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#1
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Brian Kelly wrote:
I'd like to build a compact antenna/100W rig patch panel instead getting involved with big expensive coax switches. Could be done nicely with BNC connectors & RG-58. Does anybody have a link to a site which provides freq (160M-440) vs. power handling ratings for BNC connectors? I don't know about a website, but it has often been discussed here. Try searching through http://groups.google.com/advanced_group_search It all comes down to the RF current through the center connection. This is partly about skin effect and surface conductivity, but equally important - and less predictable - is accurate assembly of the center pins. If at all possible, use connectors with captive center pins. This removes the biggest source of inaccuracy in amateur assembly. All the contact pressure in a BNC derives from the rubber washer inside the bayonet ring. A good BNC should need quite a hard twist to make the bayonet click into place... and in old surplus plugs, this springiness does wear out. Bottom line: BNCs in good condition are fine for 100W at 440MHz, so they're good for that power level at any lower frequency too. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
#2
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BNCs are almost universally used for non microwave test equipment. So, I
have used them a lot. My biggest problem has been the shield not making good contact with the body of the connector after a while. By far, I have had the fewest problems with the kind where a sleeve is crimped over the outer insulation to provide strain relief. On the better connectors, this sleeve is about an inch long. You do not want to allow any flexing of the bare shield. Tam/WB2TT "Brian Kelly" wrote in message om... I'd like to build a compact antenna/100W rig patch panel instead getting involved with big expensive coax switches. Could be done nicely with BNC connectors & RG-58. Does anybody have a link to a site which provides freq (160M-440) vs. power handling ratings for BNC connectors? Tnx, w3rv |
#3
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Crazy George wrote:
All the contact pressure in a BNC derives from the rubber washer inside the bayonet ring. A good BNC should need quite a hard twist to make the bayonet click into place... and in old surplus plugs, this springiness does wear out. Ian, you need to chop one apart again and look at the construction. The contact pressure is provided by the wavy washers behind the shoulder. The rubber washer, which is on the other side of the shoulder, if anything opposes the contact pressure direction as it 'seals' against the end of the female cylinder. Well, thank you, George - they do say "Learn a little every day"! I've sawn up several BNC plugs, but never in that particular way. Even though it's a wavy washer, the fact remains that the spring eventually weakens (it happens it in C plugs also). -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
#4
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Hm, I assembled about a gazillion BNC connectors in a previous life.
They were whatever brand the Air Force bought, and they didn't contain a wavy washer. The pieces were the shell, the tip, and the screw end; and to hold the braid on the inside there were only the rubber washer, a strange-shaped washer, and a flat washer (to go between the screw end and the rubber washer to reduce the friction when tightening). One surface of the strange washer was flat (actually, stepped), and that was where the braid was smashed against the boss inside the shell. The other was tapered in such a way that it would force the rubber washer to expand outward to squeeze tightly against the shell. When disassembling one, we'd often find that the rubber washer would be cut nearly in two. The only pressure on the braid was from the rubber washer via the force of the screw end. A common mistake was to put the strange washer in upside down, since it just looked right that way, with the braid nicely cascading over a sort of angled surface. When that was done, the washer wasn't properly expanded by the tapered end of the strange washer, and you could easily yank a connector off. When properly assembled, there's no way you can yank one off. I have a bunch of connectors in my junk box which are essentially the same as I've described, but with a couple of more parts relating to the tip and insulator. I assemble one from time to time when needed and, like their military counterparts, they've been very trouble free. Roy Lewallen, W7EL Ian White, G3SEK wrote: Crazy George wrote: All the contact pressure in a BNC derives from the rubber washer inside the bayonet ring. A good BNC should need quite a hard twist to make the bayonet click into place... and in old surplus plugs, this springiness does wear out. Ian, you need to chop one apart again and look at the construction. The contact pressure is provided by the wavy washers behind the shoulder. The rubber washer, which is on the other side of the shoulder, if anything opposes the contact pressure direction as it 'seals' against the end of the female cylinder. Well, thank you, George - they do say "Learn a little every day"! I've sawn up several BNC plugs, but never in that particular way. Even though it's a wavy washer, the fact remains that the spring eventually weakens (it happens it in C plugs also). |
#5
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Roy:
Take an unwanted BNC and the biggest pair of diagonal cutters you have. Clip the latching collar off the shell at the rearmost point of the two latching slots. May take a couple of tries on each side depending on the cutters and amount of force you can muster. Inside you will find the components which create the mating pressure, usually including several half washers which immediately fall out. If you have never cut the latching collar off of a BNC, you have never seen that part of the construction, which is hidden inside the knurl. And, yes, all the BNCs the Air Force purchased had the wavy washer inside, or they would not stay latched. You are describing the cable retention hardware, an entirely separate issue. BTW, after you remove the latching collar, you now have a universal plug which will mate with female BNC, TNC and N. Depending on brand, the retention is iffy, but I find them very useful for quick connect/disconnect applications. Trompeter plugs, with their machined sleeve, are quite good without the latch. -- Crazy George Remove NO and SPAM from return address "Roy Lewallen" wrote in message ... Hm, I assembled about a gazillion BNC connectors in a previous life. They were whatever brand the Air Force bought, and they didn't contain a wavy washer. The pieces were the shell, the tip, and the screw end; and to hold the braid on the inside there were only the rubber washer, a strange-shaped washer, and a flat washer (to go between the screw end and the rubber washer to reduce