RE: [linrad] SDR Hardware

[Giancarlo Moda <i7swx@xxxxxxxxxxxxx]

Bob,

thanks for the clarification.

I downloaded the articles by AC5OG, regarding the
SDR1000. I went though all four witha "fast
eye"...need more time to digest it....hi!

The title is certainly ok for the "Masses" of PC users
and not the "ancient" ham still at analog and just a
bit at digital technology,like me.
It is an interesting design. There is a lot of work
for the PC and its audio card. The Hardware is
certainly not much if we confront it to commercial or
othe homebrew design.

I can see that the first conversion has no protection
from the antenna signals except for what the input BPF
can provide. I expect there is a lot of work for the
PC to do filtering.

I see there is a gain distribution between the first
conversion analog gain and the second conv digital
gain (<40-60 at low signals). from Table 8 I can see
how the gain is changing in both stages.
Certainly, demanding most of the activities to the
software the system become quite flexible. 
As this world is not perfect, I believe there is no
perfect receiver. We have always to compromise.

It would be interesting to see if there could be a
worstening or improvement adding a first classic
analog conversion to the SDR1000, with IF around 9MHz,
using the H-Mode Mixer (G3SBI or I7SWX config IP3 =<
+40dBm). In this case a 9MHz xtal filter,3kHz or less
bw) would be the roofing filter, properly matched /
terminated (input with a diplexer). An IF amplifier
could follow with a gain between 12 to 20dB (W7AAZ
JFET IP3 => +35dBm). Then, the quadratic sampling
mixer, as it is now, with a lower IF gain (30-20 dB)on
the ULNOPA. This solution will certainly add more
complexity and electronics to the actual simplicity of
the SDR. It could be a compromise with a possible
improvement in noise and spurs...all to be
domonstrate. 
The amplifiers of 1st and 2nd IF will amplify the
noise and signals going through the roofing filter.
The sound card and PC will have to work "lighter" to
reduce not desired signals and their "energy" used for
other improvements.

BTW, I have seen some notes on the Tayloe mixer. 
I believe Tayloe had an improvement on his mixer
following my idea to use Fast Bus Switches to replace
the SD5000 in the G3SBI H-Mode Mixer (beginning of
1998). He was able to replace the 74HC4052 with the
FST3253 (2001).
I also read the comments of the originality or not of
Tayloe's mixer. From my point of view, a similar
circuit was used by Chris Bartram, G4DGU, on a SSB
generator for a "third method" exciter. The switches
were CD4016, to get the 90 degrees phasing, driving
active filters (I & Q equivalent). The digital
phase-shifter was a CD4027 2 x JK ff. This idea was
published in Radio Communication, Technical Topics,
(RSGB)November 1975, nearly 30 years ago.

If someone is interested on it, I could scan the page
and e-mail it (is it possible to distribute it as a
file attachment to the group?) 

This comment of mine is an idea. We can always learn
from ideas or mistakes.

73

Gian
I7SWX

--- Robert McGwier <rwmcgwier@xxxxxxxxxxx> wrote:
> Hello Gian:
> 
> The R2Pro and SDR-1000 do not have "all that gain"
> at
> audio.  The SDR-1000 is a a dual conversion receiver
> with the last IF at 11025 Hz and the last mixing
> done
> digitally.
> 
> Bob
> 
> -----Original Message-----
> From: owner-linrad@xxxxxxxxxxxxxxxxxxxxxx
> [mailto:owner-linrad@xxxxxxxxxxxxxxxxxxxxxx]On
> Behalf Of Giancarlo Moda
> Sent: Friday, December 12, 2003 10:31 PM
> To: linrad@xxxxxxxxxxxxxxxxxxxxxx
> Subject: RE: [linrad] SDR Hardware
> 
> 
> 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
> > 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
> 
> 
> 


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