OK1DIG wrote: I am considering to stack the 40 m 2 element moxon beam
below my existing
40 m 4 el 40M4LLDD @ 30m agl.
If you feed these as a stack, getting the phasing proper will not be
easy. It will either require a very accurate modeling job or many trips
up and down the tower. A more practical way would be to use separate
feedlines and do the phasing on the ground. Even if you succeed in
getting the phasing correct, I think you will be disappointed at the
results. You will loose a significant amount of low angle gain versus
using only the 40M4LLDD. The combination will fill in the first null
from the 40M4LLDD but that should be at a high angle (maybe about 45
degrees), so the combination would only be useful for very close stations.
You could use them as separate antennas and switch between them, but I
think the only time the lower antenna will be useful will be for very
close stations (so you wouldn't want it fixed). When used as separate
antennas I would also expect to see some amount of interaction, maybe
some degradation in F/B of the top antenna depending on the directions
they are pointed. I would expect to see a more significant pattern
distortion of the bottom antenna caused by the top antenna. That would
require a modeling job.
If you think about using these as a stack, I think you can see what
will happen. You will be decreasing the power to the top antenna by 3
dB and applying that power to a lower antenna that sends most of the
signal up at a high angle. However since the lower antenna has less
gain than the top antenna, it's gain at low angles is not enough to make
up for the 3 dB low angle gain loss in the top antenna. The effect is a
lot like creating a stack where the bottom antenna is too low. Stacking
identical antennas at good spacings is not the same.
Jerry, K4SAV
Daniel Glanc wrote:
> Hi everyone,
>
>
>
> I am considering to stack the 40 m 2 element moxon beam below my existing
> 40 m 4 el 40M4LLDD @ 30m agl.
>
> I am not sure if this is a good idea. I can't model the situation. My idea
> is to put it @ 15m agl beaming into one direction (NA).
>
> I would appreciate any comments or hints form the community.
>
>
>
> Thanks in advance
>
>
>
> Daniel / OK1DIG ( also OK7M and OL6X )
>
> _____
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