AC EMI Filter ?

[BOBRR]

Hello,

As I've written, I, finally, pegged my noise source in the 2-3 MHz am range to a very
old color CRT TV in the kitchen. Wife wants to keep the TV due to its very wide off-axis viewing. Still works great.

So,

I'm assuming that the noise is somehow being radiated back thru the ac power line, and not thru the air.
Is this likely ?

The TV is fed by the Comcast box (small length of coax between the box output and the TV signal IN)
that also accepts the hand held Remote signals.
Is this a more likely path for the noise ?

**If you experts on radiated noise (I'm obviously not) feel it likely that it is being fed back from the TV
thru the ac power line(s), might you suggest a hopefully
inexpensive filter I can simply plug the TV into, and the normal house ac outlet ?

Much thanks for all the help and thoughts
I've received with this.

Regards, stay well,
Bob

 

[WA0CBW]

Does the noise go away if you disconnect the antenna from the radio?
Bill

 

[BOBRR]

Hi,

No ant.

Receives its signal via "cable" via Comcast.
There's a Comcast "box" that feeds the TV.

Shut the TV off (Comcast box still powered on) and the noise goes away.

Bob

 

[WA0CBW]

If you leave the TV on and disconnect the antenna from the"radio" does the noise go away?
Bill

 

[BOBRR]

Hi Bill,

Oops ! That old age problem again.
I misread what you were asking. Thought you were referring to the TV ant. (there isn't any; Comcast cable setup)

So,
if I disconnect the radio outside ant., noise goes away. (as does, of course, all other signals).

What does this show/prove ?
If coming thru the ac house wiring, would you still expect it to show up ? Hmm, interesting to ponder.

Thanks again for your help and time with this, Lots for me to learn; but trying.
Bob

 

[WA0CBW]

It means you are picking up a radiated signal not a conducted signal. Your radio antenna is picking up the noise. Your house wiring may be acting as an antenna transmitting the signal from the device that is generating the noise.
Bill

 

[RFI-EMI-GUY]

Disconnect the cable box from the TV does the problem go away? If not definately conducted on the power wiring. Need common mode filtering chokes on the AC feed. If it goes away, put some chokes on the CATV cable to the rear of the TV.

 

[BOBRR]

Hi,

Thanks guys.

Had no idea that the house wiring "may" be radiating the noise.

Assuming it is, what would possibly be acting as the receiving ant. ? My outside ant. ?

Again, appreciate the help, and education.

Regards,
Bob

 

[RFI-EMI-GUY]

Most houses are wired with Romex these days which is crappy. I had two previous homes that had NICE QUIET grounded metallic conduit and that is rare. The Romex is simply unshielded wire and any device in your house that creates electrical noise can conduct that noise onto the wiring and it will radiate that noise around yours and neighboring houses. If you have a SW receiving antenna in that field it will pick it up.

Electronic devices are supposed to meet some minimum conducted radio frequency interference specs. It is not very stringent in the US and that conducted RFI turns into radiated as soon as you plug the device into your Romex house wiring.

Why doesn't the FCC make those specs more stringent? Because the FCC loves the industry and they don't think you should bother with an archaic SW receiver, old school off the air TV and AM radio broadcast etc. You should be paying for pricey internet and cable TV. What are you a cave man?

 

[WA0CBW]

I think you have already identified the offending device but I have used a "sniffer" probe (short length of coax with a loop or two about two inches in diameter of the center conductor shorted to the cable shield) connected to a portable receiver to search for the offending device.
Bill

 

[BOBRR]

Hi,

Yup, an 84 year old caveman !

Lots of good information for me.
Very appreciated.

RF interference is certainly a subject I'll be trying
to learn more about. Very weak overall on it.

I have a bunch of Ferrites, and will try them.

Thanks again guys,
Stay well,
Bob

 

[cmdrwill]

Did you try another TV ? A different TV or "cablebox" ?

 

[slowmover]

Turning off household circuit breakers (one at a time) and using your chart of what’s on every circuit (the chart you made yeeeeaarrss and years ago) is also Good Housekeeping.

.

 

[ArloG]

Chasing RFI is a pain. Have you tried running your rig on a battery to see if things get better?
You say the TV is in the kitchen so it's probably not that big. The power supply could have gone "dirty" over the years or other circuits in it.
What would happen by distancing it from your equipment to check for a reduction? The cable box a culprit?
Does the interference persist if you unhook the cable going into the cable box (not box > tv)?
An isolation transformer or any filtering/power conditioning unit may be hit or miss and usually not cheap.
Sorry you're chasing gremlins.

 

[BOBRR]

Hi,

Seems to be the TV, and not the Comcast cable box feeding it.

Next step is to try a bunch of those Ferrite clip ons, all over and see if any improvement.
Different TV not a viable option, right now.

Thanks for all the thoughts,
Bob

 

[dlwtrunked]

You are wasting your time. Interference from old TV is largely due to being generated by signals around the deflection yoke at the neck of the CRT tube. About only thing that helps significantly is to shield the whole TV (but you cannot shield the front of the TV CRT and see it). "Different TV not a viable option, right now."--then getting rid of the interference is not an option right now.

 

[ArloG]

BOBRR. Good luck with chasing those old TV bugs. Considering that your cable box is a newer model it should have an HDMI output. 4:3 NTSC CRT TV's are just obsolete these days, as are any CRT displays. I know that the xyl may love her old TV (as much as her old man, I hope).

But if you have a computer monitor with HDMI inputs to try out and see in place of the current TV. I would swap it out for a test.
Maybe head out to an office supply store and check out the monitors they have on display to check out the off axis viewing experience.

You may be surprised at what you see. Viewing angles with newer LED displays are pretty good. Plus the picture quality would surpass the 4:3, 60 Hz, 525 lines of your CRT TV. And since you have the antenna input occupied by the cable box right now, I suspect you're not using it for OTA broadcasts. Then you don't really need a full fledged TV with HDMI/Antenna inputs at all.

It could be that your budget limits getting anything new. But then again, it could be a new modern TV in the kitchen would make both of your lives happier. As well as your rig usage.

If it were me in your shoes I'd take the TV and put it in the fridge or freezer with the doors closed for a metal shield and see how much the noise on your radio goes down. Because right now your only solution is to wait until the kitchen TV is off.