[hpsdr] Diversity - OpenHPSDR mRX PS v3.3.6

[Warren C. Pratt]

Hi Barry,

There was a bug sometime ago where RX1 and RX2 were not always getting 
set to the same DSP buffer size ... that would of course cause this kind 
of effect due to the differences in delay.  However, I recall that we 
fixed that, AND, that would not explain the timing difference changing 
after a transmission.

That all said, there is nothing in the software that would explicitly 
guarantee that RX1 and RX2 would produce their output at exactly the 
same time.  Their processing is independent and, to an extent, it 
depends upon when Windows wakes up their processing threads.  I think 
that may be what you're hearing.

This is of course very different for "pure Diversity" where the buffers 
of samples are mixed on a single thread and the result then passed to 
the RX1 receiver channel in the DSP.

73,
Warren  NR0V

On 12/8/2015 7:49 AM, Barry N1EU wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> I use the Stereo Diversity function, not pure Diversity, and I often
> observe a sudden anomalous introduction of a phase shift between the
> receivers which is usually (not always) subsequently corrected after a
> xmsn.  I've been observing this in all versions of OpenHPSDR mRX PS
> since v3.2.23 added the Stereo Diversity "SD" feature.
>
> Barry N1EU
>
> On Tue, Dec 8, 2015 at 10:42 AM, Joe Martin <k5so at k5so.com> wrote:
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Hi Jim,
>>
>> Very interesting report.  In my initial investigation I see that with either HPSDR PowerSDR mRX PS v3.3.6 or HPSDR PowerSDR mRX PS v3.2.27 (probably others as well) a random phase shift is introduced between the two IQ streams if the RX2 button is activated any time after diversity mode has been opened/closed/reopened.
>>
>> As long as the RX2 button is not cycled (diversity mode off) the phase relationship between the two diversity IQ streams is maintained regardless of whether PowerSDR is shut down and restarted and/or the hardware is powered off (for at least 15 seconds!) and restarted.  The deep null settings are identical in these cases.
>>
>> Contrary to your stated process for bringing up diversity mode, you should NOT need to cycle the RX2 front panel button at all.  In fact, it seems that cycling the RX2 button introduces a random phase shift.  I will investigate this further but the issue does not appear to be associated with the new HPSDR PowerSDR version exclusively but rather seems to be associated with the use of the RX2 button on the front panel in between running sessions in diversity mode.
>>
>> To bring up diversity mode you need only power up HPSDR PowerSDR then click on the Diversity tab on the front panel, no use of the RX2 button should be required whatsoever; indeed, it appears that using RX2 before enabling diversity mode introduces a random phase shift between the two IQ streams, the source of which, admittedly, we need to understand.
>>
>> Hope this observation helps you in the short term.
>>
>> 73, Joe K5SO
>>
>> On Dec 7, 2015, at 8:38 PM, Jim Barber wrote:
>>
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>> A bug confirmation, I don't remember the original poster.
>>>
>>> PowerSDR mRX PS v3.3.6
>>> Anan 100D
>>> Windows 10, AMD 1090T (6-core, 3.4 gHz)
>>>
>>> To operate diversity here at least it's necessary to first:
>>> (1) Set RX2 to ADC2 if not already
>>> (2) Turn RX2 on, then off
>>> (3) Enable Diversity
>>>
>>> It also seems that the the phase angle between receivers changes between program runs. IOW, if I null a noise source then close PowerSDR and reload it, the best null may be at a different phase angle.
>>>
>>> I enjoy diversity a lot, since most of my operation these days is evenings on 160M. Without it, 160M is basically useless between power noise, plasma TV's and the like.
>>>
>>> Thanks and 73,
>>> Jim N7CXI
>>>
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