Hum in local AM BCB stations

[kenglish]

I mentioned something over in one of the AM HD Radio treads about this, but rather than hijack that thread, I figured I'd open this up here.

Although I've been tracking down interference for a couple of decades, this has me stumped....and, it's in my own home!
When using any AM Broadcast Band radio, whether it is a portable, a hi-fi component tuner, or a communications receiver, I hear a strong, harmonically-rich 60-hertz hum about 20 dB down in the audio of LOCAL STATIONS ONLY. This happens on virtually every strong local AM station. Tuning off a few kilohertz, I hear white noise, with the expected minor crackling buzz that has existed for years from the neon signs, power lines etc that live in the neighborhood. Using a loop antenna does not help, since there seems to be no obvious null in any direction. Outside antennas don't clear it up. It is heard on the balcony and out on the lawn, even.

I can get a very clean signal from distant AMs, like KNBR and KFI, with just the minor electrical-interference buzz. I can even null the neighborhood electrical noise on those. But, tune to almost any local station, and the hum is back.

This affects the NAB SuperTuner (Denon TU-680NAB), it affects a Sangean HD tuner (going to Digital mode cleans it up, analog hums until it locks), it is heard on a Sony portable (on battery), it is heard on a TenTec communications receiver. The receivers that can get shortwave or HF, though, are clean on HF frequencies, but hum on AM BCB.

Turning off the AC power to my apartment doesn't help. In an earlier time, I've been known to cut power to the entire building (24 units) when no one else is home (for a quick test), but I don't want to do that nowadays, due to so many folks having computers and such.

Any ideas?

 

[OKCRadioGuy]

Spectrum analyzer and a loop (directional) AM antenna..l. Find someone in the market that has one and go look for it. If you don't have that, maybe a little pocket radio with a pretty directional antenna may help. Take some directional measurements outside the place a bit and see what direction it is coming from. If you do it in three or more places and put it on a map (google sat view printed out might help) you may at least be able to sort of triangulate the source. Hopefully it's not just re-radiating the noise all over due to inducing the hum in the electric lines itself. Good luck!

 

[w9wi]

I mentioned something over in one of the AM HD Radio treads about this, but rather than hijack that thread, I figured I'd open this up here.

Although I've been tracking down interference for a couple of decades, this has me stumped....and, it's in my own home!
When using any AM Broadcast Band radio, whether it is a portable, a hi-fi component tuner, or a communications receiver, I hear a strong, harmonically-rich 60-hertz hum about 20 dB down in the audio of LOCAL STATIONS ONLY. This happens on virtually every strong local AM station. Tuning off a few kilohertz, I hear white noise, with the expected minor crackling buzz that has existed for years from the neon signs, power lines etc that live in the neighborhood. Using a loop antenna does not help, since there seems to be no obvious null in any direction. Outside antennas don't clear it up. It is heard on the balcony and out on the lawn, even.

I can get a very clean signal from distant AMs, like KNBR and KFI, with just the minor electrical-interference buzz. I can even null the neighborhood electrical noise on those. But, tune to almost any local station, and the hum is back.

This affects the NAB SuperTuner (Denon TU-680NAB), it affects a Sangean HD tuner (going to Digital mode cleans it up, analog hums until it locks), it is heard on a Sony portable (on battery), it is heard on a TenTec communications receiver. The receivers that can get shortwave or HF, though, are clean on HF frequencies, but hum on AM BCB.

Turning off the AC power to my apartment doesn't help. In an earlier time, I've been known to cut power to the entire building (24 units) when no one else is home (for a quick test), but I don't want to do that nowadays, due to so many folks having computers and such.

Any ideas?

Someone's TV set?

Seriously, a co-worker here in Nashville had that problem, admittedly at least 15 years ago. He'd be listening to WSM on his way home from work (at WSM...) and as he pulled into his driveway it would start humming. Leave for work in the morning & when he got out to the street it would clean right up. Weaker stations were fine. (i.e., everyone but WSM...)

He'd just bought a new TV. Unplugged it, and the hum was gone. A ferrite choke core on the TV power cord ended up being the practical solution.

