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I realize this is similar to a recent topic but a bit different.
As the "TDR" function in the nanovan is not actually a time-domain process, is there a wat to differentiate between a short or open fault in a cable?
I have previously built a generator which can produce a very short pulse or a step with fast risetime. I have used it in conjunction with a scope as a TDR. It works reasonable well and you can clearly see an open or short in a cable.
Is there a way to replicate tis with a nanovna?

If you turn on Transform and select Low Pass Impulse you are in "TDR mode". You need to set trace to "Real" and then you will see the difference between a short and an open.

Roger

On 6/21/23 2:22 PM, Geoff Peters - AB6BT wrote:

I realize this is similar to a recent topic but a bit different.
As the "TDR" function in the nanovan is not actually a time-domain process, is there a wat to differentiate between a short or open fault in a cable?
I have previously built a generator which can produce a very short pulse or a step with fast risetime. I have used it in conjunction with a scope as a TDR. It works reasonable well and you can clearly see an open or short in a cable.
Is there a way to replicate tis with a nanovna?

It should work identically - short and opens have 180 degree difference in the phase of the reflection, and that shows up in the synthetic TDR from the frequency sweep.

Roger...I was in Logmag mode. I'll try Real tomorrow

Jim...In Logmag mode the short and open appear identical as far as I can tell

I do fault locating with the Anritsu SiteMaster and the CellMaster. I prefer to use a short when testing because it seals off the end of the cable and avoids/reduces interference. This can help when testing on a heavily RF populated site.

Joe

Joe.. What I'm trying to do is locate a short or open in a multi-channel audio snake. I really can't afford the high priced spread...

I was just trying to point out that if you have a choice between using a short or open on any device, the short would minimize or eliminate interference that might enter the end of the cable.

Joe

On 6/21/23 5:41 PM, Geoff Peters - AB6BT wrote:

Roger...I was in Logmag mode. I'll try Real tomorrow
Jim...In Logmag mode the short and open appear identical as far as I can tell

Log mag is *always positive* (it's absolute value)..
Yeah, you need to be in a linear signed mode

On 6/21/23 6:56 PM, Geoff Peters - AB6BT wrote:

Joe.. What I'm trying to do is locate a short or open in a multi-channel audio snake. I really can't afford the high priced spread...

real mode will do you. I've used the NanoVNA on Cat 5 network cables. SMA to BNC: BNC to clipleads (EZ-Hook variety).

On 6/21/23 8:05 PM, Joe wrote:

I was just trying to point out that if you have a choice between using a short or open on any device, the short would minimize or eliminate interference that might enter the end of the cable.
Joe
On 6/21/2023 9:56 PM, Geoff Peters - AB6BT wrote:

Joe.. What I'm trying to do is locate a short or open in a multi-channel audio snake. I really can't afford the high priced spread...

You might make up some XLR cal loads - Open's easy. Short, and I'd go for a 100 or 120 ohm load, since it's probably shielded twisted pair.

But yeah, if you're looking for a fault somewhere in the middle, then shorting the far end minimizes hassles.

I assume you're not looking for a channel to channel short.

This is great non RF application for the NanoVNA.. you should write up how you did it and what you found out. WIth these sorts of things fixturing is what it's all about. If you've got a snake with XLR on both ends, then cobbling up some adapters is probably a good thing.

Propagation speed in a multichannel audio cable, whether shielded twisted pair or multiple coax is going to be something you'll have to figure out. But you know the physical length. FWIW, mic cables aren't 50 ohms, but you knew that.

Jim...All good points.

Yes, I have been thinking about a dedicated nanovna and fixture and the various options needed for different cable types. For the multi-channel snakes the VF is pretty similar as the construction and materials is similar. This would be the main use. And the stimulus scan frequencies will probably require changing as well.

I would like to make this as easy for individuals with varing technical experience. It might necessitate a PC connection but I have not researched that aspect...very new project.

Single mic cables can have a VF much lower, I've measured some less than 50%.

And yes the impedance is as you mention although manufacturers don't always specify except for AES/EBU whis in nominally 110 Ohms.