Thanks Brian
and a sort of funny part of getting your explanation...
I've been running JT65HF on 12/17 meters for the last two hours and
writing the email question and this reply during my transmissions. LOL
So I'm as good as Curiosity...just a whole lot cheaper!!!!
On 8/10/12 1:36 PM, Brian Lloyd wrote:
On Fri, Aug 10, 2012 at 10:48 AM, bill <[email protected]
<mailto:[email protected]>> wrote:
How long does it take from the time Curiosity takes a
pictures/processes it for transmission to reception by NASA?
Is the picture sent in segments and does NASA use a 'checksum'
type system to make sure of proper reception.
Today's pics were better than I took of my dogs yesterday, and
they were just a few feet away from me lying in my lawn!
I presume you want a serious answer. No, they do not use a "checksum"
system because it takes too long to send back a NAK to say, "sent that
one again." (It is a 20+ minute round trip for the radio signal.) They
actually use forward error correction with enough redundancy so that,
when the bits arrive back on earth, even if some of them are wrong,
the receiver can correct the errors so an error-free data block (or
part of a picture) is recreated in the receiver.
In ham radio we have a couple of systems that work this way, e.g.
Olivia, MFSK16, Contestia, DominoEX/FEC, Thor, MT63, JT65, WSPR, etc.
That is why they get good copy on a poor signal without having to
retransmit the data.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
[email protected] <mailto:[email protected]>
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
--
Bibliophobia - Fear of books.
---------------------------
W9OL-Bill H. in Chicagoland
webcams at http://w9ol-towercam.webhop.org:8080
My weatherpage at http://home.comcast.net/~w9ol/WX/HH.htm
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