John Miles wrote: > ); SAEximRunCond expanded to false > Errors-To: time-nuts-bounces+cfharris=erols.com+cfharris=erols.com@febo.com > >> I have made >> numerous shielded opens for network analyzer use by crimping an >> SMA connector >> nut onto a piece of copper semi-rigid shield tube without using any center >> insulator, or center pin. >> > > You can (supposedly) mess up an expensive 3.5mm female connector if you mate > it with a male SMA without a fixed center pin. Never done this myself but > have read about it. I have a bad habit of using the 3.5mm-APC7 adapters > from my cal kit for making general SMA connections to the 85046A test set, > and I always wonder if I'm going to mess them up. Unfortunately, the damage isn't terribly visible. I make it a general policy not to mate APC-3.5 with SMA, but I do the same thing with my APC-3.5 to APC7 adapters. I haven't yet found the appropriate SMA to APC7. I am looking to score a couple of APC7 to N Female adapters for a reasonable price, and then I will sin no more. One thing to be very careful with the APC7 is to not allow the two connectors to rotate relative to each other. That causes the gold mating shield contact to peen its gold into a little burr that extends into the air space between the shield and the center conductor. It also loses the gold on the shield contact. -Chuck Harris

Hi Chuck, You may be correct, the deformation is not obvious when looking at it with the naked eye (never actually measured it, but you prompted my curiosity, so now I will have to check :-) That may explain the relative vulnerability of these connectors. Regardless, the manufacturer of the type of crimp-on SMA connectors we use does not recommend their usage above 18 GHz. They do show strange VSWR patterns above 18 GHz. I have a particular narrow band product operating just above 21 GHz where I was planning to use them (I thought it would be close enough), but it did not work well enough. On the other hand, the equivalent soldered type is specified up to 26.5 GHz. I know the standard SMA spec is only going to 18 GHz but a number of vendors offer 26.5 GHz rated SMAs. There may well be 26.5 GHz rated SMA crimp connectors, but not from our regular vendor and we do not use them. As a matter of fact, for most everything I build that operates above 18 GHz, I prefer buying pre-made cable assemblies. Considering the cost of connectors, cables and tooling, it's not that much more expensive. For reference, the 21 GHz cables we buy are soldered, not crimped, and they work much better than those we made. Didier KO4BB -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Chuck Harris Sent: Saturday, July 28, 2007 1:09 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] HP 5370B low frequency modulation Hi Didier, I believe you are mistaken about what holds a crimp SMA connector together. The crimp force is entirely taken up in trying to constrict the circumference of the solid copper jacket. Because a cylinder is one of those perfect structures discovered by the ancients, this crimping pressure doesn't apply a significant amount of additional pressure to the center insulator. I have made numerous shielded opens for network analyzer use by crimping an SMA connector nut onto a piece of copper semi-rigid shield tube without using any center insulator, or center pin. The screw on BNC's that you can get at Radio Shack hardly qualify as a connector. -Chuck Harris Didier Juges wrote: > ); SAEximRunCond expanded to false > Errors-To: time-nuts-bounces+cfharris=erols.com+cfharris=erols.com@febo.com > > I was referring to the crimp connectors like the SMAs where the cable is > press-fit in the connector. These work well at t=0 and in low stress > equipment, but are not too good in high vibration or thermal cycling > environments. > > Also, I believe the deformation of the outer conductor where the 1/4" > semi-rigid cable is squeezed introduces impedance changes and reflections. > Since most of these cables have Teflon insulation, cold flow and thermal > expansion create additional problems. These problems are not eliminated by > using solder type connectors though, as I have seen a number of soldered > SMAs with cracked solder joint. > > They are very easy to apply though, considerably easier than the solder > types, and you are less likely to let a badly crimped connector go through > inspection than a badly soldered one. Problems tend to be obvious. A cold > solder joint, or too much heat applied to the cable (melting the insulation) > while soldering are much harder to spot. > > I have occasionally used crimp BNC connectors and they were as you describe > for the most part. Other than that, my personal experience is mostly with > solder-type coax connectors. > > The cheap but not inexpensive screw-on BNC connectors you can find at Radio > Shack do not have an inner sleeve either, if I recall correctly. Not that I > would recommend using those for ANYTHING (well, I had to try them, so I > did....) > > Didier KO4BB _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

