SWR Power Meter v1.0       

AD8310 based.       

This project came out as the supplementary for 8x8x8 ATU-T. At some stage (while building 8x8x8) it was - obvuiously - found, that the resolution of common/cheap SWR meter (for example MFJ-870) is not enough, and specifically lacking low power (less than 1W).

The decision was made to extract AD8310-based Tandem-match from 8x8x8 and make ESP32-based control board for it.

The initial idea of AD8310-based SWR/Power meter came from very well known 8307-based projects of DJ0ABR and TF3LJ / VE2LJX. What changes/add-ons introduced:
      - replaced AD8307 with AD8310 (as last one is newer and has better parameters)
     - and make simple Control, which can accomodate ESP32D/U 30-pin (with in-build WiFi antenna) and 38-pin (with external WiFi antenna) dev doards.
     - obviously, new code for ESP32.



There are few things should be considered prior building AD8310-based SWR/Power meter:

1. Please note AD8310 supported frequesncy range. Obviously, for higher/lower ranges AD has different set of logarithmic amplifiers (like AD8311-AD8318). It also possible that your project may require even AD8363.

2. When AD8310 supports RF detection from 1 μW, it is hard to make some kind of "full range" from 1 μW to 10KW meter. There is very simple reason for this - very low power (less than 0.01mW) will require more precise RFI protection. However with minimal RFI precausions we were able to operate our construction from -10 dBm (0.1mW) of RigExpert AA-600

3. In some cases WiFi may interfere with HF measurements. In this case it is recommended to switch off ESP32 OTA/WiFi, and use TFT display only for output.


Design / Features overview
The following design assumes:
- SWR and Power measurements in range from 0.1mW to 2KW
- WiFi and MQTT support (on ESP32)
- TFT 3in display
- there are two boards: Tandem-match and Control
- uses +5V external power

Boards schematics
Click to see full res in separate window.


KiCad schematics for both boards (in case you want to make own PCB design) and BoMs are in zip file>.
Gerber in zip file>.
PCB sizes (mm): Tandem 55x70, Control 55x60

Pictures
Note: There are few boards left from the order, please let me know if you want to get them (AUD $7 both boards + postage cost to your location).
below are real boards pictures (FR4 / TG150, 1.6mm, 1oz, dual layer):




Example construction in box:


What it sends to MQTT:


Firmware
Firmware for ESP32 is C++ based open source code.
https://github.com/VK6NX/SWR-Power-meter-AD8310

Calibration
AD8310 calibration process is described in post #14 here: https://eesdr.com/en/forum-en/remote-control/8674-remote-atu-w-tci

Calibration is, obviously, recommended to accomodate given AD8310 parameters. The difference between "white" and "clone" AD8310 is also explained in the above post.

Assembly instructions
Check zip archive with KiCad schematics and BoMs. There are some important notes in .sch files.

When making Tandem transformers, make sure you use proper core material. Both toroids, obviously, have to be same material. Use 0.5-0.8 mm wire for T2-T3 winding. Important - wire direction must be equal for each T2 and T3. If you flip T2 and T3 connector 1 with 2 synchroniously - you will get RWD and REF swaped. But if you flip them non-synchroniously - this is the problem and most likepy you will not get proper measurements.

R1 and R2 need to be chosen with care and calculated against expected max load. For max 1KW the 3W thick film is enougn. For up to 2KW better upscale to 4W thick film. Alternativel - calculate your own. Measure R1 and R2 nominals before soldering, as thick film resistors have 5=10% usual tolerance. Make sure you have as much as possible close matching nominals.

R5-R6 and R7-R8 pairs can be replaced with single nominal (each pair). I.e. instead of 220R + 220R I often use single 442R. Obviously, use Pi-att calculator to adjust the nominal, if needed. Also make sure the footprint size of 1206. It is recommended to use thin film precision resistors with max 1-2% tolerance and 250mW power is enough for those resistors.

R3-R4 also need to ne 250mW 1206 think film precision with 1-2% tolerance.

Capacitors nominals are not that wery critical, and replacement might be chosen from close nominal. Like 0.1uF can be 0.2 or so. Just make sure you match the pairs nominals. I.e if you replace,say C1 with 0.02uF, than also replace C2 with the same nominal.

L1 inductor on Tandem can be replaced with jumper wire. It is there only for the applications, where RFI is present, soueced form GND RF towards GNDD. It is good idea to check RFI with oscilloscope. Same thing about L2-L3 on Tandem and L1-L2 on Control. (I often use L2-L3 and do not use L1-L2 on Control). Those inductors are RFI protectors and you do not need them if there is no much RFI detected in your application.

Make sure the cable between Tandem and Control (between J5 and J3) is very well shielded. When unshileded - this cable is pretty much guarranteed source of interference.

Components
You may estimate the componets and PCB cost of this project in between USD $60-$90, including some wires and self-soldering. The final is very dependent on your location and shipping/tax. If you do not have spare project box or 3D printer - add another $10-$30.

For this project you, perhaps, have to deal with few sources.

ESP32 usually is sold on Ebay or AliExpress on reasonable price. Please note that ESP32U will require additionally WiFi Antenna and short cable with SMA / IPEX-K connectors. Beware that when dealing with Aliexpress always look not only at unit price but also shipping price, because some guys at Ali are "way too smart" :)

When choosing between ESP32D or U - think ahead and mean you application. Do you need WiFi at all? Will you be using MQTT? Or just need to display the data on small screen? The definition of the project will certainly help to understand whether you need D or U version of ESP32.

ADS1115 is also can be purchased from Ebay or AliExpress. Mouser, DigiKey or Element 14 will sell you Texas chip only and it will be overpriced. You better get small blue color board from Ebay - this is more than enough for this project.

AMS1117-3.3 - Ebay. No concern with this component, it is cheap, and you probably will find it is sold in quantity of 10 minimum.

AD8310 - this is more "religious" question :)
You can get the clone version from AliExpress for about $5-8/piece including shipping. Or you can get it from Mouser or Element14 for $14-15/piece inc VAT/GST and shipping.

FT82-43 or FT50-43 - search you local Ham radio shop, this would be cheaper. Alternatively, order from Fair-Rite or Amidon distributor.

All capacitors and resistors I strongly recommend to buy from either Mouser or Element14 - you will get what you have ordered (in terms of nominals and tolerance). With Ali and Ebay suppliers you will be kind of gambling.

Shipping is the killer these days. Try to get the order with Mouser/Element14 all together, as they usually ship for free with $50+ order. And watch the shipping cost + VAT/GST on Ali if you order from there.

From time to time I am ordering components myself, hence you may email me and ask if I have any leftovers.

Team
VK6NX and VK3FDMI