[600MRG] Amazon/eBay special remote vector swr meter

[Ben Gelb]

Amazing what you can piece together for $25 these days!

I wanted to monitor the vector impedance of my 630m antenna / matching
network to better track how it moves over time / weather / start alignment
etc.

I cobbled together an AD8302 gain/phase detector with a small ADC and
ESP8266 microcontroller. The ESP8266 is intended for IoT applications, so
it has wifi capability.

This can be connected to a directional coupler (you have to raid your
junkbox for this) and then can report return loss, vswr, complex load
impedance etc.

See this URL (note data is garbage while I'm not transmitting, though
annoying reports close to 1:1 swr due to my choice of attenuators in front
of the AD8302):

http://gw.gelbnet.com:8100

Picture: https://photos.app.goo.gl/yjh61n3nZPMSH1Wj1

Here's the shopping list:

AD8302 Module:
https://www.ebay.com/itm/AD8302-NEU-Amplitude-Phase-RF-Detector-Modul-IF-2-7GHz-Phase-Detection-New/172995156780
ADS1115 Module:
https://www.amazon.com/gp/product/B01DLHKMO2/ref=oh_aui_detailpage_o08_s00
ESP8266 Module:
https://www.amazon.com/MakerFocus-NodeMcu-Development-Compatible-Arduino/dp/B076RM8MYW

I had to replace the 1nF coupling caps on the AD8302 board w/ larger ones
(I had 0.33uF on hand so i used that) in order to get it to work at 475kHz.
But after that seems to have usable accuracy out of the box (1-3dB error)
and a little bit better with some simple spreadsheet-based calibration. I
haven't tried to measure the phase accuracy, though at least the 0 point
seems in the right place (473.2kHz).

Since its wifi, you could locate this at the antenna instead of the
transmitter... if you wish (only a short run of coax away in my case
though).

Happy to share more details with those interested.

73,
Ben (N1VF)
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