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 <rmowery42@charter.net>
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: <MPG.40a04e77980a8718989f6a@news.eternal-september.org>
References: <c71t2j1970vdo512sgmchlil2drip46al7@4ax.com> <4k2t2jdaq5jotm57mvss543qmsk060stnq@4ax.com> <pMlnTlGzzQMmFwm9@brattleho.plus.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 <pMlnTlGzzQMmFwm9@brattleho.plus.com>, 
ianREMOVETHISjackson@g3ohx.co.uk says...
> 
> >A much bigger problem is that 50 and 75 ohm BNC connectors use
> >different center pin sizes.
> ><https://www.vintage-radio.net/forum/attachment.php?attachmentid=30120&d
> >=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.