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S9 Noise in 40 Meter Band - How Can I Track it Down?

Bill Alpert
 

I'm seeing and hearing loud noise sometimes at S9 on 40 meters. Strangely, 80 meters (as well as 20,10, etc.) is relatively quiet. Yes, I'm close to power lines, and yes, my antenna situation is less than optimal. Still, I'd like to understand the source (is it local?) and nature of the noise. Why is it strongest on 40 meters?? Walking the neighborhood with an AM radio didn't immediately point to any obvious source. 

Note that I've tested this while on battery power with the main power of my house off. No change. I have noticed that the noise reduces slightly when I orient my magnetic loop antenna horizontally. 

Would it be worth buying a cheap portable shortwave radio to try and locate the source. Any other testing ideas? Thank you!
--
Bill / KG6NRV

Neil Smith G4DBN
 

Hi Bill, is there any structure to the noise?  Does it have any characteristics which show up in AM mode or FM or SSB? Any periodic changes? Does the noise extend way out of the band? Any difference with an attenuator in line? If you look at the AF spectrum, do you see any peaks/troughs?  Any sign of the PK indicator being hit? Where does the noise start to drop off as you look LF and HF of 7MHz?  Any strong signals anywhere from DC to 55MHz?  Are you close to any TV broadcast stations with 6MHz channel spacing? Could be rusty-bolt mixing product of digital TV?

Any sign of 60Hz or 120Hz components in the noise?  Hae a look at the audio spectrum of the noise in each mode using Spectrum Lab or something to see if it is pure white noise, or has any modulation or periodicity.

Good luck.

Neil G4DBN

On 09/11/2019 17:21, Bill Alpert wrote:
I'm seeing and hearing loud noise sometimes at S9 on 40 meters. Strangely, 80 meters (as well as 20,10, etc.) is relatively quiet. Yes, I'm close to power lines, and yes, my antenna situation is less than optimal. Still, I'd like to understand the source (is it local?) and nature of the noise. Why is it strongest on 40 meters?? Walking the neighborhood with an AM radio didn't immediately point to any obvious source.

Note that I've tested this while on battery power with the main power of my house off. No change. I have noticed that the noise reduces slightly when I orient my magnetic loop antenna horizontally.

Would it be worth buying a cheap portable shortwave radio to try and locate the source. Any other testing ideas? Thank you!

Bill Alpert
 

Hi Neil, No structure that I can tell. Just a raspy sound, which is most objectionable in AM mode. No periodic changes detected. Yes, ATT does reduce it.

I did a wide band scan and noticed peaks in a few differing wide bands, so I made audio recordings of the Elad's audio output. In one case, I also recorded the sound from my Icom 7300 on the same frequency in the 40M band. The noise seems more objectionable on the Icom.
I also took some screen shots of the FDM-S2 software that match the audio recordings.
I put the recordings and screenshots in this folder; if you have a few minutes to take a look and listen, it would be greatly appreciated.
Dropbox link: https://www.dropbox.com/sh/3hjuozttoxf98hi/AAAdkfzv-OuCnrILXn65o-R4a?dl=0
--
73 de Bill / KG6NRV

Neil Smith G4DBN
 

Hi Bill, there is a very strong 120Hz component in the 7045kHz recording, and also strong lines at 240 and 360Hz. Also weak lines at 60Hz, 480Hz and 720Hz.

In the 3000kHz recording, there is a very strong 60Hz component, then 120, 180

, 240, 360 and 720Hz

Same artefacts in the Icom recording, but the Icom filtering reduces the 60 and 120Hz components radically.

In the 14MHz recording, there are also regular amplitude dropouts, but that could be electric fence pulses or something pumping the AGC.

Right, so it is power-line related in some way.

1) First obvious thought is that there is a broken insulator or faulty transformer on a power line pole somewhere and it is arcing, but you should be able to use a medium-wave portable radio to locate that. 

2) If there is nothing of that sort within a quarter mile or so, then the huge level or harmonics could point to it being a series-wound motor with a commutator, but I think we'd see other frequencies related to the rotational speed. 

