AM Radio Hum (on some stations and not others)

Jim 2018

Active Member
Tried Googling answer to this but no luck.

So I've noticed with several radios, both tube and solid state, that I get a a hum on some AM stations. It seems like the stronger and or closer the station is to me, the more likely it will hum. Not all strong(er) stations hum. However, no weak or moderate signal stations hum.

I am assuming this has nothing to do with bad power supplies since it isn't a problem on all AM stations.

Strong stations that are somewhat nulled with a directional AM antenna seem to be more prone to this but that is not absolute.

When tuning between stations, it is just ordinary white noise, no hum or other interference (unless I've got a dimmer on somewhere).

Curious if anyone has ever observed this cocktail of symptoms or knows what it is.
 
I'm just SWAGing here, off the top of my head, but it sounds a little like a beat product (mixing). Since it happens on certain stations meaning certain frequencies, and with strong stations that may provide enough energy for the product to be audible, it's plausible. Are the stations harmonically related? Is there a correlation of any type to say 455kHz plus or minus the station frequency? There would, of course, need to be a source of the interference signal also like a switching wall wart as an example.
Just some random thoughts.
 
I'm just SWAGing here, off the top of my head, but it sounds a little like a beat product (mixing). Since it happens on certain stations meaning certain frequencies, and with strong stations that may provide enough energy for the product to be audible, it's plausible. Are the stations harmonically related? Is there a correlation of any type to say 455kHz plus or minus the station frequency? There would, of course, need to be a source of the interference signal also like a switching wall wart as an example.
Just some random thoughts.
We had KALL, an otherwise well run jazz /news station on 910kc in Salt Lake City that heterodyned on many AM sets. A pity but luck of the draw, probably allocated before 455kc became the common default IF bandpass.
 
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Thanks for the replies everyone. So let me ask this, would a station operating at a multiple of 455kc cause a hum vs. some other undesired audio artifact? And if so, would it have to be an exact multiple or close to it?

I'm in the Chicago area and the biggest offender is WLS 890 and I am the closest to their tower. WBBM on 780, WGN on 720, and WSCR on 670, are also problems but not as much so. On the other hand, WILL on 580 (Urbana, IL), WIND on 560, and WMVP on 1000 are not. Suburban AM stations with less power are not issues. Also, nighttime sky wave is not an issue, even for very strong signals including St. Louis, Des Monies, and Louisville.
 
A station at 910 would cause a constant tone or whistling sound in a receiver with a 455kc IF. I doubt this is the problem in your area.
Your problem could be some sort of signal overloading or intermodulation.
If a loop receiving antenna is involved, try changing it's orientation.
 
Changing antenna direction helps but doesn't solve it completely. I just find it odd that some stations have this and others don't.
 
Changing antenna direction helps but doesn't solve it completely. I just find it odd that some stations have this and others don't.

That may or may not be something you can consider. If moving the antenna is helping to null the interference then you might have something to work with there. If it's just reducing the signal strength of the station, that may not help. Is it possible to move the radio and antenna to another part of the house, preferably as far away from your current location? The best test would be to carry it all outside (I saw you're in Chicago, probably not a good idea) and eliminate all sources of interference in your house and see what happens. AM radio and your directional loop are commonly used by the ham community to sniff out all kinds of sources of interference. To say AM BCB is sensitive to RF intrusion would be an understatement.
Just some more SWAGing - keep us updated on your progress.
 
What's the frequency of the hum?

Do you hear the hum with a battery operated receiver?

EDIT: Walk around with a portable radio, inside and outside your house, and see if the hum changes.
 
Hey C.coyle. It's more pronounced on AC powered tube equipment and solid state equipment with external loop antennas. However, just tested this on a battery powered Grundig shorwave radio I have on AM 890 and there's very very slight hum though it is more pronounced as I try to null the station but still slight. None of the other stations seem to have it on this radio.

In response to some of the more recent comments on this, I don't think this has anything to do with AC line noise or transformer hum. If it did, I would think the Grundig test would have had zero hum and even on AC powered equipment, I would have hum on weaker stations.

