T-Network and L-network       

Remote ATU       

This is fairly new project (started in Dec'20) and it is in active progress now (as of June'21). Intended to add-on or replace bulky and heavy (weight) of my current remote ATU for DXpeditions.

Brief description:
ATU 8x8x8 is the Remote ATU is mounted on mast, attached to antenna input, fully remote-controlled via WiFi and MQTT with SunSDR integration via TCI.
Add-on software includes MQTT (which runs in a background on same PC where ESDR runs), TCI to MQTT Gateway (runs in background on same PC) and ATUconnect (runs on same PC, described below in this review).

Remote ATU integrated Control board allows device to join common WiFi 2GHz network and receive commands from ATUconnect controlling software. ATUconnect at the same time integrates with ESDR2/3 via TCI protocol.

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". 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.


Design overview
The original idea of "ATU board" (coils, capacitors, relays) design is the combination of "ATU-100 Extended board by N7DDC" and my T-match P-140 based ATU. 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.

In general, the ATU board composed out of three "relay networks" (with 8 relays in each network), integrated Tandem-match circuit and Control part. Detailed description is below in this document.

The relay networks forms what is called in this project by term of "8x8x8 T-match" design starting from v.0.4 has the in-build on-demand L-network capability: additional relays can turn T-match into two types of L-match by one relay's click. However default operational is T-match:



Features highlights

     1. Capability of T-match and 2x L-match configurations within same device. It either operates in classic T-match C1-L-C2 mode, or C1-L, or L-C2 mode. Moving from one mode to another is SW function and sully supported in remote mode. All "relay networks" can be operated in auto or manual mode.
     2. Flexible tuning options - each described above mode operates via two different tuning algorithms. Accordong to the experience, different types of portable antennas may require different kind of tuning. As an example - T-match primary algorithm when L tunes first, then hot C, then cold C; and secondary algorithm when hot C goes first, then L, then cold C.
     3. 0.01W (tested) to 200W (tested) tuning power and from 0.01W to 2KW operational power. Fully suitable for the range from QRP to US legal limit.
     4. ATU type presets (unlimited) and Antenna presets (unlimited). Antenna presets allow to pre-calibrate antenna on band(s), which speeds up tunign time. Additionally Antenna presets is enabling next feature
     5. "Follow VFO" function is TCI-based feature, which reads current frequesncy from SunSDR VFO and swich between antenna presets automatically.
     6. Automated tuning mode and Manual tuning mode functions. In Automated mode the TCI communication is used to set SunSDR tunign power, VFO. TX, operate with PA mode and engage/disengage Tune..
     6. WiFi (as primaty communication media) and (in fiture)CAN protocol (TJA1051) (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 CAN there is a need of another small box, where receiving CAN board will be.
     7. Dimentions: At this stage the construction fits it into 150mm diameter and 320mm length PVC pipe, mountable on antenna mast. Fully assembled boards total weight is 1150 gr. Add extra weight for enclosure (for example pipe, as described above, is about 1.5 kg extra with both sides caps and RF connectos/cables).
     8. 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.


Boards schematics
Current v0.6 boards Schematics:

KiCad schematics for L-C1 and C2 boards in zip file.
Gerber files: L-C1 board, C2 board, Power Supply board

The photos
below are real boards pictures (FR4 / TG150, 1.6mm, 1oz, dual layer):
L/C1 board 320mm x 150mm (click on pic to see full size in new window):


C2 board 320mm x 60mm:


Power board front 89mm x 86mm:


Firmware and Software
As mentioned, there are few pieces of code required: MQTT, TCI-MQTT-Gateway, ESP32 firmware and ATUconnect frontend software.

MQTT purpose and description can be found at vendor's web site.

Firmware for ESP32 is open source code. It is currently under "work in progress" policy and beta version is located here. In a brief - this piece of code is responsible for Power/SWR measurements and relays (in case of 8x8x8) or motors (in case of 2 or 3-motor P140-based version) operations.

TCI-MQTT-Gateway is a TCI proxy. It is working as TCI client and reads/writes TCI commands directly from/to ESDR. Currently supported TCI stack is ESDR2 (ESDR3 support is pending ESDR3 specification release by EE). main purpose of this proxy is to translate whatever communication is performed within MQTT into TCI and vice-versa. This piece of SW is definitely needed ar this stage and up until TCI C++ library will have full intergation into Qt QML.

ATUconnect application is the operational software, defined to run on same PC with ESDR2/3. It is integrated with SunSDR/ESDR via TCI and provides core user functions, i.e. ATU profiling, Antenna's profiling, ATU initialisation and ATU operations (tuning). Current SW version supports single ATU in TX/TX mode. In future versions the second ATU (primarily dedicated to RX mode) will be suported.
Latest UI consist of two Tabs - Dashboard and Setup:

Typical nessessary setup would include MQTT:

ATU profile:

and Antenna profile:

At glance - the combination of user-selectable starting tuning C1/C2/L values, starting step size and direction and selection of particular tuning algorithm (L first or C first) - provide quite powerfull mechanism to tune wide range of antennas.

