Where could my mast head antenna go to? Not to the radio or AIS as I've checked

[ritchyp]

Hi,

I have to do some work at the mast head and I can see a thick black cable coming down the inside of the mast and from a video shot by a drone I know its a V Tronics VHF antenna. I traced it back to the chart table but it doesn't connect to anything. In fact it carrys on down towards the stern of the yacht. I have no idea why this is. The DSC-VHF & AIS are iComm and there is a little iComm mushroom antenna on the stern rail. I have a cockpit connection to a hand held that plugs into a port in the cockpit and 2 additional battery operated hand held icomm radios. Perhaps it goes to a Master splitter??

I dont know if the Vtronics mast head is old and no longer in use or if it goes somewhere important (as mentioned above) and is still very much in use. It all looks to be in good condition and pretty new looking cable, I just cant trace its destination. After the chart table

 

[john_morris_uk]

The only way I can think of finding out is to physically follow the cable. It might require a bit of detective work in unscrewing panels etc but it’ll appear at some point further back in the boat. Buying or borrowing an endoscope camera might save some time.

 

[KompetentKrew]

The DSC-VHF & AIS are iComm and there is a little iComm mushroom antenna on the stern rail.

The mushroom won't be the VHF antenna - too small.

The short antenna on a handheld is too small really - I'd be very surprised to find an antenna for a fixed VHF on a boat that was shorter than about 1m in length. The long antenna at the top of the mast is very likely indeed to be the one currently in use by the VHF.

In my experience it's easy to mis-trace a black cable - you identify it going into a conduit or behind a panel, and then you identify it coming out, but it turns out (after much frustration) that it's a different cable. You can get the wrong cable even if you lose contact with it for a couple of inches - trust me, I've done this.

 

[john_morris_uk]

The mushroom won't be the VHF antenna - too small.

The short antenna on a handheld is too small really - I'd be very surprised to find an antenna for a fixed VHF on a boat that was shorter than about 1m in length. The long antenna at the top of the mast is very likely indeed to be the one currently in use by the VHF.

In my experience it's easy to mis-trace a black cable - you identify it going into a conduit or behind a panel, and then you identify it coming out, but it turns out (after much frustration) that it's a different cable. You can get the wrong cable even if you lose contact with it for a couple of inches - trust me, I've done this.

Good point. That’s why I always wiggle the cable to make absolutely sure I’ve got the right one. You don’t need to just wobble it, you need to push and pull it (or get someone else to) to see the cable moving back and fore at the other end of the conduit. If it’s not possible to push it you need another person to pull and you watch which cable retracts a little. Then you pull from your end and the other person confirms its the same cable. It’s usually possible to find enough slack to sort out which cable is which.

 

[Sandy]

Where do the cables in the VHF and AIS go?

 

[Refueler]

Is the Mushroom antenna connected to the VHF its GPS ? You don't say which iCOM it is .... Its unlikely to have a mushroom antenna for its VHF / AIS duty ...

I suspect your masthead antenna is actually your VHF / AIS antenna .... just taking a long path to your radio ?

 

[srm]

Having removed a few Kg of redundant wires from a previous boat I would suggest that the answer will be found on your boat if you patiently follow the advice given by @john_morris_uk.

 

[ritchyp]

UPDATE! (I thought I had solved it but not in the end)

My very good friend rang me up at 19:30 (as he is coming down to help me for a few days)
Mate! its 30 degrees and your crawling around and pulling up the floor panels. I bet you haven't eaten since breakfast or drunk much water. Your probably dehydrated and got heat exhaustion and really stressed and not thinking or seeing things very well, just knock it on the head and have another look tomorrow when you are fresh. Of course he was correct on all counts.

The thick black cable almost 10mm goes into the conduit. I looked behind the boat's main switch panel which is like a telephone exchange box inside. I saw a loom coming with a dozen other wire and cables all held together with cable ties of course but I located it and it had the same markings on the side "BICC GROUP <VER>MADE IN GREAT BRITAIN" I followed it and its a power cable with Brown, blue & Green/yellow wires in it. Heavy duty current I would say as they are 3 or 4mm thick.
The brown goes to mast head light switch, the blue goes into main matrix (like a telephone exchange) and the Yellow and green goes to navigation lights. Not what you would expect but I know it is live (That's a whole different story I figured out months ago.)

