Noise spikes across the spectrum

[elsh...@gmail.com]

Hi all. I'm having a real hard time trying to figure out the source of some intermittent noise I'm getting across large parts of the spectrum.

See attached image. The peaks are spaced at approx 380kHz regardless of which frequency I'm tuned to, and seem to be most prominent between 120-200MHz.

The crazy thing about this is I've had the SDR setup working fine without spikes for some time, and the next time I go to use it they re-appear. I have a Nooelec nano and also a 'Black stick' dongle, swapping between them doesn't cure the noise. I've tried multiple USB extenders, with and without clip-on ferrite. I see the problem on my home PC and laptop, and also on my work PC which is 10 miles from home!

The image was taken using the following in a metal case: No antenna -> Ham it up -> Nooelec Dongle -> 0.5m long USB extender. I've tried running the Ham it up on USB power and an external linear PSU (not switched mode!)
I get the same if I swap over to: Telescopic -> 'Black stick' Dongle -> 2m long USB extender.

I would be most grateful if anyone help me with this problem and allow me to start using what promised to be a great budget SDR setup!

El

[Leif Asbrink]

Hello El,

This kind of interference is obviously deterministic and for
that reason it can be removed by appropriate algorithms.
Such algorithms remain to be developed however....

Maybe you could make a recording (at the widest possible bandwidth)
and make the recording available to developers.

Regards

Leif / SM5BSZ



> <https://lh5.googleusercontent.com/-9fv1Qumlx5U/U8qsbr70viI/AAAAAAAAAJQ/l_ECbje7vOU/s1600/sdr+noise.jpg>

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[jdow]

That can be literally anything from unfiltered lighting fixtures (usually
fluorescent or maybe LED) to an illegal CB radio station to a ham with a power
amplifier featuring parasitic oscillations to a computer's clock to ....

Your simplest best shot is a diary. Note when you see the noise and when you do
not. Then make intelligent guesses. Of course, your best shot is a small loop
antenna on a handheld radio tuned to the peak of the noise. Then use it as a
direction finder (null in plane of small loop) to zero in on the noise. That
appears to be broadband noise so it's probably not bad wiring, a neighbors
electric fence, or the like. But it could be some other appliance you or a
neighbor owns. (Plasma TV's have a different pattern spacing but are VERY ill
reputed as EMI sources.)

A local ham might point you to a group of local hams who are into finding hidden
transmitters. They might help you find the source of your noise as an exercise.
(Approach him politely - "I have a noise problem and figure you might have some
idea how to track it down or know somebody who does." You will find that your
neighborhood ham radio operator is VERY unlikely to be the source of that kind
of noise.)

{^_^} Joanne

On 2014-07-19 10:57, elsh...@gmail.com wrote:
> <https://lh5.googleusercontent.com/-9fv1Qumlx5U/U8qsbr70viI/AAAAAAAAAJQ/l_ECbje7vOU/s1600/sdr+noise.jpg>

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[jdow]

Now for a general usage suggestion - a 5 meter extension with at most one 5
meter active extension cord (no external power but regenerates the signal) can
be used to remove the antenna from the vicinity of your local computers and
their noise. In rare situations, some notebooks I figure, the active extension
may be a bit too much.

{^_^} Joanne

On 2014-07-19 10:57, elsh...@gmail.com wrote:
> <https://lh5.googleusercontent.com/-9fv1Qumlx5U/U8qsbr70viI/AAAAAAAAAJQ/l_ECbje7vOU/s1600/sdr+noise.jpg>
>

[Larry Dighera]

Here's some RDF information:

<http://homingin.com/>
<http://homingin.com/joemoell/ardfinla.html>
<http://homingin.com/equipment.html>
<http://www.foxhunt.com.au/>
<http://www.rdfantennas.com/our_story.php>
<http://homingin.com/revdfjr.html>

I wish I could be of more help.

[elsh...@gmail.com]

Thanks for the replies everyone - most helpful.
I'm not totally convinced this is external noise caused by a nearby transmission because, as mentioned before, I was able to re-create the effect on another computer, located some 10 miles from where I usually have my setup. That said, it would be foolish to rule it so I won't, and I'll continue to investigate to see if I can achieve a noise-peak-free SDR setup!

I'll be sure to report back if I have any luck!
Cheers

[elsh...@gmail.com]

The only thing I can confirm is that it's not due to external interference, instead it appears to be some kind of interference from the host PC or USB connection. The big mystery is why I can re-create it on 2 separate dongle/cable/PC setups that have no common components.
If anyone here fancies a bit of research (and is feeling charitable :-) ), you could always try replicating the conditions I use to re-create the problem and reporting back:

Plug Dongle into PC using good quality 3M USB extender plus optional ferrite
Plug small telescopic or short piece of wire into dongle antenna input
Run SDR# with RF gain set to ~35dB and tune to 125MHz
Move antenna and USB cable around to see if you get spikes every ~390KHz on the spectrum display

Cheers
El

[Kevin]

I can tell you that I experienced the exact same thing. Upon creating a log of the times I started researching and noted that a ham radio repeater that was nearly 60 miles away was so strong that I was picking up harmonics all over the place. The activity continues and it completely blocks out weaker signals in the area. As soon as they key up on the repeater I see it nearly across the entire spectrum. The signals they are sending out is so strong that I did not notice a difference when I was 3 miles from their tower site and 60 miles away at my normal location.