the friction when tightening). One surface of the strange washer was flat (actually, stepped), and that was where the braid was smashed against the boss inside the shell. The other was tapered in such a way that it would force the rubber washer to expand outward to squeeze tightly against the shell. When disassembling one, we'd often find that the rubber washer would be cut nearly in two. The only pressure on the braid was from the rubber washer via the force of the screw end. A common mistake was to put the strange washer in upside down, since it just looked right that way, with the braid nicely cascading over a sort of angled surface. When that was done, the washer wasn't properly expanded by the tapered end of the strange washer, and you could easily yank a connector off. When properly assembled, there's no way you can yank one off. I have a bunch of connectors in my junk box which are essentially the same as I've described, but with a couple of more parts relating to the tip and insulator. I assemble one from time to time when needed and, like their military counterparts, they've been very trouble free. Roy Lewallen, W7EL Ian White, G3SEK wrote: Crazy George wrote: All the contact pressure in a BNC derives from the rubber washer inside the bayonet ring. A good BNC should need quite a hard twist to make the bayonet click into place... and in old surplus plugs, this springiness does wear out. Ian, you need to chop one apart again and look at the construction. The contact pressure is provided by the wavy washers behind the shoulder. The rubber washer, which is on the other side of the shoulder, if anything opposes the contact pressure direction as it 'seals' against the end of the female cylinder. Well, thank you, George - they do say "Learn a little every day"! I've sawn up several BNC plugs, but never in that particular way. Even though it's a wavy washer, the fact remains that the spring eventually weakens (it happens it in C plugs also). |
#6
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Well, Roy, here is cut and paste from Ian's post:
"All the contact pressure in a BNC derives from the rubber washer inside the bayonet ring. A good BNC should need quite a hard twist to make the bayonet click into place... and in old surplus plugs, this springiness does wear out." "....rubber washer inside the bayonet ring." sure doesn't sound like cable retention to me. Sorry for the confusion, I guess. On the other hand, when the rubber washer deteriorates, the connectors mate much more easily once, as the female contact is destroyed in the process. Ian, I suspect that is your failure mode, as I have chopped up some very old connectors, and the spring washers still seem to retain their shape, while the rubber is rotten. On the other hand, I have seen some cheapies which are soft from the manufacturer. I send those back. -- Crazy George Remove NO and SPAM from return address "Roy Lewallen" wrote in message ... Ah. We're talking about two different things. I thought that the subject had come up about securing the braid within the connector. Ian's initial response was along the line of what I've observed. And that's what I was talking about. But you're talking (I think) about what secures the male connector to the female, another issue altogether. Yes, I've never broken the latching collar off a BNC, so I've never seen the associated components. I fully believe you that there's a wavy washer to apply the pressure. Roy Lewallen, W7EL |
#7
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My mistake. Sorry.
Roy Lewallen, W7EL Crazy George wrote: Well, Roy, here is cut and paste from Ian's post: "All the contact pressure in a BNC derives from the rubber washer inside the bayonet ring. A good BNC should need quite a hard twist to make the bayonet click into place... and in old surplus plugs, this springiness does wear out." "....rubber washer inside the bayonet ring." sure doesn't sound like cable retention to me. Sorry for the confusion, I guess. On the other hand, when the rubber washer deteriorates, the connectors mate much more easily once, as the female contact is destroyed in the process. Ian, I suspect that is your failure mode, as I have chopped up some very old connectors, and the spring washers still seem to retain their shape, while the rubber is rotten. On the other hand, I have seen some cheapies which are soft from the manufacturer. I send those back. -- Crazy George Remove NO and SPAM from return address |
#8
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On Mon, 4 Aug 2003 22:06:49 -0500, "Crazy George"
wrote: On the other hand, when the rubber washer deteriorates, the connectors mate much more easily once, as the female contact is destroyed in the process. Hi All, Another failure mode is mixing HV BNC (quite rare) with standard BNC. 73's Richard Clark, KB7QHC |
#9
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Richard Clark wrote:
On Mon, 4 Aug 2003 22:06:49 -0500, "Crazy George" wrote: On the other hand, when the rubber washer deteriorates, the connectors mate much more easily once, as the female contact is destroyed in the process. Hi All, Another failure mode is mixing HV BNC (quite rare) with standard BNC. Yes, if you're hamfisted enough, you can easily connect a BNC signal lead to an MHV high voltage supply. They're rare compared with BNC, but they do appear at hamfests. Whoever invented this booby-trap should have been connected to it! As amateurs, we only need to know two things about the MHV series: 1. Plugs and sockets look like a "stretched" BNC. 2. Avoid. -- 73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB) Editor, 'The VHF/UHF DX Book' http://www.ifwtech.co.uk/g3sek |
#10
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I used to think crimp on connectors were just the lazy mans way of putting
on a BNC. After 15 years of using them I have come to believe they are better than the old style. I just removed an old radar system from service whith hundreds of BNC connections. None of the crimp ons were bad, not so for the others. I am sure this was the cause of many of the intermitent problems that had plagued this radar. "Tarmo Tammaru" wrote in message ... BNCs are almost universally used for non microwave test equipment. So, I have used them a lot. My biggest problem has been the shield not making good contact with the body of the connector after a while. By far, I have had the fewest problems with the kind where a sleeve is crimped over the outer insulation to provide strain relief. On the better connectors, this sleeve is about an inch long. You do not want to allow any flexing of the bare shield. Tam/WB2TT "Brian Kelly" wrote in message om... I'd like to build a compact antenna/100W rig patch panel instead getting involved with big expensive coax switches. Could be done nicely with BNC connectors & RG-58. Does anybody have a link to a site which provides freq (160M-440) vs. power handling ratings for BNC connectors? Tnx, w3rv |
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