Updated March 29,
here to go to our main page on microwave connectors
here to go to our page on how (not) to trash a cal kit!
Click here to go to our page on cable care (new for April 2013!)
Your connectors and adapters
cost someone a lot of money. Show some respect. Read the material
below so you'll know how to treat connectors so they'll have a long
and productive life.
torque (separate page)
wrenches (separate page)
How to deal
with stuck connectors
saver - what's that?
(not) to trash a cal kit (separate page)
Connector Do's and Don'ts
Some things you should know about
1. Don't use pliers on a "stuck" connector for any reason.
There are wrenches for every size adapter, even SMA bullets. If
you can't fit a wrench to your stuck connector, see
2. Learn how to clean connectors with alcohol
and cotton swabs. Cleaning the threads is good practice, but stay
away from cleaning the center conductor of an air dielectric connectors
such as 3.5mm, 2.9mm and 2.4mm.
3. Learn how to gage connectors to determine if they are out of
spec. One bad connector can damage many.
4. Don't use higher frequency connector than you need. Save the
2.9mm and 2.4mm parts for millimeterwave measurements.
5. Never use any part of a calibration kit as an adapter. Ever.
If you need a special adapter, buy it, borrow it or steal it, but
not from the cal kit.
6. Use a torque wrench.
For most connectors with 5/16 inch hex nuts, use 6-8 inch-pounds.
It's OK to use less torque, but not more. Check out our page on
7. Remember, righty-tighty, lefty-loosey! The total damage done
by people turning stuff in the wrong direction is second only to
damage caused by klutzes who "thumb" hybrids.
8. Remember, you are not tightening lug nuts. The hardware you hold
in your hands could very well be worth more than your automobile.
So be gentle with it. Pretend it is made of eggshells and filled
with explosives (unless you are in an airport!)
9. When you are tightening or loosening a connector, try not to
spin the mating surfaces against each other. Here's
some photos of what will happen! You should only be turning
the threaded sleeve. Turning the mating surfaces means you are wearing
out the connector for no reason other than you have poor motor skills.
Did you ride the short bus?
You've just bought a nice new
set of coax adapters for that new lab project. They come with some
plastic caps on each end... so you take off the caps and throw them
WRONG! Those plastic thingies
are called dust caps for a reason, they keep your connectors
clean. Keep them as long as you keep the adapters, and your adapters
will last a lot longer, like the happy SMA to 7-mm adapter shown
in the photo below:
Adapters and connectors are precision
items, that's why they cost a fortune. So why does everyone treat
them like common hardware? Check out the picture below, whoever
"owns" a bench that stores connectors like this should
never be allowed back in your lab! Those two-cents worth of stainless-steel
screws are full of contaminates like oil, skin, and the worst culprit,
tiny pieces of metal. Store them separately, and keep the dust caps
on the adapters, or instead of being called a "lab rat"
(a term of endearment) you will be called "persona non grata."
Speaking of moronic behavior,
check out the photo of the 7 mm connector below, then remember to
never do this. What are we talking about? We're talking about setting
the 7 mm connector down on its contact spring. The contact spring
is the doohickey that allows the 7 mm connector to be sexless; it
is a precision machined, gold-plated beryllium-copper spring contact
that sticks out from the center conductor ever so slightly, so that
when two 7 mm connectors mate the center conductor make spring contact.
The way to protect the connector is to always spin the sleeve clockwise
to extend the threads, then push on a dust cap. Someone paid a lot
of money for this connector, show some respect! If you see someone
treating 7 mm connectors like the one in the photo, bust them one
in the mouth for us.
Never drop a torque
wrench (or any other hardware in your laboratory for that matter),
since the shock of hitting the floor can degrade the calibration.
In some laboratories and factories, torque wrenches that have been
dropped have to be sent back to Metrology for re-calibration. We've
heard this is sometimes a union labor trick, drop all the torque
wrenches on the floor, and then there's nothing left to do but read
the sports section of the Boston Herald. Oh well, better wrenches
than GaAs wafers, right?
We have a separate
page on connector torque settings,
located here, and a page on torque
wrenches as well!
How to deal
with stuck connectors
The female to female SMA adapter
is the cause of much pain in the microwave laboratory. Why? because
it tends to get stuck. The photo below illustrates the problem.
The "bullet" on the left is the cheapest possible adapter
you can buy. Too bad it doesn't have a useful place to grip it with
a wrench (sure, it has two tiny flat spots, but you can't get even
the thinnest open-end wrench onto them once it's screwed into something).
