Feedback on Tennadyne HF Log Periodic?
Mon, 3 Feb 1997 09:05:21 -0800
Was reading the replies to your inquiry about the Tennadyne HF log LPDA
antennas. The one from KE1Y was very intriguing.
He comments that he has used two 10 element Tennadyne's (one at 60' and another
at 120') and offers a comparison to a 4 element monobander at 150'. We don't
know several things that could affect the comparison, such as what frequency the
monobander is on and how long the boom is (or possibly even a modeled gain
figure), as well as the terrain. The number of tests and period of time that the
tests were run is very important, too. Anectodal tests are quite useful if they
are run over a long period of time and the results carefully tracked.
The interesting point is the observed difference of 1 S-unit. If we accept the
ARRL Handbook's estimate of 6dB per S-unit, this difference is a lot. Even if an
S-unit is 5 dB, the difference is still a lot.
The reason is that the 4 element monobander probably has a forward gain figure
in the vicinity of 6dBd. Depending on the design, maybe a little more, maybe a
little less. So, when the 10 element log periodic shows up as being 1 S-unit
less than the monobander, the question is what does that mean in terms of
possible forward gain of the 10 element log?
Why, then, would someone comment that the 10 element log is a great antenna,
when it appears to be substantially inferior to a 4 element monobander? Let's
assume the worst case: the log has zero forward gain (equivalent to a dipole).
The answer is that a horizontal dipole is an excellent antenna and if the dipole
is improved by a dB or two, it is even better. A high, horizontal dipole is
excellent. This is borne out by current comments on the Reflector about
rotatable 40 mtr dipoles and how well they perform.
We also should not lose sight of minimizing the impact of 1 S-unit. This
represents a lot of gain, regardless of what an S-unit might actually be
(3-6dB). Anyone who operates the low bands (in particular) would give a lot
sometimes for 1 (maybe 2) more dB in receiving, transmitting, or both! It often
makes the difference between a QSO and not being heard.
73, Tom, N6BT
Force 12 Antennas and Systems
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