[RFI] Investigating receive noise - got a few questions

Wed Nov 28 23:14:45 EST 2018

One thing to keep in mind and this list seems to ignore. Not all 
switching supplies generate noise although many, if not most do.
In general, "wall warts" are a commodity, built to save money. I do have 
a number of them that appear to be custom type for the drive enclosures 
as well as powering servers. I've never heard a "peep" from these on any 
band.  OTOH I've not looked at any of these with my spectrum analyzer.
Even the chargers for the smart phones and one tablet are clean.

Computer power supplies are all switchers as far as I know. The 
relatively inexpensive desk top computers "in general" use cheap ($10 to 
$20 new retail), hash generators and being in a plastic case does 
nothing to eliminate, or even reduce said RFI. These can be horrible on 
networks as well.  OTOH "most" home brew and gamer computers do not use 
cheap power supplies. Many even have power factor correction and I've 
not found any components skipped to save a few cents. Still, these are 
not inexpensive power supplies with the good ones starting around $100 
and up depending on the total ratings (up to 1400 W) and number of 
buses. I use 850W (~$200) supplies on all the computers

"In general" cheap equates to noise.
I have 6 wall warts and in the AC line 5 VDC power supplies here in the 
den including the network router that feeds 5 computers and a whole 
bunch of WiFi devices. No interference to the station, or to the 
computers.  Of course the next one could negate all of that.  I still 
fear solar panels. None in the area at present.

73 Roger (K8RI)

On 11/11/2018 3:39 PM, David Eckhardt wrote:
> If you're a ham and care about HF, just say no to any and all SMPS's!!!! !
> !   They are everywhere.  And Part 15 was supposed to prevent this
> happening.  Yea, sure,........ that's when FCC still cared!  Read my rant
> on my QRZ page.  35 to 40 years as an EMC / RFI Engineer sez it all.
>
> Dave - WØLEV
>
> On Sun, Nov 11, 2018 at 8:36 PM Jim Brown <jim at audiosystemsgroup.com> wrote:
>
>> Good advice all around.
>>
>> More specifics.  1) Study my tutorial app note on this.
>> http://k9yc.com/KillingReceiveNoise.pdf  2) Study the material on NK7Z's
>> website.  3) Your spectrum view is FAR too wide to tell much about what
>> you're seeing. I suggest that you start with 100kHz - 300 kHz views of
>> the ham bands you care about the most. Then repeat all of your turning
>> off breakers tests. Do this with the assistance of another ham -- one of
>> you flips breakers, the other watches the display and changes bands. 4)
>> Search out and destroy (replace) every switch-mode power supply in your
>> own home. The average home has several dozen. 5) Repeat steps 1 and 2.
>>
>> 73, Jim K9YC
>>
>> On 11/10/2018 3:02 PM, David Robbins wrote:
>>> The only thing I can tell from the first few seconds of that recording
>> are
>>> that the big wide pulses are probably lightning, though there is a
>>> possibility of local power line arcing.  It also looks like you are
>> hearing
>>> lots of actual band activity, sw broadcast and ham and other stuff, hard
>> to
>>> tell as the scales aren't readable to even know what bands you are
>> listening
>>> to.
>>>
>>> Some general things:
>>>
>>> 1. You can't clean up the whole hf spectrum so concentrate on the ham
>> bands.
>>> 2. You can't see local noise when the bands are open, so check the high
>>> bands at night and the low bands at midday and when there aren't any
>>> thunderstorms in range.
>>> 3. Most of the stuff you'll chase in your house will either be periodic
>>> spurs (harmonics of switching supplies or digital devices) or wide raspy
>>> crap from bad power stuff (if the source is in your house these can be
>>> dangerous, unless it's a furnace igniter maybe), note that cheap high
>> power
>>> stuff like battery chargers can make noise that wanders quite a bit
>>> 4. don't forget to unplug and turn off ups's, their chargers can make
>> noise
>>> if powered on, and their inverters can make noise if unplugged or if the
>>> breaker is off.
>>> 5. Once you have cleaned up your own house then figure out if there are
>>> external noises that are interfering with what you want to hear... if
>> there
>>> are then you have the harder job of figuring out if they are nearby or dx
>>> sources.
>>>
>>>
>>> David Robbins K1TTT
>>> e-mail: mailto:k1ttt at arrl.net
>>> web: http://wiki.k1ttt.net
>>> AR-Cluster node: 145.69MHz or telnet://k1ttt.net:7373
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: RFI [mailto:rfi-bounces at contesting.com] On Behalf Of Andy KU7T
>>> Sent: Saturday, November 10, 2018 21:58
>>> To: rfi at contesting.com
>>> Subject: [RFI] Investigating receive noise - got a few questions
>>>
>>> Hi,
>>> I am trying to sort out receive noise issues with my Flex.
>>>
>>> I am not exactly sure how clean the spectrum could/should be. I have the
>>> feeling that I may be more concerned about this just because I can see
>> the
>>> spectrum.  I am in an residenial area with 5 acre lots, with miles to the
>>> next town and businesses. I always throught/hoped I have no noise issues.
>>>
>>> I took some time last night to turn off all breakers, one after another,
>>> until only the shack was left. Then I reduced everything in the shack so
>> the
>>> only thing left was the 12V power supply, radio, computer and monitor.  I
>>> also adjusted the noise offset on the Alinco Powersupply with no changes,
>>> turned off the computer, and unplugged it. At this point any wall warts,
>>> modems, routers, etc were also  off. Still no significant changes.
>>>
>>> Take a look here at my spectrum, recorded while I turned off a breaker
>> every
>>> 30 s. There is no difference between beginning and the end:
>>> https://1drv.ms/v/s!AiAwh4TnZjYMhtoFCHwTeJdHO2MFGw
>>>
>>> I really have not found any major decreases in hash or noise.  Here are
>> my
>>> questions:
>>>
>>>     1.  Do I go right about this at all?  Should I only look at the ham
>> bands
>>> instead of looking at the half the HF spectrum?
>>>     2.  There is quite some pulsing/jumping of noise going on below 10 Mhz
>>> (see in video's top spectrum). Are those normal static atmospheric
>> crashes
>>> or something else outside I should be investigating further and if so
>> how?
>>>     3.  There are patterns around 4 - 5 Mhz that are definitely some
>> patterns
>>> from some device. Is it worth worrying about these, considering there are
>>> not near any ham bands of interest? Goes back to question 1 also: do I
>> care
>>> whats outside of ham bands?
>>>     4.  I have some harmonics, some spikes between 12 and 15 Mhz. the
>> distance
>>> between the spikes is about 17.6khz. Any ideas what that could be? Is
>> likely
>>> not in my house though.
>>>
>>> Any tips and ideas how to proceed?
>>>
>>> 73
>>> Andy
>>> KU7T
>>>
>>> Sent from Mail<https://go.microsoft.com/fwlink/?LinkId=550986> for
>> Windows
>>> 10
>>>
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-- 
Roger (K8RI)