3) Could it be a thermostat on a water heater or refrigerator or freezer or aircon which is arcing?

4) It doesn't sound like anything I've heard from power-line communications or broadband internet services. The lack of any obvious modulation doesn't necessarily mean it *isn't* something like that, but usually you only see a 60Hz or sometimes 120Hz modulation on power-line comms.

5) Are there any machine shops or workshops nearby which might have a rotary phase converter running all the time, or VFD inverter for three-phase machinery perhaps? 

6) Any locals with ground-source heat pumps or well pumps or ornamental fountains or pond pumps for fish?

7) Any 60Hz mains-powered electric fencing units, or bug zappers or the like?

8) Any solar panel installations which feed the grid?  Unlikely as you would probably see them stop as the sun sets.

Things to try:

1) suspect your own house first.  Can you turn off all the breakers and isolate the house power, with the radio/laptop running on batteries to see if there is any difference?  If there is, turn each breaker on and see which one makes the noise return and go hunting.

2) when the neighbourhood is very very quiet, late at night when there is no wind, have a listen for arcing of humming noises in the area. Try not to get arrested!

3) If you found a reduction with the loop horizontal, that means the signal is probably in the plane of the loop, but that could mean it is a mile away. Can you get the loop away form the house and see if you can find any nulls?  If you can, then move 50 feet and try again, to see if you can triangulate the noise source.  It will be along a line parallel to the loop.

I wish you the best of luck with tracing it, Bill. If you can get a really wide-band recording with at least 16kHz of audio bandwidth, it might help to dig out any commutator whine, but would probably be way too low to identify any SMPS.  Can you get snapshot of the waterfall spectrum of DC to 150kHz?  Might help to find a smoking gun if there is something with a faulty SMPS out there.

Neil G4DBN

On 09/11/2019 23:46, Bill Alpert wrote:
Hi Neil, No structure that I can tell. Just a raspy sound, which is most objectionable in AM mode. No periodic changes detected. Yes, ATT does reduce it.

I did a wide band scan and noticed peaks in a few differing wide bands, so I made audio recordings of the Elad's audio output. In one case, I also recorded the sound from my Icom 7300 on the same frequency in the 40M band. The noise seems more objectionable on the Icom.
I also took some screen shots of the FDM-S2 software that match the audio recordings.
I put the recordings and screenshots in this folder; if you have a few minutes to take a look and listen, it would be greatly appreciated.
Dropbox link: https://www.dropbox.com/sh/3hjuozttoxf98hi/AAAdkfzv-OuCnrILXn65o-R4a?dl=0
--
73 de Bill / KG6NRV
-- 
Neil
<a href="http://g4dbn.uk/"><small>g4dbn.uk</small></a>

Bill Alpert
 

Neil, thank you so much for your time and expertise!


On Sun, Nov 10, 2019 at 12:53 AM, Neil Smith G4DBN wrote:

Same artefacts in the Icom recording, but the Icom filtering reduces the 60 and 120Hz components radically.

In the 14MHz recording, there are also regular amplitude dropouts, but that could be electric fence pulses or something pumping the AGC.

Right, so it is power-line related in some way. 

1) First obvious thought is that there is a broken insulator or faulty transformer on a power line pole somewhere and it is arcing, but you should be able to use a medium-wave portable radio to locate that. 

Well I'm surrounded by power lines, many are labeled high voltage and everything is above ground. My antennas are very close to two sets of power lines.
I have walked the neighborhood with AM radio in hand, and some poles are definitely louder than others. Though wouldn't something like this be "off the charts" when standing underneath with a transistor radio?

2) If there is nothing of that sort within a quarter mile or so, then the huge level or harmonics could point to it being a series-wound motor with a commutator, but I think we'd see other frequencies related to the rotational speed. 

A motor like that would have to be at least 1/2 mile away. But this noise is fairly constant 24/7

3) Could it be a thermostat on a water heater or refrigerator or freezer or aircon which is arcing?

Not from my house, since I've tested this with the mains off and the radio running on battery power. Same noise.

