Klaus von der Heide wrote:
Dear all,
nearly two years ago we had a discussion about Phased Arrays
and Diversity on this reflector.
Diversity is a method to choose the temporarily best signal
from receivers that are many wavelength apart from each other.
Especially when the antenna must be omnidirectional, this is
advantageous. The 10 m relay in Hamburg is a well known example.
Phased Arrays combine several antennas coherently. For an
acceptable antenna pattern the distances of the individual
antennas should be about a quarter of a wavelength (as in a Yagi).
The combination can be done in several ways:
1. Direct combination of the antenna feeds as in Yagi-groups
2. Combination after preamplification
3. Combination after conversion
The first way is not possible on LF because of the distances.
The third way needs coherent oscillators at all wide spread
receiver frontends or a sufficiently strong pilot signal
in the LF band that could be used later to make all converted
signals coherent. Since, in any way, the signals must be combined
from distances of some hundred meters to a few kilometers
the optimum choice are IR-links that can transmit the 136 kHz
bands directly to a central station (way 2.).
The combination at the central station can be done in two ways:
a. Delaying the individual signals appropriately to realize
one directional pattern, then adding them and receiving with
a conventional receiver.
b. Downconverting all signals in parallel using the same
oscillator (which in this case is no problem), digitize
the signals and implement delay patterns for all directions
you want in parallel by a DSP. This is equivalent to a
strongly directional antenna with high gain that simultaneously
What radio amateur is going to go to all this trouble for an occasionl
QSO. At present there are only 7 active radio amateurs on 136 khz. Get
real, learn the morse code, operating procedures, get the best antenna
installed on your property that you can manage and that is all you need.
The rest is just patience, listen and work what you can hear.
From the radio amateur point of view that is all that is required,
except you intend to shift vast volumes of radio traffic. The commercial
operators on LF have invented it all and RE-INVENTED it
Years ago the radio amateur was ahead in his garden shed but today he is
so far behind in the same shed, it seems some people never learn.
G3KEV
looks in many directions.
73 de Klaus, DJ5HG
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