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RE: LF: Coast to Coast on 74kHz ground wave ?

To: "[email protected]" <[email protected]>
Subject: RE: LF: Coast to Coast on 74kHz ground wave ?
From: Laurence KL7 L <[email protected]>
Date: Thu, 2 Jan 2014 17:34:27 -0900
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Bob - Jay - thanks - Yes its the same here in the NDB world -  it was always amusing to work with (or against mostly) a certain government agency who phoned me up time and time again, mostly in the Winter and advised me that one of Blow torch NDBs needed a tweak up or down a dB or two/three to maintain field levels  - which typically was indicative of the soil becoming frozen to some depth between them (Railton) and one of my sites.

They stopped calling me when I asked how there weather was- and Yes a hooge difference in propagation between 60k in winter and summer - same for over the Pole stuff too where in  Summer (when its light :-) I can just see DHO38 but in winter peaks 30-40dB over noise - I see its off at the moment.

I see a number of papers around using various forms of ground penetrating radar to improve the conductivity/permittivity measurement for radio and non radio means (and as Bob says seasonal dependent measurements) - the comments about the old maps were similar to Bobs "Dont mean stink, well ok as a generalisation...it still looks like a Peanut to me" :-)

Yep Bob its needs a signal

Laurence KL7 L


From: [email protected]
To: [email protected]
Date: Thu, 2 Jan 2014 21:16:07 -0500
Subject: Re: LF: Coast to Coast on 74kHz ground wave ?

Laurence, Bob
 
I cherry picked the winter and summer SNR levels of WWVB at different US locations ...  see
 
 
The daytime path from Boulder to Cutler ME is about 7 dB better SNR in the winter and fairly flat from 1600 - 2000Z. The daytime path from Boulder to San Diego is a bit more 'peaky' with best SNR at about 1800 Z but is only a few dB better in winter vs. summer.
 
While this doesn't shed a lot of light on what to expect coast to coast it does confirm the advantage of wintertime conditions at 60 kHz. I don't have information as to whether the SNR differences are due to changes in ground conductivity, lower background noise, or some combination of both. 
 
Jay W1VD  WD2XNS  WE2XGR/2  WG2XRS/2  
----- Original Message -----
From: Bob Raide
Sent: Thursday, January 02, 2014 8:09 PM
Subject: RE: LF: Coast to Coast on 74kHz ground wave ?

Laurence;
It would be easy to determine coverage of radio signals of longer wavelengths using the soil map.  However, the "soil map" is only an estimate and changes DRASTICALLY from season to season.  When the ground freezes the conductivity in my area goes from about a 3 [soil map shows I'm in 4] to over 12-14 and the colder it gets the higher it goes!  I have been and still am in the broadcast business building my first AM station licensed to Penn Yan NY in 1980.  Transmitter site just west of where I am sitting right now.  I found 850 kHz fit here perfectly for a KW daytimer.  My consulting engineer Harold Munn in Michigan said "no so fast".  You see, measurements takes precedence over the soil map.  It happens that I was up against the Cornell University 870 5KW station and clearance was somewhat close but signals did not overlap.  I rented a calibrated field set [FIM41] and took the measurements in March.  Broadcast engineers and communications attorneys want to see cold weather measurements not those taken in 100 degree July heat!  My council tendered my app along with my measurements.  This measurement program was not to end here!  Before it was over with Cornell's engineers and council 3 sets of measurements were taken and finally joint measurements were agreed upon in October of the following year!
I have since built or modified and owned 4 other AMs-all requiring measurements to show the allocations or modifications fit for one reason or another.
Needless to say for an attempt at west coast groundwave I would also look at as close to 68 kHz as I could find clear! Lower the freq the further the groundwave per meter of signal strength.
This is why I made the statement that a signal must be put on the air to determine coverage!  I would only attempt such a feat as hitting the west coast groundwave in dead cold frozen ground of Winter!!!  Frozen ground is cheating a bit and engineers taking measurements would never agree to such measurements unless they could be averaged with mid summer measurements and the average taken for the allocation. 
The soil map?  In the world of broadcast engineering "don't mean stink".
 

From: [email protected]
To: [email protected]
Date: Thu, 2 Jan 2014 15:20:00 -0900
Subject: LF: Coast to Coast on 74kHz ground wave ?

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.
 
 
 
 
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