PBO antenna test, help me choose pls

The main factor in the range of your VHF is the height of your antenna, so the mast would be best, there is a formula to work is all out, on the rail you may have little more range than a handheld.
 
simonfraser said:
Fitting one on the stern is a whole lot easier than top of the mast.

My trimaran is not gona heal more than 25 degrees at most, more like 15.

So, fit a mobo antenna to the stern ?

All comments welcome :)
Click to expand...

The higher the greater the potential range
 
I own a Metz Manta VHF antenna which I bought from Salty John from this forum. I cannot recommend this highly enough. One thing I will say is that you MUST fit the RG8X coax (or better) cable rather than the cheaper stuff even for a short run.


http://www.saltyjohn.co.uk/metzmantavhfantennaaerial.htm - Antenna
http://www.rocketradio.co.uk/rg-mini-8-342-c.asp - Coax

Rocket Radio will sell you the cable without the connectors fitted.

Salty John does sell the cable but it's expensive from him. (Sorry SJ!)

No connection to either, I'm just incredibly pleased with my setup and I can also vouch for the service of both companies in question being excellent.

Just for reference, I was anchored between St Agnes and Gugh in Scilly a few weeks back and with a mast height of about 12M I could receive the Irish CG, the French CG, Milford Haven CG, and Brixham CG..... Obviously Falmouth CG as well. The TX range is also excellent.
 
Agree the masthead is the proper place for your antenna, but that still leaves the question of which type. Most of those in the recent PBO test were 3dB gain as typically used on a monohull. A 6dB aerial, as used on MOBOs, should give better performance on a cat in all but the worst sea conditions - although that may be just when you want it to perform! The difference is basically that the higher gain antenna radiates nearly all its power in the plane horizontal to the antenna, so can miss the receiver when tilted. Much of the power transmitted from a 3dB antenna is in a lobe around that plane, so although at the horizontal it is lower powered, and therefore has shorter range, as it tilts some power is still available to the receiving station. I'm pretty sure from your question that you are already aware of that, but I guess you'd like maximum range whilst remaining readable.

I guess the best of both worlds would be to use a 6dB antenna for the VHF and a 3dB for AIS, so you could swap them for making a Mayday call in really rough conditions!

Rob.
 
I think this test has already been discussed in this forum, and is considered to be mainly twaddle. Much as I appreciate PBO doing gear tests, they should have done this test in conjunction with an RF lab. Many magazines are guilty of this, my computer magazines often do tests of cameras and speakers, which are not their field of expertise.

Top of the mast is best, with good quality cable. A higher gain antenna will lose power more rapidly as it goes off axis, so best avoided on a boat that may heel. As to the make, whatever your local chandler has in stock, there isn't a lot to choose between the reputable manufacturers.

[Later] My mistake, the earlier thread was on the VHF test, but the same caveat applies.
 
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QUOTE=G12;3736971]I own a Metz Manta VHF antenna which I bought from Salty John from this forum. I cannot recommend this highly enough. One thing I will say is that you MUST fit the RG8X coax (or better) cable rather than the cheaper stuff even for a short run.[/QUOTE]

+1

I fitted Metz 5 years ago with RG8X after having poor results from the main stream offerings; excellent, reliable comms.

I have one at the mast top and a spare one on the pushpit in case of dismasting and a hand held vhf. The masthead always outperforms the spare and the handheld.

Brad
 
VHF antenna

I think that much of this theory about antenna gain is correct in theory but in practice you would not notice much difference. I have always ran my VHF antenna from the stern rail. I have not found it wanting in range.
My current antenna is actually an extension of the back Stbd upright. It is about 500 mm taller than if it were cut off level. This tube makes the ground plane. The antenna is a piece of stainless steel 3mm rod. I heated it flattened it and drilled a hole for a screw and lug to attach the coax centre. The coax screen is connected electrically to the top of the SS tube. A piece of plastic tubing holds the ss rod in the centre of the tubing top. The total length of exposed coax centre and rod should be 17 inches. It works a treat.
Yes a mast top antenna would be better but more prone to faults and lost if mast is lost. good luck olewill
 
Fitting a masthead VHF antenna is awkward to do, takes some time, and may not always be reliable - so why not fit two, while you're about it - not much extra cost compared to the time taken, and having a ready-rigged spare could be a lifesaver. Add a third one on the pushpit for AIS, which could also be used as a VHF antenna in an emergency if you got dismasted, and you're sorted!
 
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