Hello everyone,
Reading the discussion on arc-welders and possible HF interference, I wonder
whether this could be a clue to a problem I had a while back. I was running
19F on an Inova 500 (i.e. transmitter at around 470MHz) and observed a tight
bunch of signals of varying phase and intensities spanning about 120Hz. This
interference would suddenly appear either around 7 in the morning or at
about 3 in the afternoon and always at about the same starting frequency.
The interference continued after first appeance for 1-2 hours. During the
first hour, the interference moved approximately exponentially (nice smooth
curve) to lower frequency, shifting about 2000Hz in the process, it also
sharpened at the same time until there was just one intense spike left. This
spike would hold constant frequency and intensity for maybe an hour more and
then suddenly disappear. Starting time could vary some and duration of the
phenomenon also, but the 'warm up' time (exponential progress) seemed to
always take about an hour. This behaviour continued for several weeks -
after which we moved to other interests and didn't run 19F so intensely -
so it may be still there now.
We considered various causes, amongst these television, radio and mobile
phone transmitters (but would they warm up/behave like that?) but could find
no evidence of anything near us which might be causing it. Could this have
been due to arc-welding or has anyone other explanations for the phenomenon?
David
David Grace
Amersham Health,
Oslo, Norway
Received on Fri Aug 30 2002 - 10:58:15 MST