VHF radio

[Garygee]

While I agree that antenna height is a very important factor in increasing range, antenna type is also vital.
On a handheld the typical antenna type is a helica. These can be typical -3 to -6 dBi gain.
A fixed antenna is typicaly +3dBi gain.

A good compromise which I use is a handheld with a fixed antenna. If you look at the figures you will see why

5 Watt handheld with -3dBi helical = 2.5W ERP (effective radiated power). On top of this the helical being close to your head etc is often at a poor angle (should be vertical) and detuned bey things around it.

5 Watt handheld with +3dBi antenna = 10W ERP

This gain is also on receive !!.

There are antennas available with upto 6 dBi gain. While these look good they have a very low angle of radiation which means that on a RIB which may be pitching a lot the angle of the antenna may chamge so much that the receiving antenna goes in and out of the beam so apperaing to fade in and out of contact.
These antennas are good on big boats but not for RIB's

Of course the best answer is a fixed VHF at 25W = 50W ERP and a handheld as a backup.
It may be that you carry a fixed antenna which in case of poor signal and need you attach to your hand held and hold above your head. If anyone has tried that you would be amazed how much better it is than a helical on a handheld.

[nigelt]

I have an Icom IC-M1 Euro handheld and would be very interested in linking it to a fixed antenna but am not sure it is possible. If not, what handhelds are you taking about which can be attached to a fixed antenna?

Nigel

[Alan Mckewan]

I havent tried it with the M1 Euro, but I have regularly used both a Navico and an older Maxcom through the masthead aerial on a yacht. You simply take off the rubber duck and fit a BNC-to-PL259 adapter (available from Maplin etc.) and then plug on the VHF PL259 plug. On a yacht it makes a massive difference becuase of the mast height, but I dont think the difference will be so great on the RIB. I have also done the opposite - after breaking off several fixed VHF aerials on one of the club rescue boats I resorted to fitting a PL259-to-BNC adapter on the back of a fixed Navico VHF set installed in the console, then fitted a rubber duck straight onto the back of the fixed set. The rubber duck sticks out straight into the middle of the console. The reception is not as good (understandably as the SWR on the rubber duck is probably crap) but at least the somewhat careless rescue crews cant break it off!

[Garygee]

Hi

I use a Swiftech M198, quite old now and big but has a standard BNC mounted antenna.

With regard to use on yachts yes you will get a very big difference as your getting a good antenna AND height. But the test I have done show that a call that is totally unreadable on the hand held helical can be fine on the fixed antenna.
The other minus you have on a yacht is the long cable run has quite some loss while the cable lenghth on a RIB is often short. This wont give the difference advantage of the height but helps .

Regards Gary

[sea rabbit]

Originally posted by nigelt
I have an Icom IC-M1 Euro handheld and would be very interested in linking it to a fixed antenna but am not sure it is possible. If not, what handhelds are you taking about which can be attached to a fixed antenna?

Nigel

I have an Icom M21 handheld and contacted them about adding an external antenna: I was told that an adaptor was available (principally for test purposes) that converted the antenna socket to a BNC (I think). You need to make sure that you fix the correct type of antenna, and I'm still researching this. The bottom line seems to be that whilst antennas will improve both Tx and Rx on a handheld, you then have to worry about trailing leads and ensuring that you maintain a good connection; then if you find yourself in the water - you won't have your radio available in its designed state. It's down to the right tool for the job really, though goodness knows how I would fit a fixed set and it's power supply into my boat! Good Luck

[nigelt]

Thanks Sea Rabbit. Almost a year since I posted that!!

I have however just bought a fixed Icom M401 last weekend so am not worried about the handheld and will use it as back up only from now on.

Nigel

[dmoore]

On the hand-held vs Fixed set issue, I use a hand held but have connected an external aerial on the top of my frame to aid proporgation. I cant proove this is better but it seem logical that the better aerial and about 1.5M extra height would make better use of the 5W power. I also use the 12V off the boat supply to make sure I get the full 5W. All I need now is a waterproof fist mike and I will have a detachable fixed rig!!!

[Jelly]

Nigel
For refference you need a SMA male to probbably BNC female or SO259 ( female PL259) to hook up an Icom M1e
Jelly

[thewavehumper]

OK guys I need to know some stuff now

SMA is that the portable antenna connector
what does SMA stand for
BNC (British Naval Connector) has a bayonet firtting, where does that go,
Most of the fixed antenna's I have seen have a UHF plug on the end of them is that what a PL 259 is

I snapped two aerials in one day on the first leg od the Round Ireland Challenge, and could have done with an adaptor at the time. But I guess it serves me right for buying a silly boat