Author Topic: MiniVNA Tiny users: quality issues?  (Read 1000 times)

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Online borjam

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MiniVNA Tiny users: quality issues?
« on: March 20, 2017, 07:17:06 PM »
Hi,

Last month a local colleague mentioned on a mail list that he had two miniVNA Tinys with problems. One of them was unusable for transmission (S21) measurements, the other one for reflection (S11).

Mine works fine, but I am wondering wether they have some quality control issues. We can "compare notes" here to check how well ours work.

Mine was purchased from Wimo in Germany. I have seen miniVNA Tiny units for sale on Aliexpress, but I am not sure wether they are knock-offs or Mini Radio Solutions just purchased a product in China to sell as their own. Data points should be completed with the origin, please.

I include two sample plots. One of them is a FM broadcast band notch filter designed by F1JKY, the other one is my MFJ 1788 loop antenna on 40 m. The matching of the latter is not perfect, but it's placed indoors.

The measurements are certainly usable in my case, and what I see on the VNA matches what I see on the HF transceiver when I
use the antenna.

« Last Edit: March 21, 2017, 01:38:56 AM by borjam »
 

Offline Andy Granis

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Re: MiniVNA Tiny users: quality issues?
« Reply #1 on: March 21, 2017, 01:09:43 AM »
Hi,

I have had the miniVNATiny for about a year and I have observed that when measureing S11 (reflection) at the DUT-port the result changes slightly if DET-port is terminated with a 50 Ohm termination or left open.

So I have taken the habit to terminate DET-port with a 50 Ohm resistive termination when measuring S11 and calibrating S11.
 

Offline vaughn22

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Re: MiniVNA Tiny users: quality issues?
« Reply #2 on: November 26, 2017, 02:19:06 PM »
Mine works okay as far as I know, although I observed something similar to Andy where results change in reflection mode depending on the DET termination. I got mine from Aliexpress, and have made some matching circuits with it with modest success, so I don't think it's a knockoff. The real issue is figuring out all it's noise and response drift quirks. I wrapped mine in foil to harden it from external rf interference and I make sure to only use it once it has warmed up to fix stability issues, but there's still that DET termination phenomenon I still have to figure out. Don't think it's broken though.
 


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