Sunday, October 14, 2018

SNOTEL on 40 MHz in the USA...

This post is about the SNOTEL network in North America which shows how 40 MHz signals from remote weather stations are relayed by meteor scatter back to base stations.

SNOTEL (SNOwpack TELemetry). Across the western half of the USA, remote weather stations in mountainous locations record the level of snowfall in their respective areas. This data can then used to calculate the potential amount of melt water in the catchment area of a particular river.


Radio bursts around 40 MHz are sent at the remote sites and these signals are then reflected off trails of ionised gas left by small meteors in the upper atmosphere. These trails decay quite rapidly so the signals tend to be of a short duration.

The frequencies I have seen listed for SNOTEL are 40.530 MHz, 40.670 MHz and 41.530 MHz.
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More information is presented below...







40 Mhz SNOTEL WEATHER STATIONS!
taken from the OneList VHFSKIP Listserver!
 Date: Thu, 4 Nov 1999 15:53:36 GMT
From: David Gordon
Subject: [vhfskip] RE: SNOTEL info...
From: David Gordon

Hi there...here is a message sent to me about the SNOTEL network:
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Meteor communications was discovered by the military in the 1950's, but really didn't get off the ground until the Natural Resources Conservation Service (NRCS) began to explore what method was the most cost effective to use for automated weather stations to send their data back to a central point.

Contractors began looking at the various technologies in early 1970.  They looked at line-of-site systems, satellite, and meteor burst.  The one that we choose was meteor burst. So, in 1975, the system began to take shape and in 1976, the first SNOTEL data was transmitted using meteor burst communication.




NRCS owns and operates two master stations which act as central receiving stations.  Only one is required, but because of the critical nature of the information that SNOTEL provides to it's users, two were installed for redundancy purposes.  Each master station is able to communicate with up to
3,000 remote sites within a radius of 1,000 miles.  Once the master station receives the data, it is forwarded via landlines to Portland, OR and made available. 



Currently, SNOTEL has over 650 remote sites in twelve western states.  SNOTEL uses two frequencies; 40.530 and 41.530 MHz.  Our output power from the master stations is around 1500 watts.  The remote sites transmit on 41.530 MHz at about 100 watts.  The remote site transmitter is only on for about 0.1 seconds.  The master station transmitters are always on and must establish
the link between the master station and remote site.  Alaska has its own meteor burst master station and the data from it are delivered to Portland.




Using meteor burst communication was the cheapest method for us to use, plus it is totally under NRCS control.  If we want data, we don't have to wait for 3 to 6 hours for the satellite (GOES) to acquire the remote sites data.  With meteor burst, we can reliably get hourly data from most geographic areas, where GOES needs to have a clear view toward the south.  That means that if we wanted to put a site down in a canyon where the southern skyline was obscured, we couldn't get data out using GOES, but can with meteor burst.

If you would like to access additional information, please visit our web site at
 http://www.wcc.nrcs.usda.gov

We use two types of encoding, a 90 degree FSK for the first ~ 10 seconds of each minute then a 30 degrees FSK for the rest of the minute.  We do this to allow our two types of meteor burst radios to work.

From: "Garry Schaefer"



As you can see, this post illustrates the potential of the 40 MHz band for meteor scatter communications and experiments.

Links....
1) SNOTEL on Wikipedia
2) SNOTEL (SNOwpack TELemetry) And  SCAN (Soil Climate Analysis Network)

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