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Isolate any jacks/controls from metal chassis? #ubitx

Rob French (KC4UPR)
 

Are there any controls or jacks that I should isolate from my metal chassis?  Specifically, I'm thinking of the PTT and C/W key inputs, since those are wired to the Raduino.  Since they are part of the digital circuitry to some extent, should they be isolated from the chassis ground assuming I've got, e.g. the antenna RF out ground there?

Thanks,
-Rob

Tom, wb6b
 

A metal chassis provides a very good low impedance ground reference to all the circuitry. Best to ground everything, including making sure the screws holding down the circuit board have a good connection to the chassis in all four corners. 

The wires to each of the various jacks and controls should be fairly short and twisted together to reduce RF pickup within the metal box. Such as twisting the volume control wires in a set, the encoder in a set, microphone in a set, the antenna wires in a set. Best to let the antenna connector be at one side of the box, close to where the antenna is connected to the PC board, the power connector close to where it connects to the PC board, and the audio/digital at the other side. That would minimize the very slight possibility of the minimal ground loops (minimized by the low impedance of the chassis ground) having any effect. But the big common ground should be a benefit virtually in all cases. 

Tom, wb6b

iz oos
 

My front and back panels are plastic, all the rest is metal. So all connectors are isolated. I used a small piece of coax for the RF connection from the board to the panel instead of the stock twisted line. I think it is doing a good job as well. I chose this enclosure either because I had it for a long time, it was easy to drill and just to exclude the possibility of ground loops if any.

Il 22/ago/2019 04:15, "Tom, wb6b" <wb6b@...> ha scritto:
>
> A metal chassis provides a very good low impedance ground reference to all the circuitry. Best to ground everything, including making sure the screws holding down the circuit board have a good connection to the chassis in all four corners. 
>
> The wires to each of the various jacks and controls should be fairly short and twisted together to reduce RF pickup within the metal box. Such as twisting the volume control wires in a set, the encoder in a set, microphone in a set, the antenna wires in a set. Best to let the antenna connector be at one side of the box, close to where the antenna is connected to the PC board, the power connector close to where it connects to the PC board, and the audio/digital at the other side. That would minimize the very slight possibility of the minimal ground loops (minimized by the low impedance of the chassis ground) having any effect. But the big common ground should be a benefit virtually in all cases. 
>
> Tom, wb6b

Tom, wb6b
 

On Wed, Aug 21, 2019 at 11:44 PM, iz oos wrote:
My front and back panels are plastic
Even though it has been considered the best practice to use metal chassis for RF designs (and sensitive audio or other types of sensitive projects), many modern designs include a very sound ground distribution on the PC board itself and often some kind of additional shielding via a conductive coating on the inside of the plastic case or other techniques. That being said, a large number of folks have built their uBitx transceivers into 3D printed or other plastic cases with remarkable success. 

Tom, wb6b

Jim - KJ7EZN
 

Electric guitar body cavities (pickup mounts, etc) often use a conductive copper tape for shielding.  If anyone is having a shielding issue with 3D printed cases or wood cases, this might be a good solution.  Available here.
--
73! de KJ7EZN   Jim

jim
 

Got mine from a "stained glass shop" 30 or so years ago ...are any of those things still around?

Jim

On Thursday, August 22, 2019, 4:54:45 PM UTC, jhowell39 via Groups.Io <jhowell39@...> wrote:


Electric guitar body cavities (pickup mounts, etc) often use a conductive copper tape for shielding.  If anyone is having a shielding issue with 3D printed cases or wood cases, this might be a good solution.  Available here.
--
73! de KJ7EZN   Jim

Ian Reeve
 

We can buy this in the UK as a deterrent to slugs and snails guzzling our seedlings.I bought mine from a "*pound*" store in the gardening section


From: BITX20@groups.io <BITX20@groups.io> on behalf of jim via Groups.Io <ab7vf@...>
Sent: Thursday, August 22, 2019 6:08:28 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Isolate any jacks/controls from metal chassis? #ubitx
 
Got mine from a "stained glass shop" 30 or so years ago ...are any of those things still around?

Jim

On Thursday, August 22, 2019, 4:54:45 PM UTC, jhowell39 via Groups.Io <jhowell39@...> wrote:


Electric guitar body cavities (pickup mounts, etc) often use a conductive copper tape for shielding.  If anyone is having a shielding issue with 3D printed cases or wood cases, this might be a good solution.  Available here.
--
73! de KJ7EZN   Jim

Gwen Patton
 

I used a spray-on conductive nickel coating inside my uBitX plastic case. It worked really well for shielding. I do recommend using a clear coat of lacquer over it, just a thin coating, to keep the nickel from flaking and landing on the PCB. You can always lightly sand a bit off at the edges where the case closes to keep shielding integrity. I have that copper foil tape, and it's very good, but I've been using it lately for small transmitting loop radiators.

73,
Gwen, NG3P

Ian Reeve
 

I use the copper tape to shield wires that are suceptable to rf like the wires,taped to the case.Keeps them secure and screened as well. 


From: BITX20@groups.io <BITX20@groups.io> on behalf of Gwen Patton <ardrhi@...>
Sent: Thursday, August 22, 2019 7:30:05 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Isolate any jacks/controls from metal chassis? #ubitx
 
I used a spray-on conductive nickel coating inside my uBitX plastic case. It worked really well for shielding. I do recommend using a clear coat of lacquer over it, just a thin coating, to keep the nickel from flaking and landing on the PCB. You can always lightly sand a bit off at the edges where the case closes to keep shielding integrity. I have that copper foil tape, and it's very good, but I've been using it lately for small transmitting loop radiators.

73,
Gwen, NG3P

Tom, wb6b
 

On Thu, Aug 22, 2019 at 09:54 AM, <jhowell39@...> wrote:
Electric guitar body cavities (pickup mounts, etc) often use a conductive copper tape for shielding
I bought a roll on Amazon some time back. The copper tape is handy.

One thing to note is: The tape claimed to have conductive adhesive. There was absolutely nothing conductive at all about the adhesive. 

I cut a hole in a piece of paper and stuck two pieces of the tape together so they only make contact through the 1/2 inch hole in the paper and I could not measure any resistance less than an open circuit.

If I stuck two pieces of copper tape together where they overlap (the edge of one going down the center of the other) then I measured a low resistance connection between them.

I believe in the case of the overlap, the rough edge of the copper tape where I cut it was making contact with the top of the copper foil I stuck it to.

I still like the tape, I just make sure I add some solder bridges across the overlapped layers. Even if the adhesive was conductive, probably not a good idea to rely on it for a solid electrical connection.

I've found this tape handy for adding big ground areas to prototype board projects, too.

Tom, wb6b

Jim
 

Used sticky back copper foil to line the plastic case on my SDRPlay. Worked well. Cleaned up some noise issues.

Jim
WA3APC