[hpsdr] caution with cal routine

[Joe Martin K5SO]

Hi Helmut, 

RRR, yes, you are correct. 

First thing to realize about the PA Gain Calibration routine is that it doesn't achieve its calibration by starting high and sucessively stepping lower in output power until calibration is achieved, nor does it start low and incrementally step toward a higher value, as one might expect such a routine to do.  Rather, no matter what value you have set in the PA Gain calibration window for the band to be calibrated is (even a max power output value of 38.8), the routine will start at a low value initially and from that measurement it takes a giant step to correct toward the final value.  The dramatic overshoot occurs in the first correction step.  As the first correction step in the program uses dBm values for the desired and measured power values, not linear power values, the correction can easily overshoot, and it does; horribly so when the Calib Target value is large.  The cure is to moderate the size of the correction steps.  

As I mentioned,  the problem occurs is in the first step toward correction; it overshoots dramatically if the Calibration Target is set anywhere near maximum.  I have just now modified the calibration method in the program here by dramatically reducing the size of the correction step that is taken by the method and that seems to have prevented the overshoot problem entirely without increasing the number of tries the method takes to achieve the specified accuracy of the calibration.  Calibration is usually completed in three tries even with the modification, but without an overshoot.

Doug and I are still examining this issue and will settle on a reasonable choice for the correction step size shortly.  If you would like, I'd be happy to send you the PowerSDR version I just now modified so that you can test it there and report back on your observations.

73,  Joe K5SO

On Oct 9, 2012, at 10:13 AM, Helmut, DC6NY wrote:

> Hi Joe,
> 
> a reduced value of the target power doesn't cancel the problem. The routine
> starts according to my tests in every case with the 'ALC value' of 38, that
> means full power from Penny. 
> 
> 73, Helmut DC6NY 
> 
> 
> -----Ursprüngliche Nachricht-----
> Von: hpsdr-bounces at lists.openhpsdr.org
> [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von Joe Martin K5SO
> Gesendet: Dienstag, 9. Oktober 2012 15:27
> An: HPSDR list
> Betreff: Re: [hpsdr] caution with cal routine
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> 
> While I certainly don't disagree with Helmut's suggestion, judicious use of
> the "Cal Target" setting improves things considerably.  In particular, if
> you use a lower-than-maximum power value for the calibration target setting
> things work out better than using the max setting of 100. 
> 
> As an example, with my 200w max out PA I use 40w as the calibration target
> setting with no problems.  Doing so (still) results in the front panel
> slider power control (Drive) range of 0-100 to correspond with 0-100w output
> from the PA.  
> 
> 73,  Joe K5SO
> 
> 
> 
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