Mechanism of the hum isn't exactly clear but I suppose the WSM signal was strong enough to cross-modulate with the AC line in the rectifiers and/or primary-side power transistors. In an apartment I can see the interference being conducted via the power lines, at which point it's going to be nearly impossible to direction-find.

 

[nmoore6676]

I mentioned something over in one of the AM HD Radio treads about this, but rather than hijack that thread, I figured I'd open this up here.

Although I've been tracking down interference for a couple of decades, this has me stumped....and, it's in my own home!
When using any AM Broadcast Band radio, whether it is a portable, a hi-fi component tuner, or a communications receiver, I hear a strong, harmonically-rich 60-hertz hum about 20 dB down in the audio of LOCAL STATIONS ONLY. This happens on virtually every strong local AM station. Tuning off a few kilohertz, I hear white noise, with the expected minor crackling buzz that has existed for years from the neon signs, power lines etc that live in the neighborhood. Using a loop antenna does not help, since there seems to be no obvious null in any direction. Outside antennas don't clear it up. It is heard on the balcony and out on the lawn, even.

I can get a very clean signal from distant AMs, like KNBR and KFI, with just the minor electrical-interference buzz. I can even null the neighborhood electrical noise on those. But, tune to almost any local station, and the hum is back.

This affects the NAB SuperTuner (Denon TU-680NAB), it affects a Sangean HD tuner (going to Digital mode cleans it up, analog hums until it locks), it is heard on a Sony portable (on battery), it is heard on a TenTec communications receiver. The receivers that can get shortwave or HF, though, are clean on HF frequencies, but hum on AM BCB.

Turning off the AC power to my apartment doesn't help. In an earlier time, I've been known to cut power to the entire building (24 units) when no one else is home (for a quick test), but I don't want to do that nowadays, due to so many folks having computers and such.

Any ideas?

Experienced the same issue for months on KGIL-1260 in North Hollywood and I finally traced it to a desk lamp containing one of those new CFL curly fluorescent bulbs. The problem being that the hum appeared only when the lamp was switched off. Never figured how and why only on 1260 but now I've moved to Ottumwa, Iowa and I get the same hum on local station KBIZ-1240 but not on KLEE at 1480.

Is it due to proximity or is it related to the frequency, near 1200 Khz? Oh, I left the offending fixture in NoHo but there are a lot of those CFLs around me here.

 

[Tom Wells]

Do you know if any of your radios have BOTH sides of the AC line bypasssed with a cap to chassis ground?
You may want to put line filters on your whole AC service. I have only two 30 amp lines, so it was not difficult to find
a 2-pole 30 a EMI filter, which is NOT the same as an RFI filter, but it did take care of a LOT of re-radiated noise.
If you're in a multi-unit building this will not be much help, as the neighbors' wires will be conductiing the local signal and re-radiating it
with the -20db hum. I've seen the same thing with my AM part 15 here in the house, where sometimes, it's the only signal
that gets hum on it, its NOT there in the car, etc. But it's only a few spots in the house where that happens.
If you are in Ottumwa, you are probably down near the river, as are the power lines, and very likely the stations
with this issue are somewhere nearby on flood-plain land. Couple that with the much higher conductivity in your new region,
and I think you are seeing something that is not a "problem" with your radios, but your location.

 

[nmoore6676]

Do you know if any of your radios have BOTH sides of the AC line bypasssed with a cap to chassis ground?
You may want to put line filters on your whole AC service. I have only two 30 amp lines, so it was not difficult to find
a 2-pole 30 a EMI filter, which is NOT the same as an RFI filter, but it did take care of a LOT of re-radiated noise.
If you're in a multi-unit building this will not be much help, as the neighbors' wires will be conductiing the local signal and re-radiating it
with the -20db hum. I've seen the same thing with my AM part 15 here in the house, where sometimes, it's the only signal
that gets hum on it, its NOT there in the car, etc. But it's only a few spots in the house where that happens.
If you are in Ottumwa, you are probably down near the river, as are the power lines, and very likely the stations
with this issue are somewhere nearby on flood-plain land. Couple that with the much higher conductivity in your new region,
and I think you are seeing something that is not a "problem" with your radios, but your location.

