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Has anyone experienced strong interference on an AM frequency driving by a house decked out with christmas lights? I always get a buzzing sound. Is this a grounding issue?
Total posts : 45366This is probably due to the proliferation of LED Christmas lights. These are all diodes that are typically operating on pulsed, unfiltered DC. When they switch on and off, just like normal diodes, they create high frequency hash. This can be radiated many feet from the string, unfortunately. 🙁
Total posts : 45366Maybe we could get our Field Strength experts to weigh in on this one? 🙂
Total posts : 45366One of the many uses of part 15 is to certify household items as spectrum-safe. These little diode-driven spark gap transmitters might have missed that step in the rush to get to market. One wonders if a complaint should be submitted to the authorities as these items might need a review. I have seen field notices issued for other imported electronics items that have not been reviewed and certified – there was a battery charger for a Chinese electric scooter that had to be pulled from the market for the same reason.
Total posts : 45366This is also true with some car stereo amplifiers.
One car I was unfortunate to be behind at a traffic light was not only subjecting the other cars around them to ungodly deep bass tones, but also causing the receiver of my CB Radio to blank out whenever the bass would hit.It was so bad that the s-meter slammed to the wall .
As the light changed to green and the offending car pulled away from me the interference slowly faded away.I have seen these lights around here but never had the radio on to experience the interference you mentioned. If we need to take extra measures to be sure we don’t cause unwanted interference with our part 15 setups then the manufacturer of these lights or the car stereo amp should have to follow the same rules we do.
Do any of you remember when some questionable cordless phones made it to America that had the range of several miles?
If memory serves me correctly, they were in the Ham bands.Some how things like this make it through customs and onto the marked or Ebay.
Can you imagine though? A guy spends two hours decorating their house with lights then darkness falls as he admires his handy work.
Goes to bed and wakes the next morning to the f.c.c standing on his doorstep. lol
Total posts : 45366Hi Guys:
My wife’s car has a steering wheel system
that puts out weird loud swishing sounds
on 1700 kHz on the car radio. This happens
only when the steering wheel is turned. If
we are going straight it doesn’t happen.That is another reason why I went to 1690 Khz
during the daylight hours. The interference is
almost nonexistent on that channel. So if I’m
checking the coverage area of my Part 15 station,
1690 works a lot better. This is all moot right
now because my AM transmitter is off for the
winter. I have to rewire the ground system in
the spring.Hi Rock95Seven: That info about the car sound
system putting out on 27 MHz is amazing. I
wish I was there to see that. It may be real
obnoxious, but it is really interesting.Best Wishes
Bruce, MICRO1690/1700
Total posts : 45366Most high power car amps host two or more toroid coils, some as thick as a Bic lighter and the diameter of a coffee cup.
These are used to generate enough power to drive the high demand speakers.My guess is they generate a large magnetic field that increase’s as the amplifiers volume increase’s. Unfortunately, the car stereo’s these kid’s have these days are in the 1000 to 50,000 watt range.
Some have been known to cause the rear glass to shatter in some vehicles, heart trouble and mood swings. Then again, I have a house full of teens and mood swings are a normal thing around here (without a large amplifier) 🙂Power inverters have a similar setup as well.
I can only guess at this without real proof, but i imagine the wiring in the car was acting as an antenna while the amps were generating magnetic fields on more than one frequency.Why anyone would want to subject themselves to this much pressure is beyond me. The windows rolled up and the bass down low.
I value the hearing i have and i am in no hurry to destroy it any time soon. I have already lost some hearing in my right ear which makes tweaking the sound of my stations a pain in the eardrums.
I am sure someone here can give a better explanation for the use of teroids in amplifiers. I just find loud stereos in cars to be a nuisance.
Total posts : 45366Those crazy 1000 watt or whatever car amps can easily cause RF noise if they aren’t designed right. So, there are a bunch on the market that are lower priced and likely have design deficiencies. To get 1000 watts into a 4 ohm speaker requires a high B+ voltage. At absolute best, a 4 ohm speaker requires 63 volts for 1000 watts. The voltage required goes up with less than 100% amp efficiency. To get the higher B+ at high power, the standard way is a switching power converter (cheap = RF noise!). Another way to handle the power is to use a Class D switching amp (cheap = RF noise!). Both approaches can be designed correctly without RF noise (cost!).
It’s a loosing battle with all this stuff coming from China, probably without FCC certification. Same goes for the Christmas lights. I don’t think the FCC has the resources to track down all this stuff in a reasonable amount of time. Even if they do finally get around to issuing a notice, typically after a year or two, the manufacturer has already discontinued the specific model number stated in the notice and moved on to new model numbers that probably have the same problem. Manufacturers avoid any fines by responding that they have stopped selling the offending model number. It’s easy to keep one step ahead of the FCC by changing model numbers regularly so the FCC never catches up.
In my mind, the FCC is in a state of collapse when it comes to enforcing “unintentional radiators”, and sadly, 99% of the population doesn’t know or care.
Total posts : 45366The government needs our deputized help. We hereby draft the Part15.US Enforcement Squad making mass “citizen’s arrests” and confiscating tree lights and auto boom-boxes as “evidence.” Do we get to have badges?
Total posts : 45366The Mexican outlaws recruited into service in the movie “Blazing Saddles” may have said it all…..”We don’t need no stinkin’ badges.”
Total posts : 45366Totally funny. We don’t need badges.
Total posts : 45366I think that the quote originally came from “The Treasure of the Sierra Madre.” A band of Mexican robbers claimed to be the police, and Humphrey Bogart asked to see their badges. There are other variations, too, like “I don’t need no stinkin’ green card!”
Total posts : 45366Although my favorite line from TTOTSM was when HB said “I’m young, and I need DOUGH – and PLENTY of it!”
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