[Discuss-gnuradio] Building a RF-Frontend

[Maurice Massar]

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