Aerial SPLITTER - useful, no use, problematic?

Robert Wilson

Robert Wilson

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Splitters. Any of the Wise Ones have anything to say about these aerial thingies?
I put one in three years ago with a very old cassette radio and a useful ICOM VHF set, both came with the boat.
I have no idea whether it works - well, ok and badly. But both sets do work.

About to re-wire mast, bonding and nav lights and probably replace old casstte radio with a CD Radio.
Now there's another problem - FM/AM or LW/MW (for shipping forecast, CG forecast etc) ??

Please don't blind me with electronic technological science :confused:

Thanks in anticipation,

RW
 
fisherman said:
Surely the aerial parameters for BBC etc and marine are too different to use in this way?
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I did ask politely not to be deluged with tech stuff !! ;):confused: But thanks for speedy response :)

As far as I know, the splitter thingy deals with "splitting" incoming signals thereby using one aerial at the mast-head. Whether either/both VHF set and radio suffer/don't work I have no idea.

I seem to recall a recent post getting involved with a debate on the matter. As usual, some for/some against.

Thanks

RW
 
Even if both could use the aerial via a splitter the latter may degrade your VHF output, though there are ones available that are described as lossless. The other issue is that the splitter will cost a lot. It may be worth while using a splitter if you plan to have VHF and AIS but even for that I would consider just mounting an AIS aerial on a pole fitted to the pushpit rather than use a splitter. I would have thought that a modern CD/radio receiver would work perfectly well on board with an internal aerial unless you have an all metal boat that shields it.

P.S. The splitter does a vital job of stopping the transmission from the VHF from destroying the other receiver. It has to block the transmission from reaching the connected receiver, it does not just split incoming signals. In some ways the word splitter is a misnomer as it does not really need to split incoming signals but it has to isolate the outgoing signal from one set from reaching the other one.
 
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One rope, one job
One aerial, one job

Especially for your VHF aerial, which is primarily a safety feature, you don't want to be introducing additional points of failure. Whilst you're re-wiring the mast, put in an AIS aerial (even if you don;t have AIS now you might want it in the future) a separate VHF aerial and a separate FM radio aerial. You might even want to add a TV aerial up there whilst you're at it?
 
Norman_E said:
Even if both could use the aerial via a splitter the latter may degrade your VHF output, though there are ones available that are described as lossless. The other issue is that the splitter will cost a lot. It may be worth while using a splitter if you plan to have VHF and AIS but even for that I would consider just mounting an AIS aerial on a pole fitted to the pushpit rather than use a splitter. I would have thought that a modern CD/radio receiver would work perfectly well on board with an internal aerial unless you have an all metal boat that shields it.
Click to expand...

That, I think, is happening. Last summer asking for radio check with Stornaway CG (yes, we still have a "local" :) ) I could hear them fine, but they reported poor transmission. Hence my Post, before I commit to a total re-wire etc.
I actually still have the splitter, but I'm interested by your comment re internal aerial. I shall investigate at Muplins today.
Thanks

Tony Cross said:
One rope, one job
One aerial, one job

Especially for your VHF aerial, which is primarily a safety feature, you don't want to be introducing additional points of failure. Whilst you're re-wiring the mast, put in an AIS aerial (even if you don;t have AIS now you might want it in the future) a separate VHF aerial and a separate FM radio aerial. You might even want to add a TV aerial up there whilst you're at it?
Click to expand...

That's good advice, and non-tecky. Thanks. Although I think the TV aerial may be OTT - Don't think TV reception reaches up here!
Got to buy some Coax cable this week, so is AIS and VHF cable one and the same? Thanks again.
 
I had a splitter for years, both VHF and audio radio worked perfectly well. My VHF has always been particularly good and remarked upon by people who heard me many miles away. When we moved away from proximity to UK and had no further need for entertainment radio I took out the splitter and ran the radio on a single wire aerial, around 2 metres long inside a locker. It seemed to make very little difference to the signal strength.
 
Robert Wilson said:
Got to buy some Coax cable this week, so is AIS and VHF cable one and the same?
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Yes. It has to be 50 ohm. For marine use it should be tinned, against corrosion, and the centre core should be stranded - so it doesn't fatigue and break with movement.
For short runs, up to about 6m, you can use RG58, up to 25m or so you can use RG8X, for longer runs you should use RG8U, or RG213.
 
Salty John said:
Yes. It has to be 50 ohm. For marine use it should be tinned, against corrosion, and the centre core should be stranded - so it doesn't fatigue and break with movement.
For short runs, up to about 6m, you can use RG58, up to 25m or so you can use RG8X, for longer runs you should use RG8U, or RG213.
Click to expand...

I have a roll of RG58 if anyone wants it for free. Collect from Shamrock Marina. I use RG58U which appears much better quality (more screening) then RG58.

