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<font face="Arial">Tom, <br>
The measurements I took of differential and single ended clock and
data waveforms on the 36 meters of 5E which I posted on the Google
repository were done at 100KHz clock speed on the Pi. Clean, no
ringing and end to end delay was as expected. So 106 meters
should pose no problem. <br>
Thanks !<br>
Jules K2KGJ<br>
</font><br>
<div class="moz-cite-prefix">On 4/30/2020 9:57 PM, Tom McDermott
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CACO3nRSbpsN4GgAA0FkQRQk2-gXheDxDHpEAvx_ptpoL10uLvg@mail.gmail.com">
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<div dir="ltr">
<div>Hi Julius. You may need to be careful with the length.
One thing that limits the length is </div>
<div>round-trip propagation time of the cable. The local end
clocks out the data, that clock</div>
<div>travels up the cable to the remote. The remote sends data
back down the cable</div>
<div>to the local end. The local end then clocks in the data
from the remote based</div>
<div>on the local sending clock. The received data has been
delayed by two cable prop delays.</div>
<div><br>
</div>
<div>I2C has several speeds. The slowest is 100 kilobits/sec.
Fast is 400 kilobits/sec.</div>
<div>Super is 1 megabit/sec. I recommend using the slowest
speed for long cables.</div>
<div><br>
</div>
<div>100 meters of cable will probably have a round-trip delay
of roughly 900 nanoseconds.</div>
<div>(3 nsec/meter, velocity factor of 0.66). There is also some
additional delay due to the differential</div>
<div>transmitters and receivers. I think the receiver clocks
on the half-clock edge.</div>
<div>So 100 kb/s allows ~5 microseconds total prop delay, 400
kb/s allows 1.25 microseconds, etc.</div>
<div><br>
</div>
<div>-- Tom, N5EG</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
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<br>
<div class="gmail_quote">
<div class="gmail_attr" dir="ltr">On Thu, Apr 30, 2020 at 5:39
PM Julius Madey via TangerineSDR <<a
href="mailto:tangerinesdr@lists.tapr.org"
moz-do-not-send="true">tangerinesdr@lists.tapr.org</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;padding-left:1ex;border-left-color:rgb(204,204,204);border-left-width:1px;border-left-style:solid">
<div> <font face="Arial">Re: Contents of TangerineSDR digest
4/26/2020<br>
<br>
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.<br>
<br>
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.<br>
<br>
Jules K2KGJ<br>
<br>
</font><br>
<div>On 4/26/2020 12:00 PM, <a
href="mailto:tangerinesdr-request@lists.tapr.org"
target="_blank" moz-do-not-send="true">tangerinesdr-request@lists.tapr.org</a>
wrote:<br>
</div>
<blockquote type="cite">
<pre>Send TangerineSDR mailing list submissions to
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When replying, please edit your Subject line so it is more specific
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Today's Topics:
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 <a href="mailto:wittend@wwrinc.com" target="_blank" moz-do-not-send="true"><wittend@wwrinc.com></a>
To: Julius Madey <a href="mailto:hillfox@fairpoint.net" target="_blank" moz-do-not-send="true"><hillfox@fairpoint.net></a>, <a href="mailto:tangerinesdr@lists.tapr.org" target="_blank" moz-do-not-send="true">tangerinesdr@lists.tapr.org</a>
Subject: Re: [TangerineSDR] cal results
Message-ID:
<a href="mailto:CABJ3BVPMzE1VMpF8N4i1pX0NdFE=3L-RRmXXA=NS_mNi05wfLA@mail.gmail.com" target="_blank" moz-do-not-send="true"><CABJ3BVPMzE1VMpF8N4i1pX0NdFE=3L-RRmXXA=NS_mNi05wfLA@mail.gmail.com></a>
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 <a href="mailto:hillfox@fairpoint.net" target="_blank" moz-do-not-send="true"><hillfox@fairpoint.net></a> wrote:
</pre>
<blockquote type="cite">
<pre>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
</pre>
</blockquote>
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------------------------------
Message: 2
Date: Sun, 26 Apr 2020 09:45:01 -0400
From: Julius Madey <a href="mailto:hillfox@fairpoint.net" target="_blank" moz-do-not-send="true"><hillfox@fairpoint.net></a>
To: David Witten <a href="mailto:wittend@wwrinc.com" target="_blank" moz-do-not-send="true"><wittend@wwrinc.com></a>, <a href="mailto:tangerinesdr@lists.tapr.org" target="_blank" moz-do-not-send="true">tangerinesdr@lists.tapr.org</a>
Subject: Re: [TangerineSDR] cal results
Message-ID: <a href="mailto:e76685f0-e330-283c-7bd7-56afdb5c55f4@fairpoint.net" target="_blank" moz-do-not-send="true"><e76685f0-e330-283c-7bd7-56afdb5c55f4@fairpoint.net></a>
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:
</pre>
<blockquote type="cite">
<pre>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 <<a href="mailto:hillfox@fairpoint.net" target="_blank" moz-do-not-send="true">hillfox@fairpoint.net</a>
<a href="mailto:hillfox@fairpoint.net" target="_blank" moz-do-not-send="true"><mailto:hillfox@fairpoint.net></a>> 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
</pre>
</blockquote>
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