Aren't we being a bit imprecise here?
LF sigs are used by submarines submerged because the sea is transparent at
lower frequencies. If that is so then there is no (less) reflection at the
surface the presence of which is detrimental.
Franks interesting bit about reception in NC refers to 770khz - a long way
from 136 - which in turn is a long way from the navy/submarine freqs.
(anyone know what the navy freqs. are ? )
What works at 770 may not apply at 136. as we know from day/night MW
broadcasts
I have done plenty of amateur /MM operating from small sail-boats from 10m
to 80 . Making a low resistance connection to the sea is not that simple and
I could waste a lot of the lists time on the subject, but I certainly have
far better results from simple vertical wire antennas than ever on land.
does anyone know what happens to lf radio waves transitting the sea/air
interface either from under or above ??
Bryan G3GVB - AC4UA
----- Original Message -----
From: "Frank Gentges" <[email protected]>
To: <[email protected]>
Sent: 15 January 2004 01:11
Subject: Re: LF: Re: lf andnoise and offshore.
Peter,
AMRAD conducted several winter trips to the Outer Banks of North
Carolina to listen to LF signals in the days before transatlantic
amateur signals were common. The Outer Banks are a long narrow strip of
land several miles offshore from the North Carolina mainland. We
observed LF broadcast signals and compared to what we were seeing at
sites more inland were stronger. We attributed this signal difference
to sea gain and would put its value at 10 or more dB in the few cases we
observed although we did not make careful measurements.
The ITU has put together a model for radio propagation and includes a
factor for sea gain. It only works out to be worth a couple of dB in
the test cases we ran. I think the ITU model does not recognize the
amount of sea gain that is available from moving to the sea coast for
the really best conditions at least below 200 kHz.. I am convinced it
is there and is significant.
Also the noise was low but we could find quiet sites inland and we just
could not hear the Transatlantic signals nearly as well inland.
<caution, speculation on> I speculate that the LF waves are combining.
and adding in phase due to the long wavelength, at the sea water
interface and traveling in as surface waves stronger than the low angle
sky waves that created them.. Similar to glints or mirages we see
optically. <speculation off> We can hear other surface waves at 770
kHz on the Outer Banks from New York City duirng the day and night. We
cannot hear them much past a mile inland as the land kills the surface
wave propagation. While we did not conduct a similar experimant on LF I
suspect they would also fade down to the sky wave strength if we went
inland.
Frank K0BRA
Peter van Daalen wrote:
>Sorry,
>
>I made a most ennoying typo :
>
>I wrote :
>
>snip.....
>" Does sea again ( if any at all ? ) and low man made and evironment
noise
>add
>substantially to the LF performance ? "
>snip.....
>
>
>While I meant to write :
>
>" Does seagain ( if any at all ? ) and etc... add substantially to LF
>performance ? "
>
>I do know something on sea gain on 144 Mhz ( for /MM EME purpose on
moonrise
>and moonset ) but I am unaware of the seagain effects on LF.
>
>
>
>
>
>
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