Path: ...!3.eu.feeder.erje.net!feeder.erje.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Ralph Mowery Newsgroups: sci.electronics.repair Subject: Re: Signal Generator Source Impedance Date: Sat, 4 May 2024 14:54:32 -0400 Organization: A noiseless patient Spider Lines: 48 Message-ID: References: <4k2t2jdaq5jotm57mvss543qmsk060stnq@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Injection-Date: Sat, 04 May 2024 20:54:33 +0200 (CEST) Injection-Info: dont-email.me; posting-host="c0dfe691837b4339459648f863bded52"; logging-data="1423785"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1/7WGFvGXqP61azL+sa0XDqTT3Me7FK154=" User-Agent: MicroPlanet-Gravity/3.0.4 Cancel-Lock: sha1:grHYPFR5pi76SLMHAv6WBoNYLtA= Bytes: 3323 In article , ianREMOVETHISjackson@g3ohx.co.uk says... > > >A much bigger problem is that 50 and 75 ohm BNC connectors use > >different center pin sizes. > > >=1258015846> > >I wrecked the 75 ohm receptacle on a CATV sweep generator by force > >fitting a 50 ohm BNC plug. Color coding my cables have largely > >prevent a recurrence. Green tape or nail polish for 50 ohms and > >violet for 75 ohms. > > > Despite over 40 years in the CATV industry, I've never seen any 50 or 75 > ohm BNCs that weren't mechanically mateable. The mating parts of the > metalwork are usually pretty-well identical. > > OK, with some 50 versions the point of the male pin might be just a > little bit blunter, but there's little chance of it splaying the female > receptacle. Otherwise, the diameter of the pin is the same. But note > that with the 75 ohm the hole at the rear end of the pin and receptacle > might be a rather tight fit for the inner of 50 ohm coax. > > What makes one connector 50 ohms and the other 75 is that the amount of > the PTFE dielectric is considerably cut back in the 75 (making it as > air-spaced as possible). IIRC, the 50 is the more constant-impedance, > which makes it more-usable to higher frequencies). > > On the other hand, the N-connector is a very different beast. The pin of > the 50 ohm has a much greater diameter than the 75 (which may be what > the photo shows). If you insert a 50 ohm male into a 75 ohm female, you > will almost certainly cause irreparable damage to the female (in some > companies I believe it's still a hanging offence), while a 75 male into > a 50 ohm female won't male contact. > > Finally, the inner parts of a female BNC and an N are very similar, and > you can usually mate either with a 75 ohm N (but not with a 50, as the > pin diameter is too large). > > > > That is the way I have seen it in the US. Ok to mate the 50 and 75 ohm BNCs but not the 50 and 75 ohm N connectors. I do not recall which way it is if you stick a BNC to a N connector. Just that it can be done if the pin size matches up.