L and T-Network Remote ATU       

This is fairly new project and it is in active progress now (as of Dec 2020 / Jan 2021). Intended to replace bulky and heavy (weight) of my current remote ATU for DXpeditions.

Target design principles - mounted on mast, attached to antenna input, fully remote-controlled via WiFi/RS-485 and MQTT with SDR integration via TCI, lightweight (as much as possible), less power consumption (as much as possible) and less wind resistant construction (as possible) - all "as possibles" assuming best achievable without sacrifising quality of operations.

Additional source of information regarding this project can be found at EE forum. As current page does not provide any feedback form, you may use forum to ask any project-related questions (alternatively contact me directly via email). Also the news regarding project progress are published on this forum at the same time as on this page.

A bit of warning: below is the area of programming. And the prerequisite is basic level of C++ (either familiar or willing to learn). Because of project is in active phase, I will be filing this page on ad-hoc manner. It you have any questions at this stage, please email me.

Important: The following section is for real nerds (like myself) only. For those of you, who want to know exactly "what is inside, before I buy the idea".

Disclaimer: At any point of time I do not insist that constuction, elements or software concept is "best" of "final". It is exactly opposite. The team approaches to this project in a mood of experiment, based on previous successful works.

Expectations: At any point of time I do not expect this construction will be close (or even near) on its performance/tuning capability to my current remote ATU (called by myself "140" (photo) in a name of P-140 old soviet radio station, from which the variable coil is taken). What our team target for current project is to get "new replica" as close as possible on tuning parameters to "140", while significantly reducing weight, power requirements and size. No one is expecting, that fix capacitors and coils will be same selective and descrete as variable. However, I have strong believe in ATU; on my experience it saved more than one DXpedition, which at certain point seem to be "lost", because of broken antenna.

Who is the user? DXpeditioner (as primary). I am opposite to "antenna snobs", saying that "antenna has to be 1:1 without ATU, otherwise it is not an antenna". For IOTA DXpeditioner, his "antenna snobism" evaporates after first disembarking in 4-ball waves, or after first gully landed on antenna during 1KW transmission. After that, usually, DXpeditioner has to use "finger" as an antenna, to give you your IOTA QSO. Withdraw and fail DXpedition is an alternative.

Design overview
The original idea of "ATU board" (coils, capacitors, relays) design came from "ATU-100 Extended board by N7DDC". With the requirement to meet Australian Advanced license and to ensure continuous operations for DXpeditions, the materials selected to provide x2.5 safety factor: Amidon Т130-2, 3kV+ NPO type capacitors and high voltage relays.

Please note that there are two different ATU board designs supported: :
      T-match (or T-Network) 8x8x8 design This is project in active development/production/testing phase. Below explanations and functional/construction descriptions are mostly related to this T-match ATU design.
     L-Network 7x7 ATU board is also supported by same software. For functionality performance and comparative measurements I am using board version produced by UR3IQH (orderable via his web site), but with completely replaced new design Control board. For future support of 7x7 ATU the new control board design will be tested and published..

Features highlights
Both supported ATU types are operated via conbination of ESP32-based control board and universal cross-platform application (called ATU connect). Below are the highlights of what is "special" about this kind of control:

