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

Ward Silver hwardsil at gmail.com
Wed Jun 2 10:56:46 EDT 2021 

The easiest thing would be to power the RPi from a linear supply (if that's
not already the case).  Noise can be coupled to radiating cables in a lot
of ways.  Shielding the RPi with a proper bond from the CAT shield to the
enclosure will be necessary "in production."  An E-field shield around the
magnetometer (Faraday cage of thin foil, perhaps) would also be required.
I am not anticipating any electronics or programming changes to the boards
themselves.

Assuming a linear supply and some ferrite beads on the CAT cable don't
knock the noise down, there will probably have to be some sniffing with a
small E or H probe and a spectrum analyzer.  I have a quiet site at my
rural station and a spectrum analyzer so I could do some testing there.

73, Ward N0AX

On Wed, Jun 2, 2021 at 9:51 AM Bill Engelke <bill.engelke at ua.edu> 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> 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> 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> 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>
> 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>
> To: TAPR TangerineSDR Modular Software Defined Radio
>         <tangerinesdr at lists.tapr.org>
> Subject: [TangerineSDR] Magnetometer RF testing, additional results
> Message-ID:
>         <
> 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]
>
> Vertical configuration:
>
> [cid:image005.png at 01D756D7.049AA500]
>
> Straight-on configuration
>
> [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]
>
> Screenshot of 80 M on multiband vertical
>
> [cid:image002.png at 01D756D5.12202BC0]
>
> Screenshot of 160 M, multiband vertical
>
> [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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