EEVblog #23 - GSM mobile phone audio design

GSM mobile phone audio design, RF immunity, and low noise dead bug point-to-point prototyping.

Category:

Science & Technology

Tags:

• gsm
• phone
• design
• audio
• headphones
• noise
• interference
• buzz
• 217hz
• prototype
• dead bug
• point to point
• copper clad
• low noise
• construction
• tutorial
• build
• measurement

[CoolDudeClem]

What about putting the whole audio part in some kind of metal shield? That's what I did when one of my stereos kept picking that noise up.

[EEVblog]

@CoolDudeClem That doesn't help much, you can get pickup on the input and output and power leads.

[enliteneer]

If RF can inject itself on the Output going to the headphones, how would a radiation immune IC prevent that? Wouldn't you still need the RF Traps (33pf | 10pf) at the output?

Also, in the beginning, you mention 217Hz is the frequency to watch out for, but in the end, your traps are only for the 800/900/1800Mhz? Where did 217Hz factor in?

[EEVblog]

@enliteneer The RF pulses are at 217Hz spacing.

[dingobabystealer]

I was really getting into troubleshooting the problem there, and then his solution turned out to be a commercial solution. I've got to say I was a bit disappointed. It feels like I've just been told, "Leave it to the real engineers." I didn't learn anything here that I couldn't have gotten from a Maxim ad.

Also, word on the street is dead-bugging chips leaves the IC itself more vulnerable to RF interference. Just sayin'.

[EEVblog]

@dingobabystealer No, it's an example of how some things are sometimes just better solved with an already optimised COTS solution. We could have dicked around for a few more weeks or months (if we had the time) and possibly came up with a discrete solution, but that didn't fit into our requirements.

Many people learned a lot from this video, so that's good enough for me.

[mineralmax]

Hello Dave! Just wanted to let you know how much I enjoy watching your videos and really appreciate the educational value in them. Found your eevblog from hackaday.

Keep up the great work and thanks!

[bloodaid]

"youre screwed in all sorts of ways" hahaha

[CoolDudeClem]

So phones in other parts of the world make the same sounding interference? I may be sounding stupid here, but I'm absolutely serious here, I thought just cellphones in England did that, since I've never heard it until now on any videos outside of England.

[Technoguy3]

Don't other technologies do that as well (not just GSM)? I thought phones on Verizon's network did that too.

[dingobabystealer]

I was really getting into troubleshooting the problem there, and then his solution turned out to be a commercial solution. I've got to say I was a bit disappointed. It feels like I've just been told, "Leave it to the real engineers." I didn't learn anything here that I couldn't have gotten from a Maxim ad.