Given the challenges of conveying messages error-free over HF links,
I would recommend against raising the bar by also striving for real-
time interactivity. No one would complain about a soundcard-based
system that could reliably convey messages from a mobile laptop and
HF rig to a remote server with 30 seconds of latency. Attemping to
reduce this latency to a level acceptable for interactive chatting
would undoubtedly extend the time required to develop the system --
quite possibly to infinity. "Perfect is the enemy of good" applies in
this case.
A small realtime Linux box containing a soundcard and a USB
connection to its PC host would be an excellent and relatively
inexpensive implementation vehicle that could download and run a wide
range of protocols. Unlike the soundcard in their PC, howver, most
hams don't already own one of these -- so we'd need some incredibly
compelling applications to drive adoption anywhere close to what's
been achieved with RTTY or PSK.
73,
Dave, AA6YQ
--- In digitalradio@yahoogroups.com, "DuBose Walt Civ AETC CONS/LGCA"
<[EMAIL PROTECTED]> wrote:
>
> When amateur radio operators who are used to keyboard-to-keyboard
QSOs and then go to a data transfer or messaging system, they do tend
to become impatient with ACK times.
>
> I do believe that if we understand that we can send several/many
seconds of data that have a moderate level FEC, we can wait for an
ACK or NARK...especially if this is a "broadcast" type transmission.
For a 5-15 second data transmission, I don't think that 5-7 seconds
of wait time will "kill us".
>
> If propagation is good, we might consider 20-30 seconds of data
transmission and 5-10 seconds of delay. If propagation is poor, then
5-10 second transmissions might still warrant a 5-10 second delay.
>
> The consideration should be the average throughput over a long
period...say 5-10 minutes which should equal a rather large volume of
data.
>
> It is good to keep all these considerations in mind; however, I
don't think they should be a reason to not consider any certain
modulation scheme or data mode.
>
> There will inevitably be a necessity to obtain a balance between
RAW data/modulation rate, delay, level of use of FEC and ARQ.
>
> The solution is to build a mode or even modes that, over the long
term, can have a substantially greater throughput than current
systems using the same or equal hardware.
>
> One other consideration is that there are differences between what
can be done with a computer and external hardware. The desire for
open software to run on a computer seems to be the push for sound
card modems while the use of external hardware, such as the Pactor
Modems, does not have the appeal to those who are running modes using
a computer alone.
>
> I would recommend that external hardware be given consideration;
however, not proprietary hardware or systems but rather COTS hardware
that will run open source applications such as the EVM boards that
were popular a few years ago. They were (perhaps still are) quite
reasonably priced and might well produce modes superior to any
current hardware generated mode. Also, one would want to consider
external COTS soundcards for mode generation...perhaps even a
combination of something like an EVM card and external soundcards.
Perhaps even entire computers such as are available for under $200.
>
> 73,
>
> Walt/K5YFW
>
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