[pskmail] SNR vs receiver bandwidth vs DSP coding bandwidth(?)
- From: "Ralph Wallio, W0RPK" <W0RPK@xxxxxxxxxx>
- To: <pskmail@xxxxxxxxxxxxx>
- Date: Thu, 20 Mar 2008 05:34:36 -0500
I am in the process of testing PSKmail for potential use with a portable 600m
station design for
emergency communications (see http://www.500kc.com/ for more about ongoing 600m
experimental license
testing). During this process I thought I had come to understand and calculate
trade-offs between
required SNR and throughput of BPSK31/63/125, et al. Recent discussion in this
list makes me
question my understanding of how DSP coding impacts demodulation bandwidth.
It has been my understanding that the front-end of DSP coding sets different
bandwidths depending on
mode. For example, bandwidth for BPSK31 is set to ~80Hz before further DSP
code starts the
demodulation process. If this is correct it does not make any difference
whether receiver bandwidth
is 2500, 500 or 300Hz, actual SNR bandwidth is much narrower.
In an otherwise empty band SNR bandwidth and performance would be controlled by
DSP coding. But in
the real world there is another concern: receiver AGC pumping by stronger
adjacent channel signals
that could be reduced, even eliminated, by using narrower receive filtering.
I will set up a controlled test to check my understanding of receiver vs. DSP
code SNR bandwidth.
TNX es 73 de Ralph Wallio, WØRPK
W0RPK@xxxxxxxxxx W0RPK@xxxxxxxx W0RPK@xxxxxxxxx
http://showcase.netins.net/web/wallio/
Hubbert's Peak - The Mother of all Perfect Storms
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