[TangerineSDR] TangerineSDR Digest, Vol 13, Issue 49

Julius Madey hillfox at fairpoint.net
Thu Apr 30 20:39:16 EDT 2020


Re: Contents of TangerineSDR digest 4/26/2020

Continuing with the use of Dave's original adapter board and the 
SparkFun 9615 differential i2c extenders he supplied me with, since the 
4/26 email, I manually loaded and verified the RM3100 cycle count 
registers (both 200 and 400 count values) and divided results by the 
appropriate gain factor for each count with some patches to Dave's 
simplei2c.c code.  As claimed in PNI documentation, readout is in 
microTeslas and corresponds to the values provided by the NOAA 
geomagnetic field model for my lat, long and altitude; it appears no 
further calibration steps may be necessary.

Have ordered 350 feet of direct burial shielded CAT5E to place the 
magnetometer in a stable electrically quiet location, about 450 feet 
from power lines and vehicle traffic, for further testing, preferably 
with Dave's latest code when available to the group. Prior bus 
measurements, available on the Google respository, confirm that the 
differential i2c bus extension over twisted pair transmission line 
should easily work to 350 feet. Remote end voltage will be supplied by a 
3.3 volt LDO regulator of the type that Scotty is using on his new 
board.  Will probably also add common mode ferrite chokes to minimize 
any conducted EMI.

Jules K2KGJ


On 4/26/2020 12:00 PM, tangerinesdr-request at lists.tapr.org wrote:
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> Today's Topics:
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>     1. Re: cal results (David Witten)
>     2. Re: cal results (Julius Madey)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sat, 25 Apr 2020 22:59:29 -0500
> From: David Witten <wittend at wwrinc.com>
> To: Julius Madey <hillfox at fairpoint.net>, tangerinesdr at lists.tapr.org
> Subject: Re: [TangerineSDR] cal results
> Message-ID:
> 	<CABJ3BVPMzE1VMpF8N4i1pX0NdFE=3L-RRmXXA=NS_mNi05wfLA at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> 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> 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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>
> Message: 2
> Date: Sun, 26 Apr 2020 09:45:01 -0400
> From: Julius Madey <hillfox at fairpoint.net>
> To: David Witten <wittend at wwrinc.com>, tangerinesdr at lists.tapr.org
> Subject: Re: [TangerineSDR] cal results
> Message-ID: <e76685f0-e330-283c-7bd7-56afdb5c55f4 at fairpoint.net>
> Content-Type: text/plain; charset="utf-8"; Format="flowed"
>
> Dave,
> 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
> values.
>
> 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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