[TangerineSDR] [EXTERNAL] Re: TangerineSDR Digest, Vol 27, Issue 3

David G. McGaw david.g.mcgaw at dartmouth.edu
Wed Jun 2 10:59:43 EDT 2021


The regulators on the magnetometer boards are very good filters of any 
noise on the Raspberry Pi power supply.  Any noise coming from the host 
system would be general system noise conducted on the cable.

David N1HAC

On 6/2/21 10:51 AM, Bill Engelke via TangerineSDR wrote:
>
> Hello all:
>
> The magnetometer is in 2 parts:  an adapter that plugs in as a 
> daughter board (“hat”) to the Raspberry Pi, and (at the other end of 
> the cable) the matching board that contains the magnetometer itself.
>
> So the magnetometer gets its power feed from the Raspberry Pi.
>
> So, what I wonder is:  does the power supply of the R-Pi have a noise 
> component that is getting superimposed on to the power supply going to 
> the magnetometer unit?
>
> BTW:  when I did my testing, I used shielded CAT-6 cable. With some 
> effort, I could add the recommended ferrite beads.  Take me a few 
> weeks…. -73- Bill
>
> *From:* TangerineSDR <tangerinesdr-bounces at lists.tapr.org> *On Behalf 
> Of *Jonathan via TangerineSDR
> *Sent:* Wednesday, June 2, 2021 9:40 AM
> *To:* TAPR TangerineSDR Modular Software Defined Radio 
> <tangerinesdr at lists.tapr.org>
> *Cc:* Jonathan <emuman100 at gmail.com>; Ward Silver <hwardsil at gmail.com>
> *Subject:* [EXTERNAL] Re: [TangerineSDR] TangerineSDR Digest, Vol 27, 
> Issue 3
>
> I’ll have to double check the schematic, but I don’t think there are 
> any switching regulators on the magnetometer board. The noise could be 
> coming from the i2c clock or possibly the internal clock of the 
> magnetometer IC.
>
> Jonathan
>
> KC3EEY
>
>
> On Jun 2, 2021, at 9:50 AM, Ward Silver via TangerineSDR 
> <tangerinesdr at lists.tapr.org <mailto:tangerinesdr at lists.tapr.org>> wrote:
>
>     Was the test unit powered by a switching power supply module?  If
>     so, replacing it with a linear supply might help.
>
>     In a "production configuration" we should recommend shielded CAT5
>     or CAT6 cable with type 31 ferrite beads or cores on each end of
>     the Ethernet cable.  If practical, a linear power supply should be
>     used for both the magnetometer module and the host SDR.  There are
>     clean switchmode supplies, as well, but they would have to be tested.
>
>     If the noise is being radiated directly from the electronics,
>     we'll have to tackle that separately.
>
>     73, Ward N0AX
>
>     On Wed, Jun 2, 2021 at 8:39 AM Dr. Nathaniel A. Frissell Ph.D.
>     <nathaniel.frissell at scranton.edu
>     <mailto:nathaniel.frissell at scranton.edu>> wrote:
>
>         Hi Bill,
>
>         Thank you for that evaluation, and like Ward, I am glad to
>         hear the magnetometer does not appear to be sensitive to RF. 
>         I’m sorry to hear about its effects on 80 and 160 m, and I
>         guess that will need to be discussed some more.
>
>         73 Nathaniel W2NAF
>
>>         Dr. Nathaniel A. Frissell, Ph.D., W2NAF
>
>         HamSCI Lead
>         Assistant Professor
>         Department of Physics and Electrical Engineering
>         University of Scranton
>         (973) 787-4506
>
>
>
>             On Jun 1, 2021, at 10:09 PM, Ward Silver via TangerineSDR
>             <tangerinesdr at lists.tapr.org
>             <mailto:tangerinesdr at lists.tapr.org>> wrote:
>
>             Glad to hear of the insensitivity to ambient RF at a
>             variety of frequencies, Bill!
>
>             This brings up the system-level issue of RFI created by
>             the PSWS as conducted emissions, most likely.  It would be
>             a problem if the PSWS interferes with its own local
>             receiver!  So we (meaning the design team) will need to
>             carefully evaluate the I/O and power lines to be sure they
>             are RF-quiet.  I can probably help with that as I am
>             winding down a series of back-to-back-to-back book
>             projects and have some time coming up.
>
>             73, Ward N0AX
>
>             On Tue, Jun 1, 2021 at 9:00 PM
>             <tangerinesdr-request at lists.tapr.org
>             <mailto:tangerinesdr-request at lists.tapr.org>> wrote:
>
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>                 Today's Topics:
>
>                    1. Magnetometer RF testing, additional results
>                 (Bill Engelke)
>
>
>                 ----------------------------------------------------------------------
>
>                 Message: 1
>                 Date: Tue, 1 Jun 2021 16:15:00 +0000
>                 From: Bill Engelke <bill.engelke at ua.edu
>                 <mailto:bill.engelke at ua.edu>>
>                 To: TAPR TangerineSDR Modular Software Defined Radio
>                         <tangerinesdr at lists.tapr.org
>                 <mailto:tangerinesdr at lists.tapr.org>>
>                 Subject: [TangerineSDR] Magnetometer RF testing,
>                 additional results
>                 Message-ID:
>                        
