I have also been bitten by the non-captive center pin on Type "N" connectors. In my particular case, I had 100 feet of RG-213 runing outside from the shack to a roof mounted antenna. Type N connectors on both ends.
Then came the cold weather. One day, no receive signal, and funky SWR. Hmmm. After a brief investigation, and a trip to the roof, it was determined that the non-captive center pin had been pulled out of its N connector and therefore, the mating N connector, by the apparent contraction of the coax copper center conductor in the cold weather. What a pain. Therefore, whenever I use Type N connectors for professional or amateur use, I specify captive center pins. Failing that, I use another type of connector. All usual disclaimers apply. Your milege may vary. Void where prohibited, taxed, or otherwise snarled at... 73, K1NR On Fri, 23 Jul 2010 14:32:11 +0000 Brian Alsop <[email protected]> wrote: > Joel, > > How do you respond to this blurb from a "DX Engineering" > guru? > > I have been bitten by the non-captive center pin > migration problem > (almost impossible to find) and won't use N connectors > again for any > non-UHF high power application. This migration if enough > creates an > open circuit. It is hard for me to tell the difference > in captive pin > and non captive pin N connectors. Also I prefer the > larger center > conductor surface area of the UHF center pin connectors. > They are > proven to have very little heat generation beyond UHF. > > 73 de Brian/K3KO > ---------------------------- > For example, DX Engineering does not offer the RR-8 > series switches with > N connectors. Using UHF type connectors, this system of > remote relays > offers superior port-to-port isolation and power handling > from 1.8 > through 54 Mhz at low loss and low SWR. Only due to > superior engineering > is this series of Remote Switches usable at 144 Mhz with > slightly > elevated SWR and reasonable loss of only 0.25 dB. > However, these units > are not intended and cannot be used on UHF, so N > connectors are > intentionally not available. > > There is no question that the constant impedance > characteristic of the N > connector make it a superior choice for low loss VHF and > UHF applications. > > However, it is a fact that on HF frequencies, very high > power at high > duty cycle modes will heat the small diameter center pin > of the N > connector. Heating can cause the center pin to migrate, > ruining the > impedance characteristics of the connector and, at > continuous high > power, potentially cause a short circuit. If this problem > were to happen > during testing or operations, one might mistake high SWR > or high loss as > a defective of the switch, rather than a problem with the > connector. > This cannot happen with PL-259 and SO-239 connectors that > are properly > installed. At low SWR they can handle several kilowatts > of HF RF. > > This is not to say that you cannot use N connectors on > HF. Rather, the > question becomes "What are the benefits derived versus > the cost of > changing to N connectors for HF, where constant impedance > is > unnecessary?". The answer > > This is not a concern if you already have N connectors, > though. You may > use adapters or short coaxial jumper assemblies with > differing > connectors at each end, as offered by DX Engineering, > with custom > lengths available by telephone. These would cause > negligible losses on > HF, and would allow you to experience the superior > port-to-port > isolation of a DX Engineering RR-8 series Remote Antenna > Switch immediately. > > Let us know if you need any additional information. We > look forward to > hearing from you. > > Thank you and 73, > > Rod Ehrhart - WN8R > DX Engineering Customer Support > > ---------------------------------------------------------- > > Joel R. Hallas wrote: > > I agree with most of what has been said in support of > UHF connectors for HF > > and low VHF -- with two reservations. > > > > 1. Many SO-239s provided as part of radio equipment are > not up to the > > quality of Amphenol units. In particular, the spring > fingers of the socket > > for the male pin loosen over time to the point that the > connection becomes > > less than solid. This is particularly a problem if the > connector is used > > repeatedly. I usually replace with Amphenol units, if I > can get to them. > > Another great option is the Oak Hills BNC kit, designed > to fit the hole > > pattern of the SO-239. > > > > 2. The other potential problem with UHF connectors, in > my opinion, is the > > integrity of the shield connectivity through the > connected pair. If the > > backshell loosens, there is no longer a solid > connection either at the > > toothed parallel portion, nor through the backshell. > This can be an issue in > > mobile or other high vibration environments and has > caught me many times. > > Note that a type N, C or BNC pair makes it's shield > connection through the > > inner spring tension sleeve, maintaining contact almost > until the pair > > separates. The backshell is just used for mechanical, > not electrical, > > purposes. > > > > FWIW > > > > Regards, Joel > > Joel R. Hallas, W1ZR > > > > > ______________________________________________________________ > > Elecraft mailing list > > Home: http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/mmfaq.htm > > Post: mailto:[email protected] > > > > This list hosted by: http://www.qsl.net > > Please help support this email list: > http://www.qsl.net/donate.html > > > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: > http://www.qsl.net/donate.html --------------------------------------------------------------------- Web mail provided by NuNet, Inc. 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