PA / Fog horn speaker output

Hadenough

Hadenough

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OK, stupid question I think but hey ho? I have a Standard Horizon VHF with the capability of outputting fog signals via a PA loud speaker horn. Before I go out and buy the loudspeaker horn, I have a perfectly good 12v electric horn operated by a manual momentary switch. Is it possible to get the PA output from the VHF to operate a relay of some sort to switch the existing electric horn?
 
Short answer.......No.

Longer answer......... Because the radio outputs an audio signal.... a tone if you like. This is fed into your speaker horn..... called a horn due to it's shape.... inside is a loudspeaker.

Your 12V electric horn is a metal plate that vibrates as the 12 volts is turned on and off rapidly by a contact arrangement inside it.

It would be like trying to get a fire alarm bell to play God Save the Queen from your iPod.


I guess....... with a bit of electronics you could "recognise" the tone and get that to activate your 12V horn via a rely..... I don't think you will find that on the shelf in a shop though.
 
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Alpha22 said:
Short answer.......No.

Longer answer......... Because the radio outputs an audio signal....
Click to expand...

I think he realises that. But it ought to be possible for the audio tone to trigger a simple circuit that closes a relay. A diode rectifier to keep all the wave above the line, a transistor to bump it up a bit, and then some kind of "damping" so that the output stays on in the dips? I dunno, my analogue electronic skills are minimal. But I know there are people here who could easily knock up such a thing.

Personally I need the logical opposite, so that I can press a button to sound a tone out of my VHF's hailer horn :)

Pete
 
Hadenough said:
OK, stupid question I think but hey ho? I have a Standard Horizon VHF with the capability of outputting fog signals via a PA loud speaker horn. Before I go out and buy the loudspeaker horn, I have a perfectly good 12v electric horn operated by a manual momentary switch. Is it possible to get the PA output from the VHF to operate a relay of some sort to switch the existing electric horn?
Click to expand...


If you could do that you would be missing out on all the different sound signals available from the SH ie. Fog, underway stopped anchored etc.

And don't forget the shouting through the PA ...
 
Standard Horzon specifies a 4 Ohm speaker, which are rare and expensive. My understanding from research on 'web is that an 8 Ohm speaker is just fine, and available for tens not hundreds of pounds

Standing by to be shot down!
 
skyflyer said:
Standard Horzon specifies a 4 Ohm speaker, which are rare and expensive. My understanding from research on 'web is that an 8 Ohm speaker is just fine, and available for tens not hundreds of pounds

Standing by to be shot down!
Click to expand...

Standard Horizon offer a 4 ohm 30w speaker for about £30. Why did you think they cost "hundreds"?
 
wizard said:
If you could do that you would be missing out on all the different sound signals available from the SH ie. Fog, underway stopped anchored etc.

And don't forget the shouting through the PA ...
Click to expand...

That only occurred to me after I'd played with the unit a bit more, didn't realise it whistled! But of course I never shout :rolleyes:
 
wizard said:
If you could do that you would be missing out on all the different sound signals available from the SH ie. Fog, underway stopped anchored etc.
Click to expand...

I don't think so. All he has to do is detect a signal on the PA output and use that to operate the horn. You might even be able to use a standard AC-coil relay (like this: http://uk.rs-online.com/web/p/non-latching-relays/8572777/) but I suspect that a little more sophistication would be needed.
 
skyflyer said:
Standard Horzon specifies a 4 Ohm speaker, which are rare and expensive. My understanding from research on 'web is that an 8 Ohm speaker is just fine, and available for tens not hundreds of pounds

Standing by to be shot down!
Click to expand...

But it will reduce the output volume as well as the price!
 
pvb said:
Standard Horizon offer a 4 ohm 30w speaker for about £30. Why did you think they cost "hundreds"?
Click to expand...

I stand corrected; when I was looking about 6 months ago the prices were up either over or close to £100 I'm sure as i then spent a lot of time looking at the option of an 8 Ohm and whether it would work.

It will reduce the volume but nowhere hear by half, apparently.

However, academic as you can get the real deal for a sensible price
 
wizard said:
If you could do that you would be missing out on all the different sound signals available from the SH ie. Fog, underway stopped anchored etc.
Click to expand...

You wouldn't be able to do the bell signals at anchor, but doing the fog signals for under way is the whole point of the exercise and would work perfectly well.

Pete
 
skyflyer said:
Standard Horzon specifies a 4 Ohm speaker, which are rare and expensive. My understanding from research on 'web is that an 8 Ohm speaker is just fine, and available for tens not hundreds of pounds
Click to expand...

Well, in the 60s/70s when we were all(!) building big amplifiers and BIG speakers, we didn't seem to worry that much about whether the speakers were 8ohm or 16ohm. Yes, the energy efficiency may be reduced , but if you have plenty of power to spare......... (always safer to use the higher impedance speaker).
 
Hadenough said:
OK, stupid question I think but hey ho? I have a Standard Horizon VHF with the capability of outputting fog signals via a PA loud speaker horn. Before I go out and buy the loudspeaker horn, I have a perfectly good 12v electric horn operated by a manual momentary switch. Is it possible to get the PA output from the VHF to operate a relay of some sort to switch the existing electric horn?
Click to expand...

Hi Hadenough. Just bear in mind that if your boat is 12m or more, the fog horn should meet the COLREGS criteria for sound pressure level and frequency. If it does, it will have come with a certificate issued by an authorised testing laboratory. If you are creating your own horn you can always have it tested for compliance. If it passes, you will be given a certificate.

Having said this, I suspect 99% of leisure boats don't carry compliant horns...!
 
wizard said:
If you could do that you would be missing out on all the different sound signals available from the SH ie. Fog, underway stopped anchored etc.

And don't forget the shouting through the PA ...
Click to expand...

Another feature is the horn acts as a mic so you can hear what is going on outside.

The shouting bit proved useful recently when a boat moored up near me recently at Helford. The tender came loose and drifted past me. I was able to alert the skipper. (Who promptly set off after his tender, running aground, but that's another story...)
 
After a week of playing with this idea in my mind I'm beginning to think it may be quite simple...

Assuming the signal produced by the radio is a sine wave, or something similar. A single diode would rectify that and make it generally positive. A capacitor would smooth it somewhat into a rough DC voltage. This would be enough to activate a simple relay of the appropriate voltage rating to turn the horn on and off. The only unknown is the voltage... a quick look with an oscilloscope would solve that.

Or is that too easy?
 
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