On Tue, 11 Aug 1998 11:21:33 -0400 Pete Smith <n4zr@contesting.com>
writes:
>
>At 11:02 AM 8/11/98 -0400, w8ji.tom wrote:
>>
>>Great Tom!
>>
>>I'm glad you also caught the serious flaw in the method used! Too
>many people rely on flawed measurements for critical information!
>>
>>> ALL THE RIGHT ANGLES ?
>>>
>>> YES and NO !
>>>
>>> N6BV used 100 ft elevation for his 80, 40 and 20 meter models,
>>> and 60 ft elevation for 10 and 15 meters, at both ends of the path.
>
>Am I the only one who recalls N6BV explaining that he used thousands
>of IONCAP runs to develop the arrival angle data for "All the Right
>Angles?"
>I use the VOACAP version of IONCAP, and as far as I can tell it
>doesn't factor the height of the transmitting and receiving antennas
>into its angle computations. Instead it makes arrival angle predictions
>based on frequency and the height and intensity of the ionospheric
>layers along the path.
>
>I would agree with N4KG on one point, though -- it seems obvious that
>under
>some circumstances the antenna at one or both ends of the circuit
>would be
>so much too high or too low that it would discriminate against the
>best
>propagation mode so much that a secondary mode could actually be
>stronger.
>In these golden days of 150+ solar flux, that probably will happen
>more than when the sun is less kind.
>
>73, Pete Smith N4ZR
..........................................
N4KG reply:
On page 23-21 of the 18th edition of the ARRL Antenna Book,
N6BV discusses "The IONCAP Computer Propagation Model"
and "Definitions and IONCAP Parameters" used for all of his
computer analysis.
Under the first heading he states: "The program allows the
OPERATOR to specify a wide range of parameters, including
detailed antenna models....., noise models....., minimum
elevation angles.....,different months and times...., and
solar activity levels..........."
(It is my understanding from a highly qualified friend that different
ASSUMPTIONS can lead to much higher wave angles using the
same IONCAP program. I will ask for more details.)
Under the second heading N6BV states: "The elevation angle
information contained in this section was compiled from
thousands of IONCAP runs......................Some ASSUMPTIONS
were needed for important IONCAP parameters.........flat,
average ground, clear shot to less than 1 degree, low noise....
TRANSMITTING and RECEIVING ANTENNAS were specified as
......inverted vee dipoles for 80M and 40M, apex 100 ft, gain 1 dBi,
3L Yagi, 8 dBi, for 30M and 20M, at 100 ft, and 4L Yagi's, 9 dBi,
for 15, 12, 10 M at 60 ft above ground............"
His results show most 20M propagation between 3 and 16 degrees
from W1 to Europe and another singular mode at 29 degrees.
The analysis shows NO propagation to Europe between 17 and 28
degrees. The radiation pattern of a 3L Yagi at 105 ft on 20M is
6 dB down from its maximum at roughly 16 and 23 degrees with
a deep null in between. Is it any wonder that propagation never
peaks at the angles for which both the transmitting and receiving
antennas show considerable pattern nulls? IMHO, this is
strictly due to the antenna patterns and does NOT reveal a
condition of the ionosphere, especially when his own data
shows a propagation mode at 29 degrees which lies within
the SECOND lobe of a 3L Yagi at 100 ft.
NONE of the published waveangle data was compiled for
LOWER antennas, typical of most DX station installations.
It is my belief that when lower antennas are used at the
DX source, that maximum received signal strength often
occurs at angles higher than the minimum angle needed
to reach the destination. Much of Europe is reachable in
3 hops at low angles. When the MUF is high, I believe
that 4, 5, and possibly even 6 hop modes may produce
stronger signals from stations with LOW antennas and
these are best received with LOW antennas at this end
as well, primarily during our daytime.
One interesting example was observed by my friend N4AR
who had installed a 4 high stack of 10M beams and reported
hearing a strong echo on European signals. When he added
a separate 4L10 at 40 ft, signals were stronger and the echo
disappeared. My conclusion is that he was forcing a lot of gain
at approximately 6 degrees but the Europeans were radiating
more energy at 12 degrees than at 6. The Echo was caused
by the RX gain peak at the first mode and the TX peak at the
second (higher angle) mode being received at near equal
levels. When the lower antenna was used, TX and RX
gain peaks were matched and the echo went away.
de Tom N4KG
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