At 15:10 12/11/2011, Jim Jerzycke wrote:
We're discussing it because a lot of people don't have a clear
understanding of what a Software Defined Radio actually is.
Well, when I wrote a talk about SDR I defined an SDR this way
(talking about rcvr, but xmit is similar):
A radio has five jobs:
1. Amplification (picowatts from the antenna to watts to the
headphones or speakers)
2. Band selection (to permit adapting some later functions to a
narrower frequency range)
3. Frequency reduction (from MHz to KHz)
4. Tuning (to reduce the region of focus from many KHz to a few Hz or KHz).
5. Demodulation (to recover the signal from its processed form
(think FM for example))
A conventional radio accomplishes ALL these functions in hardware.
Because of speed/bandwidth restrictions, ALL current radios do 1, 2,
3 in hardware or special purpose microchips.
I said it was an SDR if it used software or upgradable firmware to
accomplish any of 1-5.
Notice that the FCC appears to believe that software is easier to
upgrade than hardware. If you think about most MARS mods, this is
clearly wrong, but the FCC gives diode-lifting a free ride because it
is a hardware mod. And nowhere does the FCC consider data mods. If
band frequency and mode limitations are governed by a table, then
changing the table is NOT a software mod. Hmmmm. And firmware
mods are apparently considered hardware because they are implemented
in a ROM, not code on a hard disk or floppy or CD. Suppose it is an EAPROM?
This is clearly an area that needs rethinking by minds more
technologically competent that those used so far.
--
Dave Gomberg, San Francisco NE5EE Programming since 1959
All addresses, phones, etc. at http://www.wcf.com/ham/info.html
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