MiniVNA Pro Extender

Hi all,

I had been waiting on an order from WiMo for the MiniVNA Pro Extender. It arrived today and I was keen to check it out.

Mixed Internet Reviews

This device has been subject to some discussion on the net. There are some reviews at eham, as of the date of writing this post, there were 2 reviews. One rated the Extender a 5, and the other a zero. It seems that some people are finding that this product works and some are finding that it doesn’t.

First go

It was with some fear and trembling that I set the device up and started to do some testing. Here is the pic of the Extender hooked up to the MiniVNA Pro:

MiniVNA Pro Extender and Pro connected together

MiniVNA Pro Extender and Pro connected together


My first attempts at making use of this device did not go well. On the calibration screen in vna/j, there was no difference between short/open/load calibrations in reflection mode. Hmmm, am I like the guy on eham who said that this product only deserves to go in the bin – a bit harsh! There has to be something more than this. I tried several combinations of connecting and using either 2000 or 25,000 calibration points in vna/j. No joy. There has to be some trick to this, because there are people out there that have made this product to work.

I used an adjustable wrench or shifter to gently ensure that the SMA connector between the Extender and the Pro was fully connected. I turned on and wella. The open and short calibrations look like each other, but there is a clear change of phase. I got real world sensible results out of this device.

Second go

I had to stop at that point and do some other things. It was quite a bit later in the day that I returned to looking at the Extender to have a look at a few antennas for 70cm. I have a 7cm Jpole at home, plus a turnstyle for 2m that has worked reasonabily well on 70cm as well. I wanted to look at these antennas on the Extender. I hooked things up, and made sure with the shifter that things were well connected – no go! Rubbish results. What is the deal with this device!

After a bit of stuffing around and making sure I remember each step in what I did, I have found this following method a reliable way of getting the Extender to work. Not following this leads me to get garbage results.

1) Connect the Extender to the Pro DET and DUT ports, but not the CAT5 cable.

2) Connect USB from the computer to the Pro. (I would also presume that in Bluetooth mode, turn the Pro on)

3) Connect the CAT5 cable from the Extender to the Pro.

This seems to work, on a repeatable basis. If the CAT5 cable is connected at Pro power on, it does not seem to properly use the Extender and garbage results seem to then occur.

This behaviour strikes me as a firmware bug, and changes to the firmware on the Pro or Extender might overcome this problem in the future. Nonetheless, it seems the three step process above is a reliable work-around.

When the device is working, it seems to get pretty steady results, and I am quite happy with it. One little thing to watch out for is on the Extender, the DUT port is the RX port in reflection mode, but is the TX port in transmission mode. This is different to the Pro itself, where DUT does not change.

Here is a look at a screenshot of the 2m turnstyle antenna at 70cm:

VNA/J Screenshot of MiniVNAPro Extender in action analysing a 2m turnstyle at 70cm

VNA/J Screenshot of MiniVNAPro Extender in action

Now I know how to use this device, I am quite happy with it, and look forward to doing some work on 23cm in the future.

73, Regards Wayne Merry VK3WAM

3 comments on “MiniVNA Pro Extender

  1. tijn49 says:

    Hi Wayne

    I recently took delivery of my extender and have been having the same problems as reported in the Yahoo group. I have tried all the tricks including yours to no avail. The calibration traces are all flat lines above 32 and the subsequent scans of the 50 ohm load just look like white noise. I will muck around a bit more and if I have no luck I will send it back to WIMO. No problems with the miniVAM pro itself – it’s a great little piece of kit.


    Martin Elias

    ps-great pictures of your 8 summits trip. Reminds me of my bushwalking days in Vic before moving to Canberra in 1985.


    • waynemerry says:

      Hey there. I’m a little slow in replying as I’ve been in PNG.

      You’ll know if it is working because the short and open circuit look similar but different phase on the calibration screen. The 50 ohm load is what looks the same whether it is working or not. What I suspect is happening is that without the extender being properly initialised by the MiniVNA Pro, it just sees 50 ohms at the MiniVNA Pro, no matter what is on the extender port, short, open or load. This certainly then leads to meaningless data.

      There is definitely a firmware bug in my view. What I did works for me. Hopefully you find the “magic trick” to convince the extender to be initialised properly. If you can find the magic trick (especially a repeatable one), the extender will work well.

      I’d try talking it through with them. Take screenshots of your calibration screen that shows that your standards are all showing the same thing, and yes you did use RX in reflection mode. It’s worth persevering as the extender, when it does work, is a great piece of equipment.

      73 de Wayne VK3WAM

  2. […] my earlier post which considered use of the MiniVNAPro Extender using a USB connection, I wanted to give the […]

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