[hpsdr] Hermes transmit baseband frequency reversal ?

[Tom McDermott]

Thanks for the quick response, Phil.

Easy two-line code change to the gnuradio HermesNB software module
to flip the I and Q symbols in the output stream.

Have posted the revised source compatible with Gnuradio 3.7 to the TAPR SVN.


http://svn.tapr.org/repos_sdr_hpsdr/trunk/N5EG/GRC3.7/gr-hpsdr

-- Tom, N5EG


________________________________
 From: Phil Harman <phil at pharman.org>
To: Tom McDermott <tom.mcdermott4 at yahoo.com>; hpsdr at lists.openhpsdr.org 
Sent: Thursday, March 13, 2014 4:27 AM
Subject: Re: [hpsdr] Hermes transmit baseband frequency reversal ?
 


Hi Tom, 
 
It’s not a bug, its a feature.  In order to get the correct sideband
out of the CORDIC used in Penelope many years ago I needed to swap the I&Q
inputs.  I guess PowerSDR had them reversed since day one and its been
carried forward ever since. 
 
Not game to change at this late stage.....
 
73 Phil....VK6PH 
 
From: Tom McDermott 
Sent: Thursday, March 13, 2014 6:26 PM
To: hpsdr at lists.openhpsdr.org 
Subject: [hpsdr] Hermes transmit baseband frequency reversal
?
 
*****
High Performance Software Defined Radio Discussion List *****


________________________________
 
 
HI,
 
In
playing with some gnuradio sources, I am getting a baseband frequency reversal
going through Hermes.
This
using the definitions for I and Q in the HPSDR USB protocol document (ver
1.43).

That
is - a downward frequency chirping IQ baseband signal into transmit causes an
upward chirping
IQ
baseband signal at the receive output.
 
It
appears that the transmit I & Q side is doing the reversal, while the
receiver seems to be normal, by testing this with an external SSB receiver, and
by using various gnuradio instrumentation.

 
In
looking through my own code that formats I & Q into the transmit frame, I
cannot seem to find any
deviation
from the protocol specification (rev 1.43).  Do I have a bug in my code, or
is there a known 
issue
with Hermes that causes the frequency sign inversion on transmit?
 
--
Tom, N5EG
 
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