Press Ptt and the horn sounds...........how?

[dpb]

As the title really.
I press the Ptt on the fixed VHF and the horn sounds. Hand held
Works normal.
Any ideas how this can happen and a fix?

 

[Blue Sunray]

What brand of VHF? Many have a setting (sometimes as part of a PA menu) whereby you use the ptt to sound the horn, have you switched to this by accident?

 

[dpb]

It's a standard horizon eclipse.
I shall check what you say. But I fitted it myself and can't see how the horn circuit would be activated.

 

[jimmy_the_builder]

Bad neg somewhere being exposed when the current draw of the vhf increases during transmission?

 

[oldgit]

First Check that Plug !

Before doing anything complicated and therefore hard work...
Need to check the Pl 259 plug and its connection to the marine radio. Is it actually done up tightly ?
Is the plug fitted correctly .ie not shorted and both shield and central conductor have good clean connections.
Most plugs factory fitted are compression ie clamped on with a crimping tool but after market usually use a braid mechcanical connection,braid is bulked up and physically screwed into plug body.
Need to ensure none of the braid has crept forward and come into contact with the insulated wire in the middle.
The central wire must be soldered if at all possible.
The problem is probably 25W of RF not going up the aerial as required but being radiated somewhere inside the boat.
This is causing an old fashioned relay or some other electronic switch to think it is being activated sending 12V to your hooters.
No point putting a multimeter across the plug as most marine aerials will show a short.
Check the plug
PL259 are dead simple to fit.BNC a bit more complicated and "N" connectors a pain.
Not uncommon in cars fitted with high power radios, plug becomes loose.braid breaks away from plug and RF is filling the car causing all shorts of peculiar electronic weirdness to screens and warning lights on dash
A new aerial plug usually restores things back to normal.
The cheaper simple two part plugs are much easier to fit, try to avoid the expensive complicated soldered jobs which come with all sorts off itsy bitsy neoprene compression rings and are a nightmare to fit,let alone solder.
New plugs.
Your chandlery will charge you £10.00. (No Honest)
Your local Maplins will charge you £3.50 (ish)
Your local radio shop/truck stop/CB outlet will feel guilty about charging you £1.50-£2.00.

 

[dpb]

Re: First Check that Plug !

Thanks for replies.
I have found it only happens on 25w. Will check plug etc tomorrow.

 

[dpb]

Re: First Check that Plug !

Well I checked behind the instrument panel, removed, checked and replaced aerial plug, moved a few wires around and now all ok so no idea what that was all about!!!