Re: [Discuss-gnuradio] AM receiver

[michael taylor]

On 10/31/05, michael taylor <address@hidden> wrote:
> On 10/31/05, Gituma Nturibi <address@hidden> wrote:
> > I'm back again with a few questions about GNU radio. As I had said earlier I
> > was thinking about creating an Fm receiver. However cost and complexity
> > considerations have made me think about trying AM reception instead. Taking
> > into account I'm based in Kenya so shipping would be an issue and a budget
> > of about $120, very small!
> > The problem is that I'm on a tight time schedule and require to get the
> > project up and running soon. So I would like to know what is the best I can
> > achieve using a PC sound card or some other cheap ADC board.

Sounds like you want a SoftRock-40, unfortunately the kits are gone.
The kits were something like $28 USD.

<http://www.amqrp.org/kits/softrock40/>

QUOTE:
  The hardware downconverts and quadrature samples a 48 kHz swath of
RF that is fed to the soundcard of the computer.  Referring to the
block diagram shown below, a crystal-controlled oscillator generates a
28.224 MHz reference signal that gets buffered and divided in half
twice to produce reference clock frequencies at 14.112 MHz and 7.056
MHz.  These clocks are fed to a simple-yet-effective circuit called a
Quadrature Sampling Detector, or QSD for short, which samples the
bandpass-filtered RF signal coming in from the antenna.  As a result
of the sampling, the QSD outputs two signals at audio baseband
frequencies representing the downconverted RF signal, where the two
signals have the same frequency components but are related in
quadrature to each other, meaning they have a 90°  phase difference. 
The in-phase signal 'I', and quadrature signal 'Q' are amplified and
are then delivered as audio input to the line-in input on the PC for
processing ...

Perhaps you could build your own from the schematic. Most of the parts
are not exotic (74HC74, LT1719, OPA2228, and FST3126) and available
from sources like Digikey, Mouser, and Farnell.

Don't know if that is of any help, but maybe it is of use to you.