View Single Post
  #36   Report Post  
Old June 15th 10, 09:44 PM posted to rec.radio.amateur.antenna
Roy Lewallen Roy Lewallen is offline
external usenet poster
 
First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default BNC connectors 75 Ohm versus 50 Ohm?

Sal M. O'Nella wrote:

After I got out of the Navy, I worked as a Marine Electrician,
installing equipment on Navy ships. My foreman told me that it is
rarely done, but the Navy can perform a Quality Assurance "pull test" of
25 lbs on a connector. I think that's a lot of pull for a connector to
withstand.


In a previous life I was tasked with tailoring a large number of RG-58
cables connecting radar scopes at a new installation in Korea. This
involved cutting the cables to length and installing clamp and solder
type BNC connectors. The rumor was that the Korean troops were supposed
to be helping us, but we never saw them -- until one day, when they
showed up. The one assigned to help me sat down and, neither of us being
fluent in the other's language, I proceeded to show him how to assemble
the connector.

Now the job of one of the several pieces, a metal ring, is to push
against and expand a rubber washer, which is mainly what holds the
connector together. This piece looks like it should go upside down from
the correct orientation, but if put on that way, the rubber washer won't
expand and the connector will come off very easily, with only a gentle
tug. If assembled correctly, it'll take a lot of pulling, as Sal says,
to get it off. I've never seen a correctly assembled connector come off.

Getting back to the story, I carefully demonstrated the correct assembly
method to the Korean troop, emphasizing the orientation of the ring.
After putting the connector on, I showed him our standard test. We would
grab the connector in one hand and about two feet down the cable with
the other. Then we put our hands together, making a loop of cable, and
briskly yanked them apart, resulting in a really good sharp tug on the
connector. A properly assembled connector had no trouble with this test.

So I gave him the parts and went to work on a connector. After a while
he handed me the cable with attached connector. I gave it the tug test
and the connector snapped right off. So I repeated the mimed
instructions, with extra emphasis on the ring orientation, then put him
to work again and got back to what I was doing. When he was finished he
handed me the connector, I did the yank test, and again the connector
popped right off. He shrugged, muttered something under his breath, got
up, and left. Guess he figured he'd had enough of that game, where he
assembled connectors and I pulled them off. We never saw the Korean
troops again.

Roy Lewallen, W7EL