So there are also 3 other black cables coming down the mast all about 5mm thick. One goes into Dataline black box and connected to WIND (RED, WHITE BROWN, GREEN & BLACK) Obviously from the old wind transducer I am replacing. The 2nd black cable is a coax and it is literally chopped off! clean but no tape on the end so its obviously not live and a lot of surplus but coiled with ties and anchored with an plastic eye pad.
The 3rd black cable goes through a 50/60mm hole in the wood at the hull side of my forward facing chart table (behind the the instrument mounting panel) My AIS coax cable and the VHF coax cable come back in through the same hole so that 3rd black cable goes somewhere ?
Finally both the VHF and AIS coaxial input cables come through the previously mentioned hole and from the boats switch panel cavity, I can see they are both coming from the stern.

The question is......? Is the Chopped coax that comes down the mast, the one from the Vtronics antena? Or is the 3rd black cable that also seems to go towards the stern the one from the Vtronics antenna?

There are no panels to unscrew all the wood interior was most likely glued and a nail gun using brads. further back in the head, i can see lots of wires going to the stern if I open cupboard door under the sink. Then there is a huge locker that goes all the way to the transom. Lots of wiring in there because there is a Digital Yacht WL510 modem with long range antenna and an iNavconnect wireless router connected by Ethernet. The antenna itself is on the Pull pit rail next to the A garmin GPS mushroom and I think possibly the AIS antenna and I also just discovered another little antenna - rubber and 5" inches long, like you would have on a hand held radio but I think that is for the cockpit connection for VHF radio that plugs in to a socket on the transom.

As you can see, lots of wiring and things that need power and antennas.

ALL I REALLY WANT TO KNOW IS IF THE MAST HEAD ANTENNA IS WORKING AND CONNECTED AND IF THE COAX CABLE HAS BEEN CHOPPED OFF, WHERE IS MY VHF ANTENNA?

I am fitting a new Garmin Wind transducer that has a large diameter cable and if there are redundant wires taking up valuable space I need' I would like to remove them or in fact use them to pull the new cable through

Why would somebody chop off the cable to the Mast head antenna? Unless it no longer works of course.......? The boat is 30 years old and the wring on the antenna base looks really faded but I could just make out V-Tronics by Shakespeare and yes in italics. Could it be that it was for the original radio that was pre- Ais so it is not suitable. I have no idea about this, i am trying to learn as I go but cant find the answers I need. I have a crane booked to lift me up in a big steel basket in just over a week. I need to know what I am dealing with. I have 3 hours of tidal height before my keel touches the bottom and this part of the marina completely dries out. plus the crane is 150 and hour and It should be a quick job but it will be bad if there is not enough room to feed the cable down.

Dilemma....... :/

 

[KevinV]

I think a diagram would clarify your thinking a lot.

Also an explanation of what does/doesn't work - radio checks for no good reason are tedious, but you have good reason and with AIS /DSC you can pick something at a decent range and try, without cluttering up ch16. You'll soon know from distance achieved whether your masthead antenna is working. If it works, leave well alone and concentrate on the wind instruments that you do need to replace. You can spend the rest of your ownership tidying up the wiring while in a lovely anchorage somewhere, if you get really bored.
A 30 year old boat will have redundant wiring for redundant tech, plus wiring for the new tech, plus temporary fixes that never got done "right" because they continued to work.

That said, things that spring to mind:
- is/was there an antenna for navtex somewhere?
- ditto FM radio
- ditto SSB (which would logically come from the stern)
- was there a seperate AIS antenna that has been made redundant by a splitter? I can envisage not bothering to remove a faulty antenna on the crosstrees, just chop off the cable, put in a splitter, and deal with the faulty antenna next time the mast is down, leaving the cable in place as a mouse for a new one. Splitter works fine, and life is too short, so later remove the antenna and chop the cable where it enters the mast - why bother pulling it out when that means taking the ceiling down? Lazy, but it happens.

