K2 - Isolation box construction for digital modes

[Euan-3]

I'm building an isolation box (between K2 and computer with external
soundcard) for digital operations, containing two 1:1 transformers and
voltage divider resistors. The box is metal. All input and output sockets
are 3.5mm mono and are grounded to the box, hence all input and output
braids are connected together via the box. Is this likely to create a ground
loop problem? Advice would be appreciated before I solder it all together.

73, Euan M0GBZ
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[Bob Naumann W5OV]

If you do that, you can leave out the isolation transformers - and the whole
box for that matter.

You're "un-isolating" them by connecting the grounds together.

Bob W5OV


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Euan McPherson
Sent: Monday, February 22, 2010 5:32 AM
To: [hidden email]
Subject: [Elecraft] K2 - Isolation box construction for digital modes

I'm building an isolation box (between K2 and computer with external
soundcard) for digital operations, containing two 1:1 transformers and
voltage divider resistors. The box is metal. All input and output sockets
are 3.5mm mono and are grounded to the box, hence all input and output
braids are connected together via the box. Is this likely to create a ground
loop problem? Advice would be appreciated before I solder it all together.

73, Euan M0GBZ
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[Don Wilhelm-4]

Euan,

Your grounds should not be connected between the K2 and the computer -
that will "un-isolate" your isolation box.  At the isolation box, use
stereo plugs and jacks at your interface box and connect the
transformers to the tip and ring.  Similar if you are using an
opto-isolator on the PTT circuit - use a stereo jack and plug there too.
If you wish to use shielded cables between the box and the K2, ground
the shield only at the K2 end (use 2 conductor plus shield cable).  
Actually twisted pair conductors will be as good or better than shielded
cable - CAT-5 wires are good for self shielding.

73,
Don W3FPR

Euan McPherson wrote:

> I'm building an isolation box (between K2 and computer with external
> soundcard) for digital operations, containing two 1:1 transformers and
> voltage divider resistors. The box is metal. All input and output sockets
> are 3.5mm mono and are grounded to the box, hence all input and output
> braids are connected together via the box. Is this likely to create a ground
> loop problem? Advice would be appreciated before I solder it all together.
>
> 73, Euan M0GBZ
>  
>

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[W7GJ, Lance]

Hello Euan,

When I built my interface box here (years before K3's were available - HI), I did
have ground loop problems.  I floated all the grounds in all the cables and did
NOT connect them all together at the box.  The only place they were grounded was
at the mic connector on the radio.  The way I did this was to use 1/8" stereo
connectors in and out of the box, but to use the "right" and "left" terminals to
transfer the lines into and out of the box, while leaving the ground unused.  GL
and VY 73, Lance

On 2/22/2010 11:31 AM, Euan McPherson wrote:

> I'm building an isolation box (between K2 and computer with external
> soundcard) for digital operations, containing two 1:1 transformers and
> voltage divider resistors. The box is metal. All input and output sockets
> are 3.5mm mono and are grounded to the box, hence all input and output
> braids are connected together via the box. Is this likely to create a ground
> loop problem? Advice would be appreciated before I solder it all together.
>
> 73, Euan M0GBZ
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>

--
Lance Collister, W7GJ (ex: WN3GPL, WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX)
P.O. Box 73
Frenchtown, MT  59834  USA
QTH: DN27UB
TEL: [phone]   URL: http://www.bigskyspaces.com/w7gj
LIVE MESSENGER CHAT: [hidden email]
2m DXCC #11, 6m DXCC #815

Interested in 6m EME?  Ask me about subscribing to the Magic Band EME email!
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[David Woolley (E.L)]

You would be well advised to read "Computer to Radio Interfacing - You
Don't Need An Expensive Interface!"
<http://www.audiosystemsgroup.com/HamInterfacing.pdf>, by Jim Brown, a
frequent contributor to this list and an expert on interference to audio
systems.

Basically, throw away the transformers and provide very good functional
earth bonding between all the components.

Euan McPherson wrote:
> I'm building an isolation box (between K2 and computer with external
> soundcard) for digital operations, containing two 1:1 transformers and
> voltage divider resistors. The box is metal. All input and output sockets
> are 3.5mm mono and are grounded to the box, hence all input and output
> braids are connected together via the box. Is this likely to create a ground
> loop problem? Advice would be appreciated before I solder it all together.


--
David Woolley
"we do not overly restrict the subject matter on the list, and we
encourage postings on a wide range of amateur radio related topics"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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