Ask MetaFilter questions tagged with RF

It's the buzz buzz buzz in the drum of the ear, or, making my amplifier a tinfoil hat to stop GSM noises from my phone.

Halle — Wed, 23 Sep 2009 06:22:38 -0800

It's the buzz buzz buzz in the drum of the ear, or, making my amplifier a tinfoil hat to stop GSM noises from my phone. Like many others, I have GSM buzz in my speakers. But, I frequently don't have the option of setting my phone to silent while I'm working, because I'm working on the phone. That leaves the options as a) not getting to listen to music while working, or b) letting hideous noises that come out of my speakers every hour at a much higher volume than the music make me aggro. So, I've done some research (and read the old and inconclusive GSM noise questions here in AskMe) and I've concluded that it's most likely my amplifier lacking shielding. I'm going to put ferrite chokes on my speaker and audio cables just in case, but the main plan of attack is to put a faraday cage around the amp since it's out of sight. What is a good way to construct the cage with the following specs:

1) blocks interference really well,
2) isn't terribly expensive,
3) will last/can be moved (i.e. alternatives to tinfoil),
4) has some possibility of heat dispersal so it doesn't kill the amp.
5) no negative electrical safety implications (I can't imagine what these could be but I thought I'd throw it in there in case there is anything I'm overlooking in this department).

Thank you!

RF remote control

jjcurtis — Mon, 08 Jun 2009 13:58:07 -0800

Have AT&T U-verse installed and need help selecting the best RF remote control? What is the best RF remote for this type of setup? My main unit is in a closet and cannot see infra-red from the TV viewing room. A second receiver is in the bedroom. I have used a Niles remote control in the past but some say this doesn't work well with U-verse. I would like to have a unit I could program myself without depending on a dealer, but if those that can only be programed by dealer are the best I would go that way.

Through the luminiferous aether

strangecargo — Mon, 26 Jan 2009 15:05:55 -0800

RFInterferenceFilter: This is a continuation of this question. Summarizing: I'm experiencing a loud buzzing noise in my stereo, accompanied by interference from local FM radio stations. I've done more investigation and have eliminated my power as a (direct) cause of the noise. The original post has a more detailed description/history of my problem. After some investigation with an oscilloscope, I ended up with this image of my AC power superimposed over the noisy preamp output (close-ups here and here). My working theory at the time was that the hiccups at the top and bottom of the sine wave in the AC output were causing the corresponding jumps in preamp output (which would conveniently explain 120Hz buzzing). In order to test this theory, I got my hands on an AC power regenerator and tried powering my preamp with that. The noise didn't go away (and didn't really change). In the course of scratching my head at this development, I also discovered that the noise doesn't go away when I physically unplug the preamp and allow it to run for a few seconds from only the power left in the power supply reservoir capacitors. Of course, the noise goes away when the energy in the capacitors is used up.

So now I'm left with this: 60/120Hz buzzing and FM radio interference when everything is physically isolated from my AC power (ie: preamp has been totally unplugged, driving the inputs of a laptop running from batteries). This leads me to believe that the cause of the noise is RFI/EMI, and that the hiccups in my power are not the cause of my issues, but are instead also caused by whatever is causing the noise in my preamp, which would explain why they are temporally coincident. I'm still inclined to believe that this is somehow power-related, as the hiccups and my AC power are in perfect synchronization, but nothing as simple as the line-noise-sails-through-power-supply that I had initially hoped for.

I'm an engineer, but not an electrical one; I've managed to debug this problem to this point, but I'm pretty much out of my element here. I don't understand enough of the principles at work to figure out this issue past this point or what I can do to try and fix it. Suggestions, please!

Lite Rock, Less Talk? I'd like neither, please.

strangecargo — Thu, 15 Jan 2009 00:59:16 -0800

(Electronics|Stereo)filter: What is causing this infuriating noise in my preamp and how do I fix it? Links to sound files and long list of symptoms in extended. I have this preamp and ever since moving to my current apartment in San Francisco, it generates a really loud noise that sounds like a combination of 60 Hz hum and FM radio broadcasts. The noise is loudest when the volume knob is turned all the way down, but it doesn't go away when you turn the volume up. And this is what it sounds like when you go from zero gain to full gain and back. The noises don't sound that loud when played back on a computer, but that level of noise is pretty dang loud when sent to the input of a power amp.

The maybe pertinent facts (numbered because there are a lot of them):

1. I recorded the linked sound files by plugging in the output of the preamp into the line in of a MacBook Pro. No mixing or diddling with the file other than that.