Notice the damaged threads due to some fool that jammed it into
a male connector, over-torqued it, and after it was stuck used common
slip-joint pliers to remove it. Now that the stainless-steel threads
are damaged on this connector, it will damage every male connector
that it mates with, and it will continue to get stuck every time
it is used. Our sage advice is to throw this connector out!
You can avoid ever having a stuck
SMA bullet if you will always buy adapters that can accommodate
a wrench. One inexpensive answer is to buy bulkhead-mount female-to-female
adapters, as shown in the right of the photo above. Such a part
is designed to be used to pass RF signals through a panel, with
coax cables attached to both sides. It makes a great adapter for
the lab because it has a 5/16 inch hex nut built-in. And, trust
us, it doesn't have "double the loss" of the bullet on
Since it's bound
to happen, how do you deal with a stuck connector? You should have
on hand a pair of soft-jaw pliers, they pay for themselves
every time you remove a stuck connector without damaging it. Below
are two solutions to this problem that have been evaluated by Microwaves101.
The larger pliers are available from Protech
Products for $12.95 plus shipping and have replaceable nylon
jaws. These are made in Japan, and will serve you for a long time.
The plastic pliers are from Ted
Pella and are $4.80 plus shipping. They are designed for chemists
that handle nasty stuff that might dissolve metal pliers. It's hard
to say how long these plastic pliers would last before they break,
but they are the perfect solution for a microwave lab or factory
that has a problem with tool theft (don't they all?) Buy a couple
of dozen and put one on every bench, no one is going to rip off
these Cracker Jack prizes! Then keep one of the Protech pliers locked
up for emergencies. Whichever pliers you buy, tell them that Microwaves101
sent you! To view a better resolution picture of these pliers, click
If you use type N and 7 mm connectors
in your lab, you might want to pick up a pair of the larger "AN
connector pliers" (pictured below) that are marketed by all
the big tool companies such as Contact
East, for around $30. The smallest diameter connector these
can handle is 3/4 inch, so they won't help you with stuck SMAs.
Do yourself a favor and remove
pliers such as these from your all of your microwave lab benches,
unless you enjoy paying for replacements for all of your damaged
be cleaned and inspected periodically. It isn't hard to do, all
you need to clean connectors are some cotton swabs and fifty cents
worth of isopropyl alcohol, as shown below. Say, who's the model
in the picture? You can tell that Dude is hot! Like an otter!!!
Here is some info on the difference
between isopropyl alcohol (shown in our picture) and denatured alcohol,
sent in by Glenn from a leading connector company (thanks, we agree!)
"You state that to
clean RF connectors to use isopropyl alcohol. I have always found
that using this type leaves a serious film on my connectors and
did not want to risk the electrical integrity of my measurements.
Instead I went to a denatured alcohol. This leaves a very clean
finish and I never had a problem with a film. Although I never
found a problem with the film, I think most people don't know
that this happens with regular isopropyl alcohol."
involves starts by dipping the swab into alcohol. Outside threads
of connectors should be rigorously cleaned as shown on the left
below, using a circular motion. Cleaning the inside of a connector
(center photo) requires some common sense, and a gentle touch.
It's OK to clean the inside of an SMA male and female connector,
everything is supported with the Teflon dielectric. However, if
you clean an air-dielectric connector, you have to be extremely
gentle. Don't do anything that would bend the center conductor.
Better yet, just clean the outside threads of the females, the
dirt that is inside the males will eventually end up there anyway.
Throw out the swab when it looks like the swab on the left in
the photo on the right!
threads are cleaned, you will be able to hand-tighten all connections
to within 1/2 turn of the proper torque. Note that if you find
yourself having to tighten a connector from start to finish with
a wrench, something is wrong with this picture. Either you are
mis-aligning the connector while you are tightening it (which
can cause damage), or one of the connectors in the pair is already
damaged. Connector damage is often the result of a component that
has been dropped and lands on the threads of the female, causing
the connector to become slightly "D-shaped" instead
of perfectly round. If you have a connector like this it needs
to be replaced, don't keep jamming it into other connectors, you
are spreading the bad news.
saver - what's that?
A connector saver
is an adapter that you put
on an expensive piece of equipment, and make all future connections
at this interface. This protects your equipment, because when
some idiot trashes the connector saver, you replace a relatively
inexpensive adapter rather than send your equipment out for repair.