In a message dated 97-01-09 01:13:26 EST, you write:
>
>3. I use 5 of them here and stretch them a total of 175'. At the far end
>I terminate with a 600 Ohm resistor (not critical, I've used 470 to 750
>Ohms) to an 8' ground rod.
When the distributed series inductance of a longwire is increased, the
impedance increases while the velocity of propagation decreases.
Slowing the velocity of propagation increases directvity of a l;ongwire, up
to a limit of perhaps vp = .50 . When vp is slowed beyond the rate of about
.50 freespace pattern becomes a mess.
I have no idea of the distributed inductance of a slinky (it would depend on
how far you stretched it out), but the surge impedance would be MUCH higher
than 600 ohms and would be critical. Since C remains the same....the more L
per length, the higher the impedance.
If the antenna has F/B ratio without proper termination, it is only because
the antenna has so much transmission loss termination is not critical.
I've done the same thing with ferrite coating, strings of beads on a wire,
and lumped inductors. Four or more evenly spaced inductors will do the same
thing as a slinky. In ALL cases, surge (and proper terminating) impedance
went up into the thousands of ohms. If terminating (and feed[point) impedance
does NOT go up, you didn't change (electrically lengthen) the antenna.
73 Tom
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