80 m: New HB9ABX Antenna
6th. October. 2005 / Update 14.4.2007


One of the most demanding challenges is the
development of a short antenna for 80 m, which can
compete with large antennas.
Now I have finished the construction of my 80 m
version and completed the first transmission tests.
The first problem is the antenna efficiency.
As short antennas have a very low radiation resistance,
one has to adapt the 50 ohm cable impedance to the
low radiation resistance in order to transmit the
available input power into the space.
If one manages to keep the sum of all loss resistances
below the radiation resistance, the resulting efficiency
is above 50 percent.
I could reach this target with my new antenna principle.
The SWR can be adjusted exactly to 1.0 , as on the
other bands.
Then comes the next hurdle: The bandwidth.
All short antennas have a relatively low bandwidth.
My antenna shows on 80 m a bandwidth between
40 to 50 Khz for SWR below 1:2.
Now I developed a remote frequency adjustment
which allows to adjust the resonant frequency of the
antenna between 3.5 and 3.9 Mhz. This is done
without tuner or external adaper box.
The complete adjustment ist done within the 5 cm
diameter tube of the antenna, which permits the remote
setting of SWR 1.0 to any frequency of the 80 m band
within a few seconds.
The complete antenna measures 1.8 m length and
yesterday I made the first QSOs with it.
The first contact was with Croacia, from where I
received at 15.30 h a report S8, despite the high
afternoon attenuation.
Then followed several contacts within Switzerland
where most received reports were between S9
and 9+20 dB.
An experienced HAM from Winterthur (Fred, HB9JW)
made the following comment:
In some way you must be cheating, as on 80 m
with 100 W and a 1.8 m long antenna, one cannot produce
such a strong signal ...
As next, I will collect comparitive reports, as I have
done on the other bands.

Felix Meyer HB9ABX

Update: 14.4.2007
Measured bandwidth and picture of antenna here.


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