> birdies were not present on the transformer version. I
> suggest to anyone
> who does not believe this: try it yourself.
I have, several times and the results were not good. It
would also be interesting to see how others who have built
arrays weigh in on this. I know ZL3IX and others use active
elements.
At quiet locations a 25-30dB gain amplifier with a few dB
noise figure and 3000 ohm impedance amplifier won't get you
into atmospherics. This is especially true in a small array
with close spacing, since the signal from the elements don't
add in phase. For example at my location I barely get into
propagated background noise with an active element 10 feet
tall.
Leaving 25-30dB gain out of a system that often needs even
more gain isn't a good idea. Of course if the element is
long enough then the rest of the system can have loss
without problems. That's a heap of gain to make up for in
the shack!
The other thing the amplifiers do is have a source impedance
of about 60 ohms or so to drive the 75 ohm cable. A
reasonable and stable (over frequency) output impedance is
necessary to maintain phase in the elements. As I pointed
out earlier the elements can be very reactive (capacitive)
or they have to appear to be a broadband resistance, either
is OK.
73 Tom
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