[hpsdr] SDR-1000 /Janus TX noise sidebands

[Al]

In an attempt to suppress the high freq noise, I constructed an RC 30 
Khz low pass filter to insert in the TX I & Q lines. The exact corned 
freq is a bit unknown since it is dependent on the the output impedance 
of the ADC in Janus. 
Attachment one, 'RC Low Pass_', is the low pass filed which plugs into 
the back of the SDR-1000.  ( 560 ohm series R, .01 uf shunt C )
Attachment two, 'SDR TX Janus w filter_' is the spectrum of the SDR 
output with the filter installed ( 1 Mhz per horizontal division ). 
Compare to 'SDR TX W-Janus_' in original message.
Attachment three, 'SDR TX Janus w Filter_1' is the same except the scale 
is 50 Khz per division.

The TX spectrum of D44 is also improved with the low pass filter.

  This is only to suggest that improvements in the TX spectra are 
possible.  Further refinement of the low pass filter is required. Items 
for consideration include but not limited to sound device output 
impedance,  SDR-1000 input impedance, component tolerance ( for 
phase/gain tracking), optimum corner frequency (it may need to be higher 
for AM/FM modes which are generated at an offset from the DDS frequency ).

AL, K0VM
-------------- next part --------------
A non-text attachment was scrubbed...
Name: RC Low Pass_.jpg
Type: image/jpeg
Size: 18005 bytes
Desc: not available
URL: <http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/attachments/20070630/d41ebe72/attachment-0012.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: SDR TX Janus  w filter_.jpg
Type: image/jpeg
Size: 19991 bytes
Desc: not available
URL: <http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/attachments/20070630/d41ebe72/attachment-0013.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: SDR TX Janus w FIlter_1.jpg
Type: image/jpeg
Size: 20779 bytes
Desc: not available
URL: <http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/attachments/20070630/d41ebe72/attachment-0014.jpg>