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eHam Forums => SWL (Shortwave Listening) => Topic started by: NO2A on October 30, 2017, 09:31:03 PM



Title: Ac "hum" on 650 WSM
Post by: NO2A on October 30, 2017, 09:31:03 PM
I'm listening to WSM and hearing what sounds like ac hum on their signal. I'm hearing it on two different radios,even with the antennas pointed 90 degrees away from that direction. In not hearing the hum on any nearby frequencies. Doesn't matter what room in the house I'm in. Anyone else hearing this right now at 11:30PM 10/30/17?
Central time. 


Title: RE: Ac "hum" on 650 WSM
Post by: NA4IT on October 31, 2017, 05:53:09 AM
Have you tried killing the power to your house and running the rig on pure battery power?
AM broadcast stations monitor their signals closely. If they had a hum, they would be fixing it pronto.


Title: RE: Ac "hum" on 650 WSM
Post by: W1VT on October 31, 2017, 08:07:54 AM
http://home.computer.net/~pritch/shortwav.htm
This page explains how unbypassed rectifier diodes in a power supply can add hum to broadcast signals.


Title: RE: Ac "hum" on 650 WSM
Post by: RENTON481 on October 31, 2017, 08:29:31 AM
Some stations have hum from time to time. One AM station in Yakima, WA had it for over a year. I not only heard it on all of my battery operated portables, but it was heard I Eastern WA also. They finally fixed it.

So, it can happen. Isn't always your radio.

Thanks for the link to the article. Those RF chokes look handy.  :)


Title: RE: Ac "hum" on 650 WSM
Post by: NO2A on October 31, 2017, 10:27:33 AM
This is happening on my Zenith Royal 300 and Royal 50,transistor radios. They both run off batteries. I went outside last night and didn't hear it,so maybe it is coming from the house. It didn't get any stronger when I went from room to room. I could see if it was rf hash like that from a wall wart,but this is strange. It's stronger on the '300,but that also has an extra transistor. It's not the florescent lights in the kitchen, and it's not the garage door opener, which is close by. I probably will have to cut the power circuit by circuit. In the meantime my radios have grown an ac power supply by themselves.    ;) ???


Title: RE: Ac "hum" on 650 WSM
Post by: RENTON481 on November 01, 2017, 06:17:50 PM
If it sounds like hash, don't forget to check your CFL lightbulbs, if you have any. When they start to go, they can still put out good light, but blast the lower MW channels with hash.

I had one on my front porch that gave off great light, but blasted the MW band with hash from 520 to around 680.

It wasn't AC hum, though. Just AC sounding hash, like what you get on HF when a power pole is acting up. Only worse. :-)


Title: RE: Ac "hum" on 650 WSM
Post by: NO2A on November 01, 2017, 07:55:26 PM
I listened today,and now in the evening, and I'm not hearing it. It wasn't as loud as hum from a tube radio. But definitely sounded like hum. Just much weaker.  The only appliance that operates at night is an outside motion detector light,which is on now,but no noise. It didn't get any stronger going from room to room. So I can't isolate it as coming from the house, yet. We'll see. Thanks for the responses.


Title: RE: Ac "hum" on 650 WSM
Post by: KR4BD on November 02, 2017, 07:50:52 AM
I listen to WSM-650 most every evening.  I have not heard any hum on their signal.  However, lately, WFAN from New York (right next door on 660) has really been bothering them with their IBOC digital signal which sounds like a hissing noise (white noise) on an analog receiver.  MANY AM stations who tried digital broadcasting have now given it up because it caused so much interference to adjacent frequencies.  WFAN, KMOX, WBBM and others, however, continue to broadcast their digital transmissions making “clean” reception on adjacent frequencies impossible, even with an excellent receiver. 


Title: RE: Ac "hum" on 650 WSM
Post by: NO2A on November 02, 2017, 11:15:41 AM
I listen to WSM-650 most every evening.  I have not heard any hum on their signal.  However, lately, WFAN from New York (right next door on 660) has really been bothering them with their IBOC digital signal which sounds like a hissing noise (white noise) on an analog receiver.  MANY AM stations who tried digital broadcasting have now given it up because it caused so much interference to adjacent frequencies.  WFAN, KMOX, WBBM and others, however, continue to broadcast their digital transmissions making “clean” reception on adjacent frequencies impossible, even with an excellent receiver. 
I can get all those stations here except for WFAN. I'll try listening and see if I can hear that white noise .


Title: RE: Ac "hum" on 650 WSM
Post by: KAPT4560 on November 03, 2017, 06:58:18 AM
 How far away are you from the WSM transmitter? Some radios of mine will have a hum on the local clear-channel station (WHAM-Rochester, NY) if I am using too much antenna or too much RF/IF gain.
 The hum may be from the receiver AGC/AVC design?
 Usually using less antenna and backing off the RF gain helps.
I listen to AM-DX in the evening and they come in with no hum.


Title: RE: Ac "hum" on 650 WSM
Post by: RENTON481 on November 03, 2017, 08:16:58 AM
On some MW channels adjacent to a strong IBOC station I can hear a churning noise, but I wouldn't necessarily classify it as hum.

Perhaps the OP is hearing IBOC churning noise? Hard to describe, but it can be heard.

I hope NO2A is able to figure it out and solve it.


Title: RE: Ac "hum" on 650 WSM
Post by: NO2A on November 03, 2017, 11:08:43 AM
How far away are you from the WSM transmitter? Some radios of mine will have a hum on the local clear-channel station (WHAM-Rochester, NY) if I am using too much antenna or too much RF/IF gain.
 The hum may be from the receiver AGC/AVC design?
 Usually using less antenna and backing off the RF gain helps.
I listen to AM-DX in the evening and they come in with no hum.
I'm in northwest FL,right on the panhandle. I replaced all the electrolytics when I bought the radio. The avc circuit required a 16uf cap,I used a 15 that tested  just over 17uf. No adjustable rf gain,and only using the built-in ferrite loop antenna. I can hear WWL very strong here with no hum. I wouldn't think stray capacitance would be a problem on these low frequencies.


Title: RE: Ac "hum" on 650 WSM
Post by: RENTON481 on November 06, 2017, 06:17:06 AM
I have a hum I forgot to mention, on a local sports station on 950 kHz. It even shows up while the radio is on batteries, on a three year old radio (PR-D5). The hum, when it occurs, is directional.

In my case, it might be an electric radiator heater, or some other local RFI source. As I don't know exactly what it is, I'm just placing a guess as to the source. It was there last night, but isn't there now. Why it seems to hum on 950 and no other apparent frequencies I don't know.

You may be encountering a similar phantom sourced bit of RFI.


Title: RE: Ac "hum" on 650 WSM
Post by: NO2A on November 06, 2017, 07:49:12 PM
I have a hum I forgot to mention, on a local sports station on 950 kHz. It even shows up while the radio is on batteries, on a three year old radio (PR-D5). The hum, when it occurs, is directional.

In my case, it might be an electric radiator heater, or some other local RFI source. As I don't know exactly what it is, I'm just placing a guess as to the source. It was there last night, but isn't there now. Why it seems to hum on 950 and no other apparent frequencies I don't know.

You may be encountering a similar phantom sourced bit of RFI.

That's what I'm thinking too,some kind of phantom signal. It doesn't appear to be coming  from the house.