On Nov 21, 2013, at 8:26 AM, Jeff Blaine wrote:
> There is a lot of "modernization" and "flexibility" listed - but who, beyond
> the PACTOR guys, would actually benefit from this change. Figure that out
> and we can likely connect the dots from that group to this decision.
Unless the words "modernization" and "flexibility" are synonymous with the
phrase "more data bandwidth," the ARRL proposal simply don't make any technical
sense.
As I mentioned in an earlier private email to another reflector participant,
take a look at all the advancements towards getting the most miles with the
lowest power. You need not look further than Joe Taylor's modes.
http://www.physics.princeton.edu/pulsar/K1JT/index.html
If you include the also widely used PSK31 (very good for folks with small
antennas and low power when propagation is good) the focus on narrower
bandwidths goes back for at least two and a half decades.
These folks had the freedom to use higher symbol rates and wider bandwidth, but
choose not to.
Technically, you can use wider bandwidths to counter selective fades due to
multipath in Rayleigh channels (best model for HF that has been used for
decades now). That is addressed in modern modes with good forward error
correction (FEC) and longer data frames. And even when you use simple two tone
FSK, it has been known by amateurs since the 1960s that 170 Hz is already wide
enough to derive information to apply a good automatic threshold correction to
FSK. As I mentioned in my "RTTY Demodulators" article,
"In a February 1964 article in the RTTY bulletin, Frank Gaudé reported that
there is actually no significant difference anyway between the amount of
selective fading between a wide shift and a narrow shift signal down to the 170
Hz region."
So, the need for wider bandwidths has nothing to do with finding better modes
for HF communications. It does allow you to push more bits per second through
the channel.
BTW, you can include references in your comments to the RM, and the references
can include Web links, references to RTTY Bulletins from the 1950s, or email to
your kids, if those are pertinent. Please feel free to do all the web research
that you need and include references that you decide are pertinent to include
in your own comments.
73
Chen, W7AY
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