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.
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:
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.
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:
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