> Does anyone have any REAL data or experience with mounting a 15M beam
> 10' above a 40M beam? The concensus is that 15 and 40 interact too
> much. But all I have heard is opinion and conjecture. I know several
> who have put 40M beams above tribanders and the interaction does not
> seem to be much of a problem.
One caveat ... I haven't modeled the Force-12 40 meter antennas (linear
loading is a bit beyond me right now). However, to get a good feel for
the nature of the 40/15 stack problem I build AO models of a basic 3
element 40 meter yagi (full size elements 48 foot boom) and 5 element
15 meter yagi (similar to HyGain 155BA). The 15 meter antenna was
placed 10 feet above the 40 meter antenna in free space.
Here are the performance data for each antenna alone and for the pair
in the stack:
antenna alone stacked pair
gain F/B gain F/B
7.000 6.9 17.16 6.9 17.38
7.100 7.0 21.44 7.0 21.87
7.300 7.4 24.36 7.4 23.39
21.000 8.5 19.26 6.7 13.74
21.200 8.6 20.86 6.9 14.52
21.400 8.8 23.91 7.2 16.29
Both antennas were mounted at the center of their boom (no offset).
Gain is in dBi.
This is only one set of data points but it shows a strong (loss
of 1.8 dB forward gain and 6 dB F/B) negative interaction between
antennas on these two bands.
... Joe Subich, W8IK/4 ex-AD8I
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