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On Fri, 21 Oct 2005 07:06:49 +0200, "Meindert Sprang"
wrote: "Tamaroak" wrote in message ... I have two VHF radios, both of which have a PA and foghorn mode and will send a 20 watt signal into a horn mounted on my flybridge. Standard Horizon says I can't just hook the two of them to the same horn becxause the one radio will backfeed into the other, causing it to be harmed. The solution is to get two diodes and wire them on the + wire before it gets to the horn. 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 this. If the horn is 20 Watt and your battery is 12V, you'll need at least a 2 Amp diode. Ask for a 50V/5A diode and you'll be fine. Higher specs on voltage and/or current are fine too if that is what is available. The price difference should be negligent. We're talking about a sub-$ component here. Meindert The solution can't work. Who proposed it? Standard? I hope not! You are making some assumptions here based on the output of the audio amp being limited to 12 volts. No such limitation exists_ The radio spec will tell you what the output stage looks like. If the 20watt output rating is into 8 ohms then it seems unlikely the output is limited to 12 volts. If it is rated into 4ohms the it is 12. But even still it is likely coupled by a cap or transformer as most speakers don't handle dc very well_ This makes the diode isolation idea sort of impossible. Well.... you might put something together to create a bias with a couple of diodes and some resistors then sum the biased AC the couple the summed with a cap to the horn/speaker but you are going to loose 50% of your output power (actually a little more) sort of a foolish way of putting two signals together and if you thought the simple diode 'or' would work this solution is probably a bit too difficult. I suggest picking up one of the auto stereo booster amps_ Get one designed to take the direct speaker outputs from the stereo and has an output that can be bridged into a mono amp. Then put one radio to the right channel, one radio to the left and bridge the horn across the outputs. Hey_ not only will you sum the outputs of the two radio you'll have a great setup for blaring rap music out of your fog horn... |
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