VHF Transmission Problems

[Ben_e_Toe]

Just installed a new VHF/DSC set (Navman 7110). Connected it to exisiting internal wiring, then via a deck fitting to new wiring from deck up the mast and finally a new aerial. Problem is that, whilst it receives perfectly, the set won't transmit beyond about 20 meters! Yesterday I took the deck fittings apart and resoldered the joints then Sikaflexed it all together. I have check the plug at the VHF set end and there isn't a short.

Any suggestions as to what to try next? Obvious thing is to shin up the mast and check the connection on the aerial base, but I wouldn't have thought it would receive if that was faulty............

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[malcp]

Check power supply voltage on input to set when transmitting. If the voltage drops significantly this can be the cause. (When you transmit the set consumes considerably more power than when receiving.)

Otherwise, see if you can borrow a VSWR metre to check the antenna out.



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[stephenmartin]

You can receive radio transmissions on a coat hangar......before you shin up the mast try borrowing a different marine band aerial and plug it directly into the back of your radio....if it works then either your aerial, coax or maybe a connection in the coax is at fault.....

If the display dims when you key the transmitter it could be a power fault.....dodgy fuse power lead not up to it....etc.....

Not a major problem in any case....unless the rig is duff....but don't assume anything....even new rigs are shipped broken

Steve

<hr width=100% size=1>Don't make the same mistake twice...Make a different one

 

[snowleopard]

2 most common causes of poor transmission are 1. low input voltage, 2. moisture in the coax cable to the antenna.

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[Ben_e_Toe]

Thanks for all your help!

I have checked the power and all ok there.

The set will transmit and receive on a duplex channel to a handheld VHF, if the handheld is near the chart table. I took the VHF plug out of the back of the VHF set and there appeared to be a low resistance between the core and the screen. I also took the deck fitting apart and the mast cable also had a low resistance between the core and screen - I would have expected it to be full insulated if working correctly.......

So I have bought new conectors throughout and will replace the cable through the boat (mast cable was recently replaced), chandler recommended a deck gland so that the connection to the mast cable is within the boat! A bit of a job but I will give it a go!

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[steve_cronin]

The Index Marine deck glands require a relatively small hole and using one of these with a PL 259 plug that has a removeable screw-in core should mean that you will get away with only drilling 10mm holes through the various panels and the deck.

It is surprising how much signal loss there is at plug and socket connections. The only one that completely screens is the Dri-Plug design which is basically a male & a female plug line socket encased in a waterproof housing. However nothing beats direct wiring with one continuous run from antenna to set.

Steve Cronin



<hr width=100% size=1>The above is, like any other post here, only a personal opinion

 

[Bergman]

Hold hard.

Did you say a duplex channel?

If you try to listen to your transmission on a H/H using a duplex channel you will not hear anything, you're transmitting and receiving on different frequencies.

Try it on a simplex channel, with a bit of luck you may not have a problem.

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[Gunfleet]

When I had this problem it was a duff new antenna (or cable to it). As someone has pointed out, a vswr meter will tell you whether the problem is in the set or the antenna. I had a hell of a job convincing the people who'd installed the antenna that the bodge up was their end.

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[Ben_e_Toe]

Thanks for your help. I'm not convinced that the connections are the problem so it may well be a faulty aerial - particularly given that I picked it up at a boat jumble as 'boxed and unused'!

What is a VSWR meter and where can I get one? Is it worth buying or hiring? It's not the same as a multimeter is it?

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[Gunfleet]

It measures the 'standing wave' reflected back from an antenna. They are about £80 for a cheap one from wsplc.com but really the best bet its to borrow one from a radio ham (and borrow his advice too!).
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