Reducing RFI off the powerline into radio set
 

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:
http://videokarma.org/attachment.php...1&d=1456019064
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.

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.

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.

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.

That's essentially what I did, though I tucked mine inside the radio cabinet behind the speaker.
http://www.wa2ise.com/radios/hb.jpghttp://www.wa2ise.com/radios/hbi.jpg
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:
http://www.videokarma.org/attachment...1&d=1456255248 Caps in the filter are X2's.
http://www.videokarma.org/attachment...1&d=1456255439
http://www.videokarma.org/attachment...1&d=1456255439

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

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. :sigh:

"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.

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.

http://www.wa2ise.com/radios/ssaf.gif

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.

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.

Here's my network from an old computer power supply - only one choke section but it is a big one! I will see later how the radio likes it.

Wow this works! This Crosley has always been terrible for picking up line buzz and now works amazing - the method of
mounting is temporary just to give it a try.

That's great! I have some coils like that, around 8 to 30mH. You may want to place the board down in the area near the volume control shaft. To be further away from the tubes. And maybe position the coil so it's 90 degrees turned in relation to the antenna coil.

It seems to have cured the buzz provlem entirely except
At the extreme low end of the dial. It's definitely in the can be lived with category now. I thought the interference was in the air and not the line until I recently tried my 1937 silvertone which has an autotransformer, and it is DEAD silent buzz and noise wise , I can't believe how much better it performs than any other AA5 I own.

I am going to stay on the look out for old power supplies now, besides big capacitors I have something new to rob them of

Regarding the interference from the neighbor building, I ran an antenna to the outside of the building and the noise got a lot worse. :scratch2:

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

Did you connect to a decent ground as well? Otherwise, results might be inclusive. :scratch2:

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

jr

http://www.videokarma.org/attachment...1&d=1456953673

Installed a similar filter in another radio, and it works as well as my first radio. :banana: This is a Hitachi AM-FM K760H. Added an extra coil to this filter board for more filtering.

does that radio have a power transformer ?

No, it's a hot chassis SS design. Originally, thus the noise would ride directly in, vs having to hop across the power transformer's winding to winding capacitance.

I believe the only definitive way to minimize noise is with a loop antenna. The loop uses the magnetic part of the radio wave and is highly directional. I use a ferrite loopstick antenna and it greatly helps. I plan on getting a much larger Wellbrook loop and another loopstick.

I did take my GE Superadio outside and the noise seems to be coming from the building behind me.
This poor reception is in my workshop building. My AM reception at my residence is good in most rooms of the house. :thmbsp:

I finally found two ways to get rid of interference from other apartments in my
building and the power line.

1) For LW, BCB and up to about WWV at 2.5 MHz, loop antennas.

2) For BCB to 30 MHz, an outside wire antenna, 25 feet long (noncritical) draped over
a tree from my balcony, and as counterpoise a good, solid connection to the
balcony's metal railing, which is large and not grounded. This is connected to radios
inside with top quality RG-6. However, the commercial F-connector attachment
points are an Achilles' heel as they are not soldered on.

#2 has the problem that the antenna does not match the coax except at
a couple of frequencies, ruining reception strength. This was fixed by adding
a 2-transistor emitter follower with built-in anti-FM radio filter, right at the
antenna-balcony junction. This has a 6kohm input impedance. Its powered by
a 9 volt battery (transistor radio batteries don't last long. I use 6 D cells.)
The results from this antenna are very good.

Please ... no comments about "you must ground the antenna".
THAT DOES NOT WORK! The noise returns. Its grounded through the
coax, and the wire is retracted when not in use.

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:sigh:

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.

The good news is that LED is steadily replacing the CFLs, to be know as the "new" dinosaurs.

Older lighting, like mercury, T12 fluorescent, high intensity discharge HID (metal halide and high pressure sodium) using magnetic ballasts are all over the place yet, but these do NOT make interference.
LED will claim them all once replacement parts are phased out of production.

I can only hope the CFLs die quickly and are retrofitted with LED >-:

But the switch to LED does not necessarily cure all RFI problems... some are very strong emitters, causing problems even to the top end of the FM band. Best to try a sample of a given bulb type first (with a good return policy) and test using the weakest stations that you normally listen to before buying more. I am about 90% converted to LED lights, and with careful selection, AM and FM distant stations still can be heard fairly well.

jr

They are after all diodes and it'd be surprizing if there wuzzn't some switching noise.

The Soceity of Broadcast Engineers is presently urging the FCC to get more involved in cleaning up the RFI mess, read about it here:

http://www.arrl.org/news/sbe-urges-f...se-environment

jr