[Yaesu] What is wrong with SMA?

Tue Jan 9 21:56:32 EST 2007

At 08:21 PM 1/9/2007 -0600, Rob Atkinson wrote:
>I have a friend who has used both sma and bnc and he prefers sma. 
>he says the bnc eventually breaks after repeated stress on the
>connector when the HT is on a belt and the duck is sticking up against
>his side, due to the nature of the bnc design in which the male can rock
>a bit back and forth on the two pins that stick out on the jack. with 
>sma the male threads on and is solid.

Indeed true. That's why you RARELY see BNCs used as the signal input jack
on high-quality spectrum analyzers and other such high-precision RF gear.
In a former life, I used to work with cable TV stuff and one of our more
important test gear was an HP 8590 spectrum analyzer with CATV option. This
option provided 75 ohm input. When I first ordered the thing, I ordered it
with the 75 ohm BNC. We were having to have that connector replaced every
year due to wear. The 3rd time, I had it replaced with a 75 ohm type N
connector, and from there on, we used what we called a "connector saver",
which was merely a male type N to female BNC adapter, 75 ohm type. So when
the BNC got worn out, we could just screw on another adapter and away we went.
We would often find several dB variation in measured signal strengths while
using that BNC, too.
SMAs have a specified lifetime too, though. THe gold plating on the center
conductors is less than a thousandths of an inch thick and wears off to the
point where HP says replace the SMA after so many connection cycles,
something like a cupla hundred IIRC. But that's mainly critical only at
very high microwave frequencies and mainly to keep the junction of the male
and female pins absolutely perfect so as to minimize any VSWR bump at, for
example, 18 GHz. You can really see a worn SMA by observing the return loss
of a connector pair above 10 GHz.
But at a cupla hunnerd megahurts..... naw, no worries unless you actually
find shredded metal in the connector.
Bottom line: no matter WHAT kind of connector it is: BNC or SMA or even
type N: MINIMIZE the number of times that you mate them. And every so
often, use canned air to blow out the shredded metal that you'll see inside
a used connector.
PL259/SO239s are already so crummy an RF connector that you'll hardly ever
notice their deterioration until they fall apart ;o(((((((((((((((
Steve, K0XP