I have researched it a bit and they have had a few complaints in the past but the FCC hasn't done anything to resolve the issue even though it's interfering with pretty much everything from power meters to NOAA reception, some P25 systems, paging and radio fax transmissions as well. it's all over the spectrum. I can tell when the repeater is active without even tuning into it.

Kevin

[Andrew "Dobie" Koch]

In this case, I think the problem is more the (cheep) SDR dongle and
it's lack of filtering. I have the same issues, but from broadcast FM
and AM radio stations within a few miles of my home.

Trying to do any weak-signal work on HF with the SDR dongles is next to
impossible because of a station at 1.250 MHz that's only a few miles
away running 5kW, and I happen to be directly in-line with it's phased
array antenna. It pretty much blows out the entire HF spectrum for me.

At least for FM I can use a trap (or two) to block them out and keep my
VHF and UHF spectrum a little cleaner, though the city public safety
transmitter near my home does a number on my UHF reception.

Unless you are specifically trying to use the dongle on that ham band,
I'd suggest building a notch filter for it and hope you can make it deep
enough so it doesn't blow away the front-end of your SDR dongle.

Andrew - K9LDT

[markotime]

Are you sure it's a HAM, and not a megawatt CBer?  In general, the former have licensing and ethics as part of their culture, the latter not so much.  CB power amps have been known to spray harmonics and intermod around like kids with silly-string in the playground.

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[jdow]

The last time I looked, a few years ago, there was a local CB station that
emitted spurs from 20 MHz through around 35 MHz. And he wasn't really all that
high power, either. He just didn't have a clue about how to setup his PA. That
didn't surprise me. Back in the early 70s I was out gardening. A neighbor walked
by and asked me about the possibility I was interfering with his TV. (I had a
"modest" 70' tower at the time.) I allowed as how I had not been transmitting
for the last few days. I got him to tell me more about what was happening. He
mentioned he was on cable. He was blocks away so getting into the cable system
from my TX was unlikely on its face. I suspect it came down to a local CB kiddie
thinking, "Gee, the cable company gots this hugemongous antenna farm. I bet if I
fed my signal back into that coax I could really get out like a bandit." CBers
generally have the intellectual prowess of Zabriskan Fontemas. (Dust off your E.
E. "Doc" Smith novels for that reference.)

The frequency of the signal will tell you a lot. If it's in a legal ham band for
your area then it's possibly a ham. And if it is overloading your dongle then
you will, indeed, see it across a major portion of the spectrum. Once the D/A
converter is overloaded the received spectrum is highly suspect.

That said, 60 miles away beggars the imagination for ham repeaters overloading
you. I have repeaters coming out the ears in this area and can receive them just
fine. The close ones, maybe 10 miles away, require me to reduce the gain from
the setting for practical optimum noise figure. So far I've not bad to add
attenuators to get the overload cured. We're playing with 8 bit samples, at
best. That sharply limits your dynamic range. A possibility if a repeater is
involved is that you are hearing a ham that lives very close to you transmitting
on the repeater input frequency.

{^_^}

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[Robert Nickels]

Here's another weird noise source to add to the list. A few weeks ago
I noticed bursts of broadband noise every 140 Khz from around 150 to
over 400 Mhz, repeating every 3 seconds. I thought for sure it was a
new switch mode power supply or AC adapter but failed to find anything,
and using portable receivers I determined that the noise was actually
much stronger on VHF than on LF.

Turned out to be one of those hard drive to USB adapters that I'd used
to check out an old HDD. I'd left it plugged into a USB port but
removed the DC power to the drive and evidently it was being polled
every three seconds with the USB cable serving as a dandy VHF range
antenna. Like rust, interference never sleeps...

73, Bob W9RAN

[Colorado Rob]

The one that overloaded my shack was a DVI to VGA adapter I used to connect one of my computers into a KVM switch.  It put broadband noise across the entire 2m band.  Took forever to find that.  Finally saw that it went quiet when the screensaver kicked in.

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[Siegfried Jackstien]

... i have a bus station close to my house (a few dozen feet away)

... the high power injection of the diesel engine of some busses makes
horrible spikes from shortwave up to uhf

Took me also several days to find that out ...

why is there only noise for a few seconds but over COMPLETE rf range??? Why
nearly every day (except Sunday)?? And always at the same times ...(sure bus
comes at the same time every day) ....

then I had my window open when that noise was there again ... and I heard
the bus just driving away ... and thought ... could it be the bus?!?!?

Yes it was!

...

