[TangerineSDR] Ferrous Metal connectors on Mag boards and SBCs

David Witten wittend at wwrinc.com
Sat May 30 17:34:58 EDT 2020


This will have to come to the attention of Scotty.  I am now completely
excluded from the design process for the magnetometer implementation.


On Sat, May 30, 2020 at 4:27 PM Julius Madey <hillfox at fairpoint.net> wrote:

> Dave,
> I specifically note the change of shield material from copper alloy to
> SS.
> I just ordered the AMP jacks and Stewart plugs in the attached data
> sheets.  Jack shield is plated phosphor bronze and plug shield is plated
> copper.  I don't know if other vendors are changing shield material re EMI
> performance (meaningful at GigE speeds but not at 100KHz differential i2c)
> and since magnetic properties of SS can vary greatly depending upon
> specific alloy and cold working, it's probably a good idea to stay away
> from them if at all possible if the RM3100 will be mounted in close
> proximity to the SS part if the hope is to see signals well below the
> microTesla range.
> Perhaps Hyomin could provide some guidance on that ?
> Jules
> Delays in 1000 meters of twisted pair cable are, of course, too long for
> 100KHz rate i2c exchange protocol, but
> On 5/30/2020 2:21 PM, David Witten wrote:
> Jules, et. al.:
> FWIW:  The Amphenol drawing w/details for the RJ45 that I used on the
> prototypes is attached.  It indicates that the shield is tin coated
> stainless steel.  Depending on the alloy it may exhibit some degree of
> ferromagnetism.
> Dave
> On Sat, May 30, 2020 at 12:59 PM Julius Madey <hillfox at fairpoint.net>
> wrote:
>> Tom,
>> From a 5/4 email from Scotty explaining the design of his new board:
>> "JMP6 allows us to ground one side of the shield only to minimize noise
>> pickup and ground loops. Note that the CAT5 cable is shielded. "
>> If I interpreted that as a 'recommendation', my bad ...
>> Molex has at least one RJ shielded plug using brass .... mine were cheap
>> eBay stuff ... so there appears to be no problem.....just have to order the
>> good stuff....non ferrous metal construction is available on both RJ45
>> jacks and plugs.
>> Jules - K2KGJ
>> On 5/30/2020 11:45 AM, Tom McDermott wrote:
>> I have no idea where the idea that the shield should be unconnected at
>> the remote end came from.
>> In my opinion this is contrary to what probably needs to be done.  I
>> think Scotty put a jumper on that
>> line so it could be tried both ways.   Normally one floats a shield if
>> ground return currents from some
>> external path are expected.   I don't see where those would come from in
>> this situation.
>> -- Tom, N5EG
>> On Sat, May 30, 2020 at 8:31 AM Julius Madey via TangerineSDR <
>> tangerinesdr at lists.tapr.org> wrote:
>>> Dave,
>>> I hadn't either until I saw the note from Phil.  I've been using your
>>> original small adapter board with the Quicc connectors so haven't run into
>>> the issue yet.
>>> Two shielded RJ45 PC through hole jacks in my parts drawer, made by
>>> BERG, have non ferrous shields.  Couldn't find the BERG part on line but
>>> DigiKey carries several candidates.  One is AMP 5558342-1, the data sheet
>>> for which shows phosphor bronze as the shield material.  Since the shields
>>> on the RJ jacks of the three SBC's I have are all non-ferrous, it may be
>>> that for RJ45's, non-ferrous construction is the usual.
>>> With regard to the shielded RJ plugs on the extension cable, since the
>>> current recommendation seems to be to only tie the shield to ground at the
>>> 'local' end, it's possible to remove the shield on the plug at the remote
>>> end; just did that with one of mine.
>>> Jules
>>> On 5/30/2020 10:34 AM, David Witten wrote:
>>> Jules,
>>> This is something I had not thought about.
>>> It does appear that Belden does sell a line of Cat 5+ connectors that
>>> have little or no metal in them beyond the contacts:
>>> REVConnect® Connectivity System
>>> <https://www.belden.com/products/enterprise/copper/connectors/cat-6a-jacks>,
>>> but these appear to be components of a building wiring system, not board
>>> mountable jacks.  Further research is required.
>>> Dave
>>> --
>>> TangerineSDR mailing list
>>> TangerineSDR at lists.tapr.org
>>> http://lists.tapr.org/mailman/listinfo/tangerinesdr_lists.tapr.org
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