Bill I will answer in line, it is a good discussion
thank you for the questions.
<Lee, I wasn't going to mention this
but since you did, I've got to ask some dumb
questions.>
<1. Why would you ever choose 4 separate phase-
controlled TXs instead of simply using one
Comtek 4-square controller costing $350?>
W8JI has introduced a 4 element receive antenna that
covers an octave of bandwidth. His focus was on
cleanliness of pattern and low noise. I would like my
4 element transmitting antenna to cover an octave of
bandwidth. To accomplish this using comteck boxes
would require about 5 or 6 boxes/antennas ground
fields. How much work is that?
<2. Why would you want to run 4 separate
feedlines instead of one to the controller box?>
<3. Why would you want to have 4 separate amps at
375 Watts output each instead of one at 1.5 kW?>
2&3 375 watts is easily do-able with transistors and
automatic antenna tuners (like the LDG series), and it
would not be too hard to actually mount the amp/tuner
at the antenna, so you could use 4 cheap feedlines to
drive them. Also on transmit you really only care
about maximum forward gain in the given direction you
are interested in reaching, and not "pattern", so you
could choose the "phasing" and even the array geometry
that maximizes gain in the particular direction you
are interested in. If you mount the amp at the
antenna you don't care if it has a lot of blower noise
for example. Also there is no feedline loss. Given
the class of amplifier they are considering it is not
too far fetched to choose transistors that will give
you 375 watts out of the flex radio box. If you are
80% efficient 100 watts of dissapation will cover you
to 400 watts output power. If that's the case all you
would need is a tuner at the base of the antenna for
multibanding and some way to measure phase/gain at the
base of the antenna.
<4. What would happen to phase coherency
when passed through 4 separate amplifiers
and tank circuits?>
4 Phase coherency could probably be dynamically
controlled by measuring the phase/gain at the base of
each element. Something like a souped up LP-100 meter
could probably do this. Larry uses this idea in his
beam antenna.
<5. Has anyone actually computed cost
comparisons for 4 TX, 4 amps and 4 feedlines
versus 1 TX, 1 amp, 1 feedline and 1 Comtek
controller?>
5. What is the cost of multiple 4 squares with
multiple ground fields, multiple comtek boxes and an
alpha 87?
Note this particular array could easily fit on a lot
an acre or probably a little less. Combine this with
a W8JI receive array on another corner of the lot and
you could put a very nice high performance station on
the air. What is the cost of 30 acres in the country?
73 W9OY
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|