Like I said, a rough diagram and what the actual problem is would go a long way. At £150/hour I wouldn't be wasting time up there trying to sort out a messy wiring panel.

 

[Refueler]

First thing ... get a Multi-meter and set to OHMS ..... now test that chopped off end to see if you get any resistance reading .... it meter stays at 1 - then its most likely its not connected to anything. If it shows 0 or something near - then its touching mast and shorting OR its connected to something up there.

There is one test you can do - BUT WITH CARE.

Before disconnecting anything - go to VHF menu and run SELF TEST. This will usually give PASS or FAIL for various items incl Antenna. At this point all should say PASS
Now unscrew and disconnect antenna ..... Do SELF-TEST again .... now it should say FAIL for antenna. DO NOT DO ANYTHING ELSE WITH radio ... if you tried to TX - you can fry the RF section. SELF TEST does not send full power - its a diagnostic.

Now the cable you disconnected from VHF .... you can now test by having yourself at mast head ... IF the antenna allows you to unplug the cable from it ... meter to see that meter reads 1 - that its not connected, you can then short the inner to the outer ... go down and meter again at bottom connection you removed from VHF to see if cable is now reading 0 or something near. If it does - then that antenna is your VHF / AIS cable. (If you have another guy at bottom - he could short cable inner - outer and you meter at masthead - no different.

This then means that if first chopped off cable shows no connection - its redundant. Second that masthead Antenna is connected to VHF via different cable.

 

[Refueler]

was there a seperate AIS antenna that has been made redundant by a splitter? I can envisage not bothering to remove a faulty antenna on the crosstrees, just chop off the cable, put in a splitter,

As I understand it - he has a combination VHF / AIS radio - so splitter would be internal to radio.

 

[KevinV]

As I understand it - he has a combination VHF / AIS radio - so splitter would be internal to radio.

Ah, so, if that replaced previous seperate units using seperate antennae there'd be a redundant coax knocking about, probably to either crosstrees or pulpit.

The OP hasn't actually said that the VHF/AIS isn't working - the main aim as far as I can make out is to free up space in the mast conduit.

 

[Refueler]

Ah, so, if that replaced previous seperate units using seperate antennae there'd be a redundant coax knocking about, probably to either crosstrees or pulpit.

The OP hasn't actually said that the VHF/AIS isn't working - the main aim as far as I can make out is to free up space in the mast conduit.

My SELF TEST post is to find out if that antenna (as I suspect) is the main VHF / AIS item. I think we both suspect that there may be a redundant cable hanging in there .... not unusual when a cable gets caught at the crosstrees fittings ...

 

[KevinV]

My SELF TEST post is to find out if that antenna (as I suspect) is the main VHF / AIS item. I think we both suspect that there may be a redundant cable hanging in there .... not unusual when a cable gets caught at the crosstrees fittings ...

Totally agreed, I'm just more of a bodger than you and would jump to the assumption that if everything is working then the spare coax is redundant. Your approach is more correct.

I can imagine if the new unit was installed by a pro that he'd just cut the redundant coax where he's working and coil it up neatly out of his way, leaving the end exposed to show it isn't live. Not his job to be messing around up masts pulling redundant cables that aren't in his way, and it might be repurposed.

As for it being stuck up there, you may well be right, but I hope for the OP's sake that it just never got pulled and is still attached to a redundant crosstrees antenna. Sod of a job to pull a new cable past/ through a tangle

 

[ritchyp]

Hi thanks for all your time and input. The VHF is an icom IC-M505.
The AIS transponder is a Class B
icom MA-500TR

The radio is recieving traffic on Channel 16 it. I looked in the menu for self test and didn't see that option. I just flicked through the manual and didn't see anything about it either.

When I turn on VHF at the switch panel. The AIS starts looking for a GPS signal and the VHF says no position, then after 30 seconds, the AIS shows all the vessels transmitting AIS and shows them on the screen as small triangles on a target like screen. Circle with cross hairs. Then the VHF radio shows the current position of the vessel in Lat and Long.

