Page 001AntennasŠiauliai
Forty metres of wire in a garden thirty metres long
The garden behind this house measures thirty-one metres from the back wall to the fence, and a half-wave wire for the forty-metre band wants forty. Everything I have learned about antennas here began with that shortfall and with what a person is willing to do about it.
- Date
- 21 April 2024
- UTC
- 0733
- Band
- 17 m
- Mode
- LISTEN
- Typed up
- 12 August 2024
- Reading
- 7 min
The garden decides the antenna
Books begin with the antenna and then ask where it will go. On a plot this size the question runs the other way round. The garden is a long rectangle lying roughly north-east, with the house at one end, a pear tree two-thirds of the way down and a fence the neighbours put up in 2019 that I am not going to argue with. There is one usable high point, a chimney bracket at about nine metres, and one usable far point, a spruce at the corner that sways more than I would like in an October wind.
Working from those fixed points, the honest list of antennas that fit is short. A full-size dipole for twenty metres goes up easily and does well. Forty metres needs bending. Eighty is a compromise in every direction I have measured, and one-sixty is a wire that wanders round three sides of the garden and pretends. Before putting anything up I drew the plot on squared paper at a centimetre to the metre and marked the immovable things in ink. That sheet has saved me more disappointment than any instrument I have bought since.
Bending the wire and living with it
A wire that will not fit in a straight line can be bent, and the usual advice is to keep the bend away from the middle, where the current is highest, and to let the ends do the wandering. That is what I did. The flat top runs twenty-four metres from the chimney bracket across to the spruce, and the last eight metres on either side drop away at an angle towards the fence posts, held off the wood by a short length of plastic pipe so that nothing touches anything that gets wet.
The result is not a textbook dipole and does not behave like one. It sits lower at the ends than a flat wire, which lifts the take-off angle a little, and the drooping sections interact with the fence and the gutter in ways I have never properly measured. What I can say after three years of logs is that it works, that the resonant point moved about forty kilohertz down the band when the pear tree came into leaf, and that it moves obediently back in November.
Noted in the margin
- Keep the bend out of the middle third of the wire
- Run the ends away from gutters, fences and washing lines
- Expect resonance to fall when the trees come into leaf
- Leave half a metre of slack at each end for ice and wind
The feed point, and what I got wrong for a year
For the first year the coax went straight to the centre of the wire with nothing between them, which is the commonest mistake in amateur radio and the one I had read about most often. The antenna loaded perfectly well. The trouble showed up somewhere else entirely: a hum in the audio whenever the heating pump ran, the desk lamp flickering on transmit, and a receiver noise floor that climbed two points every evening at about six o'clock.
The outside of the coax was acting as part of the antenna and carrying the whole business back into the house. A current choke at the feed point — a length of the same coax wound through a large ferrite ring and taped down — took one evening to make and changed this station more than anything else I have done to it. The lamp stopped flickering. The evening noise dropped by a genuine point and a half, and the reports other stations give me have been steadier ever since.
What it actually does on the air
Across an ordinary winter evening the bent wire on forty metres hears the whole of Europe and a good deal further east, with the first dependable openings towards the Urals about an hour after our own sunset. It is not a directional antenna in any sense I can control, although it is very slightly deaf off the ends, which on this bearing means slightly deaf towards Norway and towards the Black Sea. That is worth knowing on a night when the band sounds empty.
The thing it cannot do is make a signal out of nothing when conditions are poor, and for a whole season I blamed the bend for evenings that were simply bad. The log sorted that out. Comparing one winter of notes against the next, the poor evenings clustered around disturbed days and not around any feature of the antenna at all. A compromise wire in a small garden is a compromise, which is a different thing from an excuse.
Noted in the margin
- Slightly deaf off the ends: north-west and south-east from here
- First eastern openings roughly an hour after local sunset
- Resonance checked in April and again in November
- No argument about the pattern is worth having without a log