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Old 07-08-2018, 20:44   #1
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Advice on radio/antenna placements

Hi all,

Hereís the blank slate:

Heavy cruiser with deckhouse, easily accessible by wheel steering outside under a good Bimini.

LONG way down to the main cabin.

Nav station in main cabin, near companionway, currently a blank slate.

Two VHF radios, one new radio, one a few years old. New one has DSC.

HF down below in main cabin, rear stay antenna.

Masthead short VHF antenna. Good condition and installation, always heard clearly by others.

New 2.4m VHF whip mounted at rear on the davits.

AIS system fully independent of the VHF radios with its own 1.2 m antenna at the stern on the davits.

So, where would YOU put each of the vhf radios and which antenna would you connect to which radio?

Really keen to the logic for your choice if you would be happy to share.

Matt
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Old 07-08-2018, 21:16   #2
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Re: Advice on radio/antenna placements

Connect the new VHF radio to the masthead antenna. Put the radio in the nav station and put a remote speaker in the cockpit. If there is an option for a remote mike consider it.

Connect the AIS to it's antenna and put the unit in the nav station.

Put the old VHF in a box and save it in the unlikely chance that the new one fails. You might want to test fit it in the nav station to be sure you can in case you need it someday.

Remove the extra VHF antenna and put it with the old radio.

You do not want to transmit on a VHF antenna at the same height and only a few feet away from the AIS antenna.
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Old 07-08-2018, 22:00   #3
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Re: Advice on radio/antenna placements

Sell the old VHF, buy a new hand held that you can keep by the helm..... handy for port arrivals, talking to ships while you are also having to run the deck, etc, and other times when you just can't get downstairs.

Leave the new VHF ant on the davits... you may need it one day after your mast has fallen down...... or sell it to help pay for the hand held.....
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Old 07-08-2018, 22:12   #4
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Re: Advice on radio/antenna placements

Matt, don't put the AIS down below. it needs to be on deck where you can easily see it, change settings and silence alarms. You will be monitoring it closely in traffic situations.

I too would hook the best VHF to the best (mast head) antenna, but feel that either mounting the whole unit in the deckhouse or better with a remote mike near the helm is the best solution... especially since you contemplate single handing. Kinda crucial to be able to use the VHF whilst active in the cockpit or wheelhouse.

Jim
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Old 08-08-2018, 00:13   #5
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Advice on radio/antenna placements

Ok, intending to put the ais in the deckhouse. Not the nav station so no worries there Jim.

Sorry stormalong, but no way am I putting the main radio downstairs. It would useless to me down there. By the time I clambered down to it to respond to a call theyíd have sent out a search party.

I donít have the option of a remote on either radio. Couldnít afford that on my budget. But the one in the deckhouse is very convenient to the wheel, can reach both from sitting in one spot. The Swanson 42 has the wheel very close to the deckhouse entrance.

El P, your handheld idea was good but I donít think I can make the $ work.

Definitely the plan for the vhf on the davits was to give me options in case I did a Jim & Ann and let the mast fall over the side. Itís a good 2m or more from the AIS antenna so not too worried about interference.

Most interested to see which radio people would chose to have connected in the event of an emergency and the merits of the risk of losing the mast vs going downstairs to handle a serious problem etc etc.
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Old 08-08-2018, 00:26   #6
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Re: Advice on radio/antenna placements

Quote:
Most interested to see which radio people would chose to have connected in the event of an emergency
Well, it's kinda a no brainer to have the DSC radio hooked to the masthead antenna if emergency comms are your driving concern. If you should loose the mast and its antenna, simply swapping co-ax connectors will get it hooked to the spare antenna (if you were wise enough to put patch cables in place ahead of time) with little drama.

Jim
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Old 08-08-2018, 00:43   #7
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Re: Advice on radio/antenna placements

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Definitely the plan for the vhf on the davits was to give me options in case I did a Jim & Ann and let the mast fall over the side. It’s a good 2m or more from the AIS antenna so not too worried about interference.
Interference is not the issue. The issue is that transmitting so close to the AIS would fry the front end of the AIS. Two meters is about one wavelength, an ideal distance to put maximum power from your VHF transmission into your AIS.

I do not know how congested your waters are or how much you will depend on your AIS but around here we almost never use the VHF and we maintain a visual watch for traffic. AIS will only alert you if the other vessel has an AIS transponder. Maybe 25% of small pleasure craft are equipped with AIS so while you are expecting AIS to warn you of a potential collision 3/4 of the boats around you will be invisible to it.
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Old 08-08-2018, 01:40   #8
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Re: Advice on radio/antenna placements

What I had when I bought the boat .... a vhf downstairs in the navigatorium.... dumb dumb dumb...

What I have now ... A deckhead mounted VHF just inside the companionway hatch... can operate - and hear - it from outside or inside...

What I also have... a handheld with DSC.. can take in liferaft when boat sinks...

Deck mounted ants not getting you noticed when push turns to shove? Worked for me when my mast fell off... used something that looked like this but more primitive.. https://www.whitworths.com.au/banten...enna-156-8-mhz .. that came with the boat. Called up a hull down BP tanker and arranged a fuel drop...

You have redundancy with you AIS ant.... but if you disconnect your AIS and hook up your VHF how you going to know there is a ship out there to call up.....
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Old 08-08-2018, 01:59   #9
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Re: Advice on radio/antenna placements

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Interference is not the issue. The issue is that transmitting so close to the AIS would fry the front end of the AIS. Two meters is about one wavelength, an ideal distance to put maximum power from your VHF transmission into your AIS.