4) It doesn't sound like anything I've heard from power-line communications or broadband internet services. The lack of any obvious modulation doesn't necessarily mean it *isn't* something like that, but usually you only see a 60Hz or sometimes 120Hz modulation on power-line comms.

5) Are there any machine shops or workshops nearby which might have a rotary phase converter running all the time, or VFD inverter for three-phase machinery perhaps? 

Possible, but at least 1/2 mile away. And that stuff wouldn't be running at night.


6) Any locals with ground-source heat pumps or well pumps or ornamental fountains or pond pumps for fish?

Not likely

7) Any 60Hz mains-powered electric fencing units, or bug zappers or the like?

Not likely

8) Any solar panel installations which feed the grid?  Unlikely as you would probably see them stop as the sun sets.

A few panels in the neighborhood. But the noise persists into the night.

Things to try:

1) suspect your own house first.  Can you turn off all the breakers and isolate the house power, with the radio/laptop running on batteries to see if there is any difference?  If there is, turn each breaker on and see which one makes the noise return and go hunting.

Yes, I"ve done this. Noise is not from my home.

2) when the neighbourhood is very very quiet, late at night when there is no wind, have a listen for arcing of humming noises in the area. Try not to get arrested!

Will try this!

3) If you found a reduction with the loop horizontal, that means the signal is probably in the plane of the loop, but that could mean it is a mile away. Can you get the loop away form the house and see if you can find any nulls?  If you can, then move 50 feet and try again, to see if you can triangulate the noise source.  It will be along a line parallel to the loop.

I'll have to figure out how to do this, perhaps set up a portable shack in the back of my hatchback car and drive around. Would a Yagi type antenna be better for this type of fox hunt?

I wish you the best of luck with tracing it, Bill. If you can get a really wide-band recording with at least 16kHz of audio bandwidth, it might help to dig out any commutator whine, but would probably be way too low to identify any SMPS.  Can you get snapshot of the waterfall spectrum of DC to 150kHz?  Might help to find a smoking gun if there is something with a faulty SMPS out there.

Not sure how to make the 16K recording, but I'll look into that
Here's the screenshot. Several weird unexplained peaks and something going on at 500 hz which sounds like a loud wind tunnel. Since I live near the ocean, I though that this LF stuff was marine related. But perhaps not! 
https://1drv.ms/u/s!AgUf4SSxaAwailI9ZIdLbC_XEjd9?e=oMakWu
 
Again, thank you so very much!

--
Bill / KG6NRV

AndersH
 

Bill, Neil,

It makes sense to chase down the mystery noise by car if the indoors environment has been cleared from all suspicions. A short capacitive probe antenna should be fine, as long as the right spectrum peak can be tracked continuously without any risk of confusion with other signals.

I recommend a 20-25 cm probe, made from an RG 58 patch cable, terminated by separated red and black test leads and PVC coated alligator clips at the far end. The black (ground) alligator lead can be taped against the coax while the red test lead is kept entirely free..

I recently did field strength testing on behalf of a ham friend, testing in his car with such a probe hanging as an ornament down from the mirror at the passenger side. The accuracy left something to be desired for the higher frequencies, due to the terrain, but at low frequency and vertical polarization, 80 and 160 meters, I was definitely impressed how well the method really worked. My friend applied 100W on different bands and I checked the results at approximately 700 meters distance.

In comparison, an unwanted signal source of less than 1W should be straightforward to spot at 100 meters with the same sensitivity.  Adding a piece of single core electrical wire in the teeth of the red alligator clip will boost the sensitivity, but at 7 MHz, I don't think this is necessary.

If and when the time comes to discuss an electromagnetic problem with a neighbor or a business owner, it's good to have an informed opinion about the offending electrical field strength in V/m. This field strength can be obtained by means of the dBm value, the electrical length of your probe and the attenuation factor due to the antenna capacitance. My own values

  • 6pF antenna capacitance (close to the car door)
  • 0.125 meters electrical length.

