Portable VHF Connector

discovery2

discovery2

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I have an Icom IC-M3EURO portable VHF and would like to be able to connect the set to an external aerial (to improve the range if the main VHF or aerial failed).

The rubber stub aerial has a screw connection.

Does anyone know if there is a compatible connector (plug) to connect the set to the aerial co-ax, and if so, who may be able to supply one.
 
IMHO it is important to check what are the specs for the external aerial: while a higher aerial can be beneficial in receiving (if it has not "failed"), in transmission You must be aware that the little power emitted by a handheld coul be dissipated by the resistance of the cable and also stationary waves could limit the effective emission as well as "burning" the output part of the hand held; for this reason it is a good practice to "tune" every radio station to its aerial system using a ROS meter.
(Expert radio amateurs please forgive this layman explanation!!!)
Cheers
 
[ QUOTE ]
IMHO it is important to check what are the specs for the external aerial: while a higher aerial can be beneficial in receiving (if it has not "failed"), in transmission You must be aware that the little power emitted by a handheld coul be dissipated by the resistance of the cable and also stationary waves could limit the effective emission as well as "burning" the output part of the hand held; for this reason it is a good practice to "tune" every radio station to its aerial system using a ROS meter.
(Expert radio amateurs please forgive this layman explanation!!!)
Cheers

[/ QUOTE ]If you mean, 'Make sure the impedance of the external antenna is correct for the hand-held radio' you are correct.

However, nearly all VHF radios expect an impedence of 50 ohms and that is what the yacht VHF co-ax and antennas are as well (by some strange coincidence...)

Losses in the cable are a problem - especially when water has got into the co-ax. The biggest problem is that simple SWR bridges don't tell you whether the cable is 50 Ohms and low loss, or 50 Ohms and full of water.
 
The connector on the handheld is probably a BNC, but could be SMA. A VHF antenna terminates at the fixed radio in a PL259 plug which fits the SO239 socket at the back of the radio. To use the same antenna to connect to your handheld, therefore, you need a BNC/SO239 adaptor. (This is occassionally referred to as a BNC/PL258). This assumes your Icom has a BNC connector for its own antenna. Icom will be able to tell you.
 
The 50 Ohms is not coincidence - it is a round number halfway between the maximum power dissipation (30 Ohms) and minimum attenuation (77 Ohms).

If you attach a shop bought antenna and 5W is dissipated in the cable, or the SWR is such that it damages the PA, then they owe you a replacement radio.
 
[ QUOTE ]
The 50 Ohms is not coincidence - it is a round number halfway between the maximum power dissipation (30 Ohms) and minimum attenuation (77 Ohms).


[/ QUOTE ]

With the greatest respect, this sentence makes no sense AT ALL.

Attenuation of a transmission line is not a direct function of its impedence. You can have low loss lines of a variety of impedences.

Loss is a function of the conductivity and the dielectric medium of the transmission line.

Successful power dissipation occurs when the output stage, transmission line and antenna all have matching impedences.
 
If the antenna has a screw connection then it isn't BNC. (that has a bayonet fitting) It is likely to be TNC. Some manufactuers do not use a standard fitting so I would check with Icom.
You will find a very significant increase in range on both transmit and receive by connecting your handheld to a mast top antenna. Virtually all systems have are 50 ohm so it will be compatable. Icom sets are rugged and will safely operate into high VSWR's ( as will most handhelds since the rubber duck antenna impedance is not well defined when close to the body) so there is little chance of causing damage.
Best regards.
 
My best guess is that you want a PL259 to SMA adapter. Google shows a number of suppliers in the UK. eg http://www.kcb.co.uk/prices/plugs.htm

This question has been asked a number of times, but *as far as I know* the definitive fitting required for an Icom hand-held antenna has not been posted. if you succeed it would be useful if you could post the details of the adapter that works.

PS. I agree it certainly does not sound like a BNC, they are 'push and half turn', not screw-on.
 
I have recently researched this for an Icom M31, with a screw thread aerial fitting. Icom do the adaptors to a BNC connection-I ordered one by phone last week & checked fitting to H/H, tho' havent been down to boat yet to check boat aerial connection, but the end looks right. Cost was about £13.00. Try phoning Icom on 01227 741741 (Jamie in Sales).
 
Yes - I would like this setup as well.

My Icom M1V H/H has a screw socket with an exterior thread that is 36 TPI (whitworth?) with an O/D of 6+mm (1/4" ?)

Any ideas for a plug?

I move from boat to boat - can I assume that most fixed VHFs have SO239 sockets ?

thanks for any help...
 
BNC is almost never used as the connection between a fixed VHF and its antenna. But don't worry! BNC-PL259 adaptors are easily available, you will just have to stack them up. BNC is commonly used as the connection between anteanna and set on handhelds - but not by icom for some perverse reason.
 
[ QUOTE ]
[ QUOTE ]
The 50 Ohms is not coincidence - it is a round number halfway between the maximum power dissipation (30 Ohms) and minimum attenuation (77 Ohms).


[/ QUOTE ]

With the greatest respect, this sentence makes no sense AT ALL.

Attenuation of a transmission line is not a direct function of its impedence. You can have low loss lines of a variety of impedences.

Loss is a function of the conductivity and the dielectric medium of the transmission line.

Successful power dissipation occurs when the output stage, transmission line and antenna all have matching impedences.

[/ QUOTE ]

My reference would disagree with you (Lee T.H., "Planar Microwave Devices", Cambridge University Press, Cambridge 2004. pp. 71-73)

Power Handling:
For any given co-axial transmission line, there exists a breakdown voltage - to increase this you increase the diameter of the outer conductor which alters the characteristic impedance. There is a ratio of inner to outer diameters which give maximum breakdown voltage. This ratio is maximum at 30 ohms. Smith (of Smith chart fame received a patent for this result)

Attenuation:
is independent of conductor size, as you say. However, the resistance per unit length is caused by the skin effect. To reduce loss, you need a bigger centre conductor, which reduces the characteristic impedance, the optimal ratio of inner to outer diameters occurs at 77 Ohms.

That's why Transmitting eqpt is at 50 Ohms (halfway between max power handling and min attenuation) and Receiving eqpt is at 75 Ohms.
 
Yes, but be careful of the terminology, I am not sure if there is an agreed notation. But at least some work like this; you need a PL259 to SMA adapter to take the PL259 on the end of the antenna lead to an SMA. There is actually a SO239 socket on the end of the adapter, but its designed to take the plug so is called a 'PL259 to whatever' adapter. It makes a kind of sense.
 
Thanks for posting the querry discovery2. I had often wondered if this was possible. I followed the suggested link to KCB and have ordered a connector thingy for about £4 inc postage. I have a emergency VHF ariel in the grab bag, bit useless if the main VHF dies, this way I can use this or the mani ariel with our handheld. Thanks guys!!!
 
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