I do not know how congested your waters are or how much you will depend on your AIS but around here we almost never use the VHF and we maintain a visual watch for traffic. AIS will only alert you if the other vessel has an AIS transponder. Maybe 25% of small pleasure craft are equipped with AIS so while you are expecting AIS to warn you of a potential collision 3/4 of the boats around you will be invisible to it.


Hmmm. Thatís a worry. I am surprised that a 25 watt transmitter has the potential to nuke the AIS receiver. Iíll do some more research. I see plenty of boats with the antennas much closer than I have them so I felt it would be safe. As noted, more research required.

As for the AIS. Just needed for my longer open water passages. Only boats out where I am going are commercial ships. Around my home waters I use the Mk 1 eyeball. Nobody here uses AIS except the tankers.
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Old 08-08-2018, 02:02   #10
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Re: Advice on radio/antenna placements

Well, Digital yacht ask for at least 2 meter separation in their specs on the web site. Iíve got a bit more than that. Doing some more readings...
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Old 08-08-2018, 02:08   #11
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Re: Advice on radio/antenna placements

Well, the CF guru on all things radio, ka4wja says 36 inch minimum, which is less than a meter, so I am meeting his metric. He goes on to elaborate, and I shall attempt to follow his equations and see what I get, but in short, I think I should be safe though I will tweak things to see if I can eek out some more separation.
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Old 08-08-2018, 02:15   #12
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Re: Advice on radio/antenna placements

Quote:
Originally Posted by El Pinguino View Post
What I had when I bought the boat .... a vhf downstairs in the navigatorium.... dumb dumb dumb...

What I have now ... A deckhead mounted VHF just inside the companionway hatch... can operate - and hear - it from outside or inside...

What I also have... a handheld with DSC.. can take in liferaft when boat sinks...

Deck mounted ants not getting you noticed when push turns to shove? Worked for me when my mast fell off... used something that looked like this but more primitive.. https://www.whitworths.com.au/banten...enna-156-8-mhz .. that came with the boat. Called up a hull down BP tanker and arranged a fuel drop...

You have redundancy with you AIS ant.... but if you disconnect your AIS and hook up your VHF how you going to know there is a ship out there to call up.....
EP, mate, I wish I'd heard this advice earlier. I had dismissed the handhelds as too low power and too likely to fall in the water, but you present a compelling argument.

Perhaps I'll pick up some extra work this summer and add one to the mix, in which case I will call you first.

Like you, I love having the radio up near the wheel, and our similar boats clearly lend themselves to a similar approach.

I actually have the AIS Baten antenna, it was the most elegant of the lot. The GME antenna was nice but the bracket system they use is totally wrong for an old sailing boat, much more suited to power boats IMHO. I bought a Shakespeare for the 2.4m whip, because I liked the look of it. Always a good buying strategy. So three VHF antennas in total.

Cursing myself silly for getting rid of the original Moonraker HF whip that came with the boat. Not one of my clever moments, but I was trying desperately to simplify things and it was a complication I didn't understand or value.

Not sure what's with all this mast falling off nonsense. First Jim and Ann, now you. It's not obligatory is it? I'd rather not join that particular club.

Matt
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Old 08-08-2018, 02:55   #13
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Re: Advice on radio/antenna placements

Quote:
Originally Posted by GILow View Post
Ok, intending to put the ais in the deckhouse. Not the nav station so no worries there Jim.

Sorry stormalong, but no way am I putting the main radio downstairs. It would useless to me down there. By the time I clambered down to it to respond to a call theyíd have sent out a search party.

I donít have the option of a remote on either radio. Couldnít afford that on my budget. But the one in the deckhouse is very convenient to the wheel, can reach both from sitting in one spot. The Swanson 42 has the wheel very close to the deckhouse entrance.

El P, your handheld idea was good but I donít think I can make the $ work.

Definitely the plan for the vhf on the davits was to give me options in case I did a Jim & Ann and let the mast fall over the side. Itís a good 2m or more from the AIS antenna so not too worried about interference.

Most interested to see which radio people would chose to have connected in the event of an emergency and the merits of the risk of losing the mast vs going downstairs to handle a serious problem etc etc.

Let's just say I know a guy that purchased a cheap Chinese "Baofeng" progammable walkie talkie in Ebay for 40 bucks and after a quick google how to session, programed it with all the marine VHF frequencies and chucked on the UHF CB frequencies for good measure, too.
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Old 08-08-2018, 04:24   #14
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Re: Advice on radio/antenna placements

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Let's just say I know a guy that purchased a cheap Chinese "Baofeng" progammable walkie talkie in Ebay for 40 bucks and after a quick google how to session, programed it with all the marine VHF frequencies and chucked on the UHF CB frequencies for good measure, too.


Interesting. Iíd love to talk to such a guy.

Just to understand the theory of course.
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Old 08-08-2018, 05:52   #15
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Re: Advice on radio/antenna placements

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Originally Posted by GILow View Post
Well, the CF guru on all things radio, ka4wja says 36 inch minimum, which is less than a meter, so I am meeting his metric. He goes on to elaborate, and I shall attempt to follow his equations and see what I get, but in short, I think I should be safe though I will tweak things to see if I can eek out some more separation.
Don't equate expertise with looooooooong posts.

Proximity of both antennas in the same plane can result in de-sensing when one is transmitting. It can easily overload the other receiver sometimes damaging it.

The best practice to avoid that problem is to separate them vertically. A few feet will suffice at the typical power levels we use. Don't put both antennas on the same horizontal plane.
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