On Wed, 27 May 1998 22:22:22 -0500 Tom Champlin <w0hh@ix.netcom.com>
writes:
>.....snip.... I have a 40-2cd in the basement I never
>finished, because, frankly the thing needs to be up at about 140' to
>have any real gain.
>
>Tom W0HH
>
WRONG !
This kind of thinking results from the misconception that DX signals
ONLY propagate at the lowest angle that will link two distant locations
in
the minimum number of hops. Most propagation programs list the
waveangle that corresponds to this minimum number of hops.
In actuallity, the ionosphere will support much higher waveangles.
Several factors can combine to produce the strongest signal at
waveangles higher than those corresponding to the minimum number
of hops. These include absorption in the D layer (which is higher
for low angles since they spend more time in the D layer), LOW
ANTENNAS at the DX end (which radiate more energy at HIGHER
angles), and DUCTING effects and E-layer effects which take high
angles and bend (refract) them to lower angles aimed at the F layer.
It is fairly easy to determine the highest angle that will propagate:
Simply observe the closest stations that are heard via ionospheric
refraction. Knowing this SKIP distance, and the height of the ionosphere
will yield the highest angle supported by the ionosphere (see graph of
waveangles vs. distance published in ARRL Antenna Books and other
sources).
>From 40 years of DX and contest experience, and discussing antenna
performance vs. height with station owners having more than one 40M
beam, my opinion is that 80 to 100 ft is optimum on 40M during the
late afternoon and evenings. Higher antennnas (140 to 200 ft) pay of in
the
early morning, especially just before sunrise and just after sunrise on
the
LONG PATH to Central Asia and the SKEW PATH to SE Asia (from eastern
USA). Everyone I know with both high and low 40M beams uses their
LOW antenna for the evening opening to Europe and Africa.
Even if you can't get a 40M beam up at 80 ft, it is still beneficial.
Did you
ever hear A22MN on 40M? His big signal originated from a 40-2CD at
50 ft.
By now, most readers are tired of hearing me tell about how my 40 ft high
TH7 is often my BEST antenna during daylight hours on the high bands.
You need BOTH high and low antennas to cover ALL of the waveangles
supported by the ionosphere and the LOW antennas will OFTEN outperform
higher antennas when MUF's are higher than the band in use.
de Tom N4KG (with 20 antennas on 7 towers from 40 to 140 ft)
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