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#31
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BNC connectors 75 Ohm versus 50 Ohm?
On Sun, 06 Jun 2010 19:19:42 -0400, John Passaneau
wrote: *Snip* No the size of the center conductor pin is different between 75 and 50 ohm connectors and will either make bad contact or damage the socket. *Snip* John Passaneau W3JXP Not in years, they used to be made with different sized pins but now rely on different dielectrics for impedance. H. Who used to get yelled at by his boss for inserting 50 ohm males into 75 ohm females. |
#32
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BNC connectors 75 Ohm versus 50 Ohm?
[Sorry for being a little late to the party, but I was off newsgroups most of this week.] This thread had some discussion of adapters and I want to share my bad experience with some low-cost items, proving, once again, that you get what you pay for. I am testing all my adapters and discarding some because the assemblies are pulling apart with very little force. One manifestation: tightening the threaded ring on a PL-259 (either cable end connector or adapter) and having the ring just continue all the way on, separating from the connector body. One test for a future failure has been any lack of smoothness when I rotate the ring while tugging it gently. If it binds, rather than turning smoothly in my hands, it's going to fail. Also, some of the cheap connectors are press-fit together very poorly; they pull apart with only a few pounds of pull. Most of my early exposure to coax connectors was in and around the US Navy, where reliable connectors are the rule, so I was a spoiled child. "Sal" (KD6VKW) |
#33
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BNC connectors 75 Ohm versus 50 Ohm?
On 06/13/2010 01:50 PM, Sal M. O'Nella wrote:
[Sorry for being a little late to the party, but I was off newsgroups most of this week.] This thread had some discussion of adapters and I want to share my bad experience with some low-cost items, proving, once again, that you get what you pay for. I am testing all my adapters and discarding some because the assemblies are pulling apart with very little force. One manifestation: tightening the threaded ring on a PL-259 (either cable end connector or adapter) and having the ring just continue all the way on, separating from the connector body. One test for a future failure has been any lack of smoothness when I rotate the ring while tugging it gently. If it binds, rather than turning smoothly in my hands, it's going to fail. Also, some of the cheap connectors are press-fit together very poorly; they pull apart with only a few pounds of pull. Most of my early exposure to coax connectors was in and around the US Navy, where reliable connectors are the rule, so I was a spoiled child. "Sal" (KD6VKW) PL-259's I can handle. BNC's drive me nuts trying to get a good connection. I gave up and just buy my cables now. Bill |
#34
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BNC connectors 75 Ohm versus 50 Ohm?
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#35
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BNC connectors 75 Ohm versus 50 Ohm?
"Gaius" wrote in message ... In article , Cables can pull out, given a bit of a tug. I use solder/clamped connectors and always solder the braid to the clamping sleeve. Never had a failure..... 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. |
#36
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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 |
#37
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BNC connectors 75 Ohm versus 50 Ohm?
Roy Lewallen wrote in
: I've never seen a correctly assembled connector come off. Another story, but with a different outcome. I worked in a training school at one stage, and we thought we would get trainees to make up BNC RG58 patch cables as a practical exercise, and we would feed the output into our satellite labs where cables didn't seem to last long (trainees pulled equipment trolleys around by the coax if it didn't reach the desired socket). Total failure, the BNC field serviceable connectors were just too complicated for dissinterested trainees more interested in discussing fast cars than concentrating on the job... and they had no stake in it, if the cables didn't work, it didn't matter too much. Solving the problem of the connectors pulling off led me to the Amphenol specs, and I found that the pull out spec for the field serviceable connectors was *much* lower than the spec for the crimp connectors. So, I bought a quality crimp tool (in those days, it was a few hundred dollars), and some Kings crimp connectors, and we switched the classes to use the crimp components and a trim jig. The outcome was much better, fewer faulty cables, and the crimped cable retention was much better and consistently so. No I know that one of the large suppliers to hams advertises "crimped, not soldered", but that is just a blatant case of playing to the market. A bit like the single core 4:1 Guanella balun that manufacturers attribute to Sevik's assurance that it will work fine on a fully floating load... whan antenna system is a fully floating load. The theme is the customer is always right, if he wants something that doesn't make sense, see Rule 1. An interesting new connector type is the "compression connectors", "Snap- n-Seal" is a proprietary name. I tried some of these on RG6, and a bit suspicious of the cable retention mechanism, every one I tested using different types of RG6 (including QS), hung on until the cable tore apart some distance from the connector. Owen |
#38
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BNC connectors 75 Ohm versus 50 Ohm?
Owen Duffy wrote in news:Xns9D9948E3052AFnonenowhere@
61.9.191.5: No I know that one of the large suppliers to hams advertises "crimped, not soldered", but that is just a blatant case of playing to the market. Got that back the front, didn't I. DXE advertises "soldered, not crimped", but that is just a blatant case of playing to the market. Owen |
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