[RFI] impulsive RFI

Patrick Dyer pjdyer at swbell.net
Sun Mar 2 21:53:34 EST 2008

Any suggestions as to the source of this RFI, AM audio examples at
28 MHz ?
http://www.qsl.net/wa5iyx/nx28080301a.wav (361k - 16 seconds) and
http://www.qsl.net/wa5iyx/nx28080301c.wav (398k - 18 seconds)
is an example of its shutdown, with the FT-847 agc recovery causing
the "normal background noise" to abruptly rise after the impulsive RFI
quits.  (I tried to convert these to much smaller Real Audio files but
they sounded a bit too "muted".)

I do have some 8-mm video tape of its affects on the semi-local and
local hi-lo VHF TV stations, but to load this to a site requires my
converting it with a DVR to a DVD-R disc, and then converting that with
the XP computer to mpeg.  It shows well how short the intense impulses

It's detectable from h.f. thru >144-MHz.  RDFed with 4-el 2-m beam and
an IC-A4 on 136-MHz to one of three possible houses, complicated by two
of them being in a cul-de-sac behind my street (and, due to the street
patterns, requiring an apx 1-mile journey to get back there!)  And once
again, the heavy use of CATV or Dish sat systems here would largely
"immunize" the source and adjacent residences from noticing this RFI.

Its appearance/sound is much like fast idling ignition.
The runs are 10-15+ min, with some variability in speed and intensity.
It is apparently frequency dispersive as the RFI can be present on h.f.
while not (yet) prominent on the TV.  I'm not sure if it's from a
semi-attended or unattended (totally automated) appliance, though the
logged run times below suggest attended.

This particular RFI had been a rare occurence but became (or was found
to be) a multi-run problem during the Feb 16-17 ARRL CW DX Contest.

Some recent runs (hardly exhaustive since I don't have a strip chart
recorder and a dedicated receiver for all this) in local (CST) time:
Feb 29: 1858-1918      Mar 02: 1202-1220
        1954-<2006             1234-1235
        <2054-2058             1439-1459
Mar 01: <0828-<0834            1614-1630
        <1137-1145             <1909-1914
        1209-1219              <1942-1950

    73, WA5IYX - EL09ql

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