Reducing RFI off the powerline into radio set

[wa2ise]

Too another angle in getting better reception of weak AM radio stations. This one is to restrict RFI riding on the powerline from getting into the radio. Took an EMI filter network from an old computer monitor, like this below:

and placed it between the radio's power cord and the powerline input of the radio circuits. You can tell if this is a reasonable thing to do by this test: While listening to a weak station with powerline RFI buzzs, disconnect the power plug and quickly listen to see if the buzz goes away before the station and the radio dies. We're talking about 1/4 second, before the mail filter caps in the radio's power supply looses charge. You can repeat this test after installing this filter and see if any buzz left over still stays on the station after pulling the plug. Idea is that you effectively pulled the plug on the path the RFI was taking. That your plug in radio acts like a portable on batteries.

[Dave A]

Would this work to reduced lamp dimmer interference? This is outside of my wheelhouse of knowledge. This sounds like a nice little wall-wart sized module project.

[DavGoodlin]

Originally Posted by Dave A

Would this work to reduced lamp dimmer interference? This is outside of my wheelhouse of knowledge. This sounds like a nice little wall-wart sized module project.

The effects on the BCB from a standard rotary incandescent lamp dimmer, generating line harmonics from Triac and SCRs, should be reduced by this filter.

I used an integrated (grounded) line cord receptacle combo with M-derived filter from a CRT monitor. The 1937 Philco I put it in needed the chassis grounded anyway and it trapped almost all of the line hash, leaving the band nice and open at night.

With fluorescent lights using an SMPS as the electronic ballast , its more of an issue with HF, VHF and FM bands. Much of that interference is radiated from the lamps, not via power line. separation from and nullification with antenna placement helps.

The absolute worst offenders I found were the higher-wattage compact fluorescents operating on electronic ballasts (commercial twin and quad tube 18-42 watts) yet residential screw-in spiral types seem harmless.

The second worst offenders are the three and four-lamp electronic ballasts (2,3 and 4 foot T8 lamps) likely due to higher harmonic current drawn like the twin/quad tube compacts. Two lamp units, even with 8-foot tubes, are not too offensive.

I took great care in selecting "can" and "bowl" lighting for halls and parlors in retirement homes, thinking primarily of the residents that lived there. All the lighting supply houses and even ballast manufacturer reps were ignorant of this issue. I made sure they did when specifying.

I have found that the emission from rapid-start and trigger start magnetic fluorescent ballasts (older T12 lamps) is minimal and only a problem if the fixture is not properly grounded. cheers for old technology

[Captainclock]

Originally Posted by DavGoodlin

The effects on the BCB from a standard rotary incandescent lamp dimmer, generating line harmonics from Triac and SCRs, should be reduced by this filter.

I used an integrated (grounded) line cord receptacle combo with M-derived filter from a CRT monitor. The 1937 Philco I put it in needed the chassis grounded anyway and it trapped almost all of the line hash, leaving the band nice and open at night.

With fluorescent lights using an SMPS as the electronic ballast , its more of an issue with HF, VHF and FM bands. Much of that interference is radiated from the lamps, not via power line. separation from and nullification with antenna placement helps.

The absolute worst offenders I found were the higher-wattage compact fluorescents operating on electronic ballasts (commercial twin and quad tube 18-42 watts) yet residential screw-in spiral types seem harmless.

The second worst offenders are the three and four-lamp electronic ballasts (2,3 and 4 foot T8 lamps) likely due to higher harmonic current drawn like the twin/quad tube compacts. Two lamp units, even with 8-foot tubes, are not too offensive.

I took great care in selecting "can" and "bowl" lighting for halls and parlors in retirement homes, thinking primarily of the residents that lived there. All the lighting supply houses and even ballast manufacturer reps were ignorant of this issue. I made sure they did when specifying.

I have found that the emission from rapid-start and trigger start magnetic fluorescent ballasts (older T12 lamps) is minimal and only a problem if the fixture is not properly grounded. cheers for old technology

I have a 13 Watt CFL Bulb in my lamp on my night stand in my bedroom and in the lamp in my old room at my parents house and I've noticed that those 13 watt (and larger) CFLs (which are electronically ballasted) send severe amounts of EMI interference to my alarm clock Radio next to my bed in my bedroom and to the boombox that's in my old room at my parents house on the FM Band specifically between 88.1 and 98.1 Mhz on the FM dial, I haven't tried the AM Band recently because I haven't had a need to listen to it recently although on my old transformered AM Radios from the 1930s-1950s the AM Band comes in flawlessly even with all of my lights having CFLs in them. Another thing I've noticed is that at my parents place they have 2 Electronically Ballasted 2 bulb T8 Style Florescent lights that replaced 2 2 bulb magnetic ballasted T8 Style florescent lights and anyways whenever the overhead lights are turned on in the basement of my parents house every radio in the house using the FM Band becomes unlistenable and hums like mad and cannot pick up any stations at all, especially on the lower half of the FM dial, so I think that these Electronically ballasted florescent lights whether they be overhead lights or CFLs are extremely noisey when it comes to interfering with radio signals when they're on and need to be banned from use or at the least better regulated and designed to meet FCC Regulations for EMI Interference (which currently as it sits the FCC doesn't regulate nor do they know about the electronic ballasts effects with EMI interference, which means that technically electronic ballasts as they sit right now with all of their EMI interference that they give off are illegal because they aren't regulated by the FCC for their EMI Interference (like TVs, radios and satellite and cable boxes are) and like I said the FCC isn't even aware that Electronic Ballasts give off large amounts of EMI Interference, so because of that these Lighting manufacturers were knowingly manufacturing these ballasts illegally knowing that they gave off large amounts of EMI Interference, and never even bothered to contact the FCC to get their ballasts properly certified or even to get the proper amount of EMI Interference levels from the FCC so that they can make their ballasts within proper and legal specifications concerning EMI Interference emissions.
What I think really needs to happen is to boycott these florescent light manufacturers by buying only Incandescent lights until these florescent lighting manufacturers can properly make their electronic ballasts within legal specifications or go back to making magnetic ballasts again, because its absolutely rediculous that I have to loose my ability to listen to my favorite stations just because these floresent lighting manufacturers are too lazy to make their light fixtures the right and legal way!