2. You can clearly hear the station identifier for KOIT in the first sound file I linked. This is an FM station. What the heck? I was under the impression that FM was way too complicated for equipment to randomly pick up unless it was designed specifically to, you know, receive FM radio.

3. Changing the vacuum tubes inside the preamp doesn't change the nature of the noise.

4. I have other audio equipment (both solid-state and tubed) that doesn't make this sort of noise.

5. The noise is generated independent of what I have connected as an input or output (or if there's anything connected at all).

6. I can't seem to reproduce this noise outside of my apartment (friends' places, hifi shops, etc). Whenever I try, the preamp is noiseless and dead silent.

7. Physically moving the preamp around my apartment doesn't seem to change the noise either.

8. I live in an old apartment without grounding in most of the electrical sockets, but the noise doesn't change if I plug the preamp into a grounded outlet. I've checked that the grounded outlets in my apartment are indeed grounded with one of these devices.

9. I live sort of near Sutro Tower (but who in SF doesn't?). Wikipedia tells me that KOIT broadcasts from Sutro Tower. I also live right next to the N Judah MUNI line. Sometimes my lights dim when it goes by. I suspect the power is probably kind of dirty.

10. Using a different power cable doesn't do anything.

11. For what it's worth, here's a look at the circuitry inside the preamp.

I've been investigating this problem on and off for the last year or so and I still haven't figured out what's causing the problem. Do any electrical engineer types have an suggestions for further testing or solutions to this problem? I have a digital multimeter and oscilloscope at my disposal for the collection of further data.

I'm quite attached to this preamp (more so when it isn't making this noise), so please don't tell me to replace it.

RF Position tracking?

helltoupee — Thu, 09 Oct 2008 10:59:00 -0800

Anyone know of a reliable way to quickly & accurately track position over a 200 foot range? I am trying to get a camera to follow a moving subject over medium range distances outdoors.I have seen several products on sparkfun that transmit/receive RF, but do not know if they will work for position tracking. THANKS!

How to reduce/eliminate RF noise in my home studio?

scottandrew — Tue, 19 Feb 2008 13:31:45 -0800

My little bedroom studio could use some help. It's hard to find a spot where the mics and guitar pickups don't pick up RF noise. And when I do find a spot, it's usually closely facing a wall, and/or too far away from the recording computer. Actually, even with the computer off and the lights off, the guitar picks up a ton of gnarly RF static.

I also have a weird issue where my reference monitors pick up even *more* noise when I turn off the LCD monitor on my recording PC. I don't get it :/

I've googled up quite a bit of info on RF noise online, but most of it goes right over my head when they start talking impedance, Hz, etc. It helps to know the science, but I really just need some practical things to try at home. Tips, tricks, suggestions?

Do I need an RF mouse?

royalchinook — Fri, 11 Jan 2008 12:26:03 -0800

I want to be able to click through some Powerpoint slides in a really large room when my computer is at the other end of it (about 100 ft away). There are no physical boundaries in the way (it's in direct sight). Do I need an RF mouse for this? If so, does anyone have recommendations of good ones to buy? and where? It doesn't need to be overly fancy, probably a click and maybe a RMB click would be sufficient...

le monde du bruit

mykescipark — Sun, 08 Apr 2007 18:58:27 -0800

RF Filter (literally): I'm using my trusty Sony ICF-2010 shortwave radio (1990 vintage) with a brand-new Edirol R-09 digital recorder. Unfortunately, once I hook up the R-09, it spits up digital noise all over the bands. In this case, the predominant noise is like a kind of fast chuffing, a trilling, outboard motor-like sound. The sound changes its rhythmic qualities depending on whether the unit is in standby (the chuffing) or in record mode (noise bursts seemingly whenever "packets" of data are being written to the flash card). It gets softer or louder as one touches or handles the unit - at its loudest when the unit is being handled, as the body acts as a conductor. At its absolute quietest, it simply acts as a noise floor which obliterates quieter signals and makes a significant sonic fingerprint on all but the most powerful of broadcasters.

This also happened with my Sony TCD-D7 and my Sony MZR70 Mini-Disc recorder, and not just on this radio: my tank-like Kenwood R-5000 also suffered from the ill effects of these digital recorders. Whether they use moving parts and motors (DAT, MD) or flash cards (MP3), each creates a distinctive brand of hashy noise. What can one implement to stop this egregious leakage?

I've tried all of the following:

- standard, off-the-shelf in-line and snap-on RF chokes;
- making the line extraordinarily long (up to 50') and moving the recording device far away from the radio;
- using a third device (such as a mixing board, analog cassette deck, etc.) as a "middle man" to offset any direct line-in interference;
- using both devices with their respective "wall warts" and with batteries, in combinations;
- calling both Universal Radio and Grove for expert advice.

