Which VHF Antenna??

[Herald]

I have a 1911 23ft sloop and am looking to install a fixed VHF to this winter. I am not wanting to install a masthead antenna, but am looking at installing the antenna on the pushpit rails. Obviously don't want a massive antenna, but appreciate that coverage maybe compromised slightly due to location. Any recommendations for an antenna make and type?

 

[whipper_snapper]

[ QUOTE ]
Obviously don't want a massive antenna, but appreciate that coverage maybe compromised slightly due to location.

[/ QUOTE ]

No, coverage is largely determined by location.

Far and away the biggest difference will be due to the height of the antenna. Why not put it at the masthead ?

 

[KenMcCulloch]

Whipper snapper is dead right. having a 25W VHF with the antenna on the rail of a 23' boat is really very little better than having a 5W handheld. Antennae are installed at the masthead to maximise the range of communication.

 

[LadyInBed]

Please heed the advice, don't install the antenna on the pushpit rails.
Range is proportionate to height probably more than power.

I would recommend a Force 4 S/S Whip with Windex. I wouldn't recommend a Helical Stub Antenna I think they are more prone to failure

 

[MM5AHO]

A VHF antenna close to water level is like holding your distress flare down to water level.
But if there's no option, then one with maximum gain is required. (which probably means a long one)

 

[William_H]

I use a VHF on the stern rail and it works a treat in practice. Yes height will improve range however as most of the stations you are talking too will be at a reasonable height then you can still expect 15Nm or more.

I use a home made antenna made from a section of coax cable. It is stuffed into a piece of plastic electrical conduit tubing about 1.6 metres long which allows the antenna to be well above the stern rail and in fact about 20cms of the inner wire which is the antenna extends out of the tube so the top is nearly 2 metres above the deck.
The advantage is that it will work beaut when the mast falls down.
PM me for details if you want to make a simple antenna.
I expect you have a wooden antenna so you will need an antenna with its own effective ground plane.(ie a f/g tube about 1.5 metres long not a short ss rod) Beware some antenna require a connection to the aluminium mast to provide this ground plane to work correctly.
olewill

 

[Gunfleet]

<I expect you have a wooden antenna> I expect olewill means wooden mast! I have an antenna at the masthead and one on the pushpit. Of course the one at the masthead has a better range but don't forget the coastguard tend to have antennae on masts or hills, so the problem isn't as bad as it seems. Big ships have theirs high too. The real problem will be talking to another yacht more than very few miles away. If you can live without that the pushpit works.

 

[Talbot]

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The real problem will be talking to another yacht more than very few miles away. If you can live without that the pushpit works.

[/ QUOTE ]

So if the boat you want to talk to is the lifeboat, your in a spot of bother.

 

[Gunfleet]

No more bother than the man in a motor boat or rib. Most things in life are a compromise. Presumably the coastguard launched the lifeboat, not you, so they can hear?

 

[Salty John]

The formula is Distance in NM = 1.23 x (root of H1+H2), in which H1 is the receiver height (in feet) and H2 is the transmitter height. So if the antenna is on the pushpit and you are talking to a coast guard station or a large ship where their antenna is mounted very high then the hieght of your antenna is less important. This is why I think it is OK to mount an AIS antenna on the pushpit - the incoming signal is from a ships mast located high above sea level.
For vhf communication between small boats the higher the better. For power boats a good tip is to make sure your antenna is vertical and not swept back, no matter how cool you think that looks!

 

[RestlessL]

I may be over-cautious, but is there not a hazard associated with RF transmission in close proximity to you or your crew?

I have a pushpit mounted VHF for AIS reception and emergency VHF use, but would not wish to transmit at 25W unless the cockpit is clear.

John

 

[pvb]

I think you're over-cautious!

 

[Sans Bateau]

If your caution had any substance, RIB and mobos would have a continual problem.

 

[Salty John]

Various investigations have been conducted into any health hazard associated with RF/microwaves, mainly to do with mobile phones. They seem to conclude that there is no danger at the power levels and frequencies involved with VHF radio but I can't give you a specific reference. Apparantly the most stringent regulations allow for 10 milliwatts per square centimeter for up to 6 minutes at a time. The highest measured has been .00083 mW/square centimeter and more typical is .0001.
Handheld radios would carry warnings if there were serious concerns, I think.

 

[RestlessL]

This is a discussion I would willingly lose, and I am probably being over-cautious.

I have a recollection of an instruction to Army signallers not to transmit using a backpack at high power as the aerial was so close to the operators head. My push-pit aerial is only cms from me (particularly when using the RAM!), and because RF burns are deep rooted, it is a risk I would not want to take.

However, I would happily be shown to be wrong.

John

 

[Billjratt]

If you want the antenna on the pushpit, I would bet on the 1.5m white fibreglass rods, as used on mobos. Anybody touching the AE at transmit time is not "directly" in contact, and these are "J" configuration, therefore no groundplane considerations, and a significant DBgain on a plane whip.
Only downside is vulnerability as is anything at crew level.

 

[Ramage]

I had a Glomex white antenna on my Birchwood.
Its performance was poor. Could not receive anything until I was almost on top of it.

Replaced it with a Metz. I can now receive London VTS (Woolwich) when I am moored in Bray marina.

I am in no way connected with the makers or suppliers of either antenna.

 

[William_H]

I spent some time in my youth working at a radio transmitter site 2x 55kw and 2x 10Kw transmitters. The radiation level was so high in places you have to grasp metal objects firmly to avert a small arc and resulant burn. Sure this was at lower freq. like 600khtz and 10megahertz but many of the old timers had worked there for a vlong time with no ill affects. So don't worry abouut proximity of a stern rail VHF antenna. olewill