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Old 08-12-2017, 13:33   #1
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Best cable to use connect loudhailer horn to B&G V50 VHF

I just bought a new B&G V50 VHF and wanted to wire up the loudhailer while I had the panels apart. The installation manual says absolutely nothing about what kind of wire to use. Thank you for that, B&G.



I was initially thinking of using 14/2 shielded speaker wire, but the wire coming out of the back of the radio is a sort of mini-coax here. So I wonder if I should be using a coax. This hailer has the "listen-back" feature so a shielded cable is a good idea since it is using the hailer horn as a type of microphone and mic cables can pick up all sorts of interference which effects the sound quality. There is no place to connect a shield/drain wire except at the cable pigtail at the radio so if I ran 14/2 I suppose I would need to connect the shield to the (-) wire along with the negative conductor of the 14/2.

The other idea would be to simply use coax. I've got a bunch of used but nice RG213 (Belden 8267) which might be way overkill here, but at least the conductor size is fairly large for the PA side of things. I don't know if 50-ohm cable would be better than 75 ohm cable or vise versa in this application. I could pick up RG-8 at Home Depot just as easy as I could pick up shielded speaker wire.
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Old 08-12-2017, 13:45   #2
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

Unless you're going more than 25 feet or so, RG-58 would be fine. So would heavier stuff if you want every last drop of loudness from the speaker.
Cable characteristic impedance will not matter for audio at these lengths.
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Old 08-12-2017, 13:56   #3
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

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Originally Posted by TreblePlink View Post
Unless you're going more than 25 feet or so, RG-58 would be fine. So would heavier stuff if you want every last drop of loudness from the speaker.
Cable characteristic impedance will not matter for audio at these lengths.
Thanks.

I think the route of the cable is about 20 feet from under the mast deck step to the radio if I remember right from the antenna wire I pulled. From there another 5-6 feet to where I think I'm going to mount the horn. I just want it high enough to get out of the worst of the salt spray and that's also about head height for someone on the foredeck to talk back to the person on the helm. My wife is hard of hearing and sometimes hand signals just don't cut it so the "listen-back" feature might come in pretty handy.

If I use coax I think I want to make sure to use a different connection method so that never-ever can the VHF antenna and this hailer wire possibly get mixed up.
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Old 08-12-2017, 14:14   #4
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

I would use 16/2 or 14/2 wire. anything. speaker or normal tinned marine. I wouldn't pull coax. that will confuse anyone who sees it. because nobody would use coax for that.
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Old 09-12-2017, 04:31   #5
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

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I would use 16/2 or 14/2 wire. anything. speaker or normal tinned marine. I wouldn't pull coax. that will confuse anyone who sees it. because nobody would use coax for that.

If the wire is unshielded, it will pickup noise in the talk back mode where the speaker is used as a microphone.
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Old 09-12-2017, 05:21   #6
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

I plan on terminating the coax with simple bullet connectors at the radio and below the mast step so that it wouldn't even look like coax to anyone, and not be confused with the VHF antenna feed ever. I'd just be a thick round-profile cable. Also, I don't want to mess around sourcing and putting a coax connector on the tiny pigtail from the radio.

I was contemplating using regular cable up to the horn those last few feet just to simplify things but I think at least It should be shielded cable, or perhaps more coax. I have some used RG-68 from WestMarine that I might use for that last bit since the Belden 8267 is pretty stiff/inflexible stuff compared to that lighter-weight cheap antenna wire. I certainly don't want to shift between 75 and 50-ohm coax as that would likely cause problems too with standing waves building up on the pickup.

I am a commercial electrician although we don't do a lot of structured wiring so my experience with PA systems is limited to pulling the wire, terminating the wire, and hooking up to equipment that was all spec'ed out by someone else. That's the engineer's job for the most part to tell me what wire to source and pull. If they call for coax we pull coax of whatever type they specify. But B&G gives NADA information to me here in the installation manual. Most of the hailer horns out there just have "bare wire" connections at the other end too. So the hookup up top will probably be butt splices under shrink tube.

But now I need to fall back on the theory I was taught in school decades ago and my own experience hooking stuff up that didn't work so well. Speaker wire typically doesn't need to be shielded but this new "listen-back" feature seems to be so new that best practices are not yet quite firmed up here. It is really a mic cable when "listening" and mic cables are always shielded, yet rarely are they single-conductors with a shield used as the return in my experience. I've wired a lot of large auditoriums and pulled many thousands of feet of audio cable in my career. I've never installed a microphone cable that wasn't shielded.

