[hpsdr] [Bulk] Re: Fwd: PSDR 3.3.7, TX problem Pure Signal

[Joe Martin]

Hi George, 

1)  To definitively test Diversity functionality on your radio you should should remove your antenna connections and instead use an external signal generator that is connected to both the Ant1 and RX2 connectors (use a tee, no need to put a splitter into the sig gen line for this test).  With that done and diversity mode activated (i.e., GREEN backcolor on the Enabled button in the Diversity control window) you should be able to find a deep null by alternately using the wheel on your mouse on the gain and phase controls to quickly find the null.  

If instead you use the radar-style display the relative gain settings between the two signals need to be relatively similar in gain.  For example, if you have, say, a 10dB difference (i.e., x10 difference in signal levels) in signal level between the two signal levels the radar-style display may not provide enough gain for the non-reference channel (length of the line in the radar display) relative to the reference channel to be able to cancel/null the total signal output.  One way to test whether this is the problem with your testing is to switch the reference channel to the other signal, in which case you will find a null condition where the length of the line in the radar display is very short relative to the outer rim of the radar display.  When using the other reference channel the radar display will not allow you to adjust for positive gain beyond the limit of the graphical display.  The gain control itself, however, will allow you to apply higher gains than does the radar display.  

In such cases that have very different signal levels on the two channels you can, if you wish, use attenenuators on the stronger of the two signal to equalize the levels then things will work as you expect.  But in practice no external attenuators are actually necessary because by using the controls in the Diversity window you have a huge amount of gain adjustment for the non-refernece channel by using the independent gain control rather than the radar display control.  In cases where addition gain or attenuation is needed and you’d prefer to use the radar control you can usually switch the reference channel to the other channel and find the null.  

2) The fact that you can obtain a null when using the same ADC for both channels is a consequence of the relative phase adjustment process in the software program.   In the software program (HPSDRPowerSDR)  the relative phase of the two channels is adjustable, digitally.  Thus, when identical signals are applied to the two inputs to the radio the Diversity controls still allow you to shift the phase of the non-refernece channel relative to the reference channel internally within the software program.  If the two input signals have identical amplitude and phase at the input of the radio, as would be the case if you select the same ADC for both channels as you described,  the Diversity controls allow you to adjust the relavtive phase of the non-reference channel to become180 degrees out of phase with respect to the reference channel a null in the combined output will occur.   

A fundamental concept to understand with diversity nulling is that one signal cannot completely null another (even if it is exactly 180 degrees out of phase) unless the two signals are of exactly equal strength when they are combined in the Diversity module.  That fact is why there is an amplitudce adjustment control in the Divertsity control window, to allow you to adjust the signals to be exactly the same strength in the Diversity modle.  That is why I suggested above that you should test the diversity function with the same signal applied to both channels if you think the feature may not be working on your radio.  

I hope this information helps you discover what may be happening on your particular systems with your various antennas.  My guess is that the two signal paths your are using are widely different in gain, so judicious selection of which one to use as the reference channel may be more important in your case when using the Diversity feature in HPSDRPowerSDR than in some other peoples cases.  

73, Joe K5SO

On May 15, 2016, at 11:33 AM, George wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi Joe,
> I have a A200D with a Log periodic connected to ANT1 and a Pixel Loop to RX2 and when I move the control around the circle I see very little change in signal strength or noise levels.  I am using the same versions of HPSDR and Orion as you and checked to make sure RX1 was set to ADC1 and RX2 to ADC2.  I have also tried using a 43' vertical connected to RX2 with the same results as above and noted by Bill.  
> 
> I had one of the early A100D and I remember that it work well in diversity mode.  I have owned this A200D now for at least two years and have never been able to get diversity to work.  Not sure what I am doing wrong since the setup is fairly simple.  By the way RX2 works when it is enabled and I can see the same signals that are on RX1 except at a lower level using the loop.  
> 
> The green enabled button is on.
> 
> As an experiment I set RX2 to ADC1 and left RX1 to ADC1 and I see a significant null on the band noise level as I move around the control circle.  This is the first time I tried this setup.  Why would this work with RX2 set to ADC1?
> 
> Let me know what you think I am doing wrong or if you want me to try another setup.
> 
> 73, George
> W2GS