Forums

So what makes this buzzing-radio sound anyway?

Started by Tim Williams November 4, 2013
www.seventransistorlabs.com/QRZ.mp3
(...QRN?  I don't remember the Q-codes.)

Recorded from a Theremin-in-progress, but the same sound shows up all over 
the airwaves, LW, SW, professional receivers or homemade.  In this case, 
it shows up when connecting only a foot of wire to a 5MHz oscillator (yes, 
rather high for a Theremin, this is for S&G's at the moment).  Said 
oscillator seems to be acting in an autodyne capacity.

The waveform seems to be a frequency modulation (advancing at least one 
cycle) every 8.3ms.  Hence the buzzing sound, and hence the FM synth 
character at different frequencies.

It must be line driven, somewhere, but it's not my power supply, and 
anyway, that wouldn't explain it being everywhere on the dial.  It also 
seems rather dubious (or impressive?) that it's having such a strong 
effect on my oscillator, despite using only a one foot antenna.

Tim

-- 
Seven Transistor Labs
Electrical Engineering Consultation
Website: http://seventransistorlabs.com 


On Mon, 4 Nov 2013 13:28:25 -0600, "Tim Williams"
<tmoranwms@charter.net> wrote:

>www.seventransistorlabs.com/QRZ.mp3 >(...QRN? I don't remember the Q-codes.)
It's QRN as in "noise".
>Recorded from a Theremin-in-progress, but the same sound shows up all over >the airwaves, LW, SW, professional receivers or homemade. In this case, >it shows up when connecting only a foot of wire to a 5MHz oscillator (yes, >rather high for a Theremin, this is for S&G's at the moment). Said >oscillator seems to be acting in an autodyne capacity. > >The waveform seems to be a frequency modulation (advancing at least one >cycle) every 8.3ms. Hence the buzzing sound, and hence the FM synth >character at different frequencies. > >It must be line driven, somewhere, but it's not my power supply, and >anyway, that wouldn't explain it being everywhere on the dial. It also >seems rather dubious (or impressive?) that it's having such a strong >effect on my oscillator, despite using only a one foot antenna. > >Tim
The ARRL has a collection of common RFI sounds on their web pile: <http://www.arrl.org/sounds-of-rfi> Under household, try the Sony TV: <http://www.arrl.org/files/file/RFI%20Sounds/sony-tv.mp3> Kinda sounds like a plasma TV. The difference is that your recording has a 2nd signal from your Theremin that is producting a beat note. Of course, you could identify the source by turning things off in your house until the QRN disappears. -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On 4.11.13 9:28 , Tim Williams wrote:
> www.seventransistorlabs.com/QRZ.mp3
> (...QRN? I don't remember the Q-codes.) QRZ? = who is calling? QRN = man-made noise.
> Recorded from a Theremin-in-progress, but the same sound shows up all over > the airwaves, LW, SW, professional receivers or homemade. In this case, > it shows up when connecting only a foot of wire to a 5MHz oscillator (yes, > rather high for a Theremin, this is for S&G's at the moment). Said > oscillator seems to be acting in an autodyne capacity. > > The waveform seems to be a frequency modulation (advancing at least one > cycle) every 8.3ms. Hence the buzzing sound, and hence the FM synth > character at different frequencies. > > It must be line driven, somewhere, but it's not my power supply, and > anyway, that wouldn't explain it being everywhere on the dial. It also > seems rather dubious (or impressive?) that it's having such a strong > effect on my oscillator, despite using only a one foot antenna. > > Tim
It could be e.g. a Chinese energy-saver lamp switcher fed with raw full-wave rectified supply, with the power line filter components saved from the BOM. -- Tauno Voipio, OH2UG
On Mon, 04 Nov 2013 13:28:25 -0600, Tim Williams wrote:

