Doug Dotson wrote:

"Tamaroak" wrote in message
...

I have two new VHF radios, both of which have a PA and foghorn output and
will send a 20 watt signal into a horn mounted on my flybridge. Standard
Horizon says I can't just hook the two outputs together to the horn because
the one radio will backfeed into the other.


True. A better choice might have been a radio with a remote mic capability
like a Standard Horizon or ICOM.


Their solution is to get two diodes and wire them on the + wire before it
gets to the horn. The other option would be to have two horns which would
be ugly.


If it's their solution and they can;t tell what diodes to use I would be
suspect
of the solution. Not sure how 2 diodes solves the problem for an audio
signal.


If the audio out from BOTH radios fluctuates around a 6 volt level,
(+1 to +11 volt fluctuating audio signal), like you seem to imply an
ICON would, being at zero volts when not receiving, then both radios
can use the same horn, probably without much chance of hurting the
idle audio output amp. If both try to speak at the same time, some
distortion / temporary overload may occur.

If one radio works like that, there is no guarantee they both will,
so what one mfgr says could work with their radio may not protect a
rival brand.


Question: What kind, size, specifications do I use for said diode? The guy
at Radio Shack looked at me like I was from Mars when I asked him about
this.


A power rated diode say, 3 amps at 12 or 24 volts might be ok. Put
two diodes, one in each speaker lead, positive to radio output (bar
marked end to speaker) YMMV.


Radio Shack lost their interest in anything technical years ago. I went in
the other
day looking for a power resistor and he hadn;t a clue. I found exactly what
I
needed but no thanks to him. I suspect they will be eliminating their parts
department soon anyway.


Yeah, makes me sick, they ignore the market that got them started.
'Course, elecronics are not supposed to be repaired any more, like
computers, it's often cheaper to junk and replace stuff.


Is there some other way to do this?

Capt. Jeff

Use the boat stereo system to announce calls. Use a resistive mixer
(three resistors for each channel) to piggy back the rx audio
signals into the stereo systems power amp input.

A fancier active switch could kill the music while feeding VHF rx
through the house speakers. A simple switch could set the system
back to whichever radio was then switched to the remote horn with
another switch. Of course, then you would have no receive if the
stereo was off, and simultaneous rx on 2 radios might mute the
system altogether. The power out from the radios would be converted
to a signal only level for the stereo input, but a local speaker
could remain, able to monitor each rx at the radio location. Some
internal radio switching might complicate or simplify matters, if
for instance, the fog horn output and public address output only
goes to a remote (horn) speaker line, with a second (primary,
actually) output for local rx speaker operation.

An alternative is to use the push to talk signal to select one or
another radio to be sent to the single horn using a relay system.
In the case of simultaneous rx signals, the one not selected might
be muted. This could be incorperated into a couple of small boxes
with connectors wired between the mics and the radios.

Why not just use one radio system with two microphones, one horn and
and two local speakers?

Pretty is as pretty does. Simple is better. I would use two
seperate horns, to make the system somewhat redundant, external horn
speaker wise.

Terry K