ATUconnect is Qt.6 based cross-platform application.
Current version for macOS can be found here (important - tested on 10.15.7).

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 8x8x8 remote ATU and provide more flexibility in tuning "unknown" DXpedition's antennas.



To the construction facts:
C1 network and C2 network
5pF / 10pF / 22pF / 39pF / 78pF / 160 pF / 330pF / 660pF
total 1304pF with 255 step tuning combinations and 5pF/step for each network
Measured parasitic capacitance of assembled boards is about 35-40pF.

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 / 0.1uH / 0.2uH / 0.4uH / 0.8uH / 1.6uH / 3.2uH / 6.4uH
total 12.75uH with 255 step tuning combinations and 0.05uH/step

0.05uH, 0.1uH, 0.2uH, 0.4uH and 0.8uH coils are frameless inductors, made from above wire. Remaining coils are wired with same wire on Amidon T130-2 (1.6 on single toroid, 3.2 - on dual and 6.4 - on 3xT130-2).

Relays are Omron Electronics G2R-1-E-DC5. Using 5V relays makes crucial difference in power requirements and overall device power consumption.

Main power input 12V, then reduced to 5V by DC-DC converter (one per network and one for logic) is based on LM2596S-12 stabiliser. Input voltage can be tuned between 6 and 45V if higher power source desirable. Overall device max power consumption (all relays switched on) is around 300W (12V 2.5A). In real operations used power is about 100-150W (depends on how many relays engaged).

Relay switching is performed on positive wire (this gives fair enough RFI protection, compared to ground wire switching). HW version 2 uses SN754410 Quad Half-H bridge drivers to operate the relays. When relay is off, the "positive" is connected by bridge to the ground, preventing relay engaging by RFI.

Bridge drivers are operated by MCP23017 GPIO expander and ESP32 GPIOs. MCP23017 is operated by ESP32 via i2C bus.

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 future designs will be provided with CAN bus module. (However there is the feedback for using CAN media: additional (receiver) device is needed. 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 with total range from 2 to 4096 mV in each A0 and A1. "Lower" 2mV is the parasitic noise with given L/C filter and shunting 100K resistors (R6 and R7 on C2 board). This brings us to capability of guarranteed 1W starting measurement/tuning point. Voltage devider provides with 5mV...4V measurement range; all used ADC channels are clamped to 5V. ADS1115 is set to 16 SPS and tuning algorithm is set to wait 8 full measured cycles before engaging next tuning step.

Tandem-match is based on BN43-3312 (20:1, -26dB) combined with Pi-att (-25dB) of 56 Ohm-442 Ohm-56 Ohm and AD8310 log amplifier. This solution allows to perform tuning even on values 1uW above AD8310 intercept level. For performance reasons this current version 0.6 is set to perform tuning within the range from 0.01W to 200W PEP.

What is the difference between AD8310 and "classic" diode detector based Tandem? What is predominatly applicabe to this project case:
     - diode detector is cheap, simple and does not require any calibration
     - at the same time, diode detector is non-linear and typically affected by distorsion and interference.

Diode detector was tested during this project and we found that it does not work well specifically on the values close to diode's forward voltage minimums.

Of course, there are techniques, making possible overriding diode detector's issues on low bias. However, those techniques have their own "buts" and "ifs". And even then - practically, it is very hard to create the diode-based construction which will cover range even from 10W to 1000W. It is most likely the range from 50W to 1000W can be covered. But when it comes to extend it to 2000W, the issue appears again.

     - Log amplifiers (like AD9307/AD8310) are much more expensive. Of course we should speak about "expensive" in context and comparisson: it is $0.10 for diode vs $10 for log amp. Rounded, using log amps instead of diodes will make whole project cost $20 more.
     - log amps are better to be calibrated. Sure, it is possible to just use datacsheet and base the code purely on theoretical supply - however this approach may introduce significant risk going "out of band" for measurements. Calibration process is not really complex and once completed, it will give very precise slope and intercept values per log amp chip.
     - massive advantage of log amplifiers - those are very linear and extremely sencitive. There is no issue to detect RF Power values within range from 1mW to 10KW in steps of 0.1mW (or less).


There are currently two tuning algorithms for each supported tuner mode. For example, ATU-T can be selectively tuned with adjusting L first and then C1-C2 (Alg 1) or vice-versa (Alg 2). Each algorithm is targeted to minimum achievable SWR (withregards to different step size, step direction, etc. in each algorithm). If SWR 1:1.01 reached at any step - this ends the algorithm.

L, C1 and C2 start positions are band and antenna dependent and selectable via antenna profiles in ATUconnect. 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
0x01011111
0x11011111
0x00111111 and so on, until 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.


Atthors: VK6NX and VK3FDMI