AVR-Chat

Traditionally, it is done with an RC filter and a diode detector. If the amplitude is high enough (say, a couple of volts peak-peak), no amplification may be needed. Commonly, an analog comparator is used to look at the rectifier output. The comparator reference is adjustable to provide a "squelch adjustment". 

In software, you would need to sample pretty fast (maybe 20KHz, maybe higher). Some kind of filter would be needed. Choose what ever is easy to implement. The rectifier can be implemented with a peak detector having decay. Personally, I would choose the analog route, just because I know how to design, analyze, and diagnose things there.

Jim

On Jun 24, 2012, at 3:27 PM, enkitec@gmail.com wrote:

> 
> This is exactly what I need, but how to do it in software?
> A high pass FIR or IIR filter?
> 
> Mark
> 
> On 24-Jun-12 17:42, Jim Wagner wrote:
> > Motorola 2Way radios used this for years. It was called "noise squelch" or something like that. You have a high pass filter that cuts off above the top of the voice spectrum. Amplify and rectify the filter output. You will have a rectified output only when there is nothing to hear on the channel.
> >
> > Jim
> > On Jun 24, 2012, at 10:19 AM, enkitec@gmail.com wrote:
> >
> >> Hi,
> >>
> >> I want to build a FM radio squelch using an ATMEGA8.
> >> The ADC will be sampling the FM radio audio output and turn on a
> >> LED when there is only noise present. The LED will be off when someone
> >> is using the channel (no noise, just voice).
> >>
> >> What is the best way of doing this in software?
> >>
> >> Thanks for any idea.
> >> Mark Jordan
> >>
> >>
> >
> >
> > [Non-text portions of this message have been removed]
> >
> >
> >
> > ------------------------------------
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
> 
> 



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