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Home made feed through terminator for BNC

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david77:
While in the final stages of fixing an old frequency generator it turned out I needed a feed through terminator to terminate the output of the generator into 50R while adusting the unit.
Of course I did not have one and it was two in the morning and I wanted to finish this thing.

What do you do? First I took a BNC T plugged one of those BNC to banana adapters in one end and hooked two 100R resistors to the terminal posts. Not ideal but worked well for frequencies under about 1MHz.
Now that generator goes up all the way to 11MHz and there the rectangles coming out didn't look like rectangles at all. In fact I had a hard time triggering the scope on that. Another solution was clearly needed.

I finally came up with a neat solution. It turns out that ordinary panel mount BNC sockets fit into ordinary solder type BNC plugs, the thread is the same. At least in the types I had in my drawer.

I soldered three 0805 150R resistors between the centre pin and the ground to get to the desired 50R impedance.
The pin of the plug is soldered straight onto the solder cup of the socket with a wire to give some stability.



The finished product looks like this:



Probably not ideal but it was a cheap solution that helped me finish the adjustments on my function generator.
It's now in my drawer waiting for future use.

Galaxyrise:
Oh, that's a nice DIY! How's it compare to the real thing?  How fiddly was it getting those resistors on there? Did you attach them before or after the pin?

david77:
Can't really say, I don't have the real thing.
I soldered the pin first the a piece of wire sticking up from the ground connection. Then I placed all three resistors in between there with tweezers and tacked them on to the pin.

c4757p:
My suspicion is that it works just as well at least to several hundred megahertz.

branadic:
You have better used a star arragement for the three resistors to minimize stray capacitance between them. But of cource, this is the old fashion style feed trough solution.


--- Quote ---My suspicion is that it works just as well at least to several hundred megahertz.
--- End quote ---

What needs to be proved.
The HZ22 for examples was primarily designed to work for scopes up to 100MHz:

http://www.mikrocontroller.net/attachment/98198/HZ22.jpg

They now sale it with the info it is usable for up to 1GHz. If you put it to a VNA or measure it with TDR you would be shocked about it's behaviour.

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