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Re: [IRCA] Max. Groundwave Propagation Distance?
- Subject: Re: [IRCA] Max. Groundwave Propagation Distance?
- From: "Powell E. Way III W4OPW" <w4opw@xxxxxxxxx>
- Date: Fri, 7 Mar 2008 14:12:47 -0800 (PST)
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--- "Jeff T. Casey" <ne2j@xxxxxxxx> wrote:
> Hi all,
>
> How far do groundwave signals travel on the
> mediumwave broadcast band? That is, beyond what
> distance can MW signals normally be assumed to be
> arriving via skywave, if there is no unusual terrain
> along the path? Or is it impossible to generalize,
> because of differences in transmitter power?
You cannot generalize. The low end of the band is far
different than the high end, and ground conductivity
plays a VERY essential part of how far a MW signal
will go out via groundwave. Groundwave NEVER goes
farther than skywave normally. There IS NO groundwave
on shortwave. There's some line of site stuff like FM,
but it's not truly groundwave.
> Although not directly relevant to the MW band, an
> empirical study reported recently in QST magazine
> found that, on the high frequency bands (I believe
> the study involved 3.5, 7, and 14 MHz), ham signals
> from surprisingly short distances -- as little as
> 15-20 miles or so away, if memory serves -- are, in
> most cases, arriving via near vertical incidence
> skywave (NVIS) propagation, rather than groundwave.
That is correct.
> However, the lower the frequency, the farther
> groundwaves travel, so this study's results would
> have presumably been somewhat different, if the
> researchers had studied MW signals.
There is very poor groundwave on the upper end of the
broadcast band. The 160 meter band has some
groundwave, and it's not good when you have only a
limited amount of power. High power on the upper end
of the BC band shows there is always some skywave
component even in summer, but it's high angle and can
cause grief to groundwave reception at 70 to 90 miles.
Powell
NNNN
POP email is powell at backroads DOT net
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