At 05:44 PM 3/18/01 -0600, JayTerleski wrote:
>The parasitic array as we both understand are not meant for ultimate
>F/B. I like them only on the low bands where one can listen on a
>Pennant, or Beverage system.
I believe this is only partly true. The W9LT/K8UR/K3LR parasitic dipole
arrays can offer substantial F/B. My modeling indicates (and experience
verifies) that such an array can offer very substantial F/B at frequencies
a few percent above the resonant frequency of the dipoles, particularly for
higher-angle signals. I have repeatedly observed F/B on the order of 25-35
dB on US signals when my array is pointed to Europe on 75 meters (it is
resonant at the bottom of 80m). The downside is that the pattern is quite
broad, and for that reason the S/N ratio is not as good as, for example, a
long beverage. Also, the F/B ratio declines dramatically 100 kHz below the
dipoles' resonant frequency.
I've tried EWEs and a short (250') beverage on 75/80, though, and have not
found any significant advantage over the transmitting array.
As for gain, modeling could lead you to expect gain from such an array
similar to a 4-square. However, calculating the loss in the feedlines and
substituting loads of the appropriate R +/- X for transmission lines in
NEC-2 yields meaningfully lower gain, presumably due to the feedline losses.
In my case, the tower appears to play an important role in the array's
performance. Hence, I guess I should stress that YMMV.
73, Pete N4ZR
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