Software Defined Radio on Xilinx Virtex 4

Let me right again in this forum on the same topic. But know in
English. Whatever my English is very poor.
I am working for about 4 month's ego with an ML405 Xilinx Virtex 4
board and I wanted now to implement a Software Defined Radio (SDR).
I understand everything that relates to SDR (theory, operation,
Etc..) Very good. Likewise, I also understand VHDL and VERILOG.
Now I would like to know if someone is thus also employs
An SDR Board on the above (or others) to implement appropriate
Experience exchange.

In following a detailed overview of what I Made now:

First, I strive times only to receive an AM signal.

Hardware is on the board as much: DA converter (LM4550)
National and an external A / D converters (LTC2208) by Linear
Technology. I have prepared all software developed
(ADC.vhd, DAC.vhd, DDC.vhd ,...)I make already the simulation. Now, I
must try my signals: and with a
Function generator, I would like to generate a sine wave, and then the
sine wave through the FPGA with the process by the AD and DA
converters. I Am suppose to have the same signals again after the

Sine (1Khz) ----> ADC -> FPGA ---> DAC ---> sinus (1Khz)
I can hear something (signal) at the output (by the DA converter) with
Headphones. However, I cannot measure it with the oscilloscope.
I had already tried without much success, and ask what the problem
Lie? Whether it down sampling, or rather in a
Clock functions?

Did someone get an idea or a tip for me?

I look forward to all suggestions and thank you in advance...