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Author Topic: Extremely regular 20 M digital noise problem  (Read 557 times)

WB6JZL

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Extremely regular 20 M digital noise problem
« on: July 18, 2021, 04:03:31 PM »

Hi.
I got back on the air after a long time off (29 years).  I have a severe digital noise problem.  It's rendered the 20 meter band unusable. I live in a rural area and only have two neighbors located around 150 feet for one and about 300Ft. for the other.  The 20M band is completely covered with this noise (see link below for audio of it plus spectrum analyzer display).  It is "on" for about 3 seconds and off for the same amount of time.  Looking at the waterfall display shows it's repetitive nature.  I shut off my entire house at the breaker box (ran the receiver on battery) and I still have it.  If I use the small telescopic antenna on the TinySA, I don't receive it but if I connect my vertical outdoor antenna, I get the spectra shown in the link below.  It happens 24 hours/day so I think that rules out solar inverters.  When we had a power failure, it went away.   The peaks are about 5 KHz apart.  I even hear remnants of it on 40M.  I was wondering if anyone here can spot a familiar pattern to the signal.  Thanks.  Barry

The link to the spectrum analyzer display and also a file with an audio recording of the noise:
https://www.dropbox.com/sh/nb5l45lriq572aq/AAB8oI_F1v_ua6LKtUgIMrVWa?dl=0
« Last Edit: July 18, 2021, 04:23:17 PM by WB6JZL »
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W9IQ

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Re: Extremely regular 20 M digital noise problem
« Reply #1 on: July 18, 2021, 04:59:52 PM »

Have you taken your TinySA around the neighborhood to locate the noise?

Do you have common mode chokes on your vertical antenna coax? What are the details (size, radials, etc.) of your vertical?

- Glenn W9IQ
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- 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.

AC9XH

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Re: Extremely regular 20 M digital noise problem
« Reply #2 on: July 18, 2021, 05:30:02 PM »

Have you thought about electrical smart meters that transmit their data broadband over powerline and some just transmits the data openly? I have a similar problem. But mine is on 80 40 30 20 17 21 12 10 and 6. periodically a junk noise i call it, comes over the bands im working at the time. its not all the time but repetitvely. iit comes on as a low powered signal then grows in strength almost like a noisy microwave oven. then it goes back to low and then gone. this will happen on any of my bands . especially when im running digital or cw. Ive left it on when tuning ssb and it does it also washing out any information at that time . If running ft8 ,you have to wait 3 to 5 cycles of the program for it to clear up. and it happens all day,all night.Im suspicious of the meters the electric company replaced around where i live. I refused the upgrade which they are charging me an extra $10 a month to manually read our meter. Didnt have all this noise on the bands before they replaced those electric meters.I live in clarks hill Indiana
73
David
ac9xh

hope this helps
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WB6JZL

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Re: Extremely regular 20 M digital noise problem
« Reply #3 on: July 18, 2021, 05:32:47 PM »

Hi and thanks for the reply.  I tried a Palomar Engineers common mode choke but it didn't have any effect.  I tried the test of just connecting the center conductor of the coax as mentioned by Palomar.  It did very slightly reduce the interference but not much effect.

I have made a directional antenna (a loop) but it's very narrow bandwidth (it uses a tuning capacitor).  I need to continue experimenting with it but it's such narrow bandwidth, I can only tune it for one of the "spikes".  I'm wondering if it's someone with an electric fence but there are no livestock in the area.  That doesn't necessarily mean there isn't a fence though.

