hi,
for some simple experiments I want to build a simple
transceiver which works with a soundcard line-in/out.
My current target communicates at 25 kHz with on-off-keying
at a rate of 1600 Hz, but for future experiemnts I want
a RF-Frontend for from 20 kHz up to at least some Mhz (the more
the better).
As I understand it I need a circuit which schematically
looks like this:
____ _______ __________
| \_ | | | |
/---*-->| AMP |-->| Mixer |---->| Low-Pass |------> Line-In
| ^ | __/ | -> | | Filter |
| | |__/ |_______| |__________|
| | ^ ___________
C | | | |
o | *<---| Frequency |
i | | | Generator |
l | | |___________|
| | ___v___
| | | |
| \---------<----| Mixer |<----------------------- Line-Out / Speaker
---- | <- |
-- |_______|
(common Ground)
(roughly resembling http://en.wikipedia.org/wiki/Image:Superhet2.png)
my questions are:
- does this design make sense? Did I leave out an important Stage? (some
more Amplifier?)
- which ICs should I use for which Block?
- is an OpAmp good enough as RF Amplifier?
- is an passive Low-Pass filter ok?
- for the mixers: TCA440 or NE612 or something different?
- for the local Oscillator: I want something adjustable either
via poti or electronical if I can interface it to a Computer
somehow.
- ideally I want to use this circuit with my laptop, but where should
I draw power from?
thanks for your time & cu,
Maurice Massar
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