Topband: Vertical antenna near field efficiency

John Kaufmann
Thu, 19 Apr 2001 22:03:52 -0400

At 02:35 PM 4/19/01 -0400, John Mitchell wrote:
>   Other
>sources I've read dispute the need for very low angle radiation on 160M,
>citing increased D layer absorption, for one thing.  My sense is that angles
>much below 15 degrees or so are probably less important than for the higher
>bands, although they cannot be discounted completely.

I haven't seen any data on angle-of-arrival statistics for 160 meters, 
although data (from propagation analysis programs) exists for higher 
frequencies.  The trend certainly seems to show that higher angles are more 
useful for DX work at lower frequencies than they are at higher frequencies.

I have quite a bit of experience in direct observations of angle-of-arrival 
on 80 meters in W1 land which might be relevant to 160.  This is based on 
my operations with the monster 80-meter antenna system at KC1XX, which I 
have described on the Topband reflector before.  That system consists of 
stacked 2-element delta loops at 150 and 300 feet.  The upper and lower 
arrays can be operated either in-phase or out-of-phase by remote switching 
from the shack.  Modeling shows that in-phase produces a single 
well-defined lobe with a takeoff angle around 10-15 degrees and sharp 
cutoff above 30 degrees.  Out-of-phase produces a single lobe with a 
takeoff angle around 45 degrees and a sharp cutoff below 30 
degrees.  Comparing signal strengths in the two configurations gives you a 
pretty good idea of angle-of-arrival.

Short-hop high-angle signals from W3 or VE1 into New England are typically 
20 dB better out-of-phase (no surprise).  For DX signals, however, the 
results are quite varied.  Very long haul DX, like deep Pacific or central 
Asia, is indeed low angle, being consistently much better 
in-phase.  However, angles for medium haul DX like Europe seem to be not 
that low most of the time, at least not during this part of the sunspot 
cycle.  In-phase is usually better here, but typically by not more than a 
few dB.

During the middle of the evening, in-phase and out-of-phase are often about 
equal into Europe, which suggests arrival angles in the range of 30 
degrees or so.  Occasionally--usually during the onset of ionospheric 
disturbances--out-of-phase is significantly better.  During the recent ARRL 
DX SSB test, this was the case on Sunday afternoon/evening.

No more than 5 or 10 percent of the time do I see really low angles into 
Europe where the in-phase stack is significantly better.  This occurs 
primarily when the band first opens or when the band closes into 
Europe.  This is very much like what we observe with stacked antennas at 
KC1XX into Europe on 20, 15, and 10 meters , too.

Now if we ever put up our 160 stack, I'll have some real data to report 
next time for 160.   ;-)

73, John W1FV

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