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Author Topic: RF Noise at Night: Ruins Everything  (Read 2516 times)
NU9J
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Posts: 109




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« on: June 09, 2011, 06:44:55 PM »

Just built my first 10m antenna, installed in my apt (that's another thread). I thought something was wrong last night when I got it assembled, because the noise floor was S9 (or above!) across every single band. Early this morning, it had dropped to S3, and I actually caught several QSOs in BPSK-31 on 14.070 from MD, Dominican Republic, CA, etc. Now, 8:30pm, the noise is back up to S9, completely crapping all over everything again.

This has got to be some piece of equipment that my neighbors have right? How can I find this god-awful noise?
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~Philip
KB4QAA
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« Reply #1 on: June 09, 2011, 06:55:54 PM »

Welcome to apartment living as a ham!
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NU9J
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« Reply #2 on: June 09, 2011, 07:05:13 PM »

I should say that in SSB, it looks like white noise, but in AM, there are very clear distinct traces in the waterfall at multiples of 120 Hz. When I record it, it looks like:

http://farm6.static.flickr.com/5040/5816508143_706d3fa5e3.jpg
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~Philip
N3OX
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« Reply #3 on: June 09, 2011, 07:16:35 PM »

Something that comes on at 8:30 p.m. (about sunset, right) and has noise at 120Hz multiples sounds like a light to me, probably a big one like a parking lot light if it's very loud and isn't inside your apartment.  Sodium and mercury vapor streetlights don't tend to make any troublesome noise until they fail... so keep an eye out for flickering/dim ones.  That would be a winner from your perspective because you can just go to management and say "hey, the light across the parking lot from my apartment is going out, can you get someone to take care of that."  

Of course, it could also be in your apartment or a neighboring apartment.  You should always assume that the problem is in your place until you've ruled everything in your place out because the sources in your apartment will be massively stronger than those in neighboring apartments.  Things that would be more or less innocuous if they were thirty feet from your antenna can cause you great trouble if they're only a foot away.  

For example, I don't get any particularly noticeable RFI picked up on my outdoor antennas from the compact fluorescent lights in my house, BUT if I were to string up a 10m dipole a few feet from one, I would probably hear it easily.  I can certainly hear a super loud noise coming from them from 1.8 thru 432MHz if I get an antenna right up near them, but it drops off very quickly if the bulb is of good design and doesn't couple much RF onto the wires.  

Now, I don't want to bias you too much by talking about lights, and I wouldn't necessarily recommend spending TOO much time coming up with predictions for what the culprit might be. It's more important to go through a systematic process of elimination, removing power from EVERYTHING, just in case the problem is in your apartment.  If you have access to your circuit breaker panel and a way to run your receiver from battery power, that can be a fairly easy way to eliminate almost everything in your apartment (watch out for things with battery backup)
« Last Edit: June 09, 2011, 07:18:12 PM by N3OX » Logged

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

Monkey/silicon cyborg, beeping at rocks since 1995.
N4NYY
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« Reply #4 on: June 09, 2011, 07:28:27 PM »

I bet you a dollar that someone has a Plasma TV. They are death on receivers.
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NU9J
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« Reply #5 on: June 09, 2011, 07:43:16 PM »

Now, I don't want to bias you too much by talking about lights, and I wouldn't necessarily recommend spending TOO much time coming up with predictions for what the culprit might be. It's more important to go through a systematic process of elimination, removing power from EVERYTHING, just in case the problem is in your apartment.  If you have access to your circuit breaker panel and a way to run your receiver from battery power, that can be a fairly easy way to eliminate almost everything in your apartment (watch out for things with battery backup)


This is what I want help with: the systematic walkthrough.

I know it's not my rig/power supply because I have a battery-powered long/medium/short-wave radio that gets the exact same noise at all frequencies. I have turned off all lights in my place, and started walking around placing my shortwave radio close to everything I can think of. The problem is that the noise is pegged out pretty much everywhere, so I'm not getting much info from the shortwave.
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~Philip
NU9J
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« Reply #6 on: June 09, 2011, 07:48:23 PM »

I bet you a dollar that someone has a Plasma TV. They are death on receivers.