I don't want to overstate the severity of this. In most instances, it is very mild. But it's enough to notice and it drives me nuts that it happens on the strongest stations. Very counter intuitive. Was just curious if anyone out here listens to enough AM on enough different radios to have observed this. Maybe it is just something wonky in my environment.
 
In response to some of the more recent comments on this, I don't think this has anything to do with AC line noise or transformer hum. If it did, I would think the Grundig test would have had zero hum and even on AC powered equipment, I would have hum on weaker stations.
Exactly!
As I noted before, it is quite possibly something that you are receiving via the antenna. To give an example, something like a switching power supply (wall wart) will radiate its fundamental switching frequency plus a myriad of harmonics. Am AM radio is an excellent tool to determine how nasty one of these supplies is. These things also transfer noise back into your general house wiring. I'm not saying that this is the source of your problem, only illustrating that the nature of interference being coupled into an AM radio is often through the antenna.

I'll leave you to it and good luck
 
I guess the issue is that if this hum is interference of some sort being received from the antenna, then why is it not on all stations? Why not gaps between stations? For example dimmers will affect gaps between stations and weak stations the most. Stronger stations are affected the least to no effect at all. Same thing when driving under busy power lines. This hum issue is different. Maybe different interference sources have different quirks but I've not seen this one documented anywhere.
 
I have a cabin on the Mississippi in NE Iowa, and I have noticed this on Chicago AM's. 720 seems to be the best that I can receive, but I have a hard time receiving a consistent 670, 780, and 890 - and cannot really get 1000 to come in clear in any fashion at any time. Considering these are all clear channel AM's, it confounds me this occurs considering I'm not really that far away (probably 200 miles as the crow flies).

The caveat here is, I'm at river level, with 500 foot limestone/forested bluffs on both sides (live on the Iowa side) - I get practically nothing west of Des Moines 1040, Cedar Rapids 600 and Cedar Falls 1540.

It's troublesome reception unless it's say ENE to south. Modern receivers are effectively useless. I've used a Grundig S350 (?) AM/FM shortwave that works really well and also an unrestored late 60's Zenith Trans-Oceanic 3000 that is still pretty good, but I wanted to be able to use a analog tuner cause being a cabin, I'm inside, outside etc, and hate hauling a portable radio around.

Didn't matter if AC or battery - every radio I tried, Chicago was a pain to receive.

After much experimenting as far as radio/antenna orientation etc - I settled on a Panamax power conditioner to power either a Sony STR-6055 or a Kenwood KT-615 (depending on what setup I want to use any given year ;) ), along with a CC Radio Twin Ferrite antenna (appears they may not sell these any more, "not available" on their website).

Not perfect, but cleaner power and a much better antenna helped for my overall reception (mostly at night). I've added Philadelphia 1210, San Antonio 1200, Cincinnati 1530, New Orleans 870 and 1110 Charlotte - and improved Cincinnati 700 Louisville 840, Pittsburgh 1020, St. Louis 1120, etc to where they almost never fade.

And yet 670, 780, and 890 can be "troublesome" but at least now at daytime they come in a lot better now. 1000 though...didn't help a bit. I've always thought "there's something about Chicago AM that is not conducive for good reception". I get 700 and 1100 in Ohio at night utterly perfect - yet 670 while "mostly strong" still "produces the issues you describe" often enough to test my patience. Not static or fade or the "gong" type stuff...just like a "blank hole" coming in and out with the content.

I don't know if the Chicago stations are highly directional or it's something with tower locations or what's going on there. But aside from 720, I've always had trouble with them. I don't believe it's a "reception strength issue".
 
I guess the issue is that if this hum is interference of some sort being received from the antenna, then why is it not on all stations? Why not gaps between stations? For example dimmers will affect gaps between stations and weak stations the most. Stronger stations are affected the least to no effect at all. Same thing when driving under busy power lines. This hum issue is different. Maybe different interference sources have different quirks but I've not seen this one documented anywhere.

I'll take my leave after noting that, as I indicated previously, frequencies have a fundamental and oft times harmonics of diminishing energy. Simple radio theory posits that frequencies will mix leaving the original along with sum and differences. One frequency can often modulate another causing distortion products. So, simply put, that is why it's not on every frequency or the spaces in between. I made the incorrect assumption in my previous responses that you knew something about radio. My apologies.