In all cases, the noise just plows on through. I'm a bit vexed that nobody in the shortwave universe has figured this out by now. I'm not terribly solder-savvy, but I'm willing to learn to find a permanently workable solution. Any bright ideas, hive mind? Specifics, if you can...

Wiring an RF modulator from a VCR.

odinsdream — Mon, 12 Feb 2007 07:48:38 -0800

I've pulled an RF modulator out of an old VCR, but I don't know what some of the pins are for on the unit. Help me wire it up to modulate a composite video signal. Here are the pins, in order:

+5V
BS
AUDIO
CONV B+
VIDEO

I only need to modulate the video - audio connection is unnecessary. I've tried hooking up a 5V 1A power supply with the ground wire hooked to the modulator's chassis. I then connected the center pin from my composite cable to the VIDEO pin. I also tried a variety of other connections, but couldn't get anything to display.

What are the other pins for, and what should I do to get this thing working?

Reason for doing this: Old TV with no composite input, tried using a VCR as a pass-through, but Macrovision gets in the way. I'm aware that I can buy an RF modulator, but I'd like to try this out first.

Can you really put the entire RF spectrum on a couple of millimeters of fiber?

arimathea — Mon, 06 Nov 2006 03:59:47 -0800

RF-to-IF over fiber. I'm not much of an RF geek lately but i'm learning a bit here and there. One of the things i've found some interest in is these RF-to-IF converters, which supposedly allow you to take chunks, or even the entire RF spectrum, convert it to a data signal, relay it over fiber, and then move it back into RF spectrum at the other end allowing traditional receivers to listen to it. It sounds to me like this is most useful for signals intelligence, e.g. if I was able to put an antenna in place X and maybe another box but not hundreds of thousands of dollars in people and receivers. Can someone provide some more information on how this would work in practice?

Get this Mother^$(ing Thump out of my Mother$(#ing car!

toxic — Tue, 29 Aug 2006 20:49:00 -0800

Very strange electrical noise getting into radio on newly imported 1997 JDM Toyota Tercel hatchback. Radio replacement is imminent, but there's So I bought this car, without checking to see if the radio worked, because I'd planned to replace the radio anyway (Japan's FM spectrum is 70-90 MHz, New Zealand's is the more normal 88-108, so even if it were working, the original Japanese radio would only get 2-3 stations).

A couple of days after I bought the car, I turned on the radio for the first time, and was greeted by very strange noises.

The noise is a repeating "Thump Thump Thump", that comes out of both speakers when the stereo is turned on. It doesn't matter what the volume knob is set to, it doesn't matter where the fader/balance knobs are set, it comes out of both speakers at the same volume (fairly loud, but not eardrum-shattering)

I'm hoping that this is just a bad amplifier in the stock unit, and that the replacement radio that I've got ordered will take care of this, but I'm concerned that it may be indicative of some other kind of electrical problem in the car.

I'm wondering if anyone else has heard similar noises from their Toyota, or has any further insight on this. Anyone?

Why might I be able to pick up cable with my uhf/vhf antenna?

Tue, 06 Apr 2004 16:12:11 -0800

Its recently been discovered that i can pick up a 70-or-so channel cable broadcast on my uhf/vhf antenna. While hoping not to jinx myself, i ask, does anyone know how this may be occurring? more inside. im certainly not complaining. but isnt cable usually accessible through, uh, a cable. it seems to be provided by a cable company and not a satellite. and while it is very tumultuous and requires a mess of tinfoil to maintain its still being pumped through the air. so, why?

My mouse and my cell phone make weird sounds come out of my computer speakers

scarabic — Wed, 03 Mar 2004 12:44:21 -0800

Two semi-related issues. Basically, both my mouse and my cell phone make weird sounds come out of my computer speakers. [more] #1: I always know a moment before my cell phone rings, because my speakers start buzzing like a beehive. I have a Nokia 3630. What's happening and what kind of phone should I get if I want it to stop? I like to keep my clock radio and my cell phone on my bedstand but I can't because it makes the speaker in the clock radio chirp all night.

#2: My USB Microsoft Wheel Mouse makes a tiny "eek-eek" sound come out of the computer's speakers whenever I use the mouse wheel. Each step in the wheel turn emits a squeak. It gets louder as I turn up the speakers, so I know it's not mechanical friction. Any advice on stopping it? It gets distracting when I least need to be distracted.