From: David Honig <honig@sprynet.com>
To: die@die.com
Message Hash: 5be75f7e11553525a810f5d7eae732b55a67bf274e57285587ef3654013ef166
Message ID: <3.0.5.32.19980806161909.007ca100@m7.sprynet.com>
Reply To: <3.0.5.32.19980806103120.007cfb00@m7.sprynet.com>
UTC Datetime: 1998-08-07 00:31:16 UTC
Raw Date: Thu, 6 Aug 1998 17:31:16 -0700 (PDT)
From: David Honig <honig@sprynet.com>
Date: Thu, 6 Aug 1998 17:31:16 -0700 (PDT)
To: die@die.com
Subject: Re: Noise source processing
In-Reply-To: <3.0.5.32.19980806103120.007cfb00@m7.sprynet.com>
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At 02:24 PM 8/6/98 -0400, Dave Emery wrote:
>
> This is expected of hard limiters below threshold (such as in a
>reasonable FM IF system fed Johnson noise). The spikes occur on phase
>discontinuities in the limiter output - what you are seeing is the input
>Johnson noise intermittantly inducing phase jumps in the output of the
>ringing IF filters shock excited by the broadband input noise. The IF
>filters tend to ring somewhat coherently until hit by another burst of
>noise which sets them off on another phase. Each phase jump shows up as
>a spike on the discriminator output. The narrower the bandwidth of the
>filters, the longer the spike and interspike intervals. Thus one needs
>an IF bandwidth considerably wider than the sample rate.
Given that the cheapo radio was 10 cm from a 21" monitor, I don't think
you need to invoke noise-driven resonances in the humble radio.
I was/am interested in robust methods that don't depend on
exquisite analog equalization, etc.
Zero crossings are analogs (pun intended) of
RFC1750's #2 method (via Shannon):
map 01 -> 1
map 10 -> 0
00, 11 are no-ops.
Note that for a digital signal you are detecting level-changes. (Vdd/2
changes?)
Waiting for zero crossing will give you perfect 0:1 ratio,
but you may have to wait arbitrarily long (but will almost
certainly not, in the formal sense ---there's a decaying exponential
in there).
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