Topband: 160m Mobile whips as a dipole, or a beam ?

[Bill Tippett <btippett@alum.mit.edu>]

K3LR wrote:

>As far as terminations, I have not experimented with putting 
resistors or other
matching networks at the feedpoints of the Valor antennas, however I do plan to
match them to 75 ohms at some point with simple L networks. I'll also add
ferrite feedline chokes at each antenna feedpoint to make certain that each
feedline is isolated. I expect to see a small enhancement to the pattern of the
array with these changes and also I expect the array gain to increase slightly
because of proper matching.

        Tim, since these are for RX only, you might
consider a 75:50 ohm transformer based on the Mix 73
binocular cores.  For an unisolated transformer you
could use 6 turns total with a tap at 5 turns for the
50 ohm side.  (1.2 turns ratio = 1.44 impedance ratio)
For an isolated transformer you could use 6 turns on
the 75 ohm side and 5 turns on the 50 ohm side if you
use small wire.  8 turns total is about the max I can
do with #26 insulated but I'm sure you could get 11
turns total by using smaller insulated wire.

        The advantage of this over an L network is that
it's broadbanded for those using the array on multiple
bands, and the isolated transformer accomplishes both
of your objectives above (matching and isolation).

                                        73,  Bill  W4ZV
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