[ANSS-netops] RFI stepping on sensors and data loggers

[Don Farrell]

Hello to all,
          Are there any networks that are seeing electronic stepping on
velocity or acceleration sensors and data loggers?  So far the 
Kinemetrics EpiSensors are the most vulnerable with one of the 
triaxial directions sometimes showing a greater amplitude. Most 
problems are with Nanometrics HRDs with Episensors, Ref Tek 
130-ANSS/02/6 data loggers with Mark products L4s and some broadband 
sensors. Freewave radios seem to be the cause of most of the problems 
but paging transmitters and SCADA are possible sources.  A cell modem 
with a Ref Tek twenty feet underground causes stepping on the MEMS 
sensors.  A recent switch to a Freewave FGRplusRE model resulted in 
stepping on one channel of a K2 and on an external vertical Mark 
Products L4. Ferrite cores rarely solve the problem.  A separate 
solar panel and battery to power the external sensors can eliminate 
or lower the amplitude of the steps.  In a recent experiment a test 
box with a 5 Hz sine wave output into an HRD showed stepping. 
Shorting the inputs in the test box still showed stepping on the HRD 
channels.  If you have seen this problem do you have any additional 
ways of eliminating it? Seismograms and PSD plots are attached.
-- 
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