Also, when rewiring you may well be ordering new connectors. i.e. PL259 to connect to the VHF. These connectors come in different sizes to fit different wire sizes. So when ordering match them to the diameter of the wire you're using.
 
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vyv_cox said:
I had a splitter for years, both VHF and audio radio worked perfectly well. My VHF has always been particularly good and remarked upon by people who heard me many miles away. When we moved away from proximity to UK and had no further need for entertainment radio I took out the splitter and ran the radio on a single wire aerial, around 2 metres long inside a locker. It seemed to make very little difference to the signal strength.
Click to expand...

Good news, and welcome advice.
I now suspect that my poor transmission is due to corrosion within the coax at the "joint" down near the bilge. This is one of the main reasons for the total re-wire; to get joints throughout the boat reduced to an absolute minimum and well clear of watery stuff.

Thanks


Salty John said:
Yes. It has to be 50 ohm. For marine use it should be tinned, against corrosion, and the centre core should be stranded - so it doesn't fatigue and break with movement.
For short runs, up to about 6m, you can use RG58, up to 25m or so you can use RG8X, for longer runs you should use RG8U, or RG213.
Click to expand...

Thank you for that advice.
All very encouraging.

RW
 
The word 'splitter' covers a variety of sins.
A 'power divider' simply divides the power, the simplest sort, easy to make broad band and well matched have a 6 dB loss, the best have a 3-and a bit dB loss
Diplexers are filters which send the higher frequencies down one wire and the lower down another. They can be much lower loss, perhaps as little as 1dB.
I have made diplexers which work fine to separate FM broadcast from AIS receive, but rating them to cope with 25W VHF transmit is less trivial. Having enough isolation not to fry the FM receiver is a problem!
'Loss less splitters' is a vague term which generally implies some sort of active switch. I have not looked at what's sold under this label in the leisure marine sector.
You'd have to look at the spec for the individual unit.
 
I would not want more than one VHF antenna on a typical mast top. Any rod antenna paralell at less than about 1 metre spacing will affect the other. Not to mention inducing huge power into the non transmitting antenna. A Tv antenna should be mounted well below the top where the VHF narine com antenna is. To avoid VHF power damging the Tv antenna or receiver. An AIS receiver antenna is really the same as a VHF com antenna and as such can make an excellent emergency antenna for VHF com. This is especially useful if dismasted. So an AIS antenna to my mind would always be on stern rail. If you want more AIS range then mount on a post or as recently described on this forum on the backstay. (But you won't be able to use that if dismasted.) As said VHF FM reciver should be Ok on an internal antenna. Try 1 metre of wire from antenna socket. If you are in a difficult receiving area try an antenna up the backstay. However an ideal antenna for VHF FM is very different from LW/MW recprtion. For LW/MW a long wire is best. Not necesarily up high. But try connecting to the rigging for LW/MW. good luck olewill
 
nigelmercier said:
Splitters are bad enough when used for their intended purpose, but using one for an FM radio is madness.

Buy a cheap car antenna, sell the splitter, buy beer with the money left over.
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So, forgetting the splitter route, if one doesn't want to install an aerial in the push-pit and if there are potential issues with having two masthead aerials in close proximity, how about a stub AIS aerial on the face of the mast say 0.5m above a raydome? (http://www.cactusnav.com/images/ZVTRHA156C.jpg). Would this work satisfactorily or would the mast shadow the signal?
 
The performance of this antenna will be dependant on the distance away from the mast. And of course there will always be a poorer performance with stations aft of you ie behind the mast. Of course a stern rail mounted antenna can have same problems. But why just a stub aerial when a quarter wave ie 17inch rod works very well provided screen of coax goes to a close large earthed area. good luck olewill
 
Thanks for that advice. I'll try the old cassette radio first with a long wire inside the cabin. May even "attach" it to the shroud plates in the lockers - unless that may cause problems of corrosion etc?
If that works then all I'll do is re-wire the existing VHF aerial. Don't think I'll be going AIS for a while, but can always use pushpit/backstay, as advised earlier.

Thanks. Hope the heat in Western Oz is punishing you. Sounds grim in the East

RW
 
Ian_Rob said:
(http://www.cactusnav.com/images/ZVTRHA156C.jpg). Would this work satisfactorily or would the mast shadow the signal?
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The mast will shadow the signal. I know you said you didn't want to use the push-pit, but it seems a sensible location.
Link to item in your picture link: http://www.cactusnav.com/shakespeare-heliflex-version-with-cable-plug-p-9755.html
Alternative: http://www.cactusnav.com/031m-heavy-duty-helical-antennaais-cable-pl259-p-12362.html

The second link looks better on paper, but it have no experience of V-Tronix.

[NOTE] I am not endorsing this brand of product in any way, just reiterating that dedicated stubby AIS antennas are available.
 
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