COMPARISON: RoomCap with EH antenna on 160m
 
1st December 2006


The EH-antenna  is offered as a compact, efficient short antenna.
The user reports about this antenna are very varying, from enthusiastic
to unusable.
Therefore, I was interested since long time to perform a comparison test
of the RoomCap with this antenna.

On Nov 30, 2006 we could do that.
Andy, HB9DWF is owner of this antenna, and he was willing to perform
a field test.
We installed both antennas in a free camp and tested exhaustively on 160m.

Comparing antenna: EH Venus from Arno (Italy, WIMO Germany)
                                  Length = 2.5m, Diameter = 8cm / 12.5cm, Weight = 4.9 Kg
Test antenna           : RoomCap 160m, radiator length = 3m, Diameter = 7,5cm
                                  with top capacity

Both antennas were installed with about 30m separation, at a height of 1.5m
above ground, and connected via decoupled coax cable and coax AB switch to
the 100 W transceiver.

First, the SWR was checked:
It was found, that the EH antenna is very narrow, in contrast to the statement
of WIMO who says:
"due to the design the entire band can be used."

The acceptable bandwith of the antenna was found to be just 20 KHz (!)
with resonance at 1.860 MHz.
In contrast, the RoomCap can be used in the full band from 1.800 to 2.000
with a VSWR 1:1, without using a tuner.
This problem complicated the testing somewhat, as we had to ask the
remote stations to change the QRG to 1.860 to allow operation of
the EH antenna on its best operating frequency.

The comparison tests began at 20.00hrs with a duration of one hour
and 20 minutes.
Until then we had 11 test contacts, and Andy said, that further QSOs
do no longer change the result. The result was clear.

In each contact the antennas were changed many times, and the remote
operators were asked to measure the signal difference.
All stations reported that the EH antenna is significantly weaker, and
they reported signal differences beween 2 to 4 S points.
The averaged signal difference was 3 S points.
Some stations were unable to measure the signal difference, as the
signal of the EH antenna was not readable.

The following stations participated in the comparing test QSOs:
F9EZ, I2BBJ, HB9ZY, F/HB9DHO, HB9BBM, HB9AGN, HB9COP,
HB9JMD, DL9FCP, DL1EFR, DB3MA.

Conclusion:
The test showed, that it is possible to make contacts with the EH antenna,
however the signal strength in comparison to the RoomCap antenna is
about 3 S points (= 18 dB) weaker.
(18 dB correspond to a power relation of 1:63).
This "good result" is obtained only, if the antenna is operated within
20 KHz of the resonant frequency. If the antenna is used outside this
frequency range, an additional signal loss of 1 S point and more is to
be expected ...


Felix Meyer HB9ABX


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