Pages: [1]   Go Down

Author Topic: What kind of noise is this  (Read 616 times)

KG0MN

  • Member
  • Posts: 89
    • homeURL
What kind of noise is this
« on: April 28, 2021, 07:54:52 AM »



Can anyone make a guess as to what this noise might be.  Thanks in advance.

Kevin ~ KG0MN
Logged

W9IQ

  • Member
  • Posts: 8866
Re: What kind of noise is this
« Reply #1 on: April 28, 2021, 08:12:46 AM »

With a ~62 kHz harmonic, there are many possible sources. Probably something with a switching supply / regulator - wall wart, solar panel inverter / optimizer, battery charger, etc.

Do you have any background or additional information on this issue?

- Glenn W9IQ
« Last Edit: April 28, 2021, 08:16:58 AM by W9IQ »
Logged
- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W6QW

  • Member
  • Posts: 462
Re: What kind of noise is this
« Reply #2 on: April 28, 2021, 08:54:46 AM »

I agree that the spectral delineation points to switch-mode RFI.  You can expect many solar panel inverters have harmonics every 70KHz so this may well be from another source. 

Can you supply a time-domain picture using the audio oscilloscope feature of your transceiver?  Change the receiver mode to AM and set the timing to 10mS per division.  Tune the frequency to the center of one of the noise peaks.  The time-domain would be useful in identifying the fingerprint of the source.

Is this RFI on other bands?
« Last Edit: April 28, 2021, 09:01:23 AM by W6QW »
Logged

K6SDW

  • Posts: 527
    • HomeURL
Re: What kind of noise is this
« Reply #3 on: April 28, 2021, 10:39:56 AM »

My 7300 is showing exactly the same display here in Sacramento!! So I put my 7300 on battery and shut power to the main panel and nothing changes....everything was off except battery powered smoke detector and display was the same.

Then I disconnected the antenna to the 7300 and display went clean not showing those RFI signals on the waterfall, I'm guessing the RFI is being picked up by the antenna input.

So, 7300 wizards what gives? Does other radios with waterfall displays show the same interference?

Tnx and 73
Logged

W9IQ

  • Member
  • Posts: 8866
Re: What kind of noise is this
« Reply #4 on: April 28, 2021, 10:41:32 AM »

My 7300 is showing exacting the same display here in Sacramento!! So I put my 7300 on battery and shut power to the main panel and nothing changes....everything was off except battery powered smoke detector and display was the same.

Then I disconnected the antenna to the 7300 and display went clean not showing those RFI signals on the waterfall, I'm guessing the RFI is being picked up by the antenna input.

So, 7300 wizards what gives? Does other radios with waterfall displays show the same interference?

Tnx and 73

What type of antenna are you using and what type of common mode chokes do you have installed?

- Glenn W9IQ
Logged
- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K6SDW

  • Posts: 527
    • HomeURL
Re: What kind of noise is this
« Reply #5 on: April 28, 2021, 01:43:34 PM »

That's weird Glenn, I did a reply 2 hours ago and nothing from my second post.

Anyhoo, I run the WH6CZB EARCI endfed the club sells, 9:1 balun and also a simple 1/4 wave vertical. The  RFI showing on the waterfall doesn't change, still basically the same.

Also, the RFI gets worse as I tune down frequency with 80 meters at night being really bad, but that's 80/75 meters for ya.

Again, when I remove an antenna from the 7300 input all RFI goes away.

Tnx Glenn, 73
Logged

W9IQ

  • Member
  • Posts: 8866
Re: What kind of noise is this
« Reply #6 on: April 28, 2021, 02:25:09 PM »

Ed,

It does sound like your antenna system is picking up the noise. You didn't reference the use of any common mode chokes so it could be that your coax shield is picking up the RFI or it could be the antenna itself.

The first step would be to install two proper ferrite based, common mode chokes - one near the antenna feedpoint (12 feet or so away for your end fed antenna) and one before the coax enters the house. This may reduce or eliminate the RFI.

If not, then you need to start scouting the neighborhood with a portable HF receiver tuned to an offending frequency. Look for solar panel systems, etc. that may be more obvious sources of interference.