Sorry for my long rant but this is how I feel about this issue and I find it frustrating that nothing has been done to rectify this issue so far.

[Reece]

Would be advisable to use type X2 "across the line interference suppression caps" for the capacitors in this circuit. They stand up better and are less likely to fail than standard caps.

[Electronic M]

Many newer TV's/monitors (80's and newer) have this or a similar network...It's easier to just cut off the section of a junk set's PCB that contains this network add some power connectors and throw it in a box than make one from scratch....I have a couple such networks laying around if needed.

I'm surprised collectors keep sources of RFI like CFLs and certain types of dimmer switches around. There is not one CFL in use here, and if we used dimmers I'd see to it that they are not RFI sources.

[wa2ise]

Originally Posted by Electronic M

Many newer TV's/monitors (80's and newer) have this or a similar network...It's easier to just cut off the section of a junk set's PCB that contains this network add some power connectors and throw it in a box than make one from scratch....

That's essentially what I did, though I tucked mine inside the radio cabinet behind the speaker.

These pictures don't show this addition, but if you look closely enough, there is room for a board behind the speaker. I also moved the power cord cheater cord socket away from the AM ferrite rod antenna. There's a masonite back cover you don't see here as well.

Better pictures:
Caps in the filter are X2's.



This mod almost makes it seem like the early 70's on the AM band, before switching power supplies existed.

[dieseljeep]

Is the large WW resistor, a voltage drop for the radio? If so, what value is it.
My older GE Superadio picks up a lot of interference from the neighbors, even when I'm using it on batteries, but much worse on AC.
It seems like The building next to me has some kind of a motion detector alarm system, that emits an RF pulse. I don't think, I can clean that up.

[dieseljeep]

Originally Posted by dieseljeep

My older GE Superadio picks up a lot of interference from the neighbors, even when I'm using it on batteries, but much worse on AC.
It seems like The building next to me has some kind of a motion detector alarm system, that emits an RF pulse. I don't think, I can clean that up.

Regarding the interference from the neighbor building, I ran an antenna to the outside of the building and the noise got a lot worse.

[Electronic M]

Originally Posted by dieseljeep

Regarding the interference from the neighbor building, I ran an antenna to the outside of the building and the noise got a lot worse.

I wonder if a grounded shield on the side of the antenna the interference is coming from would help.

[jr_tech]

Originally Posted by dieseljeep

Regarding the interference from the neighbor building, I ran an antenna to the outside of the building and the noise got a lot worse.

Did you connect to a decent ground as well? Otherwise, results might be inclusive.

A better test is to take a good portable outside, and observe the interference level.

jr

[maxhifi]

"From an old computer monitor"

What else has this network built in, would a PC power supply? Don't have any PC monitors sitting around to cannibilize but plenty of other junk. I definitely have noticed that line powered radios have much worse buzz than transformer operated radios. Some of my AA5s are almost
Unusable these days.

EDIT

To answer my own question, I looked at things like this http://www.smpspowersupply.com/ATX_p..._schematic.pdf
If the junk atx supply I have has such an input filter there's a Crosley which will be receiving some surgery tonight.

[wa2ise]

Originally Posted by maxhifi

To answer my own question, I looked at things like this http://www.smpspowersupply.com/ATX_p..._schematic.pdf
If the junk atx supply I have has such an input filter there's a Crosley which will be receiving some surgery tonight.

That should work, I'd use everything from the powerline input to the bridge rectifier. I'd also leave the ground not connected. We want to keep RFI from riding in via any ground or power wire.

The power resistor is 300 ohms, but this set runs the output transistor with a B+ of about 90V. So it's not the same as a battery portable.

[dieseljeep]

Originally Posted by wa2ise

That should work, I'd use everything from the powerline input to the bridge rectifier. I'd also leave the ground not connected. We want to keep RFI from riding in via any ground or power wire.

The power resistor is 300 ohms, but this set runs the output transistor with a B+ of about 90V. So it's not the same as a battery portable.

I was just inquiring about the resistor for another radio, I'm working on.
I know that it has nothing to do with the line noise issue.

[Electronic M]

Most modern devices with switch mode supplies (most computer and video equipment) have such networks (heck even Tivo boxes have them + a usable hard drive). It is easy to tell if you open up some junk and trace the line input wiring.

Wa2ise: I think I'd shorten the red harness to the safety interlock...That loop will help provide inductive coupling of line noise to surrounding circuits.