LF: LF and /MM performance offshore.

["Peter van Daalen" <peter@vandaalen.demon.nl>]

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" <fgentges@mindspring.com>

To: <rsgb_lf_group@blacksheep.org>

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