Poor VHF performance - is this (pic) the cause?

demonboy

demonboy

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I'm having some issues with my VHF, namely poor TX and RX, and short of rewiring it (complicated by a through-hull mast) I'm wondering if this splitter box has anything to do with it. To be honest there are so many cables next to this box that I don't even know if the VHF goes via it anyway, but I'd be interesed to know what a head amp cable is.

Anyone shed some light on what this is, whether the VHF cable runs through it and whether it would contribute to poor performance. The VHF unit is a modern Icom M421.

split2.jpg
 
Non of the frequencies I can see on the unit correspond to marine VHF, which is ~150mHz. 88 to 108mHz for example is "entertainment" VHF FM. Your ship VHF shouldn't use it IMHO. It will be filtering out the signal you want.
A guess at the meaning of head amp is aerial masthead amplifier, (for weak signals).
 
You're vhf antenna doesn't go through that box (I hope!). The frequencies are wrong.
As far as I know a head amplifier is an amplifier for enhancing music quality, from a tape deck, perhaps.
I think you'll have to look elsewhere for your vhf problems.
 
OK, so it sounds like this ISN'T the cause of my problems, and I apologise for being lazy in not following the cables before posting!

Next question: is it possible that the 20 year old cable at the top of the mast has suffered some wicking of water, say 1 ft's worth, and so does snipping it by 1 ft and re-wiring likely to work? There is a downward loop to avoid wicking but its age means it has corroded.
 
silly question but is it the radio or the aerial ? do you have an emergency aerial that you can plug in the back of the set to see.
 
I would be suspicious of cable that old. It would certainly be worthwhile to check the connector at the aerial and also check that the braid in the coax isn't corroded.
If you can cut back to good braid and core before you run out of cable it might be OK. Also check at the exit from the mast and any connectors along the way.
With the aerial disconnected and the radio disconnected check that there is no short between the centre core and braid with a multimeter.
If you can get hold of a VSWR meter and someone who knows how to use it you can confirm you have an aerial system problem.
Otherwise, all you can do is check the componants and the connections and repair/renew as necessary.
 
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Next question: is it possible that the 20 year old cable at the top of the mast has suffered some wicking of water, say 1 ft's worth, and so does snipping it by 1 ft and re-wiring likely to work? There is a downward loop to avoid wicking but its age means it has corroded.

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If water has got in, which is quite likely for a 20 year old cable, then in my experience, it will travel and corrode within the cable a long way down from the masthead. Cutting off a short length won't suffice. Complete replacement is best
 
after 20 yrs service and the relative inexpensive nature of the job, i'd think it wise to renew aerial and cable at next refit... go o treat yourself and your boat!
 
Yes, but our problem is that to lift the through-hull mast will cost us hundreds of €€€s, and this is the only way of running a cable up the mast! Hmmm, need to think about this.

Thanks for all your replies.
 
Typically you would splice the new cable to the old and use the old cable to pull the new cable through the mast. I don't see how a keel stepped mast would make any difference.
If the entry and exit holes are very tight or the route a bit tortuous you may have to do a bit of pushing as well as pulling.
 
I would suggest you buy or make an emergency antenna which is mounted on the push pit and use that until you remove the mast. For replacement as suggested. Antennae and cables seem to give a lot of trouble and an emergency antenna on the pushpit will be there for use if the mast falls down. good luck olewill
 
It doesn't appear in your photo that there is an input or exit for VHF>
Renew the cable, but first pulll a light line up through the mast from the bottom. it does need either a mast down situation or someone up the mast for 30 mins or so. Very important is to have someone feeding the bottom hole. It will also have a join for when the mast is removed, I doubt if the aerial wiring goes direct to the set from the foot of the mast.
Good luck and I hope you have a head for hieghts.
[an easier way for the hoister, is to use a 3 part pulley hoisted to the masthead and you also to pull down on the tail- It deceases your weight, if like me you have too much!]
 
This thread might help with education. I had no knowledge whatsoever of all this before doing the job.

http://www.ybw.com/forums/showflat.php/Cat/0/Number/2258525/page/0/fpart/1/vc/1

my problem was at the underdeck connection before the aerial cable leaves the cabin and goes out and up the mast.

Not sure how easy you could get a VSWR meter, but it made all the difference for me.

You need to make sure that your aerial cable goes from the set to the aerial without a connection inside the boat... so you definitely need to trace the cable. If the problem is a connection in the boat, you dont have to worry about what's happening up the mast /forums/images/graemlins/smile.gif
 
marine band VHF uses 156mhz......then the channel number halfed for the decimal place.....i.e. CH16 is 156.80mhz.....CH14 is 156.70mhz..........by the way the Coastguard and Lifeboat Channel Zero is 156.00mhz.
 
If you can find someone with a VSWR meter, put that in the cable & check the antenna that way. It's not 100% fool proof but a high vswr is not what you want. Look up SWR meter on wiki to find out more. Be careful of CB type meters. There's no guarentee they will work at marine frequencies.
 
Hopefully that unit pictured is connected to a different antenna - there is a for sale thread about these on this site.here

I had a bad VHF reception and transmit problem and I found the Buccaneer waterproof connector by the keel-stepped mast foot was doing its job well. When I unplugged it to take a measurement, water ran out. It had come all the way down from the top of the mast inside the cable owing to the antenna base having a crack in it that let water in. Because it was moulded on I threw away the cable and the antenna. Drip stopping loops dont help when the cable is wet inside.

I have also been on a recently dismasted and repaired boat where the VHF worked better with the old masthead in the water and a snapped cable , than later on with a new antenna at the top of the new mast. Turned out to be a solder bridge in the newly fitted connector at the mast foot.
 
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