VHF radio out of the ark

[Guest]

I have recently obtained a somewhat old and very bulky 24 volt VHF radio ,exact make unknown, but with the 'Redifusion' logo on, which works pretty damn well without an aeriel, but will no doubt work even better with it.And thats the problem. I know nowt about VHF aeriels etc and my local electrical shop seems to be only interested in DVDs and Scart interfaces ???. Any advice on aeriels,cables and connectors etc greatly appreciated . Thanks Rob

 

[Guest]

Rob, It seems to be aerial night tonight. Here goes with a quick lesson. First of all, all the items used aerial,connectors and cable must have the same "impeadance" as your radio. I imagine that your radio has a socket which is threaded,about 16mm diam with a 3mm hole, this will be a 50 ohm impeadance uhf socket. You will need a PL259 plug to fit this socket together with a cable adapter. Use RG58 coaxial cable, DO NOT use TV coax as this is 75 ohm impeadance. The actual aerial has to be cut to a length which matches the operating frequency, usually one quarter wavelength. You can calculate the wavelength in metres as follows 300/frequency in MHertz. so for normal boat VHF 300/158= 1.898Metres so your aerial should be 475mm long. After you have done all this it is a good idea to have the SWR (standing wave ratio)checked, this will tell you how efficient your coax cable/aerial are. All the bits you need are available from Maplin.

Hope this is useful Good luck

 

[Guest]

For appx £20.00 it is possible to buy an aerial and save all the construction hassle.

I agree that it is a good idea to have an SWR meter in the aerial lead, it is a great way to monitor the transmitter and aerial operation.

I have found some older VHF sets with "N" type 50 ohme connectors but the PL259 is the more common.

 

[Guest]

Whip aerials

You'll find most marine VHF aerials are 1/2 wavelength, about 950mm.

RG 58 coax from RS Components - look in their catalogue for the necessary plug - this could be one of a number if it's out of a commercial vessel.

 

[Guest]

It's really terribly complicated. What you have to do is to go to your nearest chandlers, ask for a VHF aerial, and hand over about £25 in beer vouchers. For that, you will get an aerial, already tuned to the right frequency and connected to the right kind of cable, complete with the right kind of plug, and instructions.