I do have an electrical multi meter so I will test the chopped off coax to see what reading I get in resistance mode.

Hopefully can tell me how to access the VHF self test. I couldn't see it on the menu options and I checked in setup to see if it had a diagnostics sub menu but alas no.

When I am in the Solent I can easily hear French transmissions so my range should be good for a 25W radio?

 

[ritchyp]

I found a diagnostics menu on the AIS transponder and did a transponder and it came back

ROM OK
RAM OK
RX OK
TX OK
ANTENNA OK
GPS OK

 

[ritchyp]

Just reading what has been discussed about old cables. From the video footage taken by the drone. It looks like some excess cable has been wrapped around the the mast head light a couple of times. Would this support the view that a new antenna or possibly a new coax cable was installed and the fitter fetched the old cable as it looks like it is a twist fit on the underside of the antenna and wrapped the excess cable around the light.
I wonder why he didn't cut it off at the top of the mast to keep things tidy....?

I have noticed that there 5 cables exiting the mast via holes drilled near the bottom of it at the front.
They look like they were drilled by by somebody later in the boats life.
They exit the mast and go through the deck roof via grommet fittings. There is a wooden access panel on the ceiling and those wires supply the power for an Echomax active radar reflector/transponder and the rest are for the mast head lights and navi lights on the pushpit & pull pit. The radar transponder needs the power from the mast head light so it has been bodged but after several hours I managed to get it to work without the mast head lights via a couple of simple 2 way switches. Turn the power on at the main board and switch one switch on the ceiling panel to power on the radar reflector and switch the 2nd switch to have them both on so you aren't using the mast hesdights during the day.

It was messed up and nav lights were coming on when mast head lights were supposed to be on and the radar reflector wasn't working. There is another white coax cable from that.

Somebody asked me if it had a
Navtex. It did but was removed at some point so there is a blanking plate on the instrument facia. There is a coax with a connector still attached and is labelled Navtex. There is also a manual for the old navtex that somebody pulled out.

 

[Refueler]

Hi thanks for all your time and input. The VHF is an icom IC-M505.
The AIS transponder is a Class B
icom MA-500TR

The radio is recieving traffic on Channel 16 it. I looked in the menu for self test and didn't see that option. I just flicked through the manual and didn't see anything about it either.

When I turn on VHF at the switch panel. The AIS starts looking for a GPS signal and the VHF says no position, then after 30 seconds, the AIS shows all the vessels transmitting AIS and shows them on the screen as small triangles on a target like screen. Circle with cross hairs. Then the VHF radio shows the current position of the vessel in Lat and Long.

I do have an electrical multi meter so I will test the chopped off coax to see what reading I get in resistance mode.

Hopefully can tell me how to access the VHF self test. I couldn't see it on the menu options and I checked in setup to see if it had a diagnostics sub menu but alas no.

When I am in the Solent I can easily hear French transmissions so my range should be good for a 25W radio?

Hang on ... AIS a separate unit to the VHF ?

Then its most likely to have a splitter connecting the two units to one antenna - if you do not have two antenna.

This can then interfere with VHF Self Test as the Splitter usually sits transmitting AIS / receiving VHF / AIS until you hit the TX button on VHF ... depends on the splitter.
If I self test my VHF - the test comes back fail on the antenna .. but if I connect antenna direct to VHF without splitter - it passes 100%.
I know splitter is ok as AIS picks up far more targets via splitter than via my aft pushpit antenna

 

[Refueler]

Personally ?

If all is working today ... I would leave it till lift-out at end of season ... drop mast and sort it all then ... far easier than hiking up in a chair and swinging about at top of mast ..... you have freedom to meter everything ... really tie down what is what ...

 

[ritchyp]

Refueler,

So it may well be that the mystery 3rd wire mentioned above, could be going to a splitter further aft and then both coming back through the same hole and individually going to the back of the VHF and the AIS, that makes sense..