[TangerineSDR] TangerineSDR Digest, Vol 27, Issue 7

Julius Madey hillfox at fairpoint.net
Wed Jun 2 11:02:41 EDT 2021


Jonathan, that's correct.  The voltage regulator on the RM3100 adapter 
board is a linear, low dropout part.   Scope photos attached are of 
experiments on voltage drop and noise at the remote end of 120 feet of 
CAT5E shielded cable.  The circuitry on the present PC boards is 
essentially the same as the test setup I used with a combination of 
SparkFun i2c differential extender breakout boards and Dave Witten's 
adapter board design.
Two exceptions:   Added low ESR 220uF cap at the remote end to suppress 
line transients due to current draw of the remote i2c extender when 
driving the line and the ground and +5 volt lines were wired as two 
twisted pair runs in parallel, eg, each twisted pair consisted of ground 
and +5 conductor.  The RJ45 jack on the present board separates the 
ground and 5 volt lines as two separate twisted pairs.

73,
Jules-K2KGJ


On 6/2/2021 10:41 AM, tangerinesdr-request at lists.tapr.org wrote:
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>     1. Re: TangerineSDR Digest, Vol 27, Issue 3 (Jonathan)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 2 Jun 2021 10:40:23 -0400
> From: Jonathan <emuman100 at gmail.com>
> To: TAPR TangerineSDR Modular Software Defined Radio
> 	<tangerinesdr at lists.tapr.org>
> Cc: "Dr. Nathaniel A. Frissell Ph.D."
> 	<nathaniel.frissell at scranton.edu>, Ward Silver <hwardsil at gmail.com>
> Subject: Re: [TangerineSDR] TangerineSDR Digest, Vol 27, Issue 3
> Message-ID: <FA88D37C-475D-4AC2-916E-E756668570BB at gmail.com>
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> 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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