Hi Chaps - I saw the discussion on the modes and losses and
wanted to add a bit -
When looking at WWVB 60Khz (close to
74?) contours for daytime I notice more of a Vertical peanut shape in the
fiedlstrength favoring North South, with highest losses over Mountaineous
terrain and likely the lowest ground conductivity, say between 0.5 and 2
milliseimens - something we see (in general) afforded by ground to the West of
Ft Collins (especially NW) and to the Eastern mountain ranges, and its not too
Bright on most bearings from here in Alaska as we have a lot of the pointy
high snow covered thingies up here too. I see they plonked WWVB there
due to having local high Alkalinity of the soil - high
conductance.
Whether given the height of the mountains even
at 60kHz we loose a bit more than flat Earth Id say a whopping Yes, that and
some of the oddities that ground waves going over glaciers can have all add up
to further attenuation.
Have a looksee at
http://www.fcc.gov/encyclopedia/m3-map-effective-ground-conductivity-united-states-wall-sized-map-am-broadcast-stations If
I look at how /4 gets up here - it would in reality have to be a fairly high
angle reflection, as Im close in to the Chugach and Talkeetna Mountains and
those mountain ranges extends hundered of miles on the /4 bearing. -
I see no signal at all (ok I wasnt using OPds) and even with a reasonable
antennae and good s/n its a sky wave opening only - well, at any reasonably
power that we can generate. Whereas he was strong in CA last night he was only
just detectable up here - though I blame the Auroral ovaly stuff too for
that.
Interestingly enough and with the limited amount of data -
if Bob was to generate another 3dB he would have probably been visisble at dot
60 every night to date over the 5000Kms path or so , ie a lot less variation
on a day to day than I see at 137.
On groundwave on 137 I did
some reasonable tests and with my 3W ERP (ish) in the main loop on a quiet
iono day in Autumn maintaining a CW just read level of some 1000Kms down to
Corpus Christi from the OKie/Kansas Border and but out West was
considerably poorer - we had poor conductivity to the West of us for a
while....
I saw with interest on the NIST web site the scalloped
nature of signal reception at night at 60KHz at some times of the
night.
http://tf.nist.gov/images/radiostations/wwvb-large/0800utc.jpg Cheers
from a soggy snowyish
Anchorage.
