[time-nuts] altinex switches

[Robert Atkinson]

Hi Chuck,
some early 75R BNC designs did use a smaller diameter center contact. The 75R male can make intermittent contact when used with a worn or top of limit 50R female. The 75R female can be damaged for use with the small contact male if used with a 50R or large contact 75R male. The do exist, but are pretty rare. A lot got changed out as faulty. I've not seen one on any modern (last 20 years) equipment.  
 
Robert G8RPI.


________________________________
From: Chuck Harris <cfharris at erols.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Sent: Friday, 22 February 2013, 6:15
Subject: Re: [time-nuts] altinex switches

In general, no, they are not.  The connector pins for modern 75ohm
BNC's are exactly the same part as for modern 50 ohm BNC's.  The BNC
gets the higher impedance inside of the connection area by removing
most of the inner dielectric.

The real problem child, in general, is the female 75 ohm N connector,
vs the male 50 ohm N connector.  In this case, the connector has no
dielectric in the mating area, so in order to keep the impedance
constant, it has to have a smaller diameter center conductor on the
75 ohm variant.  If you attempt to mate a 50 ohm male N connector
with a 75 ohm female N connector, you will split out the female
center socket pin.

Legend has it that there were some variations of the 75 ohm BNC that
don't work with 50 ohm variety.... I can't speak to whether or not
that is true, only that in my 40 years in the business, I have never
seen one where there was a problem.

-Chuck Harris

paul swed wrote:
> Good point Bob the 75 ohms are smaller in diameter. I use 75 ohm connectors.
> The 50 into a 75 hole spreads the jack.
> Regards
> Paul
> WB8TSL
>
> On Thu, Feb 21, 2013 at 4:16 PM, Bob Camp <lists at rtty.us> wrote:
>
>> Hi
>>
>> Be careful with the BNC connectors on those switches. 75 ohm BNC's aren't
>> the same as 50 ohm connectors. The inner contact is different enough that
>> they don't always play well together.
>>
>> Bob
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