[Elecraft] BNCs

[dave]

According to the specs in the RF Industires catalog, pages 7 and 14 in 
the version I have here, the center pins of 50 ohm and 75 ohm BNC's 
are indeed the same size: .053 +/-.001 inch.

The difference is Zo is generated by using dielectric in the 50 ohm 
but none in the 75 ohm, and slight difference in the inside dimensions 
of the plus and sockets.

It is a little hard to tell from the drawings whether or not you can 
plug a 50 into 75, and vise versa, with no issues. Although the pins 
are the same size, there is a slight difference in the inside 
diameters and the depths of the two fittings are different. This is 
complicated by the fact that the 50 and 75 ohm fittings use different 
reference planes to make the measurements.

The catalog is available on the RF Industries web site.

73 de dave
ab9ca/4



On 10/13/14 1:32 PM, Joe Subich, W4TV wrote:
>
>  > While you are entirely correct that there are 75 ohm and 50 ohm BNCs,
>  > the difference DOES NOT MATTER at HF, because the connector is such a
>  > small fraction of a wavelength and the difference is small.
>
> I disagree ... *DO NOT MIX 75 and 50 Ohm connectors*.  50 Ohm male
> connectors will split the center contact of a 75 Ohm female wile 75 Ohm
> male connectors will not make reliable connection with the center
> contact of a 50 Ohm female.
>
> In general, a 75 Ohm center pin will not accept the center conductor of
> 50 Ohm cable and a 50 Ohm center pin can not be *reliably* attached
> (either crimp or solder) to the smaller center conductor of 75 Ohm cable
> due to the relative sizes.
>
> 73,
>
>     ... Joe, W4TV
>
>
> On 2014-10-13 12:15 PM, Jim Brown wrote:
>> On Sun,10/12/2014 6:32 PM, Acbross via Elecraft wrote:
>>> Don't know where anyone got the idea that BNCs made for RG-8x we 75
>>> ohm. I worked in the tv industry for many years and we used hundreds
>>> of BNCs that were made specifically for 75 ohm video. By the way,
>>> RG-59 not RG-79.
>>
>> While you are entirely correct that there are 75 ohm and 50 ohm BNCs,
>> the difference DOES NOT MATTER at HF, because the connector is such a
>> small fraction of a wavelength and the difference is small. 75 ohm
>> connectors were important with analog video because of the smearing of
>> very fine detail in a high res image, and because studios do lots of
>> patching and routing.
>>
>> 73, Jim K9YC
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