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Re: Recommendation for high sample rate receiver?

From: Fons Adriaensen
Subject: Re: Recommendation for high sample rate receiver?
Date: Mon, 3 Feb 2020 21:28:16 +0100

On Sat, Feb 01, 2020 at 02:58:06AM -0500, Mike wrote:
> The target signal of interest uses pulse modulation where each pulse is
> 1 microsecond in duration, with a rise time of less than 0.1 microsecond
> and a decay time of less than 0.2 microseconds.  The goal is to identify
> the start (arrival) of a transmission at each receiver site as
> accurately as possible (better than 25 ns).
If this timing is to be derived from a _single_ pulse, this will 
require a high S/N ratio in order to achieve 25 ns precision, no
matter what your sample rate is.

> Interpolation adds no useful information regarding start time, of
> course. 

True, it does not provide any new information, but it makes it
easier to extract the available info. Assume you have sampled
the signal at 10 MHz. Locally interpolating (i.e. upsampling)
it with a linear phase polyphase filter will preserve the timing
info and allow you to compare the interpolated values for the
leading edge with some reference, e.g. half the value reached
during the 1 us pulse length. 

> Lower sampling rates lose arrival time resolution.

No they don't. But what could happen is that the filter
which limits the bandwidth before sampling isn't linear
phase and distorts the waveform.



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