Hi Kyle,
It is important that the gap in the shield be exactly on the opposite
side of the loop (as I believe you cite in your construction details).
The loops with the gap at the end of the coax that is bent around do not
actually have much electric field shielding. The details are in my paper
from last year's EMC Symposium. The paper in pdf format is on my website
at www.dsmith.org or emcesd.com.
Doug
"Ehler, Kyle" wrote:
>
> Greetings,
> 15 years ago I was doing some work at SWRI in San Antonio where I watched an
> EMC tech construct two RF probes from small diameter copper jacket hardline
> (semi-flex coax?). These probes resemble a kid's toy soap bubble loop, but
> they work wonderfully well for non-contact source investigation of radiated
> emissions ranging into the Ghz region. Our lab still uses these for debug
> work to this day, but now they are a bit worn and I suspect they will need
> replacing. Trouble is, I'm fuzzy on their construction details. Below,
> please peruse the steps I recall and offer any corrections or improvements.
> I have attached a couple .jpg's for clarity (hope I didn't stretch the
> rules).
>
> -For the high resolution probe (see photos):
> 1) Start with 6 to 8" length of 0.0625 copper jacketed solid conductor
> hardline for 0.5" diameter probe.
>
> 2) Remove 0.125" of jacket and insulation from one end.
>
> 3) Roll-form stripped end of coax into 0.5" diameter loop with exposed
> center conductor and jacket touching probe shaft jacket.
>
> 4) Solder center conductor of loop to jacket first, then outer jacket
> of coax end to jacket of probe shaft.
>
> 5) With a sharp knife (X-Acto) cut a 0.010" concentric ring out of the
> jacket at the apogee from the probe shaft, exposing the center conductor,
> but not cutting it (ok to leave foam insulation intact).
>
> 6) At other (handle) end of probe shaft, affix a female BNC (or SMA?)
> connector (your choice?) and carefully solder fillet 360' of connector to
> jacket.
>
> 7) Dip finished probe twice into 'Plasti-Dip' of your choice colour.
> Let cure in between coats and before use.
>
> -For a low resolution probe:
> Substitute 0.125" hardline in 1) above.
> Form loop into 2" diameter in 3) above.
>
> The small loop and a wideband preamp is really good for non-invasive
> pinpointing the source of radiation (chip, trace, xtal, etc.).
>
> <<hi res loop.jpg>> <<hi res probe.jpg>>
>
> Kyle
>
> ------------------------------------------------------------------------
> Name: hi res loop.jpg
> hi res loop.jpg Type: JPEG Image (image/jpeg)
> Encoding: base64
>
> Name: hi res probe.jpg
> hi res probe.jpg Type: JPEG Image (image/jpeg)
> Encoding: base64
--
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___ _ Doug Smith
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========= Los Gatos, CA 95031-1457
_ / \ / \ _ TEL/FAX: 408-356-4186/358-3799
/ /\ \ ] / /\ \ Mobile: 408-858-4528
| q-----( ) | o | Email: [email protected]
\ _ / ] \ _ / Website: http://www.dsmith.org
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