Greetz

Sigi

Dg9bfc


> -----Ursprüngliche Nachricht-----
> Von: ultra-c...@googlegroups.com [mailto:ultra-cheap-
> s...@googlegroups.com] Im Auftrag von Colorado Rob
> Gesendet: Dienstag, 26. August 2014 12:47
> An: ultra-c...@googlegroups.com
> Betreff: Re: [ultra-cheap-sdr] Re: Noise spikes across the spectrum

>
> The one that overloaded my shack was a DVI to VGA adapter I used to
> connect one of my computers into a KVM switch. It put broadband noise
> across the entire 2m band. Took forever to find that. Finally saw that
> it went quiet when the screensaver kicked in.
>
> On Aug 25, 2014 10:16 PM, "Robert Nickels" <rani...@comcast.net> wrote:
>
>
> Here's another weird noise source to add to the list. A few weeks
> ago I noticed bursts of broadband noise every 140 Khz from around 150 to
> over 400 Mhz, repeating every 3 seconds. I thought for sure it was a new
> switch mode power supply or AC adapter but failed to find anything, and
> using portable receivers I determined that the noise was actually much
> stronger on VHF than on LF.
>
> Turned out to be one of those hard drive to USB adapters that I'd
> used to check out an old HDD. I'd left it plugged into a USB port but
> removed the DC power to the drive and evidently it was being polled every
> three seconds with the USB cable serving as a dandy VHF range antenna.
> Like rust, interference never sleeps...
>
> 73, Bob W9RAN
>
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[markotime]

Diesel vehicles provide a much more hostile environment for onboard electronics than do gasoline-powered ones.  You have it right, injector EMI, but a lot of other inductive devices (relays, e.g.) are nasty. 

[jdow]

The ignition system spark plugs are only used for starting the engine on some
diesels. (Others use Ether to get the engine started.) Once started diesels do
not use an ignition system.

{^_^}

[Siegfried Jackstien]

I am guessing it is not a spark plug but the high current drawing power
injection valves...

The engine is not switched off when the bus comes to the station ... so it
is not a starting thing ... it is a permanent effect

And ... I have seen an article in a local ham magazine where the effect was
described and well explained (spark plug like noise from diesel engines)

Greetz

sigi

> -----Ursprüngliche Nachricht-----
> Von: ultra-c...@googlegroups.com [mailto:ultra-cheap-

> s...@googlegroups.com] Im Auftrag von jdow
> Gesendet: Mittwoch, 27. August 2014 07:39
> An: ultra-c...@googlegroups.com
> Betreff: Re: AW: [ultra-cheap-sdr] Re: Noise spikes across the spectrum

[jdow]

I had a suspicion about that. But I figured that noise is constant enough the
FCC would have gotten into the picture and said "Clean it up." (They may have
and were ignored. That happens a lot these days.)

{^_^}

[Baz O]

That is exactly the type of interference that I am getting more frequently.

[Leif Asbrink]

Hi El,

> <https://lh5.googleusercontent.com/-9fv1Qumlx5U/U8qsbr70viI/AAAAAAAAAJQ/l_ECbje7vOU/s1600/sdr+noise.jpg>

> The image was taken using the following in a metal case: No antenna -> Ham
> it up -> Nooelec Dongle -> 0.5m long USB extender.

Try this: No antenna -> Nooelec Dongle -> 0.5m long USB extender.

If you then see a quiet noise floor you would know the ham it up
is generating (or picking up) the interference.

If you still see the problem connect the dongle directly
to the computer with nothing connected to the antenna input.

The interference you see is VERY strong. It must be generated
by your hardware somehow.

Peaks are 15 dB above the noise and about 10 times wider than
the bin resolution. It means that the level of each signal
is about 25 dB above the noise floor. Assuming a NF of 10 dB
and that the bin resolution is 1 kHz it means that the signal
level is -174dBm(=room temp) + 10 dB(NF) + 30 dB(1 kHz bandwidth)
+ 25 dB (level of peaks in spectrum)

That sums up to -109 dBm or 0.8 uV. You have many, spaced 0.38 MHz
over a 100MHz wide range which means about 250 such peaks.
All those signals add and once every 1/380000 second they add in
phase to produce a peak at 250 x 0.8 uV = 0.2 mV. You can not possibly
pick up such levels from the outside world with the dongle and
ham it ip inside a metal can with nothing connected to the
antenna input. The above estimation is probably underestimating the
level - it is actually 200 MHz wide at its source (at least)
and my estimates of the level are a bit conservative.

I do not have the schematic or other details about the ham it up.
Something is oscillating at 380 kHz. Maybe a capacitor is needed
on the power supply line? (Here I assume that you have found that
ham it up is the source which is not necessarily correct.)


Regards

Leif

[jdow]

I find the nice 400kHz +/1 a few percent repetition rate of the spectrum rather
interesting. Playing with that number a little might be illuminating. Be might
get some salubrious results if he plays with largish ferrites on the USB cable
up by the metal case. Also is the metal case grounded to both the antenna shield
and the USB shield? That may not be the best connection possible from an EMI
standpoint.

{^_^} Joanne

[daic...@gmail.com]

I Know this is an old post, but I have included this reply for others reference in future. I believe  this has something to do with the dreaded pager transmitters, very strong signals around 145-156MHz and broadband noise multiples thereof, particularly around 51-57MHz, found at various frequencies around the world. Here are some screenshots of what I have, and a link to POCSAG from Signal identification guide.
https://www.sigidwiki.com/wiki/POCSAG