[aprssig] HF options
scott at opentrac.org
Wed Dec 19 12:28:04 CST 2007
> NVIS is a relatively "lossy" mode meaning you have to run fair amounts
> of power to achieve a reasonable S/N and data error rate. (The lower HF
Yeah, I figured NVIS wouldn't be great... I was hoping there was
something with adequate ground wave propagation to be useful.
> Further, for this kind of application (data operation at low S/N) the
> digital signal processing IF and audio filtering found in recent HF
> transceivers (that "de-noises" and "de-hisses" SSB voice operation) is
> usually less desirable for data, than the classic passive IF crystal or
> mechanical filtering (and analog audio filtering). [The DSPs in
> low-end ham gear tend to create phase jitter that mangles data.]
I figured a crystal-controlled rig would be better for simplicity. But
you're right, doing data at low S/N isn't going to be fun, and AFSK over
SSB introduces frequency stability concerns that you don't have with FM.
If the remote stations are transmit-only, though, it seems to me that
you'd only need a small number of more capable RX stations.
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