>                 <BN8PR15MB31855B741907BD4C37902902FA3E9 at BN8PR15MB3185.namprd15.prod.outlook.com
>                 <mailto:BN8PR15MB31855B741907BD4C37902902FA3E9 at BN8PR15MB3185.namprd15.prod.outlook.com>>
>
>                 Content-Type: text/plain; charset="us-ascii"
>
>                 Here is a follow-up to my last email regarding
>                 possible RF interactions with the magnetometer.  A
>                 couple of suggestions came in from the community:
>
>
>                   1.  Ward Silver, N0AX, recommended to test by
>                 transmitting with a dipole near the magnetometer in
>                 several configurations, on 2 meters with 50 w.
>                   2.  Tom McDermott, N5EG, recommended to look for RF
>                 noise being generated by the magnetometer that might
>                 get into your station receiver.
>
>                 Here are results of doing such tests:
>
>
>                   1.  I built a 2-m dipole specifically for this so
>                 that I could test with the antenna (a)broadside to the
>                 magnetometer, (b)vertical to it, and (c) pointed
>                 towards it. (photos) The antenna was located about 10
>                 feet from the magnetometer, which is buried at 2 feet
>                 in the soil (its standard installation as tested by
>                 Jules and others), and connected to the station with
>                 shielded CAT-6.
>
>                 Broadside configuration
>
>                 [cid:image004.png at 01D756D6.2EB4CD30
>                 <cid:image004.png at 01D756D6.2EB4CD30>]
>
>                 Vertical configuration:
>
>                 [cid:image005.png at 01D756D7.049AA500
>                 <cid:image005.png at 01D756D7.049AA500>]
>
>                 Straight-on configuration
>
>                 [cid:image006.png at 01D756D7.049AA500
>                 <cid:image006.png at 01D756D7.049AA500>]
>
>                 The antenna was connected via a new 50 foot RG-8 cable
>                 to an Icom IC-706MKIIG, set to high output (50 watts),
>                 145 MHz. I did my best to do what Ward suggested.
>
>                 Results: I never saw the magnetometer readings change
>                 when I keyed the rig; this was the same for the 3
>                 different antenna angles. I have to conclude that the
>                 magnetometer is not sensitive to 2 meters.
>
>
>                   1.  Using the FlexRadio 6600, I looked for noise
>                 being generated by the magnetometer on all ham bands
>                 from 160 m to 10 meters. I looked for wide band noise
>                 by watching the waterfall and turning the magnetometer
>                 on and off. If I saw noise appear, I tried turning the
>                 magnetometer off and on to see if the noise would come
>                 and go with being connected to the magnetometer base
>                 card on the Raspberry Pi. I used the appropriate
>                 antenna for each band (i.e., the one I use for my
>                 station), as follows:  (160 M) - multiband vertical,
>                 (80M) halfwave dipole at 15 ' (20 feet away) and also
>                 multiband vertical about 50' away, (60M) multiband
>                 vertical, (40 M) double bazooka inverted vee, (20M
>                 through 10 M) DX Engineering Hexbeam on 50' tower.
>
>                 Results: First the good news: I never saw wideband
>                 noise attributable to the magnetometer on the bands 60
>                 meters and higher in frequency.   I did see noise on
>                 80M and on 160M.  The magnetometer does generate noise
>                 of about 0.4 db as shown on the FlexRadio s-meter on
>                 80M. (Note that this is a severe case, as the 80 M
>                 dipole is only up 15' and about 20' away from the
>                 magnetometer - but this is probably a typical
>                 situation). On 160 M, the magnetometer generated 1 db
>                 of noise.
>
>                 Screenshot of 80 M result using dipole
>
>                 [cid:image001.png at 01D756D4.9FD34E80
>                 <cid:image001.png at 01D756D4.9FD34E80>]
>
>                 Screenshot of 80 M on multiband vertical
>
>                 [cid:image002.png at 01D756D5.12202BC0
>                 <cid:image002.png at 01D756D5.12202BC0>]
>
>                 Screenshot of 160 M, multiband vertical
>
>                 [cid:image003.png at 01D756D5.6F866360
>                 <cid:image003.png at 01D756D5.6F866360>]
>
>                 I suppose that we would recommend turning off the
>                 magnetometer if you are working DX on 80 Meters;
>                 possibly separating the magnetometer from the antenna
>                 might also help, but I was not able to test that.
>
>                 -73- Bill,   AB4EJ
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>                 End of TangerineSDR Digest, Vol 27, Issue 3
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