[RFI] RFI Direction Finding

Jim P jvpoll at dallas.net
Sun Feb 19 11:06:44 EST 2006


I have found that mobile 'trouble shooting' of the power
grid from a car is limited by the vehicle ignition systems

Peak reading instrumentation (peak amplitude reading
receivers) quite nicely 'grab' the series of spark plug
firings and show that value; this sets a floor below
which power line noise (or other sources) cannot
be read.

I've contemplated rigging up my appliance dolly for
foot-based tracking/plotting along the road - strapping
a 6 or 8' length of PVC to one of the rails of the dolly
and then moving the entire contraption (antenna,
receiver, battery, data logger) down the road.

The alternative is to convince a ham friend of mine who
owns one of the old mechanical fuel-injection mercedes
to  'drive the route' with the RF gear loaded in/mounted
on his vehicle.

The up side is, the more serious AC line impulse noise
sources will read 20 to 30 dB up scale from the floor set
by the spark plug firings. It is then easy to spot the
location/the area to return to and do foot-based searching.

Just listening by ear to a narrow band receiver (where the
sharp, narrow pulses from the arcing noise source) will 'ping'
the IF filter and cause it to ring, thereby stretching out the
pulse width, can be deceiving as to actual source signal
strength. The spark firings would yield the same effect
to an average-reading non-peak reading AM receiver, but
through artful interpretation of the audible 'noise' coming
out the speaker even a NB AM receiver can be used
fruitfully to find a lot of these offending line noise sources.

Jim P  -- WB5WPA --

----- Original Message ----- 
From: "Donald Chester" <k4kyv at hotmail.com>
To: <rfi at contesting.com>
Sent: Saturday, February 18, 2006 4:00 PM
Subject: Re: [RFI] RFI Direction Finding

> >The FM broadcast wouldn't be affect on an FM radio since noise is
> >"Amplitude" in nature.  FM rcvrs won't pick them up (usually, although
> >rcvrs may).
> I bought a $30 Radio Shack VHF aircraft radio receiver for the purpose.
> is AM, not FM, and works very well.  I can track noise down to the exact
> pole.
> But the problem I have is travelling along the road with it.  With every
> vehicle I have, ignition noise is as strong as the noise I am trying to
> sniff out.  The bicycle is usually not an option because the main  highway
> has a gravel shoulder.  I have been known to speed up in the car, turn off
> the ignition, and coast while trying to find the noise.  If I think it is
> nearby, I sometimes just walk with the radio to my ear.
> Don k4kyv

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