Sunday, 6 March 2016

Fitting an external antenna to a Standard Horizon HX280E handheld VHF

One of the mini-projects this winter was a temporary solution to my requirement for a permanent VHF. As good as the winter was in terms of crossing stuff off the job list, I never managed to get to the electrics, and a fixed VHF requires pukka 12v power. In order to resolve the issue temporarily, and to increase the range of my hand held, I came up with a plan to use it with an external antenna suitable to be used with the fixed VHF when I get it...

Now I'll be the first to say that the subject of VHF sockets/connections was Greek to me, but with the assistance of some of the guys on the Practical Boat Owner web forum, I now have a significantly slightly better idea of what's going on - but I'm no expert - so if anyone chooses to believe the following, I would advise double checking....  having said that, with the exception of the external antenna most of these adaptors and connectors come in at less than a fiver...

There are a number of things to bear in mind when looking at antenna's (and this site [clicky] gives an excellent overview of them) but my understanding is that "Gain" is the most important as that is a reflection of the 'power' of the antenna...  simply put, the bigger the aerial the bigger the gain/power.. but over 3' length and the power is at expense of the shape of the radio wave..  way too complicated, but there is a reason that most antenna's on yachts are the 3' type - they are the accepted compromise, and that was good enough for me...

The external antenna I bought then was this one - a bog standard 1mtr, glass fibre pole - in this case made by Banten (who seem to have a fairly good reputation) - you'll note the gain is quoted in decibels (3 db). By comparison my hand held has the 'usual' 6" rubber aerial attached to the handheld via a stub screw - gain on these antennas are usually quoted as 0 db..



I bought the antenna from these guys [clicky] based on price (about £37), but also because it came with the following - an adjustable mounting block, 5 mtrs of RG58 type cable that was pre-attached to the aerial (NB. over a certain length ie. 6 mtrs'ish, RG58 is not good enough - the link above gives the alternatives), and they also supplied a plug (more of which anon)...


So my main reason for doing this was to get a little extra range - I'm not planning to shift the aerial to the top of the mast (though I may do one day) as I sail predominantly in Chichester Harbour and the Solent so range is not super critical. Either way there is some maths you can do (just do a search on 'VHF range calculation' on Google and you'll even find sites that do the calculations for you) but assuming a 30 foot mast at the coastguard, I reckon I'd get about 15 miles range if my antenna was at the top of the mast, as opposed to 11 miles with it on the pushpit board... the Solent is only 4 miles wide at it's widest so I think it'll be good even taking account of line of sight...

So - antenna taken care of, how did I connect it to the handheld?

Seemingly you have two choices - and it basically comes down to choice of connector...

My aerial came with a PL-259 type like so:


I believe most fixed VHF's come with this socket, and certainly this was how the fixed VHF on my old boat connected...

The alternative is a co-ax type connection called a BNC - people who have worked in an office may find this familiar as it used to be used for LAN cabling - if you go this route you need a 50 ohm type (they also come in 75 ohms which are more commonly used for TV/Camera type applications).


Either connector (BNC or PL-259) is valid for this project, also you can get crimp on type in both, but I think the general opinion is that a soldered connection is better. Longer term I will be fitting a fixed VHF (next winter probably), so I decided to go PL-259 from the outset. In either case - whichever plug you decide on for the antenna - you will then need the relevant adaptor for the hand held, and based on advice I would suggest these..

BNC:

You need an SMA<=>BNC adapter, the Standard horizon version is their CN-3 adapter. This is a single piece unit that screws on to the handhled and has a BNC plug at the other end..



I ordered one of these [picture above - clicky] (before I made up my mind about going PL-259 )

PL-259

Same applies you need an SMA<=>PL-259 adapter (NB. Sometimes they refer to SO239 as that is the name of the socket for the PL-259 plug)

Examples include the following - you have a choice basically between a single piece unit as per the BNC example above, or one with a short length of cable between the two adaptors..

http://www.ebay.co.uk/itm/SMA-male-t.../191521373255?

http://www.ebay.co.uk/itm/PL259-PLUG...item1e74c006a5

I went for the single piece adaptor in the second link.

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