For some time we’ve been confused by e-mail data rates and cost, as it applies to boat-based communications. Recently, Mike Parker, a new Sundeer owner and old-time glider guru, brought us up to speed on this subject. Here’s what we learned.<\/p>\n
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There are eight bits of data in one byte. One byte is more or less equal to a single character (i.e. one byte – or eight bits – equals a letter, number, space, punctuation mark, etc.).<\/p>\n
When you hear about a 2400 baud connection over Iridium or Mini-M sat com, this is essentially equivalent to 2400 bits per second of data. Since there are eight bytes in a character, divide the data rate-let’s say 2400 baud-by eight to see how many characters you can send per second. 2400\/8 = 300 characters per second.<\/p>\n
When you hear about 9600 baud over Globalstar sat phones, you divide 9600 by eight to get 1200 characters per second.<\/p>\n
The average word contains about five characters, so this means the slower sat phone connections can send text at roughly 50 words\/second or 3000 words\/minute-which is why text-only messages don’t take much connect time.<\/p>\n
One of our main concerns is with sending photos and Excel spreadsheet files. Most of the larger web photos published on SetSail.com run about 18,000 to 24,000 bytes of data-this would be a heavily compressed JPG image. To see how long it would take to transmit an 18K byte photo, we first have to convert from bytes to bits by multiplying 18,000 x 8 to get 144,000 bits. Then we divide this by the data rate or 144,000\/2400 bits per second to give us 60 seconds of time for the data transmission.<\/p>\n
To this we have to add a bit of “overhead” at the beginning and end of each transmission for connection and disconnect.<\/p>\n
Bottom line – we can send an average photo like SetSail uses for about a minute of transmission time on the slower services.<\/p>\n","protected":false},"excerpt":{"rendered":"