Electronics > RF, Microwave, Ham Radio

binding post to BNC impedance analyzer test fixture?

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coppercone2:
So if you have a impedance analyzer and you can connect a BNC to banana binding post adapter to the measurement point, what frequency is this useful for?

I calibrated the impedance analyzer using a BNC short, BNC open (dust cover) and BNC 50 ohm load. When I attached the dual binding post to it, it read a capacitance of 4pF roughly when open circuit. When I added a 2pF capacitor to it, it read 6pF.

So I can easily stick a piece of braid as a short circuit (or maybe a cutout of copper sheet that conforms nicely around the binding posts like a shorting jumper on old HP equipment), leave it open for open circuit, then put say a 1/8 watt leaded resistor between the posts to get a '50 ohm' calibration. I have not tried this yet.

But anyway, any conjecture on when this stops being accurate (or gets highly inaccurate)? I measured a 330pF 1% capacitor on it and it measured correctly. I am using a old HP BNC to binding post/banana adapter. I wanted to know the theory of what starts going wrong as you increase frequency with this setup.. (its for a 4191A impedance analyzer with bandwidth of 1MHz to 1GHz). I also cross tested the APC-7 cal kit with the crappy BNC 50 ohm load and it seems to be within a few percent, and I am using a direct APC-7 to BNC adapter. It seems like a good enough idea for leaded parts...

I wanted to know if there is some kind of debilitating problem before I try ordering some precision through hole components that maybe have some frequency data to test on it (might save me a few dollars to post this).

Wallace Gasiewicz:
I don't know what sort of fixture or connector you are using, Are you using a APC to BNC or do  you have the HP fixture?
They had several fixtures for the 4191 A, but also the manual states that the APC7 could be used for a user built test fixture.
There was even a "probe" 
Their "spring clip" adapter advertised good to 500 MHz not 1 GHz  Binding post adapter good to 250 MHz  More practical HP binding post adapter good to 125 MHz See page  3-34 and 3-35 in Manual.
I suppose you have it but here it is anyway (maybe for the ease of others reading this)

https://www.keysight.com/us/en/assets/9018-05401/user-manuals/9018-05401.pdf?success=true

I suppose you could make a decent test fixture that accepts Banana and calibrate out most of the error. Probably much less than 100 MHz.
Maybe you could make a binding post design that would work at 100 MHz reasonably. Theirs uses a "guard"
Just guessing about the 100 MHz.
BNC  open short load stuff is all over the map and some are not very good. I have a bunch of brand name 50 ohm loads that are not good to 100 MHz.

If you find a reasonable good source for high quality "standards" for caps and inductors and resistors, let me know,

Wally

coppercone2:
Well I notice that those fixtures attempt to reduce inductance as much as possible (loop area?)

is this because there is complex coupling between the DUT and the fixture that you can't calibrate out easily since a fixture with a higher inductance has a higher loop area/more radiation/coupling (since its starting to be treated as distributed analysis)? (i.e. you do a 50 ohm calibration but when you stick a 500 ohm resistor in there the turns count on the coil is so high it starts working with the fixture to do complex/nonlinear things so the results are useless because the part interacts with a test fixture in a way that is not calibrated?)

its mad annoying that those parts are mad $ for something that looks like some plates lol, I wanted to know why I need to invest so much. You would at first glance think you can calibrate everything out. I am scared of the news groups because those people are like primal engineers with venom sacks still attached (TNG: Genesis, S07E19), it looks like a rough place

but this machine does look like it fell off the enterprise

joeqsmith:
Some time ago I used the NanoVNA ($50) to attempt to analyze a power distribution network.  During part of the demonstration,  I used a breadboard and plugged in some components to form a simple RLC network.  I left the long leads on the parts and ran a sweep to 50MHz.   I then repeated the test with the component leads cut short.   

It's not exactly what you are asking but it may provide you some idea of what to expect. 

Wallace Gasiewicz:
I only know enough to be dangerous.
I think the test fixtures are designed with the same sort of idea in mind as designing COAX. in that the impedance is constant over a big freq range.

I know there are fixtures for the four connector LCR meter fixtures available from Tonghui and I have one that works fine at 1 MHz. It does not look that complicated to make one and they did it for far less than the used HP ones are going for.  I do not know any sources for other test fixtures for APC connectors.

At the prices they have on e pay for the HP APC fixtures, I think you could get a machine shop to make a few...if you had the APC of course. Or design a board and get some boards made and have nice connectors made from solid silver, it would seem to be cheaper.

I wonder if anyone has just replaced the APC with a different system, I do not know. Apparently all the connections are made to the one APC connector internally, making the stray impedances less but making connection more critical, I guess...

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