Re: [Discuss-gnuradio] SDR Radio Telescope Receiver

[Marcus D. Leech]

> Hello All,
>
> I'm currently an undergraduate engineering student at Grand Valley 
> State University.  For my senior design project, I'm working on 
> designing a SDR-based radio telescope to compliment the NASA RadioJove 
> project (a direct conversion receiver for use in radio astronomy).
>
> In a nutshell, the receiver must be able to receive an AM signal with 
> a center frequency of 20.1MHz and a bandwidth of 1MHz.  On the 
> software side of things, we need to be able to plot signal strength as 
> a function of time and frequency in real time.  We are planning to use 
> analog mixing to get an IF centered around 500kHz and 1MHz bandwidth. 
>  The IF would then be sampled that with a 14-bit ADC clocked around 
> 4MHz.  The output of the ADC would then be sent to some kind of 
> controller (ie. FPGA, microcontroller, etc) which would do a little 
> bit of digital down converting to get the signal into its I and Q 
> centered around DC and send it over USB to the host PC.
>
> While I am not completely against using an FPGA in the design of our 
> receiver, I would really like to use a fast microcontroller, PSoC, or 
> similar device as I have much more experience programming in C than I 
> do in HDL.  Has anyone hear of a SDR receiver with 1MHz bandwidth 
> using a microcontroller?  I was thinking along the lines of using a 
> ARM Cortex M3 chip with high clock frequency (~80MHz), DMA, and 
> external ADC clocked around 4MHz, but I'm not sure if the ARM chip 
> would be fast enough to down convert all that data and send it over 
> USB quickly enough.  If anyone has links to resources where this kind 
> of thing has been done that would be awesome.
>
> I'm very new to SDR development so any input would be greatly appreciated.
>
> Thanks!
> Phil
A few comments:

check out the gr-radio-astronomy sub-tree.  It's old, but should still 
function.

What you might consider doing, if you're committed to building your own 
hardware, is a direct-conversion receiver, perhaps with a fixed
  LO at 20.1MHz, and then sample with a 1MSps ADC, feeding an FX2 for 
USB-2.0.  No need for an FPGA, provided you never want to
  change sample rates before the signal gets to the host PC.

The FX2 uController/USB-2.0 interface is very common, very inexpensive 
hardware, and has a nice FIFO interface that's easy to interface
  to ADC hardware.

Another thing to keep in mind, is that your *usable* bandwidth around 
20.1MHz is likely to only be a few 10s of KHz, due to lots of
  interference down there.  So your 1MHz bandwidth may be utterly wasted.

For narrowband stuff, you might consider something like the SoftRock 
series of direct-conversion receivers, or the UHFSDR.
  The UHFSDR tunes from DC to 700MHz, and gives a 96KHz 
bandpass--perfect for audio.  Combine the UHFSDR with the SDR-Widget,
  and you have a pretty-complete narrowband platform.




--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org