"To me", knowing the signature of different devices, and speculating on
the type of device is important. Based on the device signature, you can
often simplify and shorten the search and fix.
With no idea as to the type of device the search become a systematic
search, eliminating devices, one at a time, particularly if the noise is
local (in your own house) can make for a very tedious search.. Knowing
device type and any recent changes leads one to a much narrower and
faster search. OTOH a guess based on "I think maybe it's such and such
a device" can add a great deal of time.
Knowing as much as possible about devices and their noise signatures
gives the ham a "leg up" before starting the search and make educated
speculation worth while.
I have a very expensive line conditioner that originally was quiet, but
recently a horrendous noise turned up (20 over), with no new devices
added. It had the signature of a switching supply. Disconnecting the
antenna showed the noise was local, really close as there was no change
in the signal strength. Speculation told me that being that loud made
the line conditioner a prime candidate. I powered down the line
conditioner and plugged the FTDX5000MP into a dedicated 120 VAC line to
the shack. The line conditioner is on its own 30 A circuit. Turning the
line conditioner on and off told me the "majority of noise was from the
line conditioner, but there is still substantial noise (S6) with the
same signature. There are 3 so called, "wall warts" in here when the
line conditioner is off. One is the telephone. The other two are the
modem and network. Any one could be the culprit, or not. Any one could
also be triggering the hash multiplied by the line conditioner (or
not). So the next steps are clear.
73
Roger (K8RI)
On 7/24/2016 Sunday 11:36 AM, Frank N. Haas KB4T wrote:
I will not speculate as to what the source might be. As I have said in this
forum many times, I consider such attempts to be a complete waste of time.
However, I will say that the periodic character of the source should make
it easier to find. If the highest frequency at which this source can be
detected at your location is 4.0 MHz, options are limited. The first tool I
would use is a battery operated receiver and the National RF HFDF Vector
Gun active loop antenna kit.
You don't describe the antenna or radio equipment being used to hear the
source. You also don't describe the relative signal strength though from
the audio recording it would seem that the source is fairly strong. It may
be difficult to hear the source on any portable receiving system. If so,
you may have to perform an expanding circle or square search to find a
location where you can hear the source well enough to begin pinpointing it.
I have been faced with this kind of source many times over my RFI
investigation career. Patience, good record keeping, more patience and an
open mind are essential.
Don't waste time trying to guess what this source might be. Find it. Then
report your findings.
Each time one is involved in a search of this sort, the experience is
valuable, educational and, when successful, very satisfying.
Good luck and good hunting.
Frank N. Haas KB4T
Utility RFI Investigator
Florida
On Sunday, July 24, 2016, Dave Cole <dave@nk7z.net> wrote:
Hi,
I have had a new RFI source pop up here in the past few days... It
appears to be on a timer, running at night, but does not sound like a
lighting system I am familiar with. It starts about 8:30 PM, and ends
at about 8 AM the next morning. It is quite odd from my prespective, in
that I have never heard one like this before...
Audio is here:
http://nk7z.net/wp-content/uploads/2016/07/2016-Jul-24-14-13-38.mp3
Anyone ever hear something like this?
It appears to cover 1.7 MHz., to about 4.00 Mhz, and I swear, it rolls
off to protect the AM band. It reminds me of one of the Ethernet over
power line devices when I look at it with a Spectrum Analyzer. The
signal looks to be rolled off starting at 1.7 MHz., and gone by 1.6 MHz.
Anyway, any suggestions as to what it might be would be helpful to me in
locating it. My mobile antenna is under repair at this time, so I am
doing my homework prior to a locate run.
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