[time-nuts] TNC connectors

David C. Partridge david.partridge at dsl.pipex.com
Tue Jun 23 09:50:09 EDT 2009

Hmmm now all I have to do is find a TNC connector to fit FT100 (or RG6)
without paying 5 times thet value of the connector for shipping - or just
use RG58 as I've got BNC for this, and can easily get TNC for it too.

Thanks to all

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Dave Baxter
Sent: 23 June 2009 13:40
To: time-nuts at febo.com
Subject: Re: [time-nuts] TNC connectors

> Message: 3
> Date: Tue, 23 Jun 2009 07:54:02 -0400
> From: Chuck Harris <cfharris at erols.com>
> Subject: Re: [time-nuts] TNC connectors
> To: Discussion of precise time and frequency measurement
> 	<time-nuts at febo.com>
> Message-ID: <4A40C25A.7080403 at erols.com>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> Dave Baxter wrote:
> > Doing that with BNC's will lead to a flaky connection, as
> the centre
> > pin on the 75r ones is much smaller.  The other way round (50r plug 
> > into 75r
> > socket) will damage the socket.  As TNC's are very similar
> to BNC's ???
> You are thinking of the incompatibility between 50 ohm and 75 ohm *N* 
> connectors.
> 75 ohm BNC are use the same center pin hardware as 50 ohm BNC.  The 
> only difference is in the white plastic (teflon) insulator.  In the 50 
> ohm BNC, the center insulator goes all the way to the tip of the 
> center pin.  In the 75 ohm BNC, the center insulator is abbreviated.
> HP/Agilent uses 75 OHM BNC's on several of its devices that have 
> switchable impedances.  For example, the 3586C.
> -Chuck Harris

Indeed looking as some more data sheets.

However, I have somewhere in the deed box at home, some Ex BT BNC's, marked
up as 75 Ohm, that have very much smaller center pin's than the common or
garden 50r types, as well as less plastic in there too.

We once had a Novell computer network in the office, that used 93r coax
cable, and 50r BNC's, at 100MBPS.  Using Thomas Conrad cards I seem to
remember.   We still have the real of 93r coax.

(It was very much faster end to end, and much more stable than the TCP/IP
based Microsoft network we have now, but I digress.)

In general, yes indeed size for size, 75r coax will be less lossy than 50r
types, but if the RX does present a nominal 50r load, they may be some
potential issues.  However, if the antenna is an active type, it's probably
not worth fussing over.  Enough people have used what's recomended I guess
and found no problems.  Just use good quality cable, not the so called "Low
loss" TV coax.  I'd guess the foam dielectric "Satelite LNB" cable would do.
It fit's 'F' connectors too.

Cheers All.

Dave B.

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