[GreenKeys] Questions about some signals on the air.

[Randy and Sherry Guttery]

On 5/25/2012 10:30 PM, tony j. podrasky wrote:
>
> o just before it drops carrier it goes into a 50% duty-cycle mark-space tone
>     toggle for about 5 seconds.
>
>
Some time back - one of my customers called - wanting some 
help with some new equipment.  They had just replaced an 
older remote monitoring system with a new "internet capable" 
one... and were trying to get a DSL modem's firewall set up 
with some needed "pin holes".  While there - they had the 
volume up on the receiver - it was obviously FSK and right 
at first - sounded a lot like teletype.  However - after a 
few moments - the signal would cycle through some odd bits 
(something like the 50/50 described) then drop...  a few 
moments later - the signal would come back - and do it 
again.  This system is a well and tank monitoring system - 
that has several transducers that send Pump On and Pump Off 
data, Tank level, Water Pressure, and several other 
"parameters" about the well / treatment plant.   Since they 
have four or five wells - they "take turns" reporting in - 
one after another - until they all have reported in - and 
this cycle goes on 24/7/365.  With the older system - there 
were gauges and mechanical read-outs - that could only be 
read at the main "panel". The new system is all digital (has 
it's own PC) - and presents the various levels, etc. on a 
monitor screen - or on your smart phone.

While I have no idea what you're hearing there - I suspect 
it could well be some "process monitoring" reporting in.  
Ever notice when you go over a bridge crossing a creek or 
river - often there are "stage" monitoring stations - setup 
to report the water level - and they often have a yagi on a 
short pole to send their data.  Of course - these are 
usually up in the 400Mh region - but it's certainly possible 
that there could be reasons to use a much lower frequency 
under certain circumstances.

If you can get a portable sw receiver set up with something 
of a directional antenna (and a signal strength meter) - you 
might be able to track the source of that signal down - and 
knowing where it's coming from - have a better idea of what 
it is - and IF it's likely it can be (reasonably) decoded.

just .02...

-- 
randy guttery

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