Hi: I spent a few decades in work related microwave components most of which used SMA connectors. The early ones used the solid center conductor of the 0.141" coax as the center pin and so the male was just the nut and sleeve. I'm not sure if it was because of that, the ground connection being the 141 shield butting up to the reference plane of the female connector or something related to the female center contact that caused the spec for maximum number of mating cycles to be a 2 digit number. This made a big problem for satellite components which must use connector savers with a log of every connection and of course always done with a torque wrench. Are modern SMA connectors specified for more matings? Have Fun, Brooke Clarke http://www.PRC68.com http://www.precisionclock.com Didier Juges wrote: > Hi Chuck, > > You may be correct, the deformation is not obvious when looking at it with > the naked eye (never actually measured it, but you prompted my curiosity, so > now I will have to check :-) That may explain the relative vulnerability of > these connectors. > > Regardless, the manufacturer of the type of crimp-on SMA connectors we use > does not recommend their usage above 18 GHz. They do show strange VSWR > patterns above 18 GHz. I have a particular narrow band product operating > just above 21 GHz where I was planning to use them (I thought it would be > close enough), but it did not work well enough. On the other hand, the > equivalent soldered type is specified up to 26.5 GHz. I know the standard > SMA spec is only going to 18 GHz but a number of vendors offer 26.5 GHz > rated SMAs. There may well be 26.5 GHz rated SMA crimp connectors, but not > from our regular vendor and we do not use them. As a matter of fact, for > most everything I build that operates above 18 GHz, I prefer buying pre-made > cable assemblies. Considering the cost of connectors, cables and tooling, > it's not that much more expensive. For reference, the 21 GHz cables we buy > are soldered, not crimped, and they work much better than those we made. > > Didier KO4BB > > -----Original Message----- > From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On > Behalf Of Chuck Harris > Sent: Saturday, July 28, 2007 1:09 PM > To: Discussion of precise time and frequency measurement > Subject: Re: [time-nuts] HP 5370B low frequency modulation > > Hi Didier, > > I believe you are mistaken about what holds a crimp SMA connector together. > The crimp force is entirely taken up in trying to constrict the > circumference > of the solid copper jacket. Because a cylinder is one of those perfect > structures discovered by the ancients, this crimping pressure doesn't apply > a > significant amount of additional pressure to the center insulator. I have > made > numerous shielded opens for network analyzer use by crimping an SMA > connector > nut onto a piece of copper semi-rigid shield tube without using any center > insulator, or center pin. > > The screw on BNC's that you can get at Radio Shack hardly qualify as a > connector. > > -Chuck Harris > > Didier Juges wrote: > >>); SAEximRunCond expanded to false >>Errors-To: > > time-nuts-bounces+cfharris=erols.com+cfharris=erols.com@febo.com > >>I was referring to the crimp connectors like the SMAs where the cable is >>press-fit in the connector. These work well at t=0 and in low stress >>equipment, but are not too good in high vibration or thermal cycling >>environments. >> >>Also, I believe the deformation of the outer conductor where the 1/4" >>semi-rigid cable is squeezed introduces impedance changes and reflections. >>Since most of these cables have Teflon insulation, cold flow and thermal >>expansion create additional problems. These problems are not eliminated by >>using solder type connectors though, as I have seen a number of soldered >>SMAs with cracked solder joint. >> >>They are very easy to apply though, considerably easier than the solder >>types, and you are less likely to let a badly crimped connector go through >>inspection than a badly soldered one. Problems tend to be obvious. A cold >>solder joint, or too much heat applied to the cable (melting the > > insulation) > >>while soldering are much harder to spot. >> >>I have occasionally used crimp BNC connectors and they were as you > > describe > >>for the most part. Other than that, my personal experience is mostly with >>solder-type coax connectors. >> >>The cheap but not inexpensive screw-on BNC connectors you can find at > > Radio > >>Shack do not have an inner sleeve either, if I recall correctly. Not that > > I > >>would recommend using those for ANYTHING (well, I had to try them, so I >>did....) >> >>Didier KO4BB > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. >

Hi Didier, The reason that SMA connectors don't go above 21GHz is there is a wicked discontinuity in the female connector. The 141's shield comes flush with the connector/nut's body, but only the nut's body touches the shield of the connector. That leaves a step from the coax shield to the connector shield... not good! The APC3.5 solved that problem by making the connector smoothly transform from the 141's shield to the connector. To do this, it has it's own integral center pin, and teflon insulator. It is really a better connector... but you have to solder it to the coax. -Chuck Harris Didier Juges wrote: > ); SAEximRunCond expanded to false > Errors-To: time-nuts-bounces+cfharris=erols.com@febo.com RETRY > > Hi Chuck, > > You may be correct, the deformation is not obvious when looking at it with > the naked eye (never actually measured it, but you prompted my curiosity, so > now I will have to check :-) That may explain the relative vulnerability of > these connectors. > > Regardless, the manufacturer of the type of crimp-on SMA connectors we use > does not recommend their usage above 18 GHz. They do show strange VSWR > patterns above 18 GHz. I have a particular narrow band product operating > just above 21 GHz where I was planning to use them (I thought it would be > close enough), but it did not work well enough. On the other hand, the > equivalent soldered type is specified up to 26.5 GHz. I know the standard > SMA spec is only going to 18 GHz but a number of vendors offer 26.5 GHz > rated SMAs. There may well be 26.5 GHz rated SMA crimp connectors, but not > from our regular vendor and we do not use them. As a matter of fact, for > most everything I build that operates above 18 GHz, I prefer buying pre-made > cable assemblies. Considering the cost of connectors, cables and tooling, > it's not that much more expensive. For reference, the 21 GHz cables we buy > are soldered, not crimped, and they work much better than those we made. > > Didier KO4BB >