Both AC and battery radios get it. In North Hollywood I was maybe two to three miles from KGIL in Mission Hills but closer to KSPN-710 where there was no hum but they are also HD. I finally noticed that the hum was loudest near the desk lamp which I no longer have. As I said it was not heard as loud when the lamp was lit. Here in Ottumwa I notice it only on KBIZ at 1240 which is relatively near to where I am and I believe it is on flood plain land. I haven't tracked it yet to a specific appliance. Neither KGIL nor KBIZ use IBOC equipment.

Is it your conjecture as it is mine that somehow the radio frequencies are mixing (modulating) or being modulated by the AC? I have been trying to figure that some way the circuitry within the bulb is responsible and that it is negated when the lamp is energized. Any help out there, it is as yet a mystery to me.

 

[Tom Wells]

The neutral side of the line is always connected to the lamp, even when the switch is off.
I suppose there could be enough voltage float on the neutral to energize some bit of silicon in there in the hi-frequency
power supply to cause this. But I've seen this when we have no compact flourescents.

Is it the lamp a screw-in base in a ceiling socket? Maybe you should verify the hot and neutral connections aren't reversed.
If it's a plug-in lamp, try reversing the plug if it's not polarized. If it's polarized, file, nip, or cut the wider plug tip so you can try
it both ways ( sorry UL, noise abatement is of more importance ).

 

[boiseengineer]

The rectification & re-radiation of the AM signal sounds like what's happening. Switching supplies like in computers and even satellite TV receivers cause problems. Putting RFI filters at the source of the noise to keep the RF out of it works best. I've replaced more than a couple computer power supplies. One actually made more hash when turned off.

 

[nmoore6676]

The rectification & re-radiation of the AM signal sounds like what's happening. Switching supplies like in computers and even satellite TV receivers cause problems. Putting RFI filters at the source of the noise to keep the RF out of it works best. I've replaced more than a couple computer power supplies. One actually made more hash when turned off.

I think that we are on the right path here, to answer Tom's questions, it was a screw in in a desk lamp. I may try to recreate the issue later. I still have a question as to why it seems to be centered around 1200 kHz. It seems to take a proximity to the transmitter but only at 1260 or 1240 in my case. In North Hollywood I was nearer to 710 than 1260 yet the hum was only evident on 1260. Now without the lamp I may be getting it from one of the power bricks for the peripherals on my computer. The desk lamp stayed in California. Thanks to everyone for the insights so far.

 

[nmoore6676]

The rectification & re-radiation of the AM signal sounds like what's happening. Switching supplies like in computers and even satellite TV receivers cause problems. Putting RFI filters at the source of the noise to keep the RF out of it works best. I've replaced more than a couple computer power supplies. One actually made more hash when turned off.

I think that we are on the right path here, to answer Tom's questions, it was a screw in in a desk lamp. I may try to recreate the issue later. I still have a question as to why it seems to be centered around 1200 kHz. It seems to take a proximity to the transmitter but only at 1260 or 1240 in my case. In North Hollywood I was nearer to 710 than 1260 yet the hum was only evident on 1260. Now without the lamp I may be getting it from one of the power bricks for the peripherals on my computer. The desk lamp stayed in California. Thanks to everyone for the insights so far.

In the current case it has been localized to a ceiling fixture and the switch is in the hot leg. Still the only interference appears at 1240 so the question is why at frequencies around 1200Khz?

 

[Tom Wells]

It could be that the line distance from the pole distribution transfomer to your house is the right length to be reasonant for 1200 khz
(or a multiple of that length). Are your incoming lines overhead or buried? And which direction do they run, relative to the antenna of 1240?

 

[kenglish]

I haven't had too much time to chase this the past couple of weeks, but....

I remembered that we once had intermod, due to the galvanized rain downspouts touching the iron gas pipes where they come down through the gas meter pods. I found some plastic "pipe markers" to try and insulate them, but didn't get to try them out, mostly due to massive pigeon guano. I'll try that again soon, with appropriate gloves and gas mask.

