BC-DX 841 04 Jan 2008 Private Verwendung der Meldun

the exceptions I know about. J. R. Wait wrote a whole book on the subject.
And >1/R conditions can exist only for limited areas because of the laws
of conservation of energy.) Thus for a 1 MW omni 1/4 wave antenna, E ~
10,000 mV/m at 1 km, so at 1000 km E 10 mV/m unattenuated. But the
attenuation is, even for sea water at 500 kHz, substantial: 20 dB/1000 km,
so received field would actually be 1 mV/m. At the upper end of the band
the attenuation over sea water is a little over 30 dB/1000 km. Any path
over land has far greater loss. At 500 kHz even very good ground has about
36 dB/1000 km loss, while at 1.6 MHz it's over 110 dB.
2. Daytime skywave probably accounts for most N. America reception at
distances greater than 4 or 500 miles or a little further (over the 30
mS/m conductivity in the Great Plains region, for example). And despite
the fact that the Fuzzy Confusion Commisariat won't consider the concept
of daytime skywave, it's clearly a factor where powers greater than the
Region II 100 kW limit are used, and is certainly observable from time to
time in N. America as well.
I have certainly seen (or more correctly, measured) it, particularly where
the ground conductivity was poor and skywave predominated at relatively
short distances from a high power site with DA gain.
ITU-R Recommendation P.1147 ("Prediction of Skywave Field
Strengths......") at Annex 2 "A discussion on daytime sky-wave
propagation" item 2, "MF cases," states: "/Available data show that midday
sky-wave field strengths display a consistent seasonal variation pattern
with maximum occurring in winter months. The average winter-month field
strength is about 10 dB stronger than the annual median value and the
winter-to-summer ratio can exceed 30 dB.
The annual median value of midday field strength is about 43 dB lower than
its counterpart at six hours after sunset. Field strength exceeded for 10%
of the days of the year is about 13 dB stronger than the annual median
value. See also the ITU-R Handbook - The ionosphere and its effects on
radiowave propagation."
3. The reason a good ground system is important for producing skywave is
that it produces the field from the "image" antenna that is below the
"half-space."
(Ben Dawson, Hatfield & Dawson, WA-USA, dxld Mar 11)
#*#*#**#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#*#
60 YEARS AGO In the lead up to celebrations of the DX League's 60th
Anniversary in October, we note the following in the March 1948 issue of
DX BULLETIN (NZ), forerunner of the NZ DX TIMES:
A report from a radio conference in Melbourne on 10 March 1948 indicated
the extension of the medium waveband for NZ out from 1500 to 1600
kilocycles. DXers were reminded to listen out for stations running all-
night during state elections in Wisconsin, Illinois, Nebraska,
Pennsylvania, Massachusetts and Maryland. California had introduced
Daylight Saving Time meaning its stations signed off an hour earlier to
allow reception from other states.
The DX Ladder of Fame made its first appearance in the magazine, listing
NZ's leading broadcast DXers as ALBIE STANTON of Dunedin with 1112
verifications and LES HOPKINS of Waitoa with 807.
On shortwave, listening highlights reported included Test Broadcasts by
the International Committee of the Red Cross on 6345kcs most evenings,
VLG11 Melbourne 15210 commencing broadcasts on 11 March, VLW5 Perth well
received overnight on new 9610kcs, a new DX Session scripted by ARNE SKOOG