>EXPERIMENTAL RESULTS:
>
>I purchased two of the DXE active whips. On one of them, I replaced the
>amplifier
>with a transformer. The other one was unmodified (as a "control"). In
>A/B tests,
>both were equally sensitive, being limited by external noise. The
>S-meter reading
>was lower on the transformer equipped whip, of course, but the signal to
>noise
>ratio was the same. I added a 50 ohm preamp to the FT1000D, and then
>the two
>systems were completely indistinguishable from each other, except that
>the BCB
>birdies were not present on the transformer version. I suggest to anyone
>who does not believe this: try it yourself.
>
>Rick N6RK
My experimental results confirm what Rick has observed (with all due respect
to Tom and Jim).
I built an RX array in 1989 using three sets of crossed dipoles. Each dipole
was about 10 feet above the ground and a total of 24 feet long (2 by
12 ft pieces
of 1" aluminum tubing).
The three crossed-dipoles were arrayed into a right angle array and used as an
interferometer at 3.125 MHz to do a D-region partial reflections experiment at
Arecibo using their ionospheric heater as the TX source. Each dipole
was analyzed
separately so that RH and LH polarization (specifically, Ordinary and
eXtraordinary)
could be measured.
Each dipole just had a 1800-50 ohm transformer for "sampling" the voltage and
NO preamp. The sky noise was the limiting factor on sensitivity and the phase
shifts were exactly as predicted -- at least over the bandwidths used
in the pulse
system. Phase shift in this application is critical since this array
was used as an
Imaging Doppler Interferometer as well as direct O- and X-
calculations. The results
of the AIDA Act 89 (Arecibo Initiative in the Dynamics of the
Atmosphere -- 1989)
were published in a special edition of Radio Science.
I had originally intended to build a system with the traditional
voltage probe style
FET preamp, but decided it was a waste of time and money plus it added more
complexity and possible issues with MTBF. So I decided to skip the active
devices and run with transformers only. The results were as expected
and desired.
ie, It worked for me!
John W0UN
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