[TangerineSDR] cal results

Julius Madey hillfox at fairpoint.net
Sun Apr 26 09:45:01 EDT 2020

Fully understand; just wanted to share my results with you.

I'm more comfortable now with relatively simple low cost techniques to 
do some sort of calibration; the single axis Helmholz pair I built in 
1990 cost about $10 in material plus a simple regulated power supply and 
the NOAA geomag model for a specific lat/long/elevation is pretty good.

Your test code has been EXTREMELY USEFUL in my experiments and let me 
get this thing up and running quickly without spending time doing my own 
coding; the output is consistent which allows comparison to known field 

Would also have taken me a lot longer to get up and running without your 
assistance with the adapter board and the Spark Fun items.

Best regards,

Jules Madey  K2KGJ

On 4/25/2020 11:59 PM, David Witten wrote:
> Julius (and anyone else),
> Please realize that you are running far ahead of what this code was 
> intended to do.  It was meant to illustrate the general technique used 
> to interact with the device.  It was never intended to give meaningful 
> results.  I had thought that I conveyed that it is only intended to 
> show that these boards work in a physical sense.
> At the least, I know that all the vectors in this code require a 
> correction for gain.  This is not my current development repository,
> I sent Frankie Bonte and her father a much more expensive PNI 
> demonstration board. It was my hope that they would use it to explore 
> the relationship between the values from this code and  the values 
> that PNI's own code produces.  They seem to have chosen to go in some 
> other direction that I do not understand.  I never received any 
> feedback so I had to purchase another Demo board and I have not gotten 
> around to using it because I have no usable Windows machines.
> Again, do not expect the code in this github repo to give meaningful 
> results.  These results have ALWAYS looked wrong to me.
> I have another private repo that I have been working on for months, 
> and I will only make it available when it seems ready to me.
> Davei Witten, KD0EAG
> On Sat, Apr 25, 2020 at 10:18 PM Julius Madey <hillfox at fairpoint.net 
> <mailto:hillfox at fairpoint.net>> wrote:
>     Dave,
>     Made several runs with X,Y and Z sensors interchanges in different
>     orientations.
>     Y and Z  have equal sensitivities
>     X sensitivity is significantly higher
>     Using the NOAA model values for my Lat, Long and Altitude,
>     multiplying X by 0.056 and Y and Z values by 13 gives results
>     quite close to the predicted model values with the resulting LSDs
>     equal to 1nT.  Close enough to get a much better idea of noise level.
>     Looking at the Helmholtz pair test data again, the multiplication
>     values are twice those quoted above......a factor of 2 difference
>     between the two methods.  Given that the NOAA model values are
>     probably very close to what the measured values should be, and
>     since (ambient + test field) - (a,bient - test field) = 2 x test
>     field, the calculated value for the Helmholz field is probably off
>     by a factor of two .... back to my notes on the coil field ....
>     I don't see anything in the setup instructions for the 3100
>     registers to suggest such a difference and I haven't dug into the
>     code yet.
>     I don't want to post anything on the repository until the
>     calibration results check out.
>     Regards and stay well ...
>     Jules   K2KGJ

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