You may be right. This vid is very similar to my case:
http://www.youtube.com/watch?v=hTXlLxV_Xwk
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~Philip
NU9J
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« Reply #7 on: June 10, 2011, 06:14:36 AM »

Well, just found one of the major sources: the lights at the entrances to our apartment complex (they are fluorescent or something). As soon as they went off, the noise on 28.120 went from S9 to S5. However, there are still some strong traces at 60 Hz multiples until about 500 Hz.
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~Philip
KC2UGV
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« Reply #8 on: June 10, 2011, 06:21:04 AM »

Well, just found one of the major sources: the lights at the entrances to our apartment complex (they are fluorescent or something). As soon as they went off, the noise on 28.120 went from S9 to S5. However, there are still some strong traces at 60 Hz multiples until about 500 Hz.

If you run your rig off of battery, and turn off the mains, do you still have them?

60Hz sounds suspiciously familiar Smiley  That, and I have the same problem.  Somewhere in my house, I have a connection or something leaking.  I do know the 60Hz lines come from my mains line though (They go away when I switch to battery).
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AA4HA
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« Reply #9 on: June 10, 2011, 07:52:58 AM »

You are probably being tore up by a bunch of different sources. The lighting ballasts, plasma televisions, home computers, etc... Hunting them all down would be a daunting task and while you may be able to do something about a few of the noise generators you will never get them all.

Maybe you can come up with a bandpass filter with significant attenuation below 1.5 MHz and above 30 MHz. It will probably need to be a multi-stage filter with plenty of shielding. You may also need to improve the shielding on your own rig to reduce the amount of out-of-band interference from getting into the front end and mixing or driving the receiver into nonlinear operation.

A problem will be for noise sources that are mixing externally from your receiver and putting harmonics directly into the bands you want to work. (intermodulation).

There will be no magic bullet but you may be able to reduce some of the worst offenders to the point where they are just annoyances. Unfortunately if the individual noise sources are all in FCC compliance it does not help you when there are many noise sources that are all mixing together, creating new and interesting signals.

As a former compliance test engineer I always wished that the FCC would tighten up the regulations and force manufacturers to go through external, independent laboratories for every new and revised product. Now they can pencil whip a compliance document as being similar to some other design they have out there and get an FCC product registration ID.

Tisha Hayes, AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W8JX
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« Reply #10 on: June 10, 2011, 08:10:54 AM »

You might try a different antenna like a loop as they tend to pick up less noise.
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W5RRP
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« Reply #11 on: June 10, 2011, 06:02:43 PM »

Make sure our tv is turned off.
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K1CJS
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« Reply #12 on: June 10, 2011, 06:32:19 PM »

You live in an apartment, so just about anything that comes on in the evening can be suspect.  How big is the apartment building?  A few units--or many, on many floors? 

If many, the system that provides outdoor/indoor lighting after dark is the most obvious culprit.  Any outdoor lighting could be at fault.  N3OX, I think, hit on it--and you found one yourself.  You may just have a situation you can't do much about.  Sorry. 
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NU9J
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« Reply #13 on: June 10, 2011, 07:48:12 PM »

You might try a different antenna like a loop as they tend to pick up less noise.

Got any particular designs? I don't have a tuner or matching network, so it would have to be 50 ohms at the feedpoint, and I am limited to 10 ft vertical by 14 ft horizontal.

Also, thought I'd try batteries by putting 2 lantern batteries in series...turns out the transceiver won't even turn on fed that way. Only other way I know is to go plug in to my car, but then I couldn't know if it was the location or the power source.
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~Philip
K6JEA
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« Reply #14 on: June 10, 2011, 09:23:08 PM »

Also, thought I'd try batteries by putting 2 lantern batteries in series...turns out the transceiver won't even turn on fed that way. Only other way I know is to go plug in to my car, but then I couldn't know if it was the location or the power source.

I would be a bit of trouble but you could bring your car battery inside to power the radio for the test.
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