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Old 04-02-2020, 20:57   #1
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VHF receives but does not transmit

We have a Standard Horizon Galaxy VHF with GPS with a 3db whip antenna at the masthead. Last season, our transmissions were not answered by coast guard radio but a bulk carrier within sight reported that our transmission was barely audible. The battery was at full charge and we could hear other vessels’ transmissions with ease. I presume we have an antenna cable problem, likely at a connector. How likely is it that the antenna itself is faulty? What sort of meter would be needed to test this? I hope that forum members more skilled and experienced with electronics than me can shed some light.
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Old 04-02-2020, 21:22   #2
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Re: VHF receives but does not transmit

If the problem is in the cable and not the transmit section of the radio itself it could be anywhere from the connector at the radio end to the connector at the masthead to the antenna itself. Since good, working antennas (not sure if this applies to all brands and types but all mine do) show as a short on a volt meter I'm not sure what good testing with a meter would do.

Easiest, surest way to test would be to pick up another antenna and test the radio with that. You can buy a small, inexpensive, emergency antenna that connects directly into the back of the radio. Cheap and good to have in case you lose the mast or the antenna so you still have VHF. If that isn't an option take the radio to a friends boat and hook up to his/her antenna and see if it works better.
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Old 04-02-2020, 21:30   #3
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Re: VHF receives but does not transmit

Quote:
Originally Posted by Edward Bairstow View Post
We have a Standard Horizon Galaxy VHF with GPS with a 3db whip antenna at the masthead. Last season, our transmissions were not answered by coast guard radio but a bulk carrier within sight reported that our transmission was barely audible. The battery was at full charge and we could hear other vessels’ transmissions with ease. I presume we have an antenna cable problem, likely at a connector. How likely is it that the antenna itself is faulty? What sort of meter would be needed to test this? I hope that forum members more skilled and experienced with electronics than me can shed some light.
VSWR meter is the best way to determine coax and antenna problems.

The fact you can receive with ease suggests the coax and antenna is probably OK.

You may simply have a microphone problem (either the mic itself or the cord to the radio.

Ideally a VSWR meter and a 50 ohm dummy load will quickly identify with the problem lies.
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Old 04-02-2020, 21:47   #4
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Re: VHF receives but does not transmit

Also look at your power connection to the radio. Very little amperage is needed for receive mode, many amps needed for transmit. Check connections and measure voltage close to radio while transmitting. Use a channel like 26
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Old 04-02-2020, 22:33   #5
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Re: VHF receives but does not transmit

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VSWR meter is the best way to determine coax and antenna problems.
I thought about adding an SWR meter to my tool kit but cheap ones start at $40, good ones over $100. For something I might use once every few years then carry it around taking up my limited storage space it just didn't seem worth the investment.


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The fact you can receive with ease suggests the coax and antenna is probably OK.

You may simply have a microphone problem (either the mic itself or the cord to the radio.
Either of these could be the problem but as pesarsten suggested I would also check power to the radio.
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Old 04-02-2020, 22:56   #6
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Re: VHF receives but does not transmit

I agree with Pesarten above, it could be a bad 12 Volt power connection. When receiving, the radio uses only 50-100 milli amps. If the bad connection is causing for instance 1 ohm resistance, it causes a voltage drop using Ohm's law V=IxR 0.1x1= 0.1 Volt, barely noticeable.

When transmitting the current is around 5 Amp at least. Voltage drop (amp x resistance) 5x1=5 Volt, for a 12 volt battery, provides only 12-5=7 Volt to the radio; likely not enough to broadcast, and if it does, it is only whispering quietly
If the resistance is 2 Ohm, then absolutely nothing will be broadcast, while you can still receive.

The above scenario is easy to measure with a multimeter.

If there is not voltage drop on transmitting, I would check the microphone. Maybe somebody in your marina has an identical unit, swap it over and check how that works.

If that is OK, then I would look for the antenna connections.

Of course if one has a SWR meter, like Wotname suggested, one can check the antenna and its connections quickly and easily, but most of use do not have one.
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Old 05-02-2020, 04:40   #7
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Re: VHF receives but does not transmit

Thanks to all for those suggestions. I will check it out once the snow melts off her and the mast is up.
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Old 05-02-2020, 05:33   #8
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Re: VHF receives but does not transmit

I'd suggest asking around for a local amateur radio operator (ham) that has been in the hobby for a while. Most of us have easily portable inline watt meters that can test power output from the radio, and antenna analyzers that can check the coax and antenna for proper resonance and SWR.


