[hpsdr] [Flexradio] Strange Janus effect

[Gerd Loch]

I confirmed this behaviour before but never heard any comments.
Had not the time to make any investigations. 
I tried to reproduce this effect last night with svn1644 and could not hear
it but it was just a quick test and maybe not representative.

Gerd
DJ8AY

-----Original Message-----
From: flexradio-bounces at flex-radio.biz
[mailto:flexradio-bounces at flex-radio.biz] On Behalf Of a.groff
Sent: Thursday, October 11, 2007 6:47 PM
To: hpsdr at lists.hpsdr.org; flexradio at flex-radio.biz
Subject: [Flexradio] Strange Janus effect


On Aug 30 I posted to the HPSDR mailing list
-------------------------------------------------------------------------

Subject: [hpsdr] Strange Janus effect...

***** High Performance Software Defined Radio Discussion List *****

I am noticing a strange cross-talk ( ?? ) effect with Janus (& OZY ? ) when
used with SDR-1000 & PowerSDR  (v1.9.1 svn 1354, v1.10.2 ) that I do not
notice with the D44 sound card...

I notice this effect in the receive audio when I start to decrease the AGC-T
( RF Gain ) control in Power SDR.  As the received signal starts to
disappear from audibility, it is replaced by very distorted replica at a
reduced amplitude.  The effect was first observed in SSB modes but is also
present it AM mode ( maybe more so. )

Does you one else have this effect or do I have a problem with my
Janus/Ozy/system ??  How would I start to isolate the problem?

AL, K0VM
-------------------------------------------------------------------------

I received a couple of affirmative response and no "don't see it here's".

I have uploaded spectrum analyze screen shots of the speaker/head phone
audio that further demonstrate the problem.. ( SDR-1000 w/PwrSRD 1.10.3)

The first screen shot *http://www.hamsdr.com/dnld.aspx?id=676 *is with the
D44 sound ( preamp off, antenna connected to dummy load AGC-T = 120). Note
noise floor above 3khz.

The second screen shot *http://www.hamsdr.com/dnld.aspx?id=677 *is with the
Janus sound card and AGC-T=120. Note elevated noise floor above 3khz.

The third screen shot *http://www.hamsdr.com/dnld.aspx?id=678* is Janus with
AGC-T=100. Note again noise floor above 3khz compared to AGC-T=120.

The fourth screen shot *http://www.hamsdr.com/dnld.aspx?id=679   *is Janus
with AGC-T=70. Note noise floor through entire audio range.

With the D44 sound card, the noise floor about 3khz is consistently flat
with all AGC-T settings.

My first guess was that this may be a Ozy/Janus hardware problem but to the
best of my knowledge, AGC-T only operated on software, which suggests to me
that some kind of cross talk problem in the software specific to Ozy/Janus.

I would be happy to isolate this with further testing if someone can suggest
what to look for ??






 
 








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