LF: LF and /MM performance offshore.

To:	[email protected]
Subject:	LF: LF and /MM performance offshore.
From:	"Peter van Daalen" <[email protected]>
Date:	Thu, 15 Jan 2004 04:05:56 +0100
References:	<014d01c3dac6$cd3aabe0$f89a8418@Peter> <[email protected]>
Reply-to:	[email protected]
Sender:	<[email protected]>

Thanks, Frank, this is definitely most interesting info for me.

Could anyone make now a rough estimation of the possible total /MM performance gain in dB over a well equipped and favourably situated land station ?

I mean the possible " real " seagain effect as per Franks speculation plus the effect of the " virtual " seagain thru much better antenna efficiency because of the vessels' steel hull and deck etc. in salt water plus the effect of flat and undisturbed 360 degrees radiation surface ( sea ) plus the effect of reduced or near zero manmade noise at high sea ( I have 26.4 KWH DC battery banks onboard for the EME in statu nascendi and during Rx/Tx I switch AC generators off ).

All electrical/electronic gear ( except the mandatory navigation gear, but these are very well shielded ) is switched off during Rx.

73, Peter, PE1ECM

----- Original Message -----

From: "Frank Gentges" <[email protected]>

To: <[email protected]>

Sent: Thursday, January 15, 2004 2:11 AM

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

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