[aprssig] HF options

Scott Miller scott at opentrac.org
Wed Dec 19 13:28:04 EST 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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