<HTML><HEAD></HEAD>
<BODY dir=ltr>
<DIV dir=ltr>
<DIV style="FONT-SIZE: 10pt; FONT-FAMILY: 'Arial'; COLOR: #000000">
<DIV>Hey Graham,</DIV>
<DIV>You are correct that the schematics have not been released, which is one
concern of mine. There have been partial diagrams released, but not enough
to understand everything involved. Some people have also taken high
resolution pix in order to help reverse engineering, although with a multi-layer
board that’s not easy! I notice that the 1M input impedance spec also
shows the higher-voltage input (+/- 20V max). I wonder if you put it in
lower max voltage range (4V IIRC), what that does to the input impedance.
The output impedance of the DAC section is 50 ohms, so no transformation
required there.</DIV>
<DIV> </DIV>
<DIV>As far as I know, nobody has modified the RP hardware in any way so
far. There has been an ongoing discussion regarding changing the sample
clock oscillator from 125MHz to 122.88MHz to simplify interfacing the audio
samples. I wish that there was a schematic available, as I would also like
to remove the low-pass filter, so subsampling could be done with the RP. </DIV>
<DIV> </DIV>
<DIV>I performed some initial tests a while back, and found that the RP can be
VERY SLIGHTLY less sensitive than other SDRs. Another preamp may be enough
to fix that for the most demanding usage. I think it already has a
6400/6405 or similar buffer in front of the ADC inputs. It certainly
performs similar to other 14-bit SDRs, such as the HiQSDR. I need to
compare it again to my SDR-IQ. I don’t see 20dB difference by any means,
with a good (R&S) signal generator. The RP has already been used on
the air for digital modes on 20M I think. It probably won’t perform as
well as a Hermes or Mercury, but should be at least as good (generally) as the
Hermes-Lite.</DIV>
<DIV> </DIV>
<DIV>BTW, the RP seems fine for 1.8MHz and higher, but has some spurs at 474kHz
and lots of them at 137kHz. My testing was with an RP sitting out in the
open and their (noisy) wall wart. Using a clean 5V supply and putting the
RP in a metal box would clean that up to a large degree.</DIV>
<DIV> </DIV>
<DIV>It would be nice to perform more serious testing on the RP. I have
some of the test equipment, but lack the time right now. I have committed
to do some transmit testing in the near future – likely after the first of the
year.</DIV>
<DIV> </DIV>
<DIV>I still think that for the price, it’s very hard to beat. Especially
with the combined FPGA/ARM fabric of the Zynq chips. I realize that most
people here are in the Altera camp, but I’ve played a little with Xilinx, and
with people like Pavel working on it, the learning curve is somewhat less.
Pavel is actively interested in furthering his efforts related to SDR
activities, and very open to suggestions and working with others.</DIV>
<DIV> </DIV>
<DIV>73, Terry, N4TLF</DIV>
<DIV> </DIV>
<DIV style="TEXT-DECORATION: ; FONT-FAMILY: ; COLOR: ; DISPLAY: inline">
<DIV style="FONT-FAMILY: ; LINE-HEIGHT: normal">
<DIV><FONT style="face: arial"></FONT><FONT
face=Tahoma></FONT> </DIV></DIV></DIV>
<DIV
style='FONT-SIZE: small; TEXT-DECORATION: none; FONT-FAMILY: "Calibri"; FONT-WEIGHT: normal; COLOR: #000000; FONT-STYLE: normal; DISPLAY: inline'>
<DIV style="FONT: 10pt tahoma">
<DIV> </DIV>
<DIV style="BACKGROUND: #f5f5f5">
<DIV style="font-color: black"><B>From:</B> <A title=ke9h.graham@gmail.com
href="mailto:ke9h.graham@gmail.com">Graham / KE9H</A> </DIV>
<DIV><B>Sent:</B> Thursday, December 17, 2015 2:38 PM</DIV>
<DIV><B>To:</B> <A title=tfox@knology.net href="mailto:tfox@knology.net">Terry
Fox</A> </DIV>
<DIV><B>Cc:</B> <A title=hpsdr@lists.openhpsdr.org
href="mailto:hpsdr@lists.openhpsdr.org">HPSDR</A> </DIV>
<DIV><B>Subject:</B> Re: [hpsdr] FW: SBC Inforce 6410</DIV></DIV></DIV>
<DIV> </DIV></DIV>
<DIV
style='FONT-SIZE: small; TEXT-DECORATION: none; FONT-FAMILY: "Calibri"; FONT-WEIGHT: normal; COLOR: #000000; FONT-STYLE: normal; DISPLAY: inline'>
<DIV dir=ltr>
<DIV>
<DIV>
<DIV>Terry:<BR><BR></DIV>The inputs on the standard "Red Pitaya" are
oscilloscope probe inputs, and have about 20 dB loss with respect to a properly
designed receiver direct input for the data converter. <BR><BR>Are the groups
using the "Red Pitaya" as a receiver modifying the hardware? <BR><BR>I was
not aware that Red Pitaya's manufacturer had released schematics, so it would
have to be a reverse engineering effort.<BR><BR></DIV>Thanks,<BR></DIV>---
Graham / KE9H<BR><BR>==<BR></DIV>
<DIV class=gmail_extra>
<DIV><FONT size=2
face=Arial></FONT> </DIV></DIV></DIV></DIV></DIV></BODY></HTML>