     1. Unified software mainline for both ATU types. The only real difference (in control) between those two is number of controlled relays. Apart from that both ATU types are sharing same tuning algorythms, integration and feature set. There are some tuning algorithm features, which will be available only in 8x8x8, however (surely) it is obvious for anyone who undertands the difference between T- and L-match.
     2. TCI integration with SunSDR (2/Pro/DX) line of transceivers (by Expret Electronics). At this stage TUNE, DRIVE are used to automate tuning process and VFO helps ATU to "understand" which band this is all about (predominantly this function is embedded for speed-up the tuning process).
     3. WiFi (as primaty communication media) and RS485 (for situations where WiFi cannot be used). WiFi is simply connecting via either - access point or hotspot - to the network where ESDR PC is, For RS485 there is a need of another small box, where receiving RS485 board will be.
     4. MQTT as communication server (this runs in background on Win/Mac/Linux OS on same PC with ESDR).
     5. Possibly achievable compact design. We are dealling with bulky relays and toroids ... come on ... it cannot fit in a matchbox. However the target is to fit it into 150mm diameter and 220mm length PVC pipe. Why pipe? We are taking about remote ATU, right? Which should be mounted on mast? Will less wind resistance? You got it.
     6. Flexible tuning options - it will come with more than two different tuning algorithms, including "classic T-match". Accordong to the experience, different types of portable antennas may require different king of tuning algorithms - hence, here we are.
     7. 5V operations. All relays are 5V, all components are low power consumption. Everything composed to save battery power for field operations. Very usefull for DXpeditions.
     8. 1W to 100W tuning power. Hence, fully suitable for QRP operations.

* For L-network ATU (produced by 3rd party) parameters, including physical dimensions, please contact UR3IQH (link above).

Control board schematics and 3D models
Schematics for T-network are published here. The boards have arrived, below are real board pictures with measurementsL. Good quality (FR4 / TG150, 1.6mm, 1oz, doal layer):
C1/C2 board (consist of two pieces), front and back:

L board (consist of two pieces), front and back:

Control board front and back:

Here below is 3D models generated by KiCad for L-match 7x7. PCB size 80(W) x 80 (L) x 40 (H) mm:

Firmware and Software
As mentioned, there are two pieces of code required:

Firmware for ESP32 is C++ based open source code available at GitHub.

ATU connect application
It is the same application used in my other remote ATU projects. Intended to run on same PC with ESDR. Integrated with SunSDR/ESDR via TCI.

Please note : application is Qt.5 based cross-platform. The test releases for Mac and Win platform will be published here.

Please note that this software is currently under code cleanup and optimisation, hence the acceess to code is for development team only. Additionally we are working on feature enhancements:adding new features to allow granular control of the solid state remote ATU and provide more flexibility in tuning "unknown" DXpedition's antennas.

To the construction facts:
Please note - below information is about T-network device construction.
For L-network device construction and parameters please contact UR3IQH (link above).

C1 network and C2 network
5pF / 10pF / 22pF / 78pF / 160 pF / 330pF / 660pF
total 1304pF with 256 step tuning combinations and 5pF/step for each network

Parameters and datasheets:
5pf combined out of 2x10pF in series. 78pF is a combination of 2x39pF in parallel. 160pf is the parallel of 150pf and 10pf. And 660 is 2x330 in parallel.
10pF, 22pF, 39pF are Murata Electronics MLCC C0G(NP0) 3.15kVDC with 5% tolerance.
150pF and 330pF are AVX MLCC C0G(NP0) 3kVDC with 5% tolerance.

Coil wire is Single Core 2.03mm (14 SWG) Copper Wire.

L network
0.05uH / 0.1u / 0.2uH / 0.4uH / 0.8uH / 1.6uH / 3.2uH / 6.4uH
total 12.75uH with 256 step tuning combinations and 0.05uH/step

0.05, 0.1 and 0.2uH coils are frameless inductors, made from above wire. Remaining coils are wired with same wire on Amidon T130-2 (0.4, 0.8, 1.6 on single toroid, 3.2 and 6.4 on dual).

Relays are Omron Electronics G5LE-1A-E-36 DC5. Using 5V relays makes crucial difference in power requirements and overall device power consumption.

Main power input is based on LM2596S-12 stabiliser, tuned to 6V output. This makes available variable voltage input for the device - anything in between 6.1V ... 45V with almost triple 3A redindancy (as overall device power consumption is around 0.95A).

Relay switching is performed on positive wire - this gives fair enough HF interefence protection (compared to ground wire switching). N-channel MOSFETs (RFD14N05SM9A) are in use with High Side MOSFET Drivers (HT0440LG-G). Both elements selected to provide an overkill capacity for max voltage tolerance (compared to voltage used) as well as static electicity tolerance (selection is based on best value for money approach).

