ivp wrote:
>> The dsPIC sampled the analog signals at 100kHz and the
>> Manchester data rate was 10kHz
>>     
>
> This might be the Maxim AN that Michael mentioned
>
> http://www.maxim-ic.com/app-notes/index.mvp/id/3671
>
> The ASK receivers I've used output analogue noise with no
> incoming signal, and inverted digital output when receiving data
>
> A s/w time-out loop detects the start of a legitimate transmission.
> This has been reliable as the data bit time is far longer than noise
> 'bits'
>
> I've not put a scope on the receiver board to see what useable
> analogue signals there are, but your example inspires me to
>
>   
There are chips/modules with built in Squelch that work well.

The really cheap super-regenerative receivers are VERY noisy if there is 
no signal and have the disadvantage for other receivers that they are 
low power transmitters at same frequency. They should be illegal.

The other aspect is that the "noise" is usually much higher "clock rate" 
than data if you are running about 1200bps, so the polling x4 
oversampling in MPU can actually quite easily ignore it, depending how 
your "clock" sync and data recovery works on Manchester Decoder in SW.
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