[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[IRCA] coverage versus frequency over land
- Subject: [IRCA] coverage versus frequency over land
- From: Charles A Taylor <MWDXer@xxxxxxx>
- Date: Mon, 05 Feb 2007 09:56:57 -0500
"Is it true that lower freq daytime signals travel further than higher ones
since stations on the lower end seem to come in stronger than ones at the
top with the same power from the same location,(disregarding signal
direction),because the wave length is longer on the lower freqs? Also I
thought that stations on lower channels used higher towers,while shorter
towers were used by stations radiating shorter waves,but I see that does
not always apply in every case. Bill in Vic. "
_______________________________________________________________________________________________________________________________________________________
Bill,
I don't think the answers you got for your question are sufficient.
Vertically polarized MW groundwave signals travel along with their lower
end connecting with the ground. As they radiate outward, the ground absorbs
more and more of the wavefront's energy.
The equations that predict the attenuation versus distance have a factor
for frequency. This factor plainly predicts that an LW signal will travel
further than a MW signal.
Also, ground conductivity has a strong influence on the
distance-versus-attenuation behaviour of signals.
Groundwave signals above about 2 - 3 MHz attenuate so rapidly that they are
essentially useless for broadcast purposes. What you receive at VHF and UHF
frequencies are direct waves that don't involve the earth.
While the earth attenuates a LW or MW signal, it also provides a means for
their propagation.
If the earth were perfectly conductive, then signals would travel much
further than they would if they were travelling through space.
Also, horizontally-polarized signals are effectively short-circuited by
contact with the earth. That's why horizontal antennas are not used at LW
and MW frequencies.
Yes, horizontal antennas have been used by MW stations; but usually as a
top-loading for a vertical member that radiates the vertically-polarized
signals.
This all partially explains why sea paths propagate MW signals much more
effectively than lands paths: sea wave is vastly more conductive than earth.
I hope this adds to your understanding. If you want more explanation, just
let me know.
73 de Charlie
-----
Charles A Taylor, WD4INP
Greenville, North Carolina
_______________________________________________
IRCA mailing list
IRCA@xxxxxxxxxxxxxxxx
http://montreal.kotalampi.com/mailman/listinfo/irca
Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers
For more information: http://www.ircaonline.org
To Post a message: irca@xxxxxxxxxxxxxxxx