[TangerineSDR] Should have been: Updated RM3100 reslts from Julius Madey

David Witten wittend at wwrinc.com
Wed Jul 29 19:50:32 EDT 2020


> Dave.
>
> Here's the first couple of pieces on temp sensitivity.  Considering the
> full range of the RM3100, the observed effect could be considered
> relatively small. However, it's in the region we need to observe.  Although
> the basic idea of taking the differences in duty cycle of the LR oscillator
> with forward and reverse bias eliminates some major temperature
> contributions, it apparently does not totally eliminate them.
>
> One is of a GTJ run on 07072020 and the other a one hour calibration run I
> did yesterday 07272020.  Note the reversed sense of the temperature change
> effect.  I have a second RM3100 which I will also run in the next few days
> for comparison.  I used your original adapter board.  The setup in the wood
> lot at the end of 400 feet of CAT5E I believe uses the same adapter board
> you supplied to Hyomin.  Reducing the 24 hour data in Open Office Calc took
> a god-awful time to complete.
>
> Feel free to distribute these ...  I'm going to send them to PNI for their
> comment.  I did not attempt to measure the drift, if any, of the 3.3 volt
> regulator output on the SparkFun i2c differential extender at the test
> end.  I also have data which was taken with a delay between the start
> command and looking at the Status register to keep the i2c bus quiet during
> measurement and the trends are the same.  I don't think PC trace currents
> created that much local field but that's another check for the future.
>
> Jules
>
>
>> Julius Madey
>> [image: Attachments]Tue, Jul 28, 11:15 AM (21 hours ago)
>> to me
>> Dave,
>> I have no problem with sharing that my tests so far have shown that, at
>> least on the y axis which was tested,  the RM3100 is well within 5%
>> accuracy with Helmholtz coil excitation with a long period (30 minutes to 1
>> hour) sine wave of +/-50, +/- 524 and +/- 2893 nT.   And I would be happy
>> to provide graphs to the repository.
>>
>> My problem at this point is incomplete data on another aspect, which is
>> why I haven't released the stuff I mentioned yesterday.
>>
>> PNI claims that the basic measurement technique employed in the RM3100
>> eliminates temperature effects.  See the attached note.
>>
>> However, I am clearly seeing what appear to be temperature related
>> effects in the measurements, at least at lower levels like 30 to 150nT
>> variations of the sort seen at the Jenny Jump tests.  If you know the
>> tempco, it's possible to compensate in the data reduction .....
>> however......the disconcerting thing is that I'm seeing different trends vs
>> temp in the GTJ results and the runs I did in the last couple of days.
>> Tempco sign differences, which suggests magnetometers may have to be
>> calibrated before deployment ...  temperature variations of 15 C or more
>>
>> If I look at the temperature related effects of the GTJ measurements
>> (tedious work due to the large data set) it appears that the significant
>> deviation which Hyomin noted between the GTJ and JJ data is entirely due to
>> temperature variations over the 24 hour runs  !!
>>
>>
>> I have an inquiry in to PMI.
>>
>> Jules
>> Attachments area
>>
>>
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