RE: [linrad] SDR Hardware

[Giancarlo Moda <i7swx@xxxxxxxxxxxxx]

The problem with direct conversion receivers is that
all the gain is at audio frequencies.  
Why not to try a single conversion receiver where the
gain is equally distributed between IF and audio?

73
Gian
I7SWX
F5VGU

--- Robert McGwier <rwmcgwier@xxxxxxxxxxx> wrote:
> The R2Pro or the SDR-1000 are both good ways to do
> some software defined
> radio.
> I will point out again for you a design flaw in the
> SDR-1000 that I pointed
> out a few
> days ago here, maybe you missed it.  The INA's, the
> instrumentation
> amplifiers,
> provide most of the SDR-1000 system gain.  They are
> AFTER the sample and
> hold,
> mixer (which some call the Tayloe Detector, Gerald
> calls the Quadrature
> Sampling
> Detector).  This means that the signal of interest
> from the antenna is added
> to the
> phase noise and spurs and thermal noise of the QSD
> before the signal is
> amplified.
> It is clear that this is wrong to have all of the
> gain after.  You have
> competing
> interests here: linearity and noise figure.  If you
> move all of that gain
> out in front
> of the mixer, then the demands on that
> preamplifier/front end become quite
> demanding since it must operate from 0 to 75 Mhz and
> be very linear with
> good
> IP3, etc.  My current best mix is 20 dB out front
> with 6 dB after using a
> GALI-6
> in front of the mixer.  This was recommended to me
> by Mike Cresap, W3IP
> and it has been a good performer.
> 
> With the R2Pro, there is more hardware hands on to
> do:
> 
> http://www.seboldt.net/k0jd/
> 
> and with the SDR-1000, after the dust settles on
> re-doing the front end, and
> possibly adding better filters for ham band
> coverage,  all the work is
> software.  Currently, all of the work going on on
> the SDR-1000 outside of
> a couple of people is being done in the software
> arena.
> 
> http://www.flex-radio.com
> 
> and I suggest you join the forum and see all of the
> musings, etc.
> 
> 
> http://www.flex-radio.com/forum
> 
> In addition to this, Gerald's resource page is very
> helpful.
> 
> Also, the DSP-10, with the recent additions by Lyle
> KK7B make for very
> interesting SDR work:
> 
> http://www.tapr.org/tapr/html/kitsf.html
> 
> and the top three listings are for the DSP-10 and
> the KK7B DSP add on
> module.
> This same module is the new DSP module that Elecraft
> is offering for the
> fabulous K2.
> 
> GnuRadio
> 
> ( http://www.gnu.org/software/gnuradio/gnuradio.html
> )
> 
> and the upcoming USRP (Universal Software Radio
> Peripheral)
> 
>
http://mail.gnu.org/archive/html/discuss-gnuradio/2003-08/msg00062.html
> 
> 
> 
> 
> It is a very exciting time for receiver work in ham
> radio with Linrad, SDR,
> GnuRadio
> are really changing the way we think about receiver
> work and homebrewing
> receivers.
> 
> For my money, having done all of the above, the
> potential for the QSD
> (Tayloe
> detector) is extremely large.  The numbers I can
> measure in the lab tell me
> that with careful design work, this can be the basis
> for the greatest
> receiver
> in all numbers.
> 
> Bob
> 
> 
> 
>   -----Original Message-----
>   From: owner-linrad@xxxxxxxxxxxxxxxxxxxxxx
> [mailto:owner-linrad@xxxxxxxxxxxxxxxxxxxxxx]On
> Behalf Of J. Michael Thurman
>   Sent: Friday, December 12, 2003 7:47 AM
>   To: linrad@xxxxxxxxxxxxxxxxxxxxx
>   Subject: [linrad] SDR Hardware
> 
> 
>   Greetings.  I have been reading the list for a
> while and am excited about
> the possibilities presented by sdr.
> 
>   I have read the recent QEX articles on sdr and
> many others on the ARRL sdr
> page.  My question is this: what is a your
> recommendation for a homebrew SDR
> hardware platform?  I can use the designs Leif
> presents and the design for
> the SDR-1000 as a basis...but I really want some
> more thought from those of
> you who have the system running before I dig in.  
> Most of my operating is
> HF SSB, CW, and PSK.
> 
>   73
>   Michael
>   WN5T
> 


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