vhf:am/fm splitters

JimC said:
These gadgets let you use you vhf aerial for receiving entertainment broadcasts as well as marine vhf. Are they any good? They are claimed not to degrade vhf performance on transmit or receive but I feel wary about introducing any complications that could endanger a potentially life-saving link. Here is a link to one http://www.force4.co.uk/487/Force-4-VHF-AM-FM-Splitter.html
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i have had one for 10 yrs no probs 2 date
 
I have used them successfully for splitting vhf links to am/fm radio and AIS Radar, but have reservations with regard to transmit/receive marine vhf, because I am not sure if it can handle full power (25 watts?)
 
Unfortunately my experiences have not been good with a splitter between my VHF ships radio and domestic radio. It was installed in 2005, worked fine for 2 years and then started to have intermittent poor VHF reception and transmission. We didn't know it was the splitter causing the problem at the time. It was intermittent and misleading a very troublesome diagnosis to make. Eventually this year I disconnected it and my VHF is back up to 100% performance.
Based on my experience and the importance of keeping your radio and Ariel connections as simple as possible, I wouldn't consider a splitter ever again, even though when it was installed I was receiving BBC radio 2 and 4 reception in Normandy and Brittany.
 
just a suggestion....if you simply want fm reception, a length of coax with an areil plug on led behind the radio and somewhere discreetly out of sight (mine goes through to the cockpit lockers) will give you reasonably good radio reception. grp won't interfere with the signal and my fm radio gets strong signals and picks up all the stations i need. haven't tried with with a DAB receiver but no reason to think it won't work

if its am/fm you need don't compromise your vhf - radio reception can be achieved quite easily in my experience if you have a long enough coax lead
 
JimC said:
Would you mind telling what type of splitter it was that gave trouble.
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It was a Glomex splitter, of course I may have just been unlucky. Even so I wouldn't risk interrupting or compromising the aerial feed again. I now have AIS, and opted for a dedicated mast top aerial for that also. I will be running a separate fm/am Ariel in the hull for entertainment radio reception as mentioned by Burnham Bob.
 
If you have another aerial that just receives, like Ais, Navtex,TV etc, just link into it via a 0.1uF capacitor (lets the signal through, but blocks any DC from equipment driving active antennae.)
I have serious reservations about sharing an aerial used for transmitting vis-a-vis degrading the performance of what could be emergency equipment,(noted above), as well as blowing the receiver's front end apart...
My car radio/CD player shares with the telly (Nargus active ae) and is now interference free and clear as long as the aerial pre-amp power is on. (a wiring mod needed sometime....)
 
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JimC said:
These gadgets let you use you vhf aerial for receiving entertainment broadcasts as well as marine vhf. Are they any good? They are claimed not to degrade vhf performance on transmit or receive but I feel wary about introducing any complications that could endanger a potentially life-saving link. Here is a link to one

Tried one a couple of years back compaired gain TX/RX with original and found it to be degrading to both. Purchased the glomex fm rubber fm ant no problems
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Antenna

The best option is to buy another VHF (marine com) antenna and mount it on the stern rail. Use it for your VHF entertainment but ensure that it has connectors so that it can be used as an emergency VHF antenna in case of mast failure. Or more common failure of the VHF antenna up the mast. olewill
 
Burnham Bob said:
just a suggestion....if you simply want fm reception, a length of coax with an areil plug on led behind the radio and somewhere discreetly out of sight (mine goes through to the cockpit lockers) will give you reasonably good radio reception.
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If it will work with coax, it will work better with ordinary wire connected directly to the centre terminal. After all, the braid on the outside of the coax is there to shield the centre from interference from tramp radio signals. Its obviously not working very effectively.
 
William_H said:
The best option is to buy another VHF (marine com) antenna and mount it on the stern rail. Use it for your VHF entertainment but ensure that it has connectors so that it can be used as an emergency VHF antenna in case of mast failure. Or more common failure of the VHF antenna up the mast. olewill
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The trouble with the stern rail is it is useful as a grab handle.

Finding somewhere for an AIS aerial is driving me potty.

On the spreaders it is too close to the mast and shrouds.

Before the mast on the radar reflector, I fear it will be damaged during tacking and it is still too close to the mast (signal degradation).

I tried it on a Ø25 beam across the masthead;- 1 metre separation VHF one end and AIS the other. Looked awful.

Maybe a stern pole is the answer (could double as an ensign staff).

Any other suggestions very welcome.
 
