DDS
I was reading the article from the ARRL Handbook again on DDS using
the hardware method. A mostly software method however sounds better.
Thats herein below.
Since the idea is to use a digital to analog convertor for this
approach. The idea of a all hardware approach in a radio is the draw
back with this. Too much hardware or parts, etc: as well as
technolical difficulties.
It appears that the better way to go with DDS is to use software in a
PC to drive one or two D/A convertors. Where the D/A chips are
external to the PC and in the radio. Simply interfaced to the PC in
the back. Complexity then is a matter of the software and not so much
the hardware in this approach. Still filtering of the output and the
use of traps are required. Overall parts are minimized and this then
is the SDR approach since here I am talking of mostly using software in
place of hardware. {Feasibily, well, someone here will make comments
on the feasibility and we will better know!}
The D/A chips then need to be high speed CMOS devices if there is to
be some use in the RF regions. If however there are only widely
available devices that will work resonably well in the kHz regions at
best then multiplication of the RF upwards in frequency will be
required after the D/A section. Which will widen phase noise and
jitter with multiplication.
I am however sure someone is expert enough on D/A specs to let us
know what RF region devices are available for use. Being there are
already many instances of mostly hardware types of DDS systems. And so
there should be some good parts available. Mostly hardware also means
that these systems may include their own onboard micro processor such
as in the Intel 8000 series or other micro processors that might be
found in radios. Since these ideas are bit driven schemes.
Here the micro processor is the PC.
ka9rza
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