Hi Bob thanks for the reply. My question wasn't as clear as it could have been
so let me try again. Say we have 2 stations with isotropic transmitting
antennas and receiving antennas with good angular discrimination at each end of
a certain path. VOACAP predicts that X% of the openings will be at 1 degree, X%
at 2 degrees etc. My question is - when a path is open at an angle of say 14
degrees does anyone have an idea what the angular variation in signal strength
might be around the peak wave angle being propagated at that time?
73 Bob
Hi Bob
I haven't seen any answers from the experts, so I'll give it a try.
>> or is that the angle at which a theoretical elevation sampling antenna
>> would receive the highest strength signal?
Yes,and I think that:
You can think of the transmitted signal as having many "rays" above and
below the maximum angle of the lobe, all in phase. So the outgoing signal
has that "angular width". Each of those "rays" enters the ionosphere at a
slightly different point, so will refract differently; probably optimum
communication will occur if the receiving antenna has a similar lobe,
although some of the signal will miss the receiving site altogether.
If the transmitted lobe is angularly narrow, and it arrives at the
receiving location, the incoming lobe will appear to be narrow. If the
transmitted signal has broad angular width, there is a better chance of some
of it arriving at the receiving location, but the strength will be less than
in the case of "matching angular lobes".
This is complicated by the probability of the signal being dispersed
(spread) during passage through the ionosphere (broadening the emerging
lobe) , by the effect of non-symmetrical ducts, and by the effect of
multiple hops.
All this is intuitive logic, and although it is a very interesting
question, there are so many variables that the advantage/disadvantage of
wide or narrow lobes at Tx or Rx changes with every individual case. You
have to decide whether you want very good strength from the few signals that
arrive, or so-so strength from a greater number of signals. Same goes for
the Tx lobe; A wide angular lobe will get to more distances, but at the
expense of lesser strength at any given spot.
73
Bob VE7BS
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Topband Reflector
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