Each (C1, C2 and L) board is using MCP23016 GPIO expander and has dedicated 5V 1A stabiiser (AMS1117-5.0) to feed relays and logic. Same type dedicated stabiliser is used to feed central processor and ADC.

All logical elements are conneted via I2C bus - great deal against interference and significantly reduces board-to-board wiring to only 4 wires: +5V, GND, SCL and SDA.
Please note, that above statment is correct for 8x8x8 construction only at this stage, For 7x7 boards 2x16-pin connectors have to be used.

ESP32-WROOM32U with external WiFi antenna should provide up to 50-60meters (open space) signal distance coverage with acceptable signal level. For situations where WiFi is not an option, the control board equipped with RS485 module. (However there is the feedback for using RS485 media: additional (receiver) RS485 device is needed with (most likely) special RF-tolerant network protocol. This can be based on any Arduino (like Nano), or on ESP32D. I have working/tested device in hand, will add construction and code details later).

For ADC the ADS1115 is used. It is 16-bit and gives good enough resolution (compared to 12-bit ESP32 in-build ADC). ADS1115 sencitivity in the given construct is 1mV, which brings us to capability of guarranteed 1W starting measurement/tuning point. Primary voltage devider provides with 2mV...3.2V measurement range, secondary devider is engaged when 3.2V reached on primary. All ADC channels are clamped to 3.3V. ADS1115 is not the fastest in a world, it can only do upto 860 samples/sec, but it is fair enough value for money and provides with needed for this application 100-400 samples/sec.

There are currently three tuning algorithms for T-match, and two algorithms for L-match. Each algorithm is targeted to minimum achievable SWR (withregards to different step size, step direction, etc. in each algorithm). If CWR 1:1.01 reached at any step - this ends the aldorithm.

C1 and C2 start position at 85-95% of total capacity, L start position is band dependent (example: at 7MHz start position is 1.6uH). Definition of "step deviation" (below) is as following (example):

      Step 1. C1-network starting point 1204pF (0x11001111).
      Step 3. First tuning step (say, Algorithm1(below) in higher capacitance direction) will be 8 steps away from starting point, i.e. 0x01011111 (or 1277pF). At this stage SWR comparisson is performed and if:
      Step 3. - SWR becomes higher, then reverse tuning step (towards lower capacitance direction and 8 steps away from starting point) is enanged.
      Step 4. - SWR becomes lover, then algorithm will continue in same (higher capacitance) direction with +1 step, i.e
0x00111111 and so on, untill SWR comparisson will detects SWR become higher (goto step 5), or untill end of combination reached (goto step 6).
      Step 5. At this stage logic reverses to step 3 and repeats until minimum achievable SWR reached.
      Step 6 (and following further, say, for Algorithm1 below), is to engage C1 (with 8 step deviation) and then L (with 16 step deviation) on described above principle - this will complete Stage 1 and then repeats with double lowered step deviation for Stage 2 and Stage 3 respectively.

Algorithm 1 (T and L):
Stage 1
step1: C2 (8 steps deviation)
step2: C1 (8 steps deviation)
step3: L (16 steps deviation)
Stage 2
step4: C2 (4)
step5: C1 (4)
step6: L (8)
Stage 3
step7: C2 (2)
step8: C1 (2)
step9: L (4)

Algorithm 2 (T and L):
Stage 1
step1: L (16)
step2: C2 (8)
step3: C1 (8)
Stage 2
step4: L (8)
step5: C2 (4)
step6: C1 (4)
Stage 3
step7: L (4)
step8: C2 (2)
step9: C1 (2)

Algorithm 3 (T only):
Stage 1
step1: L (16)
step2: C2 (8)
step3: C1 (8)
Stage 2
step4: C2 (4)
step5: C1 (4)
step6: L (8)
Stage 3
step7: C2 (2)
step8: C1 (2)
step9: L (4)

At this stage only pre-build tuning algorithms will be in use, however manual override may be added later (this is for really "bad" antenna cases).