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[aprssig] 6.72m Propagation Network Already In Service

Jon Adams jon at jonadams.com
Sun Jan 6 06:20:14 UTC 2008


Good evening, Ev, Bob and others -

Did you know that the BNSF Railway is running a nice 44.58MHz network 
with about 600 base stations spread over a great part of the US west of 
the Mississippi? It's 9600 baud, does not rely upon meteor scatter, is 
called "Extended Line of Sight" propagation, short packets generally, 
GMSK modulation. About 100-150 locomotives, most of the trackside defect 
detectors, most of the highway vehicles that also have ability to get up 
on the rail, have transceivers now as well. All the transceivers are 
100W tx and the vehicle/trackside equipment antennas are either loaded 
1/4 or full-size halfwave antennas. Base station antennas are coaxial 
dipoles high up on towers, generally 60-100'. Network is very chatty, 
but apparently quite efficient, with dozens of packets per minute from 
any one base station. While it's not exactly continuous duty, when a 
propagation event occurs, the number of packets per minute can easily 
top 100. Packet types include location packets, for base and mobile 
devices, network beacons, telemetry packets, control packets, etc. The 
network runs in a TDMA polled mode, so the field devices only talk when 
authorized.

The reason I bring this up is that this network is already far more 
dense than most anything that hams could create. It's a great tool for 
seeing propagation in real time, and while 6-3/4m is a little longer 
than 6 and shorter than 10, it's probably a good indicator.

If you listen on 44.58MHz FM narrow, maybe you'll hear the short bursts, 
especially if you're anywhere near a BNSF line. Here at my qth, I have a 
receiver specifically for that band and service, and have received 
packets from as far away as Minnesota. We're looking for hams who would 
be willing to add a dedicated receiver and antenna to their setups to 
collect this data - we have a server that then plots the current prop on 
Google Earth as well as web pages that provide specific statistics on 
the data. There are about 19 receiving sites now, concentrated in AZ and 
IL, with a few more in SoCal, Washington state, Colorado, Iowa, New 
Mexico, Wisconsin. The radios we use for reception are generally old 
boat-anchor Motos, including Micors, Mitreks, Maratracs, Maxtracs, some 
plain-vanilla scanners work fine too. All require direct discriminator 
output, and a sound card that has really good low-frequency performance 
(there's no scrambling on the data, so there can be really long 
sequences of zeroes). Nearly all the antennas are homebrew, either 
vertical dipoles, loaded quarter waves, or fullsize ground planes.
 
While this Meteorcomm network does not rely upon meteor scatter, it does 
provide a fine tool for detecting potential meteor scatter events as 
well as other ionospheric stuff. And when the skip is in, I'm not sure 
how their network can deal with the onslaught of packets, but it seems 
to work fine.

Many of us who are involved with this are hams, with a fair number who 
are railfans and not hams. What you get in return for participation in 
this network is the propagation data in digestible format. If you're 
interested in participating, reply to me off-list.

73 - Jon N7UV








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