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Re: LF: Re: MF propagation

To: <[email protected]>
Subject: Re: LF: Re: MF propagation
From: "Alan Melia" <[email protected]>
Date: Wed, 21 May 2014 12:41:30 +0100
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Hi Stefan, The way I try to separate ground and skywave is to look at a beacon transmission during daylight hours. the groundwave strength seems to correlate quite well with the minimum in the morning and evening dips. I find tis gives similar values to those calculated by the late G3FGQ's GRNDWAV3.
 
The skywave inceases in strength to mid-day at mid path, and no there is not much if any QSB because I think the skywave is quite stable most of the day.
 
Yes water does help at all frequencies in a number of ways. There is a coast effect for station near the sea a bit like focussing. The sea is generall less "rough" than land in terms of scattering the earth clinging wave,and of course the loss is less
 
I do think the daytime skywave attenuation is greater than at say 136 but I have no sensible measrements at 470kHz .....hence the "query" rather than "statement"  :-))  I guess about half the path to Mike is over water as he is a lot further inland than me..A few more simultaneous reports would be very interesting. :-))
 
Alan
----- Original Message -----
From: DK7FC
Sent: Wednesday, May 21, 2014 1:35 AM
Subject: Re: LF: Re: MF propagation

Hi Alan,

My observation is that the sky wave attenuation at daytime in summer is in the order of 40 dB over that distance. So i think it is groundwave exclusively. Also i can't see QSB over that distances at daytime (maybe 1 dB).

Water nearly seems to act as an amplifier at 630m :-) Could that be a reason for the choice of the ex marine frequency? ;-)

73, Stefan

Am 20.05.2014 21:02, schrieb Alan Melia:
Hi Stefan interesting...... at that distance could it just be different goundwave v skywave phase at the different receivers. You really need more thn two paths to pin that one :-))
 
Alan
----- Original Message -----
From: DK7FC
Sent: Tuesday, May 20, 2014 12:41 PM
Subject: LF: MF propagation

Hi MF,

Timestamp Call MHz SNR Drift Grid Pwr Reporter RGrid km az
 2014-05-20 10:10   PA0A   0.475698   +4   0   JO33de   1   G3XDV   IO91vt   466   253 
 2014-05-20 10:10   PA0A   0.475702   -25   0   JO33de   1   DK7FC   JN49ik   449   157 


That shows the difference of MF propagation over sea water and over land at daytime! (maybe 3 to 6 dB more background noise here?).

73, Stefan
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