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Go Back   SailNet Community > On Board > Gear & Maintenance > VHF Receive but not Transmit?
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Thread: VHF Receive but not Transmit? Reply to Thread
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Topic Review (Newest First)
10-22-2012 04:38 PM
arf145
Re: VHF Receive but not Transmit?

Oh, absolutely Bill. And I might replace any others I find in the antenna cable. I assume there's a connector up at the antenna. The talk of the new radio, was, well, just because it is old, and lacks features such as AIS, RAM mike, etc. But really, a new radio wasn't high on my constantly edited upgrade list. I really want cruise control!
10-22-2012 04:32 PM
btrayfors
Re: VHF Receive but not Transmit?

Tom,

If the connector is/was the problem, you don't need a new radio. Just cut the old one off, and put on a new PL-259 connector.

Bill
10-22-2012 04:27 PM
KBuckley
Re: VHF Receive but not Transmit?

That is great news. Thanks for the update.
10-22-2012 01:56 AM
arf145
Re: VHF Receive but not Transmit?

Back from the boat, and while I didn't have time to try everything, I did apparently fix it. And it does look like corrosion on the antenna connection to the radio was the problem, so thanks KBuckley! The coax connector outside looked fine, but unscrewing and pulling the connector off revealed a layer of corrosion inside, especially up in the pin. A replacement would have been good, but as a spot fix, I hit the area in question with a very small rasp attachment on my cordless Dremel. Screwed the connector back on, connected cable to the radio and was heard loud and clear at a marina down the bay. I'll try some other tests next time, including the auto Seatow radio check, but so far so good.

A new radio might still be in my near future, but I'd rather have it be an option instead of mandatory!

Thanks again everyone.
10-19-2012 05:19 PM
night0wl
Re: VHF Receive but not Transmit?

long shot, but check the transmit mode. I once had the same experience on channel 78...turns out my radio was set to international rather than usa. I guess international, 78a is reserved, but usa its open for all.
10-19-2012 11:18 AM
asdf38
Re: VHF Receive but not Transmit?

Quote:
Originally Posted by KBuckley View Post
I should have explained my thinking. The signal levels when receiving are very very low current so the resistance of a poor contact has little effect. When you try to put 25W thru the poor connection by transmitting you will lose lots of power since the power loss is I^2R. If your problem is a corroded connection the new radio will do the same. Also, the power is reflected at the poor connection so you can potentially damage the radio. Hence the manufacturer's warning not to try transmitting without an antenna connected. A repair tech can put a meter between the radio and antenna and tell you the condition of the whole system.
First, RF is a bit of a black art - even experts in the field resort to trial and error. But in general you're over thinking it a bit. The power levels are different but the frequencies are the same and therefore, more or less, you'd expect the losses to be the same.

If you're receiving a far away signal then it's weak when it gets to your antenna - you can't afford to lose much more. If it's getting through then your antenna losses must be limited. If your antenna losses are limited then you'd at least be able to transmit short distances.

Take my example. Up until this season my coax was busted at the base of the mast (completely severed). Before realizing this I installed and tested a new radio. It could both transmit and receive short distances but not long ones.

Sure, spend some time debugging it if you want. But also keep an eye out for sales on new radios.

EDIT: Oh whoops, for some reason I mistook your post as being from the OP. Doesn't change what I said too much but explains why I say to look out for new radios..
10-19-2012 01:15 AM
KBuckley I agree that a new radio is a great idea. Tying in your GPS to a DSC radio lets you send a mayday with your location at the push of a button. An associated MMSI number gives the coast guard all your info. I hope never to take advantage of the feature!
10-19-2012 01:03 AM
arf145
Re: VHF Receive but not Transmit?

I certainly get the "why not just get a new radio" thought--I'm thinking the same thing. Just wanted to know if the antenna could be a player. It sounds like the antenna connections could be a factor (thanks KBuckley) and could damage a new unit if they are bad. I'll check the radio connection right away and get up the mast when I can. The voltmeters are no longer hooked up, but I guess I can hook the multimeter up to watch for voltage drop.

And I'll probably get a new unit in the off season no matter what--I'd like to have a remote unit in the cockpit!
10-19-2012 12:32 AM
Capt Len
Re: VHF Receive but not Transmit?

You can buy old radios by the pound, Go for a new DSC. Remember your mast head ant doesn't talk down worth a dam.(wave propagation) so the hand held is not a good tester. Isee Buckley beat me to the rest of my thought
10-19-2012 12:25 AM
KBuckley I should have explained my thinking. The signal levels when receiving are very very low current so the resistance of a poor contact has little effect. When you try to put 25W thru the poor connection by transmitting you will lose lots of power since the power loss is I^2R. If your problem is a corroded connection the new radio will do the same. Also, the power is reflected at the poor connection so you can potentially damage the radio. Hence the manufacturer's warning not to try transmitting without an antenna connected. A repair tech can put a meter between the radio and antenna and tell you the condition of the whole system.
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