In article , Dr. Anton Squeegee
writes:
In article ,
says...
John Walton wrote:
with what would appear to be a plethora of devices using SMA connectors,
why
are they still so expensive?
Precision machining. The tolerances are tighter than most connectors.
Some of the newer RF connectors are even worse. They have to be machine
assembled and ordered made to length, or with a single connector.
Regrettably true. The SMA/SMB series are the last ones I know of
that still have big enough individual pieces (barely) to be hand-
assemble capable. Those tiny center pins are a real pain, though...
The basic SMA design came about almost 30 years ago as a small
coaxial connector that would work on up to X-band (8 to 12 GHz).
In order to even approach that frequency ALL the mating surface
tolerances have to be precise in order to avoid discontinuities that
raise the VSWR. Tighter tolerances mean greater cost to produce.
The old "UHF" connectors (SO-, PL- numbers) common on amateur
HF and low-VHF equipment were obsolete for new designs a half
century ago. Those are cheap because there isn't much QC on
them and the tolerances are sloppy in comparison.
SMAs used with semi-rigid coax are quite easy to make once you
get the hang of it and are incredibly durable physically and in all
kinds of environments. The solid center conductor of the semi-rigid
becomes the "pin" just as in the TV set F connector used with
RG-59 75 Ohm semi-flexible. F connectors are good to 1 GHz
(with some higher VSWR than others) so don't anyone knock the
method. SMAs are dandy to use with stripline in aluminum hog-
out enclosures.
SMBs are on the SMA basic plan but are push-on, pull-off mating
for quick connect/disconnect. Okay for limited testing in systems
and prototyping. Note that BNC males with the outer bayonet
connecting sleeve removed will mate with N females for quick
testing too (no remarks about miscegenation, please...).
You can spot a pro in microwave RF work by the extra 3/8" across
the flats wrench within easy reach. An open-end, closed-end
combo 3/8" wrench is only about 3 1/2" long (Craftsman). I used
to carry mine on the business keychain in my pants pocket...:-)
Len Anderson
retired (from regular hours) electronic engineer person