Re: [Discuss-gnuradio] SDR Radio Telescope Receiver

[Patrik Tast]

Hi Jeff,

I'm interested to learn about Joe's hydraulic antenna pointing system.
Do you know how he handles the feedback, ie what kind of sensors
is he using to "know" the antenna position?

At the moment we're trying to use Pololu Jrk as a low cost motor control 
with feedback
http://www.pololu.com/catalog/product/1393
and
http://www.pololu.com/catalog/product/1392

Patrik



----- Original Message ----- 
From: "Jeff Kelly" <address@hidden>
To: <address@hidden>
Sent: Saturday, January 29, 2011 20:39
Subject: Re: [Discuss-gnuradio] SDR Radio Telescope Receiver


> I have been working with Joe K5SO on the OpenHPSDR project
> using two Mercury receivers for diversity reception.  I mention
> Joe because he is using his system for Radio Astronomy:
> Perhaps there would something on his site.
>
> http://www.k5so.com/
>
> Jeff
> K2SDR
>
>
> -----Original Message----- 
> From: Marcus D. Leech Sent: Saturday, January 29, 2011 12:52 PM To: Phil 
> Behnke ; address@hidden Subject: Re: [Discuss-gnuradio] SDR 
> Radio Telescope Receiver
> On 01/29/2011 12:37 PM, Phil Behnke wrote:
> > Thanks for the tips!  I'm definitely going to investigate hooking the
> > ADC directly to the FX2.  Looks like there are some inexpensive dev
> > boards for the FX2 on ebay, although I have no idea how good they are.
> >  I figure I will try to develop the receiver to always grab 1MHz worth
> > of bandwidth, and then give the user finer filtering abilities by
> > using digital filters on the PC side.
> That's probably a reasonable approach.  The FX2 is actually a
> fairly-capable chip.  It's used in the
>  USRP1 from Ettus Research, which can "pump" upto 16Msps(complex,
> 8-bit) over USB-2.0,
>  so 1Msps should be more than doable.
>
> You have to make certain that your I and Q lines are low-pass filtered,
> fairly stiffly, prior to sampling.
>  If you're sampling at 1Msps, the I and Q lines need to be low-pass
> filtered to 500KHz.  There's a nice
>  passive-filter designer on-line at:
>
> http://www.wa4dsy.net/filter/filterdesign.html
>
> I've used it for other radio astronomy projects in the past
>
> Other things to keep in mind:
>
>    o you'll need enough low-noise gain ahead of the down-converter to
> make up for the
>       *terrible* noise figure that's typical of mixers and ADCs.  At
> HF, in radio astronomy, you'll
>       probably need about 50dB.
>
>    o You'll need a good bandpass filter at RF.  Again, the
> above-mentioned site should help here.  A
>        good approach is to use a amp-filter/amp-filter/amp-filter
> topology, which gives you distributed gain
>        and filtering, and makes the individual filter stages
> manageable.  If you designed your bandpass
>        RF filter for an Fc of 20Mhz, and bandwidth of 5Mhz or so, it'll
> improve your usable dynamic
>        range, and prevent driving your gain stages into compression,
> due to "other muck" that your
>        antenna will inevitably "see".
>
>
>
>
>
> --
> Principal Investigator
> Shirleys Bay Radio Astronomy Consortium
> http://www.sbrac.org
>
>
>
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