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Old 09-12-2017, 10:55   #7
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

this is from one of the Standard Horizon manuals I found online.
22AWG or larger stranded plastic jacketed wire to connect the PA horns.
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Old 09-12-2017, 11:05   #8
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

For just speaker use, about anything will work.

He wants to use the "listen back" feature which turns the speaker into a microphone. This cable must be shielded to avoid electrical noise pickup. This is why the manufacturer designed the connection with coax coming out the back ...
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Old 09-12-2017, 14:39   #9
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

Why don't you set up a temporary cable of whatever you have, shielded or non shielded. Make it twice as long as it would be in the installation, hook the horn to it and try it out in the talk back mode and see how much noise you get. Have the engine running, maybe the vhf running, whatever. That will give you a good idea of what you will get.
I suspect/hope that there is a small amplifier in the horn which would make the noise issue less severe. You will quickly find out if shielding matters in this application.
If you have any high power transmitters on the boat, try them (radar, HF) out in transmit mode as well.

Having said that, I would think there is a reason the manufacturer uses coax so I would also use coax. The type or impedance will not matter.
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Old 09-12-2017, 15:36   #10
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

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Why don't you set up a temporary cable of whatever you have, shielded or non shielded. Make it twice as long as it would be in the installation, hook the horn to it and try it out in the talk back mode and see how much noise you get. Have the engine running, maybe the vhf running, whatever. That will give you a good idea of what you will get.
I suspect/hope that there is a small amplifier in the horn which would make the noise issue less severe. You will quickly find out if shielding matters in this application.
If you have any high power transmitters on the boat, try them (radar, HF) out in transmit mode as well.

Having said that, I would think there is a reason the manufacturer uses coax so I would also use coax. The type or impedance will not matter.

Maybe he should just use shielded cable like his photo of the mfr recommendations suggests? "Small amplifier in the horn" --- where did this idea come from? It cannot function as both a horn and a microphone unless it's a passive device.
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Old 09-12-2017, 16:22   #11
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

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Originally Posted by TreblePlink View Post
For just speaker use, about anything will work.

He wants to use the "listen back" feature which turns the speaker into a microphone. This cable must be shielded to avoid electrical noise pickup. This is why the manufacturer designed the connection with coax coming out the back ...
there is only one coax connection on the back and it's for the VHF antenna.
The other round connector is for the NMEA 183 and GPS hookup.
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Old 09-12-2017, 16:27   #12
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

I suggest using quality coax connectors for the loud hailer connections. Further I suggest using shielded twisted pair wire with the ground tied to the shield at the radio.
You'll see that the radio has two wires for the loud hailer, + and - , use the + lead for the center conductor and the - lead for the - wire and the shield.
The installation manual can be found here, wiring starts on page 14.
https://bandg.com/downloads/v50-h50-install-manual/
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Old 09-12-2017, 17:48   #13
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

The photo I inserted into post #1 plainly shows a micro coax pigtail labled "PA" -this is the loudhailer hookup.

I have the manuals, both user and installation in hard copy and .PDF versions. I posted a screenshot of page 14 which references the loudhailer connections on post #6 above. It doesn't mention anything about suggested cable types.
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Old 09-12-2017, 18:28   #14
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

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Originally Posted by TreblePlink View Post
"Small amplifier in the horn" --- where did this idea come from? It cannot function as both a horn and a microphone unless it's a passive device.
Having never looked at a device such as this. I am only guessing. I am guessing that in order for this system to work, they need to separate the function of horn and microphone ... probably by looking at the signal level on the line. It would be trivial to amplify the 'microphone' operation at the same time.

Edit: Page 14 in the manual clearly states that the 'listen back' function only works when the PA function is not active.
I would also like to point out that 'amplifying' the microphone signal should not imply the level of amplification - a small level increase will do wonders in terms of noise rejection.
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Old 09-12-2017, 18:49   #15
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Re: Best cable to use connect loudhailer horn to B&G V50 VHF

This "listen back" function is not new. Many wired intercoms used this same approach - using the speaker as a microphone.

The "horn" is passive and functions as a simple dynamic microphone when in "listen back" mode. Switching from PA output to mic input is performed in the radio. Placing the preamplifier at the horn is unnecessary and creates new switching problems.
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