Also, I got to wondering if some of the odd noises (especially on Shortwave) might have to do with DSL leaking across some of the phone lines. So, I'll try a DSL filter and a few ferrites while I'm at it.

 

[boiseengineer]

The guano is probably making the problem worse keeping moisture & corrosion going. Rent a power washer and stand back.
DSL will cause a lot of noise, but the filters won't help much since the wiring to the phones is probably old loose-twist (if any) home phone cable. CAT-5 would help there. Our business manager's older cordless phone was wiped out until a seperate circuit was installed just for the DSL.

A little skew on the topic. The cable TV around here has soooo many leaks most everything from 2 MHz to 400 MHz has a -20 dB noise floor on the old Icom. And I don't have cable.

 

[Tom Wells]

I put 4 or 5 ferrite filters in series in the line output of the DSL modem to the rest of the house. All the the phones are downstream, and no RF hash is
detectable unless you hold a radio right up to the phone.

 

[kenglish]

A little skew on the topic. The cable TV around here has soooo many leaks most everything from 2 MHz to 400 MHz has a -20 dB noise floor on the old Icom. And I don't have cable.

I lucked out on the low-band channels...my Cable TV leakage (home improvement store RG-59 and loose-ring crimp connectors) isn't bad below the high VHF band, but I can listen to everything above it on a hand-held scanner.
So, I was able to do some VHF low-band DXing this summer (post 6-12-09).

 

[kenglish]

I'm gonna "bump" this one up a bit.

Some more recent investigation indicates that the noises all seem to come from the cable TV junction box outside, probably a mish-mash of all the TVs and computers that are connected to Cable in the area.

 

[nmoore6676]

I'm gonna "bump" this one up a bit.

Some more recent investigation indicates that the noises all seem to come from the cable TV junction box outside, probably a mish-mash of all the TVs and computers that are connected to Cable in the area.

By junction box, do you mean the tap on the pole from which the drops emanate, the splitter or directional coupler on the lines or a trunk amplifier, sometimes all of the above are located together in a group.

Cable TV systems pass around 60 volt AC along the lines to power local distribution and trunk amplifiers and since the cables have an aluminum outer shield there is a strong possibility of corrosion and thus rectification.

Another issue is if your "junction box" is the local power supply which is discernible by being located down the pole and is usually accompanied by an electric meter like the one on your house. This box contains the transformers to reduce the 120v line power to the lower value and it also contains a UPS (not the brown truck) device to power the system during mains failure. The devices in that box could produce all kinds of interesting noises some of which could be transmitted along the cables as well.

By the way my problem (in the 1240-1260 area) has disappeared since moving to another apartment. I am convinced that it was in fact the CFL lamps in my previous abodes. I have none in the immediate vicinity of my radio now.

 

[kenglish]

It's a large complex, with 590 units in 36 different buildings (plus a community center and an office/gym). The Cable was originally a 36-channel (or less) SMATV, using off-air and one C-Band dish.

The buildings were originally wired with Carol (Brand) RG-59/U from a "Junction Box" mounted above the upper floor window under the eaves, for each building segment...some buildings have a single breezeway dividing the building in to two segments, some have two breezeways making three segments, some are all-in-ones with no breezeway. Most are three stories tall.
The junction box contained a few cascaded splitters, fed via RG-59 from a two-way or four-way tap in the trunk line (0.485 semi-flex), which was laid in the common trench with all other utilities, downstairs.

Since the re-build about ten years ago, the trunks now come up in to a washtub-sized pedestal at each amplifier location (one for every two or three buildings), then go to a larger-sized Junction box at standing height/ground level, where the splitters and traps are located, then run up the side of the building with RG-6/U to the old J-Boxes. There, they are barrelled to the older RG-59. In many cases, the old RG-59 has been replaced with RG-6 running on the ground and in the hedges/flower beds, then up the building's exterior walls to a new access hole. Our building, however, still uses the original wiring...no replacements for the original in-wall/in-attic wiring....just the new stuff before the old j-box.