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I've had the one your link refers to for the past 5 years. My VHF works OK, I get decent reception on my radio, and I've never had a problem with it. In my case it's done exactly what it said on the tin.
 
Graham_Wright said:
The trouble with the stern rail is it is useful as a grab handle.

Finding somewhere for an AIS aerial is driving me potty.


Maybe a stern pole is the answer (could double as an ensign staff).

Any other suggestions very welcome.
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The idea of using a rail mounted ensign staff for a VHF antenna has much to be said for it.
You will need an ensign staff that is of plastic or f/g about 2 metres tall. Or less if that seems appropriate.
You will need to be able to feed a coax cable from under deck up into the staff.
The antenna itself can be made of a section of the coax cable RG 58 that has been stripped of its outer cover and metal shield for 17 inches. You need to get some braid off a piece of RG8U 17 inches long which covers the last piece of covered RG58 and is connected to the top end of the RG58 braid.

This makes a successful antenna in fact it is my main antenna for VHF and is mounted in 20mm plastic conduit tubing . The higher the better and in fact you could substitute all all some of the top exposed conductor of the RG58 with a thin brass rod or even a telescopic antenna of 17 inches which extends out of the top of the flag staff. It is best if the top 17 inches and the next 17inches of double braid can be kept above the level of nearby metal by about 12inches min.
For your inventiveness olewill
 
William_H said:
The idea of using a rail mounted ensign staff for a VHF antenna has much to be said for it.
You will need an ensign staff that is of plastic or f/g about 2 metres tall. Or less if that seems appropriate.
You will need to be able to feed a coax cable from under deck up into the staff.
The antenna itself can be made of a section of the coax cable RG 58 that has been stripped of its outer cover and metal shield for 17 inches. You need to get some braid off a piece of RG8U 17 inches long which covers the last piece of covered RG58 and is connected to the top end of the RG58 braid.

This makes a successful antenna in fact it is my main antenna for VHF and is mounted in 20mm plastic conduit tubing . The higher the better and in fact you could substitute all all some of the top exposed conductor of the RG58 with a thin brass rod or even a telescopic antenna of 17 inches which extends out of the top of the flag staff. It is best if the top 17 inches and the next 17inches of double braid can be kept above the level of nearby metal by about 12inches min.
For your inventiveness olewill
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Thanks for the compliment, blush blush!
Why plastic?

I have two identical Metz antennæ, the one for VHF can live at the masthead; its the one for AIS that is causing the head scratching.

Just thought of another idea. I always wondered where I could stow the rudder post extension for mounting an emergency tiller (centre cockpit). That could be the ensign staff in normal use. Then, of course, in an emergency we grab the ensign staff/rudder post extension and lose the standby emergency antenna!
 
Having a mizzen mast, I thought I would be clever and put a VHF aerial on it, fit a PL259 on the end, and use an adaptor to connect to the "entertainment" radio. Reception this year was absolutely zero! It was better with the length of co-ax "(with about a foot of screen removed from the end) plugged into the socket. Unfortunately I threw out the lash-up when I fitted the "proper" aerial.

I had thought of trying a splitter, but after reading this thread, I do not think I will bother.
 
Enterttainment radio antenna

In reply to Wight Dawn we need to explain that your entertainment radio will try to receive on AM medium wave ie 520 to 1600 khz and FM 98 to 108 mhz. The VHF FM should work OK on a 160mhz antenna. If it is not the best you could try extending the metal of the antenna if it is of exposed metal. Add about 12 inches to it using the little cylinder out of chocolate block terminal with 2 screws.
However the problem is all different on MW AM. The antenna is way too short to be tuned so the signal is of very high impedance and a poor match to the 50 ohm coax. Or put another way the 50 ohm coax has a very large capacitance which in itself bypasses the signal to ground. Further the input cable tends to be used as part of the input tuning of the MW receiver so the huge a capacitance of a long coax will detune the input circuits. The answer for MW reception may well be to just connect the centre of the coax and not connect the outer earth braid. This will make all the cable, the antenna and may work well. That may be OK for VHF FM also or go back to connecting the earth for FM.
Or just poke about 1 metre of wire into the antenna socket. good luck olewill.
 
Thanks William. On the last boat, the aerial lead was connected to a staunchion base and worked well. I have not been able to access any of the fixing bolts on Wight Dawn, henc the attempt to use an aerial on the mizzen. The mast is down just now and the plastic round the base of the aerial is cracked so it for replacement anyway.
 
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