[arm-allstar] Portable node grounding issue

[Don]

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
>>> http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar
>>>
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>>>
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>>
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>>
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