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Old 01-03-2021, 12:00 AM   #1
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Aerials & Electronics

I have three aerials on my recently purchased trawler, along with a number of other electronic receivers/transmitters. I'm still working my way through the boat and have a few lingering questions:

- I understand a separate aerial is required for each VHF, which accounts for 2 aerials, so I assume the 3rd is for use as an FM radio antenna. There are 2 un-used coax cables in the boat (2nd photo) - one of those is definitely for the TV receiver (which we don't use). Does anyone know if the 2nd might be for the extra aerial? Do aerials typically have a coax connection? Would it be common practice to get an adapter from coax to stereo antenna?

- How would I test these connections to see which does what? It's a bit difficult to physically trace these - I could test by plugging into the antenna port for my stereo I suppose. Any other suggestions?

- There are 2 very small receivers on my radar arch - see photo. One at the very top and one lower. I believe at least one of these would be for the chart plotter GPS receiver, any ideas what the other one is for? AIS? Or possibly for the 2nd chart plotter, although that one is slaved to the first.

Thanks!


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Old 01-03-2021, 12:05 AM   #2
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Congrats on your new boat. As to the antennas, could be a lot of things. My AIS antenna looks just like a VHF antenna but only 4’ tall. When I bought my boat it literally had 12 unused antenna mounts on it. Who knows why, why they wouldn’t just use an existing mount when they wanted to add an antenna. And the marina told me that they had removed several and patched the holes.
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Old 01-03-2021, 12:10 AM   #3
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The small “receivers” are likely GPS antennas. Navico has a heading sensor that looks similar, so that would be a second guess if you have any Lowrance/Simrad/B&G electronics.
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Old 01-03-2021, 12:15 AM   #4
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Thanks, I have a Raymarine autopilot - could it be for that?
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Old 01-03-2021, 12:36 AM   #5
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I doubt it, but I only had 2 generations of Raymarine and don’t know all of them.
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Old 01-03-2021, 12:43 AM   #6
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One thing you can try is to make sure everything is powered down and try a "tone" "ringer" wire tracer like this one

Sperry Instruments ET64220 Wire Tracker Wire Tracer, Audio / Video Installers Must-Have, for Coax, CAT 5, Speaker & Phone, Adapter plugs: RJ-45, RJ-11, Coax & More https://www.amazon.com/dp/B00279JLBQ..._pKv8FbHA5VZ6F

There are many varieties. Mine is years old. I just posted 5he 1st one I saw on Amazon.
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Old 01-03-2021, 09:20 AM   #7
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Quote:
Originally Posted by rherten View Post
I have three aerials on my recently purchased trawler, along with a number of other electronic receivers/transmitters. I'm still working my way through the boat and have a few lingering questions:

- I understand a separate aerial is required for each VHF, which accounts for 2 aerials, so I assume the 3rd is for use as an FM radio antenna. There are 2 un-used coax cables in the boat (2nd photo) - one of those is definitely for the TV receiver (which we don't use). Does anyone know if the 2nd might be for the extra aerial? Do aerials typically have a coax connection? Would it be common practice to get an adapter from coax to stereo antenna?

- How would I test these connections to see which does what? It's a bit difficult to physically trace these - I could test by plugging into the antenna port for my stereo I suppose. Any other suggestions?

- There are 2 very small receivers on my radar arch - see photo. One at the very top and one lower. I believe at least one of these would be for the chart plotter GPS receiver, any ideas what the other one is for? AIS? Or possibly for the 2nd chart plotter, although that one is slaved to the first.

Thanks!

If you have AIS, yes a typical installation is a dedicated VHF antenna (usually shorter, say 4' or so) and a dedicated GPS mushroom. I think that's best practices, though, not necessarily mandatory... and it is technically possible to piggy-back two functions (normal marine VHF and AIS VHF) on a single antenna.

I wouldn't expect a VHF antenna to be for FM radio. OTOH, I think there are some whip antennas cut for VHF/UHF and used for TV and AM/FM radio... so if you don't have a small dish-like thing (e.g., Glomex or Shakespeare) AM/FM/TV antenna, could be one of your whips is for that.

All of the whips would likely use CoAx to feed follow-on systems (marine VHF, tuners, TVs, stereo radio, etc.).

The middle whip in your pic looks to have an appendage I don't recognize... Any brand name/model info on that?

