HF ANTENNA TESTS AND AND COMPARISONS
Copyright (c) Felix Meyer
24th July 2005 / 15.8.05 / ... / 28.5.08

Evaluation of HF Antennas 
The proper evaluation of the efficiency of HF Antennas is a
very difficult and time consuming process, if it is done seriously.
Listing of the number of contacts, signal reports, list of worked
countries etc. says nothing about the efficiency of an antenna.
In this way many publications describe the quality of new antennas.

With a piece of wire, connected to an antenna tuner one can perform
worldwide contacts under good conditions, while the best antenna
does not allow to reach any contact, if there are no propagation conditions.

Also, the SWR of an antenna does not say anything about the efficiency
of an antenna. The SWR only tells us, how good the transmitter is
matched to the antenna, but does not tell how good the waves are
radiated by the antenna.
Based on the SWR, a Dummy Load would be the best antenna,
as it shows an SWR of 1.0 on all frequencies ...

The problem arises from the very different HF wave propagation,
which shows strong variations dayly, hourly, and every minute.
A signal report of S5 may be good, while a report of S9+10 may
be a bad report, as it depends strongly under what propagation
conditions the report is obtained.

How to evaluate correctly ?

In order to evaluate correctly an HF antenna, this evaluation has
to be done in contacts with Remote Stations.
The contact to a Remote Station is through sky waves, while the
waves are reflected by the ionosphere. In sky waves the antenna
polarisation is no longer important, as the polarisation changes
permanently in a random, accidental way.
To make a valid comparison, we need a defined second antenna
with known characteristics. Both antennas have to be tuned for
lowest SWR and have to be fed with equal power.
This is accomplished best by connecting both antennas through
a coax switch (A/B switch) to the same transceiver.
In order to prevent mutual coupling of the antennas, they have
to be separed at least by half wave length distance, and the coax
cables have to be decoupled by using suitable decoupling (current baluns).

Measuring in the near field, or in the ground wave is not suitable,
as remote contacts work through the sky waves.
What for serves a strong field on the ground, if hardly something is
radiated into the sky ?
 
During the contact with a Remote Station, multiple changeover
between the Test Antenna and the Comparing Antenna has to be done,
to allow the Remote Station to compare the signal levels of the
two antennas, and to perform an averaging of the signals in the QSB.

Comparation between two antennas!
At distance at long distance (300 km to 10'000 km)
- At the same time !

This has to be done with a high number of QSOs, as there are
always some "strange reports", as some operators are unable to
read correctly the signal level, or even confuse the call signs.
Furthermore, one has to make sure, that a real signal report is
obtained, as many stations just report 59 without observing the signal.
Contests are absolutely unsuitable for this purpose!

After performing more than 20 such correct test QSOs, one obtains
the real picture of the efficiency of an antenna.

This procedure requires a real big effort, but it seems to me to
be the only valid method to evaluate the efficiency of an
HF Antenna.

Note: In case of directional antennas, the test antenna, as well
as the comparing antenna have to be directed towards the
Remote Station.
And:
In this procedure it's absolutely insignificant what type of receiver
is used, and whether the receiver is calibrated or not. The only
criteria to be observed is the signal strenth difference between
the two antennas, with the determination which antenna produces
the stronger signal, or if both antennas produce the same signal strength.
As result one knows, whether the Test Antenna is better, worse, or
equal to the Comparing Antenna.
The absolute signal strength is totally irrelevant.


Felix Meyer, HB9ABX



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