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Author Topic: 80m RFI strangeness.  (Read 2331 times)
N3OX
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« on: November 05, 2006, 09:29:04 PM »

Apologies for the double posting here and Elmers, but I don't know if anyone reads here but not over there.

 I've got a strange, rushing form of interference on 80m. It comes and goes, and appears to come from some electronic device. It sounds like sudden white noise but ends with a little warbly beep, kind of like the end of a PSK transmission. I've only noticed it on 80m, seems especially bad around 3595 and 3795 (a bad spot)

A recording is at http://n3ox.net/files/80m_rfi.mp3  That's AM mode, AGC off, wide open filters

It starts with the noise, which cuts out, then starts again 14 seconds in, and cuts out again just before the end of the file. I do know that I have powerline noise too, I'm already getting help for that ;-)

Another is http://n3ox.net/files/80m_LSB_1.mp3
LSB, AGC off, 2.4kHz filter... you can hear the warbly tone at the end better in that one.

A spectrogram showing two events of this interference is at:

http://n3ox.net/files/80m_RFI_1105.jpg

Frequency range is from 0-5kHz, AGC off, AM mode on 3790, filters wide open. Numbers on the bottom are seconds. Again, the forest of horizontal lines is from my powerline noise, but the two big red-purple blobs are instances of the "white noise" RFI. Anyone recognize this?

73,
Dan
 
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
AA4PB
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« Reply #1 on: November 11, 2006, 10:36:44 AM »

Looks like you are not getting any responses, Dan. It sounds like some sort of digital transmission to me but I have no idea what the source is. I would check to see if you can pick it up on a portable receiver of some kind (an AM broadcast band radio perhaps) so that I could walk around and look for a local source.
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Bob  AA4PB
Garrisonville, VA
N3OX
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« Reply #2 on: November 11, 2006, 07:52:47 PM »

That's a good thought... I don't seem to be able to really hear it outside of the 3-5MHz range, but maybe I could make up a 3.5MHz loopstick and just cart the FT-857 around with a SLA battery... it's a little heavier than a pocket radio but it might give me a clue.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
NB2A
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« Reply #3 on: December 22, 2006, 11:58:21 AM »

I had a bad issue with a motion activated wall fixture for a light creating white noise sound.

Switched light to non motion noise which was timed obviously went bye bye.

Just a thought.


I wish I could get rid of my RF on 80 a whole different story!

NB2A

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WB1AEX
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« Reply #4 on: January 07, 2007, 08:56:27 AM »

That is a strange sounding noise Dan. If I was plagued with that one, I would grab a portable SW receiver (Good excuse to buy one if you don't have one handy!) and start walking around. One with a whip antenna that telescopes works great for reducing gain as you get closer to the source. There are so many consumer appliances that leak into the VLF and HF spectrum that it could be almost anything. If you can determine that it is not from your home, then it becomes a matter of seeing how it is propagating to your station receiver: through AC wiring, phone lines, cable, and so on. Got any new touch lamps in the neighborhood? Those are notorious for broadband noise.

Good luck!

Rob WB1AEX
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N3OX
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« Reply #5 on: January 31, 2007, 03:51:17 AM »

If anyone's still reading this:

I found the location, it's an apartment building near my house.  

I suspect elevator variable frequency drives based on the duration and length of the noise bursts and the fact that there seems to be peak activity around the times when people would be leaving for work and returning home.

It's almost nonexistent in the wee hours of the morning.  When it does happen at, say 2am, it's generally one or two bursts and then nothing for some time.

I don't know that I'm going to pursue anything besides technical solutions right now.  I'm not going to be in the area long enough to start a battle with some apartment management company over their noisy equipment.

Dan
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
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