One cheap way to trace is to first determine what works and what doesn't.

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Old 01-03-2021, 09:38 AM   #8
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Quote:
Originally Posted by ranger42c View Post
If you have AIS, yes a typical installation is a dedicated VHF antenna (usually shorter, say 4' or so) and a dedicated GPS mushroom. I think that's best practices, though, not necessarily mandatory... and it is technically possible to piggy-back two functions (normal marine VHF and AIS VHF) on a single antenna.

I wouldn't expect a VHF antenna to be for FM radio. OTOH, I think there are some whip antennas cut for VHF/UHF and used for TV and AM/FM radio... so if you don't have a small dish-like thing (e.g., Glomex or Shakespeare) AM/FM/TV antenna, could be one of your whips is for that.

All of the whips would likely use CoAx to feed follow-on systems (marine VHF, tuners, TVs, stereo radio, etc.).

The middle whip in your pic looks to have an appendage I don't recognize... Any brand name/model info on that?

One cheap way to trace is to first determine what works and what doesn't.

-Chris
An appendage - you mean this? No idea what it is - maybe SSB?

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Old 01-03-2021, 10:18 AM   #9
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Have you tried talking with the prior owner? Or perhaps your surveyor?
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Old 01-03-2021, 10:58 AM   #10
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An appendage - you mean this? No idea what it is - maybe SSB?

Attachment 112205
That appendage looks like a radar reflector to me. A lot of sailboats have that type attached to the standing rigging up high. (Makes you show up on other boat's radars better.) Never seen one on antenna like that, I think it would block the radio signals.
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Old 01-03-2021, 11:14 AM   #11
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The 2 cables in the picture are both RG-6 used for off air television and the satellite TV antenna that is in the dome if that is what it is. The connectors on it are type F. On VHF antennas you typically see larger PL-259 or N type connectors.

I agree that the attachment on the antenna looks like a radar reflector. It could be an antenna tuner for a SSB, but they are normally in a series type connection with the antenna. If it is a radar reflector I would move it as it is not helping the VHF antenna any. The transmitting wire inside the fiberglass rod generally starts within 6 inches of the base.

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Old 01-03-2021, 11:24 AM   #12
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https://www.defender.com/product.jsp?id=6857574

Look like a radar reflector.

No idea why a 3rd VHF antenna. Question to the forum. Can a regular VHF antenna also bennused for AIS transmit?
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Old 01-03-2021, 11:34 AM   #13
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Weebles,

Yes it can, it’s just matched ideally to the AIS frequency. I use a Morad VHF antenna for my Class B and see no problems. I probably lose a little range, but less than if you used a splitter on the same antenna for a receive only AIS.

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Old 01-03-2021, 12:40 PM   #14
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Thanks everybody for feedback. Yes the appendage is a radar reflector - maybe there's a better location for it, as suggested. Yes the dome on the radar arch is a TV receiver - we removed the TV and home theatre/sound system when we bought the boat, so it's redundant. (replaced with Fusion RA770 marine stereo system). The 2 coax cables were connected to the TV/sound system so at least one of those go to the dome. Not sure if the second one also goes to the dome or one of the aerials. It might be worth buying an adapter and seeing what happens if I plug those into the Fusion stereo for FM reception. Not sure if the TV dome would provide FM reception, or perhaps the 2nd one is connected to an aerial which would provide reception. Many other good ideas in this thread for me to consider as well - thanks again.
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Old 01-03-2021, 01:11 PM   #15
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Turn everything on and disconnect cables on at a time and see which one stops working.
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Old 01-03-2021, 01:21 PM   #16
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Yes, but the 2 cables which are already disconnected are the ones I'm most interested in.
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Old 01-03-2021, 01:26 PM   #17
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TV cables. Perhaps from a cable box the PO took with him.
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Old 01-03-2021, 01:38 PM   #18
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Lose the radar reflector. They don't work well under the best of circumstances.

For the coax, I can think of only a TV antenna. It's been years since I've had an external TV antenna on a boat (pre digital) but it didn't work well. You may want to try a cheap plastic antenna up high, assuming you can find the other end in your cabin.
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Old 01-03-2021, 02:08 PM   #19
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Aim your antennas straight up and down, not at the angle of the arch. Better reception that way...
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Old 01-03-2021, 03:57 PM   #20
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Aim your antennas straight up and down, not at the angle of the arch. Better reception that way...
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