Any real drawbacks to using oscilloscope test leads and probes with the Nano VNA? I have some adapters coming to provide BNC to SMA connections. Thinking that calibrate procedure should take care of at least resistance losses.

73
Karl
KI4ZUQ

depends what you wanna measure ... in some cass that may work (lower
frequency)

dg9bfc sigi

Am 31.12.2020 um 19:58 schrieb Karl via groups.io:

> Any real drawbacks to using oscilloscope test leads and probes with the Nano VNA? I have some adapters coming to provide BNC to SMA connections. Thinking that calibrate procedure should take care of at least resistance losses.
>
> 73
> Karl
> KI4ZUQ
>
>
>
>
>

Dear Karl, scopes probes coax is'nt 50ohm. Some probes have passive
parts to compensate something. Please do not this way. It feel to me
like aligator clips. BR Willi.

Am 31.12.2020 um 20:58 schrieb Karl via groups.io:

> Any real drawbacks to using oscilloscope test leads and probes with the Nano VNA? I have some adapters coming to provide BNC to SMA connections. Thinking that calibrate procedure should take care of at least resistance losses.
>
> 73
> Karl
> KI4ZUQ
>
>
>
>
>

Dear Karl, scopes probes coax is'nt 50ohm. Some probes have passive parts to compensate something. Please do not this way. It feel to me like alligator clips and banana cables. 73 Willi and HNY

My logic on this is:
1. The scope is DC to 100 mhz and the leads are the same as in the 400 mhz model.
2. When calibrating open, short, load (50 ohm) compensates for any R in the lead.

Now, granted, like mentioned, some upper freqs may play havoc with the longer wire +/-jX stuff.
Has anyone tried using scope leads? Begs then the question, what do you use?

Tried it today and the results were not encouraging! So, what should test leads be? Just short wires and clips?

--
73
Karl
KI4ZUQ

My oscilloscope probe has 200 ohm resistance on the center connector when set for 1x, 9 M ohm when set to 10x. The 200 ohm will definitely mess with your VNA measurements!

So, yes, short (a few inches max) test leads with clips are best. I use a BNC to dual binding post adapter as well sometimes when working with leaded components or can solder short wires into the circuit.

Hi Karl.
You haven't indicated what you want to measure? Are you thinking of testing individual components or what? Did you build a balun and want to test it?

Anything you try to do with clip leads will only be good at low frequencies, perhaps mid-HF bands and down. Clip leads would completely compromise any readings you try to do at VHF and above. Of course it kind of depends what you expect for accuracy.

<https://www.ebay.com/itm/1-POMONA-2631-BNC-FEMALE-to-MINIGATOR-TEST-CLIP-LEADS-INSULATED-45VAC/321150415608>
<https://www.ebay.com/itm/2-X-BNC-Male-Plug-to-Dual-Banana-Female-Jack-Coaxial-Connector-Adaptor/121929154004>
These items are what Dave is talking about. These are suitable for low RF and audio testing. Use a short 50 ohm coax cable with a BNC connector to mate with the clip lead adapter. Or you don't have to buy the adapter, just take a suitable coax jumper a few feet long, cut off one end, then strip back 2 or 3 inches of the sheath and solder alligator clips on the wire ends. Just be sure to insulate the bare coax shield going to the clip. There are some nice YouTube videos by TRX Bench where he uses his VNA to test his homebrew HF baluns. He is just soldering the stripped coax leads to his balun under test.

If you are trying to test something over 30MHz, you should probably just settle for a couple pieces of coax and strip one end maybe half an inch so you can solder the leads to the device under test. Short leads are critical at VHF and above. If you don't have coax connections to work with, all your readings are garbage anyway. Without coax connectors you can't expect to SOLT calibrate the NanoVNA anyway....

73, Doug Reed, N0NAS.

I have read everything, I think I understand! Have done some experiments here with BNC adapters received recently and can confirm essentially what you all have said and definitely SHORT is the best!

I have a BNC male to about 24" total length cable terminated in red & black alligator clips that are completely unsat !
The 'scope leads are way longer and are worse with the length inductance and capacitance plus the compensator.

The links to the ebay adapters did not work but I will find them.

I see where this can test small components but larger things like tuning coils require something other than a multimeter approach.

--
73
Karl
KI4ZUQ

You can forget all about oscilloscope test probes! They are designed to go into a high impedance scope input with (1 MegOhm and about 15 pf of shunt capacitance). The probe tip has way too much capacitance and the probe impedance and coax cable are not 50 ohms and has up to 100 pF of shunt capacitance in 1X mode. Wrong toll for the job....

If you want to test components you need a proper test jig that can be calibrated. For HF things are not that critical but for VHF and up you need to build them carefully. I have built several. This one works well and is quite accurate up to 55 MHz. Made form BNX to Banana jack adapter and some scrap PCB.

This one works very well at much higher frequencies.

I built something like Roger shows on the photo, SMA male + 3-pin 0.1" socket stip. I use it to measure small inductors and capacitors.
It shows a parasitic capacitance of 1.4pF and negligible inductance.

73, Mike AF7KR