Forgot to mention antenna info.  It's a Hy Gain 14AVQ.  Roof mounted, four 22 Ft. radials, grounded with a 7 Ft. ground rod.
« Last Edit: July 18, 2021, 05:37:11 PM by WB6JZL »
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KI5FJ

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Re: Extremely regular 20 M digital noise problem
« Reply #4 on: July 19, 2021, 05:57:16 AM »

Barry, Did you power down devices that have a battery back-up such as alarms, internet cable connection? I always recommend using two Common Mode Chokes, one at the antenna feed-point and the other in the shack. Try disconnecting the wire to the ground rod. Is there another ground wire path in the shack ? I have added CMC torroids on all power line wires in the shack. Especially the on the green safety wire. I also use a TRIPP-Lite Ultra for the shack stuff. The Ultra-6 has 3 RF isolated and filtered paths. Drop me a email (QRZ address) if you want more of my comments. 73 & Be Well,
Joe O, K I 5 F J, NNNN

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N1UKX

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Re: Extremely regular 20 M digital noise problem
« Reply #5 on: July 19, 2021, 06:42:25 AM »

Sounds like an electric fence controller is in the area.
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K6AER

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Re: Extremely regular 20 M digital noise problem
« Reply #6 on: July 19, 2021, 07:14:56 AM »

An electric fence is just a single spike about every 4 seconds.

Smart meters only transmit the digital signal about every 20-60  seconds. The noise burst is very short. About 100 bits of information.

As others have mentioned try to find the noise area with a portable receiver. I have used a loop stick on a plastic pipe with my HF rig in the truck to fine bad insulators.

Also look for a barn with grow lights for marijuana. Especially if the noise is 24/7.

Good Luck.
K6AER - Mike
« Last Edit: July 19, 2021, 07:19:25 AM by K6AER »
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KD6VXI

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Re: Extremely regular 20 M digital noise problem
« Reply #7 on: July 19, 2021, 08:04:06 AM »

A grow light for marijuana runs 12 hours on 12 hours off cycles for 2 to 3 months.

It runs 18 to 24 hours a day during the vegatative cycle which is typically 2 weeks to a month.

Even if running separate grow and bloom rooms you will still have a huge different in noise levels on the 12 on / 12 hours off cycles.

There are varieties that will flower in 24 hours of light hut most growers shy away from them due to the substantially lower yield.  The people who want those are typically medical patients whom need a constant supply.  Commercial growers will want the higher yields of standard marijuana strains.

--Shane
KD6VXI
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W9IQ

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Re: Extremely regular 20 M digital noise problem
« Reply #8 on: July 19, 2021, 09:08:37 AM »

A few other items that can generate that RFI cadence:

  • A battery maintainer / charger
  • A high pressure sodium vapor lamp with a bad ballast / bulb
  • A decorative neon sign

I highly recommend taking your TinySA along with the small whip on a walk or drive around your area. You will likely find the locale of the RFI source fairly quickly. Then a small directional antenna will help you zero in on the specific location.

- Glenn W9IQ
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- 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.

N0GV

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Re: Extremely regular 20 M digital noise problem
« Reply #9 on: July 19, 2021, 09:54:42 AM »

Sounds like the de-sulphating cycle of a battery maintainer.

Could be an electric fence but when the power is off they still keep chugging among on a battery. The modern electric fences charge capacitors with a high kHz dc-dc converter and that is what controls their pulse energy. Seen them used around gardens for rabbits and yards for foxes and raccoons - also for bears. Not just livestock is what I am saying.

Good hunting,

Grover
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N0ETR

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Re: Extremely regular 20 M digital noise problem
« Reply #10 on: July 19, 2021, 11:38:58 AM »

 I agree with Grover. Sounds like an electric fence charger to me. They cycle on and off like that and cause lots of noise.
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GRUMPY2021

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Re: Extremely regular 20 M digital noise problem
« Reply #11 on: July 20, 2021, 06:51:09 AM »

Looks and sounds exactly like a bad street light thingy...whatever is inside those.  Look down your street to see if you have any out.   I had one way down the road and called to have it repaired.   No more interference.  But really, all the guesses aside...if it's outside your home... good luck with that.
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K0UA

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Re: Extremely regular 20 M digital noise problem
« Reply #12 on: July 20, 2021, 07:45:48 AM »

I don't know for sure what it is, but I know it is NOT an electric fence. At least nothing like the electric fences I have heard all my life. IF I had to lay down money, my money would be on the battery charger.
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73  James K0UA
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