Dee Flint wrote:
"Michael Coslo" wrote in message
...

Dee Flint wrote:


"John Smith" wrote in message
...


Dee wrote, "... only fax and SSTV have a small enough band width to be
practical."

That is not only a ridiculous statement, it is preposterous and shows a
total lack of knowledge of the state of data compaction.

However, it proves you are not aware of what is technically possible and
therefore are in a poor position to advise or inform others and, the
sorry state of amateurs technical savvy in general!

John



Ok then, show me the math that demonstrates you can transmit a one
megabyte picture in seconds on the HF bands using only 300 baud. To get
it down to seconds requires data compression/encryption techniques that
can reduce the data by a 1000 fold.

Obviously, images can be transmitted by digital modes as well as the
analog method of SSTV.



Digital images would have to be compressed/encrypted also to get the
bandwidth down to acceptable ranges for HF and we're still talking on the
same order of magnitude to do so. Even with a fast broadband internet
connection, I've seen some material that still takes a noticeable time to
download.


Is that a good way of transmitting the image? It can be. Seems I've heard
about a digital image transmission mode.



Isn't most of the stuff off the internet (mpg comes to mind) digitally
encoded. Even on my broadband connection it will occasionally jerk and
pause. If you have to slow it down to 300 baud for the HF bands so as not to
consume too much bandwidth, that would become even jerkier.

Very true.

Accepted minimum rate for a recognizable "talking head" type video is
32Kbit/second.

I made a test jpg image @ 640 by 480, level 5 (unacceptable for me, but
others may find that okay) Typical scene, some amateurs sitting around a
radio, no large expanses of sky. It was 553.6 Kbits.

Assuming that the transmission rate would be similar to Packet radio at
..3Kbit/second it is obvious that video would be impossible to do live,
and grossly impractical to do as say an mpeg.

That 640 by 480 jpeg might be within the realm of feasibility at just
around 31 minutes. Note that this does not include error checking lags.
And there will be errors.

Note that these are very rough calculations.


Does that make the Analog SSTV mode obsolete? No more obsolete than SSB or
FM. It is a fairly quick mode, and with a computer is now inexpensive, and
fun.

I'm looking forward to an education on the modes from someone with
technical savvy. Mr Smith?


- Mike KB3EIA -


I doubt if he's got the technical savvy. Simple arithmetic shows the
inherent problems.

Yeah, like I said 8^)

- Mike KB3EIA -