Tracking down AC Hum

[kb2mob]

I have a AC hum on my rig, but I can't seem to find where it's coming from. It's not a continuous hum either. It seems to build up to an s5 and lasts for like a minute or two then drops out then starts over again. When I remove the coax to the antenna it's gone. I can only really hear it on 160, 75/80, and 40 meters AM.

I'm thiking it's outside since it's not a constant hum, and dissapears when I disconnect the antenna. Could this be from the utility poles? Any other trouble shooting I can do to narrow it down?

Here's an MP3 of what I'm hearing on 80mtrs...

http://www.frontiernet.net/~mobbyg/ham/80mtramhum.mp3 - 1.29MB

[Ed KB1HVS]

Sounds like a street light cycling on and off. Take a stroll around the hood with a portable receiver and look for it. Then call the light company and try to get them to repair it.

[W1RKW]

Has anything changed at your QTH electronically recently?  Something that you may not have accounted for.  I had a similar S9 noise on 75m too that appeared out of nowhere and disconnecting the antenna made it go away also. It would come and go. Got out the portable receiver and couldn't hear it on that. My neighborhood has no street lights so I ruled that out. Ruled out my neighbors. Eventually determined with the portable receiver that the noise was coming from within my house once I got close enough to the source. Turned out to be a battery recharger for my cordless drill in the garage. I neglected to disconnect it after charging some batteries. My 75m dipole is broadside to the house so it made sense that it would pick it up.  I normally don't keep it plugged in with a battery but I guess I forgot and it caught me off guard.  Maybe you have a similar situation.  If you can do what Ed suggested maybe you'll be able to pin point it.  Good luck.

[W1DAN]

Hi:

It could be a house light (inside or out) that runs on an SCR...like a dimmer or photocell.

It could be yours or your neighbors.

As stated above, a battery receiver helps. You can kill the main breaker to your house to rule that out.

GL

73
Dan
W1DAN

[kb2mob]

I do have a street light across the street from me and it has been known to act funny.

The only thing that has changed recently is the addition of a new furnace. Aside from that, things are all the same as they were. I have an old Montgomery Ward SW reciever that almost gets to the 75/80 meter band but since it's seems to be spread across the whole spectrum on the low bands I should be able to use that.

I'll post an update after I try all these options.

[kb2mob]

UPDATE:
It's 12:12 pm EST and I'm listening to 3882Khz AM and no hum! It's gone. There is some QRM on 7326KHz though. Hmm.. I'll check again around 3 or 4pm when I posted last time before I head to work.

UPDATE #2:
It's 4:28pm and the hum is back.

[Sam KS2AM]

I have a AC hum on my rig, but I can't seem to find where it's coming from. It's not a continuous hum either. It seems to build up to an s5 and lasts for like a minute or two then drops out then starts over again.
I'm thiking it's outside since it's not a constant hum, and dissapears when I disconnect the antenna. Could this be from the utility poles? Any other trouble shooting I can do to narrow it down?
Here's an MP3 of what I'm hearing on 80mtrs...

Hi Rich,

Your recording sounds like a high pressure sodium streetlight cycling.  I've located and reported at least fourty of these to the local power co over the last few years.  The length of the cycle varies from light to light as well as the noises that it makes while trying to start up.
I've attached an mp3 of a light I had a problem with a couple of years back. If the file doesn't play just save it and rename it to a .wma file.
If it is a HPS streetlight, they're not hard to track down.  Just drive around the neighborhood slowly with the AM radio tuned to a clear frequency at the high end of the band. You'll eventually make a connection between the noise and a light that you're looking at.  Keep in mind that it may also be an "area light" that illuminates a parking lot.
Theres also a good web page that has alot of sample audio generated by different rfi sources.  Its on the arrl site (you know those bad guys that don't do anything for us).

http://www.arrl.org/tis/info/HTML/rfi-noise/utilities.html



Sam  /  KS2AM

[kb2mob]

Thanks Sam! I really appreciate it. I took that old Montgomery Ward Airline radio and tuned to about 3400KHz and stood next to my antenna. It appeared to me to be coming from a transformer on the hill behind me. But I'll be checking both the street light out in front and the transformers in back. I'm listening to W1IA on 3883KHz and the buzz is just not there or being covered up by his signal. But by later today (4pm)  it'll be there, probably due to the sun going down and the light getting ready to start up.

Cool.. more to go on.. More to come.

[Roy K8VWX]

           One thing to watch for is to see if it goes away when it rains. If it does it is not a street light etc. but a arcing insulator or a poor connection somewhere on the primary lines (7200 volts or what ever you have there) - Good luck- had that problem here and found both of the above plus one defective lightning arrestor.Power company most helpfull after I found the trouble HI  HI.

[Steve - WB3HUZ]

I bet your received hum disappears when I transmit.

[kb2mob]

Found it! There is a street light on that pole behind my house with transformers.

I put on my Yankees hat, pullover and hooked up my work headphones, and headed out with the Montgomery Ward radio. I stood underneath the pole and sure enough, there was the hum loud and clear like on my rig. After it dropped off, I moved a round the area where the pole is and got a few hums here and there when I looked at the light. But when I stood underneath it again, after a minute or 2, the hum cam back and then dropped again.

I guess next step is to call the power company.

[Ed-VA3ES]

I guess next step is to call the power company.   

Nah.... just take a chain-saw to the pole. The power company will show up soon enough!      

[kb2mob]

Couldn't find the chainsaw so I broke down and called. Said 5 to 10 buisness days.

[KB2WIG]

didn't you say it looked like it was ready to fall offthe pole?  klc

[kb2mob]

"dropped off" refers to the hum. Sorry

[KB2WIG]

It looks like its going to fall  or

the kids are still throwing rocks at it to knock it off   or

how much smoke can come out before it catches fire? or

after the bright flashes, howcome the fire goes out and not continue to burn? or

why are there a lot of dead worms all around the pole ? or

Is that a Halloween dummy the power co hangs of the poles, and if so, how do you get the flies to come back?

      klc

[WA1GFZ]

after 10 days a .22 short will also take care of it

[KB2WIG]

          "after 10 days a .22 short will also take care of it."


Ah yes, the G. Gorden Liddy method.....   klc

[kb2mob]

Ah yes, the G. Gorden Liddy method.....   klc

That reminds me. I haven't finished reading his biography yet!

[Tom W2ILA]

I have found that if you call the power company and say "I see sparks flying off this pole" they show up in fewer business days.