[arm-allstar] Portable node grounding issue

Wed Nov 7 11:10:02 EST 2018

The only caution with doing this type of shielding is that it will preclude
using the wireless capability of the Pi or at least greatly reduce its
range. This is no easy way to add an external wifi antenna to the pi
without circuit board modifications that most would not want to do.

The yellow box nodes that are being produced in plastic cases use an
internal copper adhesive strip attached to the inside of the case and
connected to the BNC connector which acts as a ground plane to the external
antenna and that seems to work well. Unfortunately most of the non DMK-URI
FOB's and especially the cheap modified Chinese FOB's have no RF
decoupling. A simple LC filter using a ferrite and a bypass cap on the
leads in and out of the FOB to the radio like in the DMK-URI usually solves
this problem.

*73 Doug*

*WA3DSP*

*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*

On Wed, Nov 7, 2018 at 10:57 AM "Don via ARM-allstar" <
arm-allstar at hamvoip.org> wrote:

> Hi Lonny,
>
> In addition to Doug's comments....
>
> I built an Allstar portable node (see links below). My build used a
> wooden box which may have similar issues to a pelican case (Both are
> un-shielded). I found that RF was getting into my control circuit board
> and falsely asserting a COS signal which cased a ping-pong effect on the
> node.
>
> My solution was to use a spray-on grounding paint called "Total Ground".
> I believe I was able to get this on Amazon.  This provided an effective
> shield from the  RF radiated by the external antenna. I tied my ground
> to the box with a wire connected to a small screw into the wood box. I
> made sure the screw and wire made contact with the "ground painted"
> surface. I have also used this paint on an audio project which was
> mounted in a pelican case. Works very well.
>
> Details on the enclosure I built for the portable node are on my blog:
>
> http://squirrelengineering.com/ham-radio/build-a-portable-allstar-link-hotspot-part-5-putting-it-into-a-box/
>
> Details of the entire build starts here:
>
> http://squirrelengineering.com/ham-radio/build-a-portable-allstar-link-hotspot-part-1-intro/
>
> I hope this info is helpful to you and others.
>
> 73s
>
> Don KJ6FO
>
>
>
>
> On 11/4/2018 8:47 AM, "Lonny Barry via ARM-allstar" wrote:
> > Hi Doug!
> > Thank you for the reply.
> >
> > FOB : RepeaterBuilder's RIM-Lite (DB9)
> >
> > Power : Wall wart to Anderson Power Poles INPUT : 120V - 60Hz / OUTPUT :
> > 12V  1A
> >                  =>  SMAKN 12v StepDown to 5v
> >                  =>  Pi pins 4 and 6
> >
> > Meters : Klien NCVT-1 voltage tester (rough identification)
> >                Commercial Electric MS8301A Multimeter for measurements
> > Radio is battery powered as I have yet to incorporate a battery
> eliminator
> >
> > The DB9 is grounded at pin 9 which is also jumpered to pin 8 effectively
> > grounding it as well.
> >
> > Intermittently im measuring .5 mV between the USB housing and the end of
> > the DB9 on the FOB, again, without the radio connected to the fob,
> >
> > On Sun, Nov 4, 2018 at 9:27 AM "Doug Crompton via ARM-allstar" <
> > arm-allstar at hamvoip.org> wrote:
> >
> >> Lonny,
> >>
> >>   The FOB gets its ground via the USB connection. Then there should be a
> >> ground between it and the radio. For the DMK-URI FOB that would be pins
> 19
> >> and 20 of the DB25. You did not mention what FOB you are using or how
> your
> >> power was connected? Are you using the same supply for the radio and
> Pi. Of
> >> course in that case the Pi would be fed through a 12V to 5V converter.
> >> Also you say voltage test and putting your hand on it. Not sure what you
> >> are using to test voltage. Do you have a voltmeter that would measure
> the
> >> voltage between the points you are suspecting have a voltage
> differential?
> >>
> >>
> >> *73 Doug*
> >>
> >> *WA3DSP*
> >>
> >> *http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*
> >>
> >>
> >>
> >> On Sun, Nov 4, 2018 at 10:20 AM "Lonny Barry via ARM-allstar" <
> >> arm-allstar at hamvoip.org> wrote:
> >>
> >>> Good Sunday morning,
> >>>
> >>> I'm looking for a little insight into portable node grounding.
> >>>
> >>> I am assembling a portable node in a pelican case.
> >>> Pi 3b+, RepeaterBuilder FOB, SMAKN 5v step down, Power Down Controller
> >> with
> >>> 9v battery, Modified 888s.
> >>>
> >>> At the moment, I'm reading current at the female end of the FOB
> (without
> >>> the radio connected).  If I grasp the DB9 connector on the FOB, the
> >> voltage
> >>> tester silences.
> >>>
> >>> It seems to me that there is a grounding issue somewhere. I've already
> >>> exchanged the USB cable to the FOB to no avail.
> >>>
> >>> How is anyone else getting a ground for a portable node, especially one
> >>> contained in a plastic box?
> >>>
> >>> As an aside, the symptom that lead me to this issue is occasionally the
> >>> node / radio will leave the PTT stuck open. By touching the USB housing
> >> on
> >>> the Pi or the DB9 connector on the FOB, the PTT closes.
> >>>
> >>> Thank you for your suggestions. I'm admittedly not an electronics whiz,
> >> but
> >>> I did get into this to learn.
> >>>
> >>> Lonny
> >>> KG5IGJ
> >>> _______________________________________________
> >>>
> >>> ARM-allstar mailing list
> >>> ARM-allstar at hamvoip.org
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> >>>
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> >>>
> >> _______________________________________________
> >>
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> >>
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> >>
> > _______________________________________________
> >
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> >
> >
>
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