Well said Frank,
When I was first experimenting with the Hi-Z all active 8 element array
through modelling I placed a simple 125 foot vertical in the model and found
serious interaction at 800 feet separation and some pattern perturbation at
1000 feet. However, we routinely can recommend nesting a 160 meter and 80 meter
version of 8 element high impedance receiving arrays (200 and 100 foot
diameter) as we have also not seen serious mutual impedance affects. RDF or
directivity with any close physically long pseudo element like power wires or
resonant element comes with a price on top band for sure. My conclusion at that
time was that a single antenna with greater than 13.5 dB RDF was not likely to
work at most ham radio sites due to interaction with something. However,
phasing two lesser-compromised high RDF antennas is working well providing
modelled and anecdotally observed RDF of 15 dB (Where is the government budget
when we need it). Fortunately even with some pattern or RDF compromising inter
ference a good receiving antenna remains much better than most simple
transmitting antennas for low noise receiving.
Lee K7TJR OR
Corollary: You can't have too many antennas except when they interfere with
each other which they often do on Topband where a wavelength is approximately
500 feet...
Even on 20 meters, the pattern of a Yagi is noticeably degraded when it points
through another 20 meter Yagi or tribander 500 feet distant or more.
Fortunately most Topband receiving antennas don't interfere with each other --
except at extremely close spacing -- because their mutual impedance is
negligible. But transmitting antennas and other antenna-like radiators such as
power lines -- even 1000 feet away or more -- can significantly degrade the
directivity of Topband receiving antennas.
73
Frank
W3LPL
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