't know how far the water was wicked. Read the report on sailing in high vessel density areas which is on the Volvo Ocean Race website. This is a lot of information on checking VHF coax performance from a real expert: Stan Honey.

Cheers,

Chuck Hawley
Co-author of the above-referenced report.
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