Jan.E.Holm@telia.se wrote:
> Ok, so no low angle signals for DX on 160 and 80, correct?
> How far from the sea do you have to be to get low angle?
> If this is correct why don´t we use high angle radiators?
> I mean., if it isn´t low angle it must be high, or what am
> I missing here?
I have not seen much data on angle-of-arrival of DX signals on
160. However, over the past year I have had the opportunity to make many
observations on angle-of-arrival on 80 with a rather unique antenna system
which has a steerable vertical takeoff angle. I think some of this is
relevant to 160. I am referring to the 80 meter system I designed and
helped build for KC1XX: a 2-over-2 stack of 2-element delta loops with the
top array at 300 feet (90 m) and the lower one at 150 feet (45 m). Some of
you contesters are aware of this system. The takeoff angle can be steered
between low and high angles by changing the phasing--0 or 180
degrees--between the arrays. When operated with both out-of-phase
(BOP), the stack produces a single high-angle lobe at a takeoff angle of
45-50 degrees. With both in-phase (BIP), the takeoff angle is 15-20
degrees, although terrain modeling analysis shows the gain response extends
to very low angles because of the drop off in terrain around the
antenna. By comparing signal strengths in the low and high-angle
configurations, one can infer something about angle-of-arrival.
What I have observed is that there is a LOT of variability in
angle-of-arrival of DX signals. Usually the BIP configuration with its low
angle opens and closes the band, and can be many, many dB superior to BOP
at these times--but not always. Just last weekend, I was working the first
Europeans at our sunset and BOP was around 10 dB stronger than BIP. Much
of the time, particularly in the first few hours of the European openings,
there is not a lot of difference between BIP and BOP, which seems to
indicate the angles are in an intermediate range. Around European sunrise,
the angle often drops and signals become loud on BIP and in the noise on
BOP--but not always. In the deep Pacific, which is a long haul from W1,
the signals are almost always low angle, and sometimes very low. When
there are ionospheric disturbances, BOP is as good as or better than BIP.
I tend to believe that because we are at the peak of the sunspot cycle
where the MUF's are high, the useful angles on the low bands are higher
than they would be during low sunspot years when the MUF drops. To
reiterate, it is hard to make sweeping generalizations about
angle-of-arrival. I think it is safe to say that both high and low angles
occur and are useful for DX work.
73, John W1FV
--
FAQ on WWW: http://www.contesting.com/FAQ/topband
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|