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Line noise problem




 
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Knightt150
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« on: September 19, 2018, 09:42:46 PM »

Hello: I have a bad line noise problem some of the time, I can't get on the air when I want to. Sometimes the noise is there on my receiver (S9 or above ) than leaves for several days than comes back, it is a BUZZING noise. The power co is glad to assist but when you call them the noise is gone, five minites later its back. Dose anyone make a directional antenna unit that would work around 7 Mhz. It looks like I am the only one that can solve my problem.

John W9BFO
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KA2DZT
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« Reply #1 on: September 19, 2018, 10:41:06 PM »

Most likely the noise is spread across a wide range of frequencies.  Start with a BC band portable radio and see if you narrow down where the noise is coming from.  Very often the noise reaches into the VHF band.  I was in the antenna business and would tract down noise interference often.  I used a CH 2 three element antenna and a field strength meter.  Sometimes I could find the noise source in 5 minutes sometimes it may take hours.  Had one noise problem at an apartment complex that took over a month to find.  It completely wipe out TV reception.  Turned out to be a bad doorbell transformer.  Cost the complex over $1800 for me to locate a bad $3 transformer.  Problem was intermittent which made it tough to locate.

I've located tons of interference problems.  Sometimes it is coming from the power lines and a lot of times it is coming from inside a house or a building and not always right near where the complaints are.  I've located interference problems that were coming from as far as a 1/2-3/4 of a mile from where the complaining customers were.

Fred
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Steve - K4HX
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« Reply #2 on: September 19, 2018, 11:52:18 PM »

https://www.arraysolutions.com/as-sal-30-mk2
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KD6VXI
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Making AM GREAT Again!


« Reply #3 on: September 20, 2018, 12:54:59 AM »

Search Google for the contesting.com rfi reflector.  W1rfi, Ed Hare the ARRL rfi go to guy is a member, as are quite a few other knowledgeable people who work in the rfi fields, emc compliance, etc.

That said, if you have rfi at 7 mhz, you want to start looking in the vhf range.  The higher in freq you can detect the aig AL, the better. Tec sun makes some decent little portables that go from am bc to vhf.  They are a favorite of rfi detection folks.

Another good thing about vhf (if you have a 2 mte ht that does vhf air, great.  Go there and switch to AM and now go detecting.

You can use your body as a shield to block signals, producing a cardioid pattern, with practice (another reason for vhf or higher detection.  Antennas with meaningful gain AND even.better, sidelobe and front to back).

Sounds like a switching power supply.  Which could be grow lights, a new led tube conversion at a neighbors, bug zapper which only gets turned on when that homeowner is outside, etc.  You can see how this can be a 'in it for the long haul' situation.

Also, do the whole house turnoff.  Use a car battery to power your rig, or gel cell, etc.  Turn off the main breaker to the house.  Even this isn't sure fire, however.  Many things now have internal battery backup and switching supplies....  Cable modems, FIOS entry equipment, dsl modems, routers, wifi access points, etc.

Hope this helps.  That rfi list is really a great place to start.....  And to ask questions.

--Shane
KD6VXI


(sorry for any typos, typed out in my cell phone)
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WA2SQQ
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« Reply #4 on: September 20, 2018, 08:58:13 AM »

Start keeping a log of when and how long it occurs. Only during the day or night? Only when it's dry outdoors, and does it go away when it starts raining? (That's a sure sign it's probably bad HV insulators on a pole.)

Walk your neighborhood and inspect each transformer up on the poles. If one has a RED light which is ON, suspect that one first. In one problem I had, that fact alone convinced my power company that I found the problem. The light comes on when the transformer is running at or over capacity / temperature.

If you find a suspected pole, while listening to the noise, whack the pole with a baseball bat. The vibration will interact with the lamination in the transformer and you can hear the noise change. I demonstrated this to the power company and they were amazed.

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WE1X
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« Reply #5 on: September 20, 2018, 09:11:46 AM »

I suffered from various forms of RFI including that from underground power lines and neighbor's failing sodium vapor flood light. I recall that somewhere on the eHam forums there was a link to a website having audio recordings of different types of RFI that can help identify the type you're experiencing.

The powerline and flood light RFI I experienced trashed all bands with S9+ noise.  The powerline was 24/7 and was caused by technicians working on upgrading the powerlines including the addition of new doghouse type ground transformers. Once they were done the noise went away.  However, it took a couple of months for that to happen. My neighbor's sodium vapor light was failing and the noise pattern I experienced tied directly to the sputtering pattern of the light. Unfortunately, he refused to do anything about it. Eventually the light died and he replaced it.

While all this was going on I installed a Timewave ANC-4 "noise canceler" with a noise sense antenna. With a lot of experimentation with the type and placement of the noise antenna I was able to reduce the S9+ interference down to about an S2 or S3. Although not ideal, it allowed me to use the bands until the situation improved.

My $0.02.

Harry
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WD5JKO
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WD5JKO


« Reply #6 on: September 21, 2018, 09:01:07 AM »

Hello: I have a bad line noise problem some of the time, I can't get on the air when I want to. Sometimes the noise is there on my receiver (S9 or above ) than leaves for several days than comes back, it is a BUZZING noise. The power co is glad to assist but when you call them the noise is gone, five minites later its back. Dose anyone make a directional antenna unit that would work around 7 Mhz. It looks like I am the only one that can solve my problem.

John W9BFO

   John,

   I am fighting the same thing here at my QTH. It is usually a compound problem layered in intensity. I had an electrician over to bring an air conditioner 220v circuit up to code, and while there he discovered the circuit breaker to a remote panel had heated connections. The main panel was "humming" when it should have been silent. Fixing that issue eliminated the audible humming, and also took a layer of noise off my ham receiver. If you have electrical noise in the house, or on the same circuit as the hamshack, sometimes having a coax switch to multiple receivers will show noise on the receiver NOT selected! This suggests to me that the coax cable shield is carrying "ground current" which is being picked up on the inner signal wire by induction.

   With all my noise, two Icom receivers are pretty much useless (R75 and R8500) with or without the NB. My Mosley CM-1 seems to do a better job than the Icoms, but the noise is still bothersome. My Flex 5000 (KE9NS SW 2.8.92) however eliminates about 90% of the noise with NB2, and with NB1 also selected, the panadapter baseline goes WAY down as if the noise was never there. Amazing! Turn off the two NB's and the noise is so bad the RCVR is useless.

Jim
Wd5JKO
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