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Originally Posted by Edward Bairstow View Post
We have a Standard Horizon Galaxy VHF with GPS with a 3db whip antenna at the masthead. Last season, our transmissions were not answered by coast guard radio but a bulk carrier within sight reported that our transmission was barely audible. The battery was at full charge and we could hear other vessels’ transmissions with ease. I presume we have an antenna cable problem, likely at a connector. How likely is it that the antenna itself is faulty? What sort of meter would be needed to test this? I hope that forum members more skilled and experienced with electronics than me can shed some light.
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Old 05-02-2020, 06:00   #9
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Re: VHF receives but does not transmit

Any chance that you have another charging circuit or transformer near the radio. I agree with the simple cheap tests - another antenna being the easiest, but I had this same problem because I left the charging sat phone sitting on top of the VHF.

The end point of my chasing that problem was my owning a spare $100 VHF and $20 antenna, which sit in storage against a future failure, but then, I have storage space on board.
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Old 05-02-2020, 06:07   #10
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Re: VHF receives but does not transmit

I would be inclined (sorry) to try some tests before the mast is up.

Check all the power connections including fuses, plugs, etc. and re-test the current setup. Try a different antenna, try a different antenna cable. Try a different VHF on your current antenna and cable and a different antenna and cable. Testing might go better if you have another friend with a VHF listening and you avoid the working and emergency channels on VHF. You could also enlist the help of a local 'ham' and ask them to bring any gear they have for testing. For me, my VHF radio issues are usually related to old cable and wet or worn coaxial connections and/or low batteries in the handheld.

Lots of good advice from the gang. Go get 'em Tiger!
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Old 05-02-2020, 08:24   #11
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Re: VHF receives but does not transmit

Spot is spot on. Find a local ham who can bring over a VHF SWR meter or antenna analyzer and a handheld 2 meter radio. The antenna on boats will work on 2 meter amateur frequencies with acceptable results. You can find ham clubs or operators by doing a search on the internet for your community. Hams will help without requesting any compensation.
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Old 05-02-2020, 08:36   #12
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Re: VHF receives but does not transmit

Spot is spot on, but, do we have to keep complicating what is likely to be a very simple problem? We don't even know if Edward and his boat are within 1,000 miles of a ham operator.

OK, I'm in a grouchy mood right now, the !@#$ printer won't print my charts on legal paper, but, VHF radios are just about bullet proof. They are nothing but a source of power, the radio, the antenna coax, and the antenna. They are nothing like the tuning of a ham radio antenna.

If Edward tests the four components in turn, using either his own cable, a spare antenna, etc., he is very likely going to find the problem. Less time than looking up local hams, less trouble.

There, I've vented. My apology to anyone put out by my intemporate words. You're one bunch of great people willing to help Edward when he's stumped, and you've helped me the same way many times.
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Old 05-02-2020, 09:03   #13
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Re: VHF receives but does not transmit

The OP is in the snow, mast down. Who is he going to test with? Maybe he is a 1000 miles from the water, land locked, in middle America. Overkill, I know, but there is probably a local ham that can help if willing. If I was near the OP I would over in a jiffy with my stuff. One test the ham can do is to a local repeater.

Where is the OP's location? Maybe some of us hams can help him locate a local ham. All we do is check the FCC database to see how many hams are in his area. Them maybe post on QRZ.com for a local ham in his area to assist. I think this has possibilities.
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Old 05-02-2020, 09:45   #14
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Re: VHF receives but does not transmit

I maintain the launch and patrol boats for our club. I must have replaced 5-6 vhf units by this point, and now use the same cheap standard horizon unit so I can pop a new one in using the same connectors when they fail.

The cables from microphone to unit go, and/or the ptt buttons go, so they don't transmit.

repeatedly.....

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Old 05-02-2020, 11:36   #15
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Re: VHF receives but does not transmit

Quote:
Originally Posted by Wotname View Post
VSWR meter is the best way to determine coax and antenna problems.

The fact you can receive with ease suggests the coax and antenna is probably OK.

You may simply have a microphone problem (either the mic itself or the cord to the radio.

Ideally a VSWR meter and a 50 ohm dummy load will quickly identify with the problem lies.
Great advise.
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