Other Directory Sites: SeekWonder | Directory Owners Forum
The following archive was created by hippie-mail 7.98617-22 on Sat Apr 10 1999 - 01:10:56
David Honig (honig@sprynet.com)
Thu, 06 Aug 1998 16:19:09 -0700
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).
The following archive was created by hippie-mail 7.98617-22 on Sat Apr 10 1999 - 01:10:56