- Glenn W9IQ
Logged
- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K6SDW

  • Posts: 527
    • HomeURL
Re: What kind of noise is this
« Reply #7 on: April 28, 2021, 03:02:22 PM »

Thanks Glenn, I do have ferrite based chokes from Palomar Engineering.
Logged

W9IQ

  • Member
  • Posts: 8866
Re: What kind of noise is this
« Reply #8 on: April 28, 2021, 04:00:04 PM »

Thanks Glenn, I do have ferrite based chokes from Palomar Engineering.

What model? Their "slip on sleeve choke", for example, would probably not be adequate.

- Glenn W9IQ
Logged
- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W6QW

  • Member
  • Posts: 462
Re: What kind of noise is this
« Reply #9 on: April 28, 2021, 06:24:30 PM »

That's weird Glenn, I did a reply 2 hours ago and nothing from my second post.

Anyhoo, I run the WH6CZB EARCI endfed the club sells, 9:1 balun and also a simple 1/4 wave vertical. The  RFI showing on the waterfall doesn't change, still basically the same.

Also, the RFI gets worse as I tune down frequency with 80 meters at night being really bad, but that's 80/75 meters for ya.

Again, when I remove an antenna from the 7300 input all RFI goes away.

Tnx Glenn, 73

There is a high probability that you are receiving multiple RFI sources based on your response.  You need to delineate the RF frequency domain and time domain for each source to identify the fingerprint of each.  Many get confused when multiple RFI sources invade their QTH and you must methodically distill the information for each.  There are numerous internet resources that will help you identify and track-down the root-offender(s).

It is a fool's errand to assume that common-mode chokes will mitigate parasitically induced RFI onto your coaxial cable.  Unless you have a superior directional antenna, common mode RFI reduction through feedline chokes will make little, or no difference in received noise level.  The signal-to-noise level seldom changes with omni/semi-omni antennas by the use of common mode mitigation techniques.

I have dispelled this misunderstanding of RX common-mode noise reduction to several groups at my antenna test range through a few demonstrations.  Feel free to contact me directly if you would like further information or schedule a demonstration of the concept at my test range.
Logged

K6SDW

  • Posts: 527
    • HomeURL
Re: What kind of noise is this
« Reply #10 on: April 28, 2021, 07:23:10 PM »

Thanks all for your help and advice.

73 ~ ed
Logged

W9IQ

  • Member
  • Posts: 8866
Re: What kind of noise is this
« Reply #11 on: April 29, 2021, 06:22:17 AM »

It is a fool's errand to assume that common-mode chokes will mitigate parasitically induced RFI onto your coaxial cable.  Unless you have a superior directional antenna, common mode RFI reduction through feedline chokes will make little, or no difference in received noise level.  The signal-to-noise level seldom changes with omni/semi-omni antennas by the use of common mode mitigation techniques.

While this can certainly be the case, there is sufficient field evidence to say that this is painted with too broad of a brush. For example, local interferors can induce a signal on the nearby outer coax shield that is coupled into the receiver. If the antenna is sufficiently distanced from the interferor, the near field decay that follows an inverse cube law (resulting in a power decrease by more than the inverse of the fourth power of distance) will greatly reduce the interferor signal strength at the antenna. The proper placement of common mode chokes can result in several S units of attenuation.

- Glenn W9IQ
Logged
- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N1UK

  • Member
  • Posts: 2326
Re: What kind of noise is this
« Reply #12 on: May 17, 2021, 11:45:16 AM »

Solar panel optimizers ?   Does the noise go away at night ?


73 Mark N1UK
Logged

N0GV

  • Posts: 627
    • HomeURL
Re: What kind of noise is this
« Reply #13 on: May 26, 2021, 02:20:38 PM »

That there is a switcher! The peaks are relatively broad and they are regularly spaced for the same general realm as a small switch mode power supply. Could be an inverter or chopping regulator/ballast but those generally are somewhat narrower in peak width.

Look for new wall warts, phone chargers, then LED lamps/bulbs, then new fluorescent fixtures. Major appliances now all have confuters in them and, like most things confucius, they can be really efficient RFI emitters (my personal private double secret code for Chinese junk).

Grover
Logged
Pages: [1]   Go Up