[RFI] New RFI source for me...

[Roger (K8RI)]

"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 at 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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