Graham Phillips, G3XTZ wrote:
. . . . my vertical is 20 meters high, but the two 10 meter loading
wires from the top have to slope down at about 45 degrees ( to fit in the
available space ). I have always thought that the effective loss of height
was a price worth paying to avoid the need for a much higher value of
loading inductance ( and loss ) at the base of the vertical. . . . .
I would like to hear what others may think of the options: (1) eliminate
the top capacity loading, and wind a bigger loading coil. ( 2 ) Fit a
small, lightweight inductance at the top of the vertical and reduce the
length of the capacity wires. ( 3 ) A combination of both. ( 4 ) Move.
They all sound like good options!
I use a basic 12 m vertical with good results. But the improvement with my 8 m
balloon-supported extension (making it a 20 m vertical) is significant (perhaps,
+6 dB?). So, it seems to me that antenna height is very important. Therefore,
I am not keen on using sloping top wires which lower the effective antenna
height.
On the other hand, I'm quite happy to compensate for the low top capacitance of
my vertical by adding a few more mH to the loading coil. I guess I see things
differently: for me, the power loss in the additional inductance is a price
worth paying to avoid lowering the effective antenna height through the use of
sloping top wires!
It's now time to try putting some numbers to this puzzle! Any offers?
By the way, Graham, if you decide on option (4), I still need GI ; GJ; GU; and
GD!!
Regards to all,
Steve GW4ALG
[email protected]
|
