cheap chinese VNA up to 6Ghz

[jujun]

Hello,

I randomly found this on aliexpress : https://www.aliexpress.com/item/6G-dual-port-vector-network-analyzer-VNA6000-Bluetooth-WIFI-2-4G-5-8G-antenna-test/32857907599.html

Any informations of what is inside ? What do you think about it ?
Maybe one of you already did a teardown if it.

Thank you,
J

[OwO]

That's not cheap at all. Two port VNA up to 6GHz should have a BOM cost of around $200 and retail for $200*2.5 = $500.

[richnormand]

As stated above by blueskull:
Would look at the xaxaxa unit on kickstarter.
I got one and it is as described and has good performance and good support from him via Github.

[OwO]

You meant those RF detector-based ones with cheap trace-based on cellphone IC-based directional coupler?

I think all of those DIY network analyzers have real receivers and do DSP to detect phase and magnitude. Look at the block diagram here:
http://hforsten.com/improved-homemade-vna.html
Same thing here: https://raw.githubusercontent.com/xaxaxa-dev/vna/master/pictures/overall_diagram.png
The directional coupler is constructed using a resistive bridge and coaxial balun:
http://hforsten.com/img/vna2/coupler_finished.jpg
I have tested a similar coupler like the one above and it was possible to get raw directivity of 25-30dB up to 3GHz. The calibrated directivity will be far better.

[loxodes]

Still, getting the lower end (<1MHz, or even <10MHz) is not possible with exotic components.
AD9361 starts from 70MHz, and cheap transmission line-based couplers usually have higher minimum frequency.

Cheap directional couplers constructed from a resistive bridge and coaxial balun can work down to hundreds of kHz.
(See nikolay2015.pdf attached to https://www.eevblog.com/forum/rf-microwave/directional-coupler-150mhz-buy-or-diy/msg1388414/#msg1388414)

[OwO]

And if you rearrange the bridge so that the balun is on the coupled port, then add a differential amplifier, it can work down to DC.
For example look at the resistive bridge here: http://www.yl3akb.lv/content/vna_v2/block_diagram_vna_v3.JPG