to (not) trash a calibration kit!
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content was contributed by Lou, a true microwave
muleskinner, who no longer lends his calibration kit to anyone.
He's got his reasons! The photos are of a 3.5 mm cal kit, but the
lessons here apply to any cal kit; when you damage one standard,
the rest of the team will get bad data until Mayor
McCheese can be convinced to pony up $10,000 to cover your carelessness.
Here's a view of Maury's "ruggedized"
3.5 mm connector (female). The center conductor internal diameter
expands to allow variations in pin diameter. It mates well with
SMA connectors that may be slightly out of spec, and it might
not get damaged if you rotate it during mating, but don't tempt
fate (we've seen these ruggedized connectors get get trashed). This
connector is from a Maury calibration kit for a
Here's Maury's 3.5
mm pin (male connector).
Packard) has their own "precision" 3.5 mm connector. The
internal diameter of the center conductor is fixed which allows
for minimum variation in impedance, which you'll need to get a good
calibration on your analyzer. The drawback is that the six spring
fingers inside are very delicate and easily destroyed.
Another view of the Agilent 3.5 mm connector.
Agilent 3.5 mm pin. It may be a little more pointed than the Maury
pin. If you thought that all 3.5 mm connectors were alike, you were
The rest of the pictures below
are from a trashed Agilent 3.5 mm cal kit. Some advice: never lend
out your cal kit to someone that doesn't know what they are doing.
It's a wise idea to label the kit with a notice about being drawn
and quartered if one rotates the standards while tightening them.
And it's best to keep your cal kit hidden.
This is what happens when you
mate an Agilent 3.5 mm with an SMA that has a burr on the pin. You
can see how the burr caught a finger and bent it in. It was probably
rotated during attachment.
Another Agilent 3.5 mm calibration standard. This one is wrecked,
it's now a worthless calibration standard.
Here's an Agilent 3.5 mm missing
all fingers. It looks OK if you didn't know it was supposed to have
six fingers down in there!
Some more advice: don't bid on
a 3.5 mm calibration kit on Ebay if the seller's name is Lou!
In summary, here's some rules
to follow in order to not trash a connector:
1) Never rotate 3.5 mm connectors
when tightening. Use a 8 in/lb torque
wrench and a smaller wrench to hold the other connector. A handy
RF connector wrench is made by grinding (on a bench grinder) down
the jaws of a small crescent wrench thin enough that it can grasp
the flat on a SMA barrel. Or you can buy a set of miniature SAE
(not metric) open-end wrenches (spanners for you limeys) that will
fit all of your connector needs. Look for thin wrenches so you don't
have to grind them ("ignition" wrenches are a good bet).
The ideal wrench set would be purely open-end, box wrenches serve
no purpose for microwave connectors (if you don't get that last
point, it's time for a new career!). These pictures were cribbed
from the Techni-Tool web site:
Thanks to Steve
from White Sands!
2) Dust out the dirt with dry
gas. Use 100% isopropyl alcohol (lab grade, not rubbing) to swab
the mating surfaces however the "proper" cleaner was banned
several years ago and they have not yet updated the cleaning instructions.
3) Buy some 3.5 mm to 3.5 mm
connectors and use them as jack savers when measuring SMA devices.
Label these as jack savers. SM Electronics actually sells 3.5mm
to SMA adapters, which would serve the same purpose and might save
you a few bucks.
Never, ever connect a SMA to
a 3.5 mm calibration standard, VNA cable, or some other expensive
3.5 mm device. Use the jack savers.