Subject:
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Re: RF transmitters
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Thu, 8 May 1997 19:29:12 GMT
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Original-From:
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Curt Mills, WE7U. <HACKER@TC.FLUKEavoidspam.COM>
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Viewed:
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1393 times
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On Thu, 8 May 1997, Randy Sargent wrote:
> Keeping the "DC" content pretty much in the middle means we restricted
> ourselves to sending bytes that had between 3 and 5 "1" bits set.
> Surprisingly (to me), this still gave us 182 values per byte (out of the
> original 256), and more suprisingly, meant that we had only a 6% loss of
> bandwidth as compared to a channel with no restrictions (log base 2 of 256
> is 8 bits, log base 2 of 182 is 7.5 bits)
A simple way to get rid of the DC component is to run the data through a
scrambler on the TX side, and descrambler on the RX side. This has been
done successfully in 9600 baud amateur radio TNC's. 2 or 3 chips on
each end of the link is all it takes. The circuit is relatively simple.
It can also be done inside a small FPGA chip (I've done it).
The same technique (but not necessarily the same circuit - not sure)
was used in the 56kbaud amateur radio modems.
Curt Mills, WE7U
Senior Methods Engineer/System Administrator
hacker@tc.fluke.com
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Message is in Reply To:
 | | RF transmitters
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| (...) We did use 900 Mhz Radio Shack RF headphones (cat # 33-1145), which gave us a reasonable analog transmission (the transmitter took L+R RCA audio in, and the we connected in place of the speaker on the receiver). We could get 9600 baud through (...) (27 years ago, 8-May-97, to lugnet.robotics.handyboard)
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