> www.seventransistorlabs.com/QRZ.mp3 (...QRN? I don't remember the > Q-codes.) > > Recorded from a Theremin-in-progress, but the same sound shows up all > over the airwaves, LW, SW, professional receivers or homemade. In this > case, it shows up when connecting only a foot of wire to a 5MHz > oscillator (yes, > rather high for a Theremin, this is for S&G's at the moment). Said > oscillator seems to be acting in an autodyne capacity. > > The waveform seems to be a frequency modulation (advancing at least one > cycle) every 8.3ms. Hence the buzzing sound, and hence the FM synth > character at different frequencies. > > It must be line driven, somewhere, but it's not my power supply, and > anyway, that wouldn't explain it being everywhere on the dial. It also > seems rather dubious (or impressive?) that it's having such a strong > effect on my oscillator, despite using only a one foot antenna. > > Tim
Like Dr. Who, only less melodious. Start turning things off around the house, and see what makes it go away. At my place, it's the florescent shop lights. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Tim Williams <tmoranwms@charter.net> wrote:
> www.seventransistorlabs.com/QRZ.mp3 > (...QRN? I don't remember the Q-codes.)
QRM, I think.
> Recorded from a Theremin-in-progress, but the same sound shows up all > over the airwaves, LW, SW, professional receivers or homemade.
From 0 to about 0.7 sec, it sounds like a "carrier", so to speak. From about 0.7 sec to about 1.5 sec, it sounds like there is "data" modulated on it somehow. Then, the theremin starts up. A quick analysis in Audacity shows some peaks at roughly 17.5 kHz, 14 kHz, 10 kHz, and maybe 6.5 kHz. http://birdbird.org/tmp/sed/williams-spectrum-begin.png Of course, doing an FFT on an mp3 is somewhat dubious. Record to .wav (or other lossless format), grab a copy of Audacity, and see for yourself locally. Not real-time but the price is right. From about 12.0 sec to the end of recording also seems to be free of theremin sounds. I still think it sounds like "data", but the frequency is different. The spectrum doesn't have peaks, either. http://birdbird.org/tmp/sed/williams-spectrum-end.png
> It must be line driven, somewhere, but it's not my power supply, and > anyway, that wouldn't explain it being everywhere on the dial.
Hit breakers until it stops. If it never stops, try it in the daytime (when streetlights and other lights are off) and and at night. If you have any overhead power lines in your area, wander the immediate neighborhood and look and listen for small arcs at the poles. Is there any (possibly unannounced) broadband over powerline in your area? Matt Roberds
On Tue, 5 Nov 2013 04:00:08 +0000 (UTC), mroberds@att.net wrote:

