Hi Tom and Group,
I agree that an S-unit relates to a significant amount of
gain. I don't want to put words in anyone's mouth, but I
imagine that the author felt the LPDA was a good
compromise. Covering five bands with gain, F/B and low
SWR with a 12 or 18 or 24 foot boom is a big plus for those
who can't or don't want to put up optimized monobanders.
(rumor has it that someone makes a nice line of interlaced
monobanders...hi)
I sent a private e-mail relating my positive experience with
Tennadyne LPDA's. I would guess from modeling that a
24' log would give up 2 db to a monobander on a similar
boom. For me, that is fine. If you expect to be first in
every 20 meter pile-up, it probably would not be fine!
I've found that even with the short 12' version at 60', I was
usually able to work the major dx-peditions on 17 meters
with 100 watts on the first day they were on. (Typically the
first or second call) On 20, where you compete against
monobanders and amps, I'd wait a day for CW and two
days for SSB and get through fast. This has nothing to
do with any great skill level, just an example of what an
average ham can do.
73,
John W0DC
----------
> From: force12@interserv.com
> To: peterjs@worldnet.att.net; towertalk@contesting.com
> Subject: Re: Feedback on Tennadyne HF Log Periodic?
To: <towertalk@contesting.com>
> Date: Monday, February 03, 1997 11:05 AM
>
> Greetings!
>
> 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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