Cheers
 
I have a cabin on the Mississippi in NE Iowa, and I have noticed this on Chicago AM's. 720 seems to be the best that I can receive, but I have a hard time receiving a consistent 670, 780, and 890 - and cannot really get 1000 to come in clear in any fashion at any time. Considering these are all clear channel AM's, it confounds me this occurs considering I'm not really that far away (probably 200 miles as the crow flies).

The caveat here is, I'm at river level, with 500 foot limestone/forested bluffs on both sides (live on the Iowa side) - I get practically nothing west of Des Moines 1040, Cedar Rapids 600 and Cedar Falls 1540.

It's troublesome reception unless it's say ENE to south. Modern receivers are effectively useless. I've used a Grundig S350 (?) AM/FM shortwave that works really well and also an unrestored late 60's Zenith Trans-Oceanic 3000 that is still pretty good, but I wanted to be able to use a analog tuner cause being a cabin, I'm inside, outside etc, and hate hauling a portable radio around.

Didn't matter if AC or battery - every radio I tried, Chicago was a pain to receive.

After much experimenting as far as radio/antenna orientation etc - I settled on a Panamax power conditioner to power either a Sony STR-6055 or a Kenwood KT-615 (depending on what setup I want to use any given year ;) ), along with a CC Radio Twin Ferrite antenna (appears they may not sell these any more, "not available" on their website).

Not perfect, but cleaner power and a much better antenna helped for my overall reception (mostly at night). I've added Philadelphia 1210, San Antonio 1200, Cincinnati 1530, New Orleans 870 and 1110 Charlotte - and improved Cincinnati 700 Louisville 840, Pittsburgh 1020, St. Louis 1120, etc to where they almost never fade.

And yet 670, 780, and 890 can be "troublesome" but at least now at daytime they come in a lot better now. 1000 though...didn't help a bit. I've always thought "there's something about Chicago AM that is not conducive for good reception". I get 700 and 1100 in Ohio at night utterly perfect - yet 670 while "mostly strong" still "produces the issues you describe" often enough to test my patience. Not static or fade or the "gong" type stuff...just like a "blank hole" coming in and out with the content.

I don't know if the Chicago stations are highly directional or it's something with tower locations or what's going on there. But aside from 720, I've always had trouble with them. I don't believe it's a "reception strength issue".
It's the skip propagation, you are probably between normal bounce hit distance. Some nights, normally unheard stations can come in strong when unusual conditions put the ionosphere at an atypical hight. I get Chicago, NYC, and St Louis here regularly, KC never.
 
That's not fair WobblySam. Context is everything and apparently you missed what I was trying to convey.

Cheers
 
BTW, I'd recommend a clean properly working GE model 7-2880B Superadio for self contained AM long distance listening. Not a boom box by any means, but a set of six alkaline 'D' cells last a really long time. It also can run off AC power, but line noise can then ride the wire into the set.
They turn up f/s reasonable U-know where. Insist on a clean battery compartment.
 
Hey Dlrhawks. I'm not sure your issue is mine, I have a weird humming issue with the stronger Chicago stations but not so with weaker stations or ones out of the area. Are you getting hum?

Regarding your station reception, I think AM 1000 is directional so even though its 50,000 watts at a relatively close distance to you, that might explain why that one is particularly bad. The other stations you mentioned are omni directional.

Anecdotally, I've noticed that 50,000 watt clear channel stations (well, semi clear channel these days) that are are not directional can go farther in certain directions. Not sure if it's terrain or what. During the day, I can get a very very weak ground signal from WHO 1040 in Des Moines. But I get a fairly decent signal with 600 WMT in Cedar Rapids which isn't that much farther away. Go figure. Also, during the day I get a weak to non-existent signal from 840 WHAS in Louisville and 1120 KMOX in St. Louis but a decent signal from WLW 700 in Cincinnati. So you might just be in a bad spot. An interesting experiment would be to drive around Iowa farm country near your cabin and listen to Chicago stations and see if the reception improves. You might be able to drive farther away and get better reception.

Is your issue weak signal, white noise, hum or other interference?
 
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