All the best!
Anders H.
SM6-8439

Bill Alpert
 

Hi Anders! Thanks for this though I'm a bit confused on the construction and purpose of the probe. Is it a complete antenna? Or is it used in conjunction with an antenna? How is the red lead used? And is the other end of the coax fitted with a PL259 and connected to a receiver?
--
Bill / KG6NRV

Bill Alpert
 

Neil, a followup and discovery! Though my mains were off, I did't realize that a computer UPS was still active and was creating a lot of RFI within the shack. Removing it did improve things considerably. Though in the interim I did walk the neighborhood with an AM radio in hand and discovered a couple of utility poles that produced the "raspy" sound in my speaker when approached closely. I'm wondering if this is typical/normal to hear at close range and to be expected.
--
Bill / KG6NRV

AndersH
 

Hi Bill!

This is a complete electrical field probe antenna, nothing else is required, just fold and tape the black lead backwards and press it tight against the RG 58 cable while allowing the red lead to hang loose. I am appending a picture of the test environment. Hidden from view to the left is an inexpensive RSP1A taking care of the antenna signal.

I understand you may have already solved the problem in a different way, but there's nothing wrong with this method. It's totally awesome in relation to the small efforts  involved and is highly recommended for local field strength testing on the go.

Best regards,
Anders H.





Bill Alpert
 

Anders, thanks for the photo. Just to clarify, are the leads connected to the center conductor and shield? 

And I"m assuming there is no directional quality to this antenna, it is simply designed to resonate when I'm in proximity to a strong signal source, yes?

Yes, I've partly solved the problem, but there's more work to do. When we had a temporary power outage today, my noise floor dropped something like 15db instantly. There's some RF snooping in my future!
--
Bill / KG6NRV

Klaus Brosche, DK3QN
 

Hi Bill,

Good luck with RF sooping ;-)

As of today, there are *lots* of devices installed in private houses as well as in public buildings
and Company offices/factories which impact your noise floor and cause interference:

E.g. LED lights, PLC (Power Line Devices), high-speed internet on copper (especially when run
via unshielded POTS lines), cable TV, Baby monitors on 433 plus garage door openers (and
the likes), etc. etc. An almost endless list :-((

It's a laborious process to find/identify these noise sources and it is quite often just practically
impossible to tame these things (or 'eliminate' them).

Living in a housing area with no industrial enterprises around makes things *a little* easier:
'cause - after identifying a noise source - you can talk to 'real' people.
My neighbour used to use PLC to get his internet from first floor to second floor.
Each of us owns one part of a twin-house. His 2nd floor PLC access point was just next
to my shack in the 2nd floor, separated by 2 walls. Terrible!
I could convince him to un-install these PLC devices. I even bought (and paid) 2 WLan
devices for him which replaced the PLC adapters. He is happy with that and for me
a main interference source has vanished :-))

For the remaining noise sources, I have made satisfactory success by adding a
'noise cancellor' ('X-Phase') little box in my coax line next to my TRX.
This thing has to be switched out (by-passed) during TXing which I control via the
TRX PTT-line (although it's got an RF-sensing switch-over control circuit built-in).
It's a little cumbersome, as you need to tune this thing if you change frequency/bands,
and you need a second antenna (some meters of wire and some experimenting
required) for it to work properly. OTOH, it reduces my man-made noise level pretty
significantly.

73, Klaus, DK3QN


Am 13.11.2019 um 02:52 schrieb Bill Alpert:

Anders, thanks for the photo. Just to clarify, are the leads connected to the center conductor and shield? 

And I"m assuming there is no directional quality to this antenna, it is simply designed to resonate when I'm in proximity to a strong signal source, yes?

Yes, I've partly solved the problem, but there's more work to do. When we had a temporary power outage today, my noise floor dropped something like 15db instantly. There's some RF snooping in my future!
--
Bill / KG6NRV


AndersH
 

Hello again Bill!

I referred to "red" as the center conductor and "black" as the shield. It's obviously a wise precaution to not take chances with the polarity.
If the alligator test leads are reversed by any chance, you just tape the other lead, everything else stays the same.

If the sensitivity with respect to your offending signal leaves something to be desired, just add a piece of wire to the free hanging alligator clip.

Good hunting!
Anders