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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