Noise from speaker

[rogellis]

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The second PAW unit I built is also producing some (pulsating) static on the speaker.  At a guess, it is about 50 hz.

The static is not from RF, because there is no noise if amp/speaker runs from a different power source, so it must be from the power supply to the amp/speaker and PAW.   

But the noise  cannot be the fault of the dc converter, because it is coincident with the PAW unit initialising itself (it is silent prior to initialisation). So this appears to be an interference back down the power line from the PAW unit itself. 

(I am not in electronics, but I presume a unit can send pulses back down its own power line.  The PAW and the amp/speaker both draw their power from a common source.)

R

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[JCurtis]

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The second PAW unit I built is also producing some (pulsating) static on the speaker.  At a guess, it is about 50 hz.

The static is not from RF, because there is no noise if amp/speaker runs from a different power source, so it must be from the power supply to the amp/speaker and PAW.   

But the noise  cannot be the fault of the dc converter, because it is coincident with the PAW unit initialising itself (it is silent prior to initialisation). So this appears to be an interference back down the power line from the PAW unit itself. 

(I am not in electronics, but I presume a unit can send pulses back down its own power line.  The PAW and the amp/speaker both draw their power from a common source.)

R

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The PAW starts off drawing only a small amount of power, then as it boots up the current draw increases, so this could be conduced emissions from the power supply as the load increases.  Many supplies are "quiet" without load then noisy when loaded, alas many is just noisy all the time too.  Can you plug something else into the supply and see is the noise returns?

[rogellis]

Can you plug something else into the supply and see is the noise returns?

I rigged up the dc converter to a mobile phone and iPad, both on charge, plus the amp/speaker - and it was perfectly quiet.

I think the interference is definitely from the PAW, as the noise is perfectly in tune with the flashing LEDs on startup.  It then settles down to some static, plus a 5 hz square-wave pulsation.  There was a nifty noise generator online, and I was able to replicate the pulsating sound.
http://onlinetonegenerator.com

As a temporary fix, I was able to mute the speaker a bit, and increase the PAW volume to 10 and that muted most of the static.  But it is still annoying. 

The other PAW gives the same sounds, but much much softer.  If I get time I might swap the amps over, but they have different connectors, so it is not straightforward.

R

[Ian Melville]

5hz? Your not a whale are you 

[exfirepro]

Rog,

It should be possible to block interference electronically by filtering. Jeremy Curtis is the ‘expert’ here as that’s his ‘business’ field, but it would probably be worth trying a ground loop isolator in the lead between the PAW and the speaker amp, or use a 3-pole TRS plug which will short the unused ‘Video’ channel at the RPi audio output to ground to see if that helps.

Regards

Peter

[JCurtis]

A lot also depends on the Amp design etc. can you post a link to the amp?

Charging a battery is generally a pretty steady state power delivery, the likes of a PAW has a very 'spiky' power consumption (I think I posted a graph on the forum a while ago showing this), this can also cause problems with supplies to especially if designed as chargers rather than power supplies.  When you rigged up the DC converter did you measure how much current was being drawn whilst powering the phones?  Should be at least 1A for an effective test.

[rogellis]

A lot also depends on the Amp design etc. can you post a link to the amp?
When you rigged up the DC converter did you measure how much current was being drawn whilst powering the phones?

Sorry, Im a pilot, not an electrician.  The recommnded Anker dc converter also made the same noise with this unit. 

This is the amp I used.  It looks nice inside, with a mutitude of ic chips, but it is not designed for this application. 

Components like this could do with being integrated into the PAW unit.  I would happily pay more, not to have this hassle.

https://www.amazon.co.uk/N4U-Online®-Microsoft-Capsule-Rechargable-Black/dp/B00WHPF20E

R


R

[JCurtis]

A lot also depends on the Amp design etc. can you post a link to the amp?
When you rigged up the DC converter did you measure how much current was being drawn whilst powering the phones?

Sorry, Im a pilot, not an electrician.  The recommnded Anker dc converter also made the same noise with this unit. 

This is the amp I used.  It looks nice inside, with a mutitude of ic chips, but it is not designed for this application. 

Components like this could do with being integrated into the PAW unit.  I would happily pay more, not to have this hassle.

https://www.amazon.co.uk/N4U-Online®-Microsoft-Capsule-Rechargable-Black/dp/B00WHPF20E

So you would be looking for a speaker for use in the cockpit rather than wiring into an intercom or headset?

I've pondered making an "aviation grade" audio mixer that can take the likes of a PAW signal (iPad, or anything else for that matter) with an output for an intercom, aux into a headset or potentially a bluetooth link too.  The design I hashed out would also have priority on the inputs, so lower priority inputs would duck for higher priority etc.   Naturally all filtered and with some power options to boot.
I may have another look at at some point when I get some free time.

[Bill Maxwell]

I have "pondered" along similar lines on and off for a few years now. A unity gain summing amplifier readily gives the ability to plug any number of inputs into such a box and allows them to be fed to the intercom. The difficult bit is adding the ability to assign priorities amongst them, including giving the comms radio the highest priority, presumably? Seems a good task for a microcontroller I suspect.

Bill

[rogellis]

So you would be looking for a speaker for use in the cockpit rather than wiring into an intercom or headset?

This is for use in gliders, and we do not use headsets.  If PAW wishes to enter the glider market, it is a problem that needs addressing. 

(I suppose the aircraft headset has a different 5v source, so does not have this PAW interference.)

I presume the main problem is the pulsed transmission from the PAW aerial, which I understand goes out at 5hz - the same as the interference clicks.  In the old days of motor mechanics, we used to put a suppressor (a capacitor) across the ignition coil, to prevent similar feedback.  Would that help?  A capacitor across the 5v output from the dc converter?   If so, what type and size of capacitor?

I will also try taking the power from the Raspberry output, to see if that smooths out the 5v current a bit.  But I have to connect it to the car, as that is my only 12v battery source.

Cheers,
R

[Paul_Sengupta]

The PAW transmission goes out every 1.8 seconds or so.

[Admin]

50hz sounds suspiciously like mains induced hum ?
Thx
Lee

[Ian Melville]

5 not 50hz

[Admin]

Hi Ian
I read this ....

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The second PAW unit I built is also producing some (pulsating) static on the speaker.  At a guess, it is about 50 hz.

[Ian Melville]

Sorry Lee, was not reading that far back.

50hz to me says 'earth loop'