Message-ID: <2ad401c9e768$92568ad0$7900a8c0@athlon1200>
From: "Dave Brown" <tractorb@ihug.co.nz>
To: <rsgb_lf_group@blacksheep.org>
References: <4A2B7CC7.4020002@btconnect.com> <002501c9e75e$10131d40$0900a8c0@AM>
Date: Mon, 8 Jun 2009 00:07:46 +1200
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Subject: LF: Re: Re: 500kHz Diurnal Noise Variation
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Back in 1997 we temporarily activated a 400 foot ex AM broadcast mast 
at Kumara on the West Coast of the South Island. With an SSB signal at 
around 100 watts PEP into the mast, we had good LF propagation (i.e. 
good reports) in  the westerly direction to Tasmania until quite late 
in the morning- circa 9.30 or so local NZ time, which would have 
corresponded  approximately to the onset of daylight over the complete 
path to VK7. The distance was roughly 2200km in a more or less 
northwest  direction from ZL.

We were working crossband, with VK7RO operating on 40 metres, so it 
was readily apparent that the LF signals on 182 kHz disappeared fairly 
quickly, having been pretty consistent up to that time, over a fully 
dark and then a partially dark path.   Signals were down an S point or 
so from the 'fully dark path' levels  which had been 5/9/9 on CW and 
5/9 on SSB, but were still quite impressive.

 I found this result somewhat surprising at the time and still do.

Would have been great to have that QTH set up as a permanent LF tx 
site, it was absolutely magnificent! They demoloshed the mast a few 
months later. I have a video of the mast coming down- spectacular to 
watch/hear, but also disappointing.

73
Dave, ZL3FJ


----- Original Message ----- 
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, June 07, 2009 10:48 PM
Subject: LF: Re: 500kHz Diurnal Noise Variation


> Hi Richard,
> I think the noise variation is very similar to that on 136k and 
> relates to
> the position of the the dawn/disk edge. In the morning as the dawn 
> sweeps
> west across Europe the night-time skywave delivery of all this noise 
> (both
> atmospheric and man-made) is wiped out by D-layer absorption. We in 
> the UK
> get no noise from the west as its is mainly water. (the condition is 
> exactly
> the opposite on the East coast of the States). There seems to be 
> less
> lightning over water too.
>
> The catch is that just around dawn there is a very quite 
> period....this is
> very encouraging and many have tried to make good DX in that period
> .....unsuccessfully. I believe that this period is dogged by intense
> absorbtion because at dawn the D-layer is first illuminated from 
> underneath
> (NM6M Bob Brown QST about 1999) by solar rays that have grazed the 
> ground
> before impinging on the D-layer about 1000km W of the ground dawn 
> line. Thus
> in this quiet period there is just no propagation by skywave so that 
> DX is
> not possible. Quite often the best time has been just before (say 60 
> mins)
> dawn (at mid path)before the absorption starts.. N<>S paths are more
> seriously affected than E<>W paths.
>
> Once the sun rises and the ionosphere is illuminated from above then 
> normal
> daytime skywave returns slowly with the best singnals around mid-day 
> at
> mid-path. 500k is complicate dby the possibility of two "reflection 
> heights"
> which give rise to the deep daytime fading not seen on 136kHz, 
> though this
> my only occur later in the day.
>
> There are difference between 136 and 500k but I think the noise 
> problem is
> similar.
>
> Best of luck
> Alan G3NYK
>
> ----- Original Message -----
> From: "Richard Newstead" <g3cwi@btconnect.com>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Sunday, June 07, 2009 9:39 AM
> Subject: LF: 500kHz Diurnal Noise Variation
>
>
>> I wonder if anyone has attempted to plot the diurnal noise levels 
>> on
>> 500kHz? I wonder if, for instance, very early on a Sunday morning 
>> is
>> particularly quiet?
>>
>> 73
>>
>> Richard
>> G3CWI
>>
>>
>
>


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