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KG6BAJ > ANTENA 22.06.08 12:31l 128 Lines 5191 Bytes #999 (0) @ NWSGRP
BID : 950_GVCITY
Read: GUEST
Subj: RoomCap Antenna - last results
Path: IZ3LSV<IK6IHL<I0TVL<CX2SA<KD4KVG<KG4IVD<W4RAL<KD4GCA<KG6BAJ<KG6BAJ
Sent: 080621/1552Z @:KG6BAJ.#nca.ca.usa.noam #:950 [Grass Valley] InterGate $:9
** NEWSGROUP: rec.radio.amateur.antenna
** FROM : hb9abx <hb9abx@freesurf.ch>
In September 2007 I conducted a short test between the Roomcap antenna
and a large horizontal
Loop antenna. The result was unexpectedly good for the Roomcap.
To have certainty in this respect we planned a long test in which the
following criterias applied:
- Installation of the test site, antennas, and cabling by
communication specialists of the Army
- Both antennas connected through A/B switch to the same transceiver
- Several operator who log their communication results
- Always two operators: One operating the rig, the other logging the
reports
The test was conducted on 40m in SSB under the callsign HB4FF.
This test took place on the 20th May 2008 in the military camp of the
communication troops in Emmental.
They installed as comparison antenna a horizontal loop (86m wire (2
wavelength long), 12m above ground
on a free field, with smartuner SG-230 in the feedpoint).
The station was in a barrack next to the antenna. Two coaxes (RG214)
were layed and led to the coax-switch
connected the the transceiver. The SWR of both antennas was 1:1.
The comparing antenna was a good one, as analysed by L.B.Cebik (W4RNL)
here:
http://www.cebik.com/content/a10/wire/horloop.html
http://www.cebik.com/content/fdim/atl1.html
To access these links you need a passwort (free), which you may obtain
here:
www.cebik.com/helpme.htm .
The installation and conduction of the test was supervised by a
militay communication instructor.
I only had to drive with the Roomcap Antenna (1.5 m long radiator) to
the parking place and connect my antenna
to the coax that was ready there. Connection was through two large
current baluns who prevented that RF was
fed to the outside of the coax cable. Furthermore, the coax cable was
laying on the ground.
Then, the test could begin. Operators were the two that came with me:
Dave HB9KT and Benoit HB3YRX,
and two operators from HB4FF: J=FCrg HB9BFC and Rolf HB9CVB.
The test was conducted according to "HF antenna tests and
comparisons", where in each contact the remote
operator was asked to observe the signal strength during several
changeovers between the two antennas.
The antennas were just called "antenna 1" and "antenna 2", to prevent
subjective influence. Important was
the signal strength difference und not the absolute value.
In this kind of comparison no calibration of the receiver is required,
as we only needed to see the difference of
the signals, or the finding that both signals are equal.
The polarisation of the antennas does not play any role, as only sky
wave contacts were accounted for. In these
waves the polarisation is changing permanently and unpredictable.
After 6 hours duration the test was ended, and evaluation of the logs
could begin.
The result looks like this: (here is the log)
- In 57% of the contacts the Roomcap antenna received the better
report.
- In 29% of the contacts both antennas produced equal signal strength.
- In 14% of the contacts the Loop antenna received the better report.
The largest difference in favor of the Roomcap was reported with 13 dB
(abt 2 S points).
The largest difference in favor of the Loop was 6 dB (=3D 1 S point).
By calculating the arithmetic mean of the signal differences, one
obtains a calculated advantage of 1.5 dB
in favor of the Roomcap antenna. This includes the fact, that the
coax cable RG214 to the Loop had 2.7 dB more
attenuation (on 7 MHz) caused by the length difference, and that the
connecting cable RG58 and the current baluns
had an attenuation of 0.7 dB. Accordingly, the Roomcap reports were
reduced by 2 dB (=3D 1/3 S point).
Here follows the list of the stations who provided comparitive
reports:
IK6ZNH, 2E1DHN, DJ6AL, DJ1JW, DL1HWT, DH7VK/p, 9A/DG2XO, DB9WJ, G3GBS,
DL7FF, PA3FRD,
DL1BPK, DK0SC, DG1BM, HB9BWV/m, DL5XDL, G0GHK, F/PA0JWV, DJ9OI,
OE2008SMC, DL1DXF.
HB9BWV/m reported a 30 dB stronger signal for the Roomcap. This report
was excluded in the calculation, as
the station was in the ground wave at a distance of 25 Km, where the
polarisation effect was responsible for
this high difference.
By switching between the two antennas during receiption, the same
signal difference was noted as received
from the remote station. This shows that the antenna works in
reciprocal way.
Conclusion:
This test proves clearly, that the efficiency of the Roomcap Antenna
equals that of large wire antennas,
and hereby confirms the results that I obtained during my own tests
during the last 3 years.
Each operator confirms the logged reports.
The physical explanation of this is, that generation of the EM waves
is done by the dynamic E field, as explained
in "Antennas and Physics". The dominating E field can be measured only
in the near field region of the antenna,
as in the far field a fixed relation between H and E field exists.
The far field does not allow determination how the
wave has been generated originally.
Many thanks to the above mentioned OMs for there voluntary, free
contribution in this antenna test.
Felix, HB9ABX
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