Introduction The 432MHz band used to be one of my favourites. In the early 1980s I owned one of the first FM321 70cms synthesised 4W FM transceivers (based on an Australian CB radio) and with this and an old Jaybeam 48el TV antenna mounted vertically on a pole and turned by hand on the side of the house I was able to work lots of local repeaters and some decent inter-G DX on FM simplex when there was "a bit of a lift on". 70cms has localised lifts every few days and that was part of the magic of the band: one day you could hear just locals and the next (in just one direction maybe) more distant repeaters or simplex stations could be heard or worked. Every day was different. Occasionally the band would be wide open and some super DX could be heard or worked. In those days I did not have any SSB transmitting gear on the band but I did listen in contests and at other times and well recall hearing an OZ station running 10W to an HB9CV antenna and being a true 59+ signal on a small indoor beam in the bedroom. The band is excellent for tropo DXing but it is much under-used nowadays. Fortunately there is still
activity during contests and on Aug 3rd 2008 there was the RSGB
70cms low power contest restricted to stations running 25W or
less. For a change I wanted to have a go /P but the problem
was I had no beam antennas for the band just a the vertical
colinear fixed on the side of the house. So, a check on the
net showed up a design for a Moxon 2el yagi using a coat
hanger! A quick search through my wife's wardrobe turned up
a suitable metal one and 30 minutes of relaxing sawing, bending and straightening
in the back of the garage resulted in a somewhat "Heath Robinson"
2 element antenna attached on the end of a 2m long plastic conduit tube.
Connection between the coax and the feedpoint was via a small
terminal block and the insulator between director and driven
elements by a piece of PVC insulation grabbed from some 2 core
cable. The whole antenna was supported on the pole using a support
bracket made from a remaining piece of the coat hanger. The Moxon Antenna Design
Testing I have no test gear for 70cms other than my FT817 and a power meter so I had to check the antenna using these. The SWR meter on the FT817 suggested the match was not brilliant (2 bars, which is about 2:1?) but not bad. A quick test using the local repeater with the antenna mounted vertically was successful and suggested some directionality. So, the next stage was to get out on the Sunday morning with the antenna and the 5W FT817 and see how it performed. Results  The results were amazing. In
a few hours of operating, much of it in the rain and with distinctly
poor conditions a total of 10 stations in 8 locator squares
all across the country were worked all with just 5W SSB apart from the best contact
(which was on CW) with F8BRK
who was 326kms away in France. The site chosen was screened
towards France by trees and rising ground making this final contact
all the more pleasing. The contact started out on SSB but he
was struggling so I switched to CW so he could clearly get my
details. |
