 This is my HF aerial set up. My main interest in the HF spectrum is rag chewing on the lower frequency
bands, 160, 80 & 40m.
For many years I used a centre fed 80m dipole fed with 450ohm balanced feeder all
the way back to an ATU in the shack. This is a classic solution and worked very well on all bands from 80 - 10m. However
being only 1/4 wave length long its performance on 160m left a lot to be desired compared to other stations using 1/2
wave aerial.
Many hours of research eventually led me to the conclusion that an Inverted L aerial fed
via a remote ATU would be a good option to try. I had already constructed the Picatune Auto ATU designed by G3XJP so now seemed a good time to put it to use.
Of course, depending on the feed-point impedance, an end fed aerial can require an effective ground system to radiate efficiently.
I installed 16 radials fanning out in a quadrant from the base of the vertical section, each 15m long. Far from ideal but
the best I could do without completely wrecking the Lawn.
One of the delightful aspects of the Picatune ATU
is that all DC power and control signal requirements are fed via the Coax feeder cable. This greatly simplified
installation. It has many other virtues that are not found on commercial Auto ATUs and these are described in the original
published article.
Results have been excellent. I have not observed any degradation in signals on 80m and
I would estimate that signals have improved by several S points (12-18dB) on 160m. The vertical section is approximately
70ft from the nearest house and although I was not expecting it, the noise level did not increase at all. In fact it is quieter
than my old aerial. This is somewhat curious and I think results from a combination of the buried coax and
the two choke baluns installed one at each end of the coax feeder to reduce noise currents induced on the outer of the coax
braid.
In conclusion the Inverted L is an excellent all round aerial for my requirement. In some respects the
aerial is shorter than ideal and I intend to lengthen the vertical section to 45ft. This will have the effect of
reducing the feedpoint impedance on 80m and cause less stress to the Picatune ATU when running 400 Watts. At the 100 Watt
level it is perfectly acceptable as it is. It does need to be planned properly and may not suit all situations. It is more
of an aerial system than a basic centre fed doublet.
A good starter reference is 'In Practice'
by Ian White G3SEK, RadCom December 2000.
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