Re: Topband: Modeling the proverbial "vertical on a beach"

[Rik van Riel]

On 08/13/2014 09:47 AM, Tom W8JI wrote:

> Transmitting is a different story, if lower angles are used. I doubt,
> however, it is ever close to 10-20 dB unless it is groundwave
> propagation. I'm sure people somewhere have actual numbers on that.

One big question is, where does the path loss on top band come from?

Is the path loss due to energy lost with each hop?

If so, bending some of the radiation around the earth a little bit,
and reducing the number of hops that way, could be a significant
factor.

On the other hand, going through the D layer at a shallower angle
could also mean more signal absorption at certain times of the
day. This may explain the "I got more signal on my horizontal
dipole right around sunrise/sunset than I got on my vertical"
anecdotes.

IIRC, this difference has been reported to be 1-2 S points
by some people.

A similar difference (1-2 S points) when going the other
direction (lower angle, over a low loss medium) seems
reasonable. 20dB does seem a little out of place, unless
the losses incurred with each ionospheric hop are larger
than I suspect :)


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Topband: losses on 160m

[Carl Luetzelschwab]

Rik van Riel asked:

"One big question is, where does the path loss on top band come from?"

Per our current understanding of the lower ionosphere, the loss due to
absorption on 160m in the lower ionosphere at night is around 10 dB per
hop. Added to that is the loss due to multiple ground reflections.

If we assume 1 kW and 0 dBi antennas, multi-hop appears to be able to go to
about 10,000 km before it's below a quiet noise level. This is why ducting
is invoked for extremely long-distance QSOs - less transits through the
absorbing region and  fewer ground reflections.

There's a natural electron density valley in the nighttime ionosphere right
above the nighttime E region peak that provides the ducting mechanism -
this is the boundary between the top of the E region and the lower F
region. Ducting on 160m can be seen when doing ray traces through the
nighttime ionosphere.

Carl K9LA
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