It looks like the RF noise from the various Plasma sets, computers and modems might be radiating from the large number of lines in the attic and the old J-Box. Now that I think about it, maybe some of the hum is being conducted by the Cable lines from the old trunk lines that are buried along side the electrical feeds in the cement. I wonder how the grounding is, on both the CATV and the building's electrical system???

 

[nmoore6676]

It's a large complex, with 590 units in 36 different buildings (plus a community center and an office/gym). The Cable was originally a 36-channel (or less) SMATV, using off-air and one C-Band dish.

The buildings were originally wired with Carol (Brand) RG-59/U from a "Junction Box" mounted above the upper floor window under the eaves, for each building segment...some buildings have a single breezeway dividing the building in to two segments, some have two breezeways making three segments, some are all-in-ones with no breezeway. Most are three stories tall.
The junction box contained a few cascaded splitters, fed via RG-59 from a two-way or four-way tap in the trunk line (0.485 semi-flex), which was laid in the common trench with all other utilities, downstairs.

Since the re-build about ten years ago, the trunks now come up in to a washtub-sized pedestal at each amplifier location (one for every two or three buildings), then go to a larger-sized Junction box at standing height/ground level, where the splitters and traps are located, then run up the side of the building with RG-6/U to the old J-Boxes. There, they are barrelled to the older RG-59. In many cases, the old RG-59 has been replaced with RG-6 running on the ground and in the hedges/flower beds, then up the building's exterior walls to a new access hole. Our building, however, still uses the original wiring...no replacements for the original in-wall/in-attic wiring....just the new stuff before the old j-box.

It looks like the RF noise from the various Plasma sets, computers and modems might be radiating from the large number of lines in the attic and the old J-Box. Now that I think about it, maybe some of the hum is being conducted by the Cable lines from the old trunk lines that are buried along side the electrical feeds in the cement. I wonder how the grounding is, on both the CATV and the building's electrical system???

What you have is not a CATV but a MATV system which has been injected with steroids. The fact that there is RG-6 in flowerbeds is definitely not proper construction. Is there no regular cable TV service available in your area?

I am surprised that given what you describe that anyone gets any decent reception at all. It is not unusual for large complexes to install their own systems but one this large would generally be built according to the same standards as any other CATV system. They can buy what I call a headend in a box which contains the processors for off the air reception and now also provide the digital to analog conversion. They also provide processing for satellite channels, pretty much anything but pay per view. They can even do local origination including a channel to see who is buzzing you from a security gate.

Unless it is only a few channels they probably have serious intermodulation issues as well since they don't likely don't the coherent carrier alignment capability of a properly constructed headend. In any event it very well could be re radiating all kinds of noise from the system itself as well as attached devices in the units. I am not sure if there is any remedy other than the goodwill of the owners were you and several others approach them with the problem. The FCC would likely be of no help unless they are radiating into the air craft navigation or public safety channels in which case they will come in.

If you have any friends with access to a spectrum analyzer you could get some documentation of what is being sent out and have a weapon to approach the appropriate agencies, or the owners.

 

[kenglish]

It's a Comcast system. It started out as a SMATV when built in 1982.
The Cable company (TCI, AT&T, now Comcast) took it over around 1984-85.

I found the replacement AC outlet for the sprinkler system was wired backwards...Hot is on the neutral pin (10 Amps), Neutral is on the Hot pin (5 amps flowing) and the Safety pin has 5 amps on it. Unplugging the timer helped some.
I also put PVC insulators around the gas pipes, where the rain gutter downspout rubbed against them. It got rid of some intermods.
Both made some improvement. Most locals are now listenable, with hum in only a few of them.
Somehow, the "Plasma Noise" has gotten better. It's only about an S7 at 3.555 MHz. It was up to about S9 +7dB.

I'm familiar with MATV and CATV systems, since I work on them.

I accidentally broke the wall jack behind my desk a few years ago. Since I have OTA, I haven't bothered to fix it....I just leave it disconnected, and pay my $30 a month mandatory fee. The desk is too heavy to move just to get re-run channels!