w5uc> Looking at the effect of varying the
phase by a small amount my simple mind said: I don't know the angle
at which local interference arrives. The only thing I can guestimate
is the arrival angle of stateside & DX signals, therefore I can
possibly reduce the overall amount of signal in the receiver front
end by increasing the high angle F/B.<
I think we all would like to know the arrival angles of signals however it
will likely be a long time before we do. Enter the often heard comment that one
can never have enough antennas. What I see here on Beverages and vertical
arrays is that signals within about 500 miles show 'Generally' no directivity
on any of my arrays and a slight bit further out on the Beverages. My vertical
arrays do not show limited directivity in their plots until about 80 degrees
elevation if we can believe the computers. Beverages slightly lower with many
lobes. I also do see the early morning high angle signals from JA/UA0 at this
Qth. I am working on a high angle array to the West. If it is local man made
noise you are talking about you might benefit from a noise canceller.
Personal observation is that if we could educate the lids to stop
transmitting right on top of the DX a lot of these interfering signals would go
away. Also using the maximum attenuation you can get away with in your radio
may increase its signal handling ability. Roofing filters rule! they really
help on handling loud signals amongst small ones. I have added an animated
graphic to my web page that shows what happens with varying the phase in steps
on a 2 element array. "http://www.k7tjr.com/rx1comparison.htm"; . As per my
previous comment some of the parameters are rather insensitive to a few degrees
of shift.
Tod K0TO recently mentioned using the DXE variable phase unit with active
two verticals. I hope he continues to post his results here so we can all see.
Three active or passive antennas in a triangular array make a really nice
array as W4TV mentions. I have the data but it will be a bit before I can put
it on the comparison page. Good RDF, F/B, and 6 directions.
I have steered away from loop type antennas as in my models I see wildly
varying front to back with elevation angle. In my models at very low elevation
angle the pattern always widens out and the RDF suffers. I have programmed
loops as high as 80 feet elevation and see no improvement. If you optimize the
front to back by setting the phase delay for a low angle, there is very little
front to back at a high angle. This makes a variable phase network or cable
length switching necessary with loops for all different conditions. This is
much less prevalent in vertical arrays. Verticals show a much cleaner low angle
response in my models than any others I have modeled.
For general DXing I suppose having a variable phase is OK but in contesting
is seems to me out of the question.
Lee K7TJR Oregon
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