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" <[email protected]>
To: <[email protected]>
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" <[email protected]>
To: <[email protected]>
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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