[RFI] Noise to identify

Dave dave at nk7z.net
Mon Jun 7 08:43:49 EDT 2021


Hugo,

I have a few entries regarding how to set up an SDR to survey your 
location for RFI at:

https://www.nk7z.net/sdr-rfi-survey-p1/

That process will give you the start/end times Don was talking about, in 
addition to a lot of other data regarding your RFI.

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

On 6/7/21 3:56 AM, Don Kirk wrote:
> Hi Hugo,
> 
> Quickly looking at your waterfall display on 160 and 80 meters, it looks
> like a repeating pattern at a frequency of approximately 6 KHz, and also a
> comb pattern at a frequency of approximately 640 Hz.  These patterns are
> not easily observable on your 40 meter display.  6 KHz is a very common
> carrier frequency on variable speed drives, but there are numerous other
> devices that could be generating repeating 6 KHz patterns, etc.
> 
> While I do look at waterfall displays to help me understand what the signal
> looks like that I'm trying to locate, I normally don't waste time guessing
> what the device might be that's generating the RFI.  What's important is
> identifying the property that's generating the RFI, and then you can
> investigate more with the property owner exactly what device is generating
> the RFI.  Even if I told you the exact model number of a device that's
> generating the RFI, it does you no good until you locate the property it's
> located on, and you have to do this using radio direction finding gear
> (your HF radio, a simple directional antenna that's easy to build , and
> possibly a preamp and attenuators or RF gain control).
> 
> Sounds like you already did the first step and determined the RFI is not
> being generated within your house which is always the first step.
> 
>   I would be interested in knowing if this RFI is present 24 hours a day, or
> if there are only certain hours of the day it's on and how often the 6 KHz
> pattern disappears as I noticed it would go off for brief periods of time
> in your video, etc.  This would help me understand when I should go
> direction finding and how not to get fooled by the 6 KHz pattern turning on
> and off while out hunting.  I would also be interested in knowing if you
> see this same pattern on additional bands as this would help me decide what
> bands would be best for my radio direction finding activities (what antenna
> would be good for direction finding and I might not even need a preamp if I
> can hear it on one of the higher bands like 20 or 15 meters where the size
> of the  portable direction finding antenna does not need to be as large and
> still not have such negative gain as a portable antenna for use on 160 or
> 80 meters as an example).
> 
> Just my opinion based on tracking down many RFI cases for myself and
> others.  Tracking down a signal with a definite signature like what you are
> seeing on 160 and 80 meters is usually one of the easiest cases to track
> down (normally less than an hour or two) as long as you have some basic
> radio direction finding equipment.
> 
> Again the key is to locate the property where the RFI is coming from, and
> then you can worry about finding out exactly what device is generating the
> RFI.
> 
> 73,
> Don (wd8dsb)
> 
> On Sun, Jun 6, 2021 at 11:37 PM Hugo Loranger <ve2_ugo at hotmail.com> wrote:
> 
>> Hi,
>>
>> I have already closed the braker and no change. I have stopped all the
>> UPS. I used my KX3 on battery power. No change.
>> Here are 3 other videos including one with the waterfall that Jim was
>> asking for.
>> The last one shows the waterfall via Nap3 on 3 bands(80m, 160m and 40m am).
>>
>> https://youtu.be/Syn973SUDSY  - Part 2
>>
>> https://youtu.be/kV89pinFfZc  - Part 3
>>
>> https://youtu.be/uKfoQV8NzpU  - Part 4 with waterfall
>>
>> I don't know if this helps more but it looks a lot like an electrical
>> problem that covers all the bands ...
>>
>> Indeed it shows that there is repetition which was not well audible ...
>>
>> The shack is just above the electrical box in the house. It is a house but
>> the other houses are very close together.
>> The power line that supplies the house is 52 feet away. The horizontal
>> antenna is therefore not very far ...
>> On the other hand, I have 2 lines within 2 km of 740kv ...
>>
>>
>> Thanks!
>>
>>
>> Hugo
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