>Is there >any (possibly unannounced) broadband over powerline in your area? >Matt Roberds
I don't think it sounds much like BPL. This is typical BPL. <http://www.arrl.org/files/file/RFI%20Sounds/w4tdk-13690.mp3> Check for BPL deployments by zip code: <http://www.bpldatabase.org> -- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
On 05/11/2013 04:00, mroberds@att.net wrote:
> Tim Williams <tmoranwms@charter.net> wrote: >> www.seventransistorlabs.com/QRZ.mp3 >> (...QRN? I don't remember the Q-codes.) > > QRM, I think. > >> Recorded from a Theremin-in-progress, but the same sound shows up all >> over the airwaves, LW, SW, professional receivers or homemade. > > From 0 to about 0.7 sec, it sounds like a "carrier", so to speak. From > about 0.7 sec to about 1.5 sec, it sounds like there is "data" modulated > on it somehow. Then, the theremin starts up.
I'd hazard a guess that it is a very badly behaved switched mode PSU, speed controller, CFL light or dimmer somewhere. To make such a mess it seems likely that the outward and return paths are not close together so that you have a room bathed in magnetic loop coupled RF noise. A bit like the method that the T setting on hearing aids uses - might be worth seeing if you can pick it up with a pancake coil and a crystal earpiece then you might be able to metal detect to the source.
> A quick analysis in Audacity shows some peaks at roughly 17.5 kHz, 14 > kHz, 10 kHz, and maybe 6.5 kHz. > http://birdbird.org/tmp/sed/williams-spectrum-begin.png > > Of course, doing an FFT on an mp3 is somewhat dubious. Record to .wav > (or other lossless format), grab a copy of Audacity, and see for > yourself locally. Not real-time but the price is right.
Daqarta (sp?) will do it in realtime if you can feed the signal into a soundcard. I have used it for public demos of Sound and Music. ISTR You have 30 days free use before you have to register and it still works as a basic signal source after your evaluation period expires. It isn't outrageously priced so if it does what you want worth buying.
> > From about 12.0 sec to the end of recording also seems to be free of > theremin sounds. I still think it sounds like "data", but the frequency > is different. The spectrum doesn't have peaks, either. > http://birdbird.org/tmp/sed/williams-spectrum-end.png > >> It must be line driven, somewhere, but it's not my power supply, and >> anyway, that wouldn't explain it being everywhere on the dial. > > Hit breakers until it stops. If it never stops, try it in the daytime > (when streetlights and other lights are off) and and at night. If you > have any overhead power lines in your area, wander the immediate > neighborhood and look and listen for small arcs at the poles. Is there > any (possibly unannounced) broadband over powerline in your area? > > Matt Roberds
-- Regards, Martin Brown
<mroberds@att.net> wrote in message news:l59qg8$r0m$1@dont-email.me...
> From 0 to about 0.7 sec, it sounds like a "carrier", so to speak. From > about 0.7 sec to about 1.5 sec, it sounds like there is "data" modulated > on it somehow. Then, the theremin starts up.
The theremin action is continuous of course, the different periods are just where I put my hand to give you an idea what it sounds like at various places. Like I said, the waveform looks like frequency modulation -- no matter what the carrier frequency; it seems like constant displacement FSK. I don't get what kind of signal is pulling the oscillator like that, nor how it can do it so strongly from so little antenna. (Is it really that sensitive? Why don't theremins in the MF range do it?)
> Hit breakers until it stops. If it never stops, try it in the daytime > (when streetlights and other lights are off) and and at night. If you > have any overhead power lines in your area, wander the immediate > neighborhood and look and listen for small arcs at the poles. Is there > any (possibly unannounced) broadband over powerline in your area?
Beats me. Unfortunately, all noise abatement advice is N/A -- I'm in an apartment, suburban area. The elephant in the room is obviously the computer (for which without, how do I record..), but based on experience, I don't think that's the source anyway. Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com
On 2013-11-04, Tim Williams <tmoranwms@charter.net> wrote:
> www.seventransistorlabs.com/QRZ.mp3 > (...QRN? I don't remember the Q-codes.) > > Recorded from a Theremin-in-progress, but the same sound shows up all over > the airwaves, LW, SW, professional receivers or homemade. In this case, > it shows up when connecting only a foot of wire to a 5MHz oscillator (yes, > rather high for a Theremin, this is for S&G's at the moment). Said > oscillator seems to be acting in an autodyne capacity. > > The waveform seems to be a frequency modulation (advancing at least one > cycle) every 8.3ms. Hence the buzzing sound, and hence the FM synth > character at different frequencies. > > It must be line driven, somewhere, but it's not my power supply, and > anyway, that wouldn't explain it being everywhere on the dial. It also > seems rather dubious (or impressive?) that it's having such a strong > effect on my oscillator, despite using only a one foot antenna. >
Could your oscilator be squegging ? Vackar's topology is particularly prone to this. -- For a good time: install ntp --- news://freenews.netfront.net/ - complaints: news@netfront.net ---
"Jasen Betts" <jasen@xnet.co.nz> wrote in message 
news:l5af5f$cgl$1@gonzo.reversiblemaps.ath.cx...
> Could your oscilator be squegging ? > Vackar's topology is particularly prone to this.
Waveform at the osc (before the mixer) is nice and clean. Of course, I can't see the FM/noise at frequency. Tim -- Seven Transistor Labs Electrical Engineering Consultation Website: http://seventransistorlabs.com