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ABS for QMX+ transceiver - V2

(Integrated Automatic antenna tuner, internal battery with charger and speaker)

ABS ATU and Audio Amplifier Board ABS Battery Board All-in-One QMX+ Field minimalistic config

This branch is for ABS ver 2. For ver.1.2 switch to version1.2 branch

After Hans Summers (G0UPL) has released his QMX+ transeiver - it quickly became popular both as a TRX and as a DIY development platform inviting projects like this.

I have made a prototype using QMX+ Dev Kit and later thought that the QRP communiuty would benefit from it too, so I designed PCB's to make the reproduction easier.

The ATU is based on N7DDC's 7x7 ATU minituarized by Barb (WB2CBA): https://antrak.org.tr/blog/usdx-sota-modular-all-mode-sdr-hf-transceiver-for-qrp-operations/

Custom firmware was written for the ATU.

Battery and charger mod is based on my previous work, which in turn, is also based on Barb's original design.

I am releasing design materials, PCB fabrication files, and code under open source license and to be free for ham radio community to embrace and enjoy DIY building. Or commercially selling.

This is a humble attempt to contribute to QRP Labs noble mission of providing high quality low cost transmitters to hams to ease their entry to the hobby.

Anyone who wants to commercialize and sell this solution as modules, semi kit or as a full kit are allowed to do so under these terms:

- Commercial seller can not alter design and has to keep it in it’s original published form.
 - Recognition of originators and designers AC8L, WB2CBA and N7DDC for their work on their site.

Because of minimum batch of 5 for the PCB order plus shipment, project is very well suited for the group build or club projects. If anyone wants to make money out of it - you have my blessings and prayers for the success!

There are active discussions on group build and group purchase on QRP Labs forum hosted by groups.io, please visit https://groups.io/g/QRPLabs.

I can only do a limited support and further development on best effort basis.

Sardar - AC8L, 4K6SA, VA3DUA.
Vienna, VA 10/13/2024
[email protected]

Notes for the ABS v2 release

Version 2 has incorporated many of useful feedback provided by participants of a first group buy organized by Cal (AD8Q) and Stan (KC7XE) and is actively discussed on QRP Labs groups.io forum. I appreciate Cal's and Stan's help and many improvement suggestions that made V2 worth to build.

Build steps at a glance

WARNING! Before you proceed with spending money and time, please take a note that the battery mod is compatible with QMX+ 12V build only!!! Do not use it with QMX+ built for 9V power supply, you will damage the rig!!!

  1. Decide how you want to build the ABS ATU/Audio board: a. Using SMA connectors; b. Using coax jumper wires for QMX+ integration.

  2. If you decided on option (a), ignore this step. Otehrwise for option (b) - build QMX+ with following mods:

    • Do not solder the jumper wire on JP501 as instructed on Rev2.00 build document's page 37! The ATU will play the role of that jumper wire.
    • Make sure to solder-in the 2-row 5-pin female connector into JP501.
    • Plug in a temporary jumper wire (breadboard prototyping wire is a good choice) into the female connector at JP501 at pins corresponding to a soldered jumper wire in the instruction document's page 37.
    • Thoroghly calibrate and test the QMX+ build according to the assembly manual. Making a couple of QSO's is a good idea.
    • Remove temporary jumper wire.
    • If QMX+ was already built and operational - carefully remove jumper wire on JP501, use suction tool to cleanup soldering pads and holes to prepare them for 2x5 female connector.

  3. Build ABS ATU/Audio board.

  4. Upload ATU custom firmware from this repository into the PIC16F1938 using supplied programming ICSP connector on the ATU PCB. board)

  5. Front panel replacement. We have 2 options for the front panel replcement:

    • Printing the replacement front panel on a 3D printer (budget option). STL files can be downloaded from here. PETG filament is recommended due to the outdoor exposure.
    • Ordering the front panel from JLCPCB (most aesthetically appealing option). When ordered along with other PCB's - the front panel will add negligeable cost. Otherwise if ordered separately the shipping cost to US (about $20) is the most cosiderable portion of the total cost. There are two versions of the PCB front panel:
      • with LED manually soldered from the back. Fabrication files are here.
      • with SMD LED factory-soldered on the front. Fabrication files are here.

  6. Rear panel replacement. There are two versions of a rear panel replacement and each version has two options - 3D printed part or a PCB:

    • If ATU is being built with SMA connectors:
      • 3D printed variant.
      • PCB variant: Fabrication files are here.
    • If ATU is being built without SMA connectors (using internal coax jumper wires):
      • 3D printed variant.
      • PCB variant: Fabrication files are here.

  7. Build ABS Battery and Speaker Board. Keep power (battery) switch on the OFF position until the last moment before closing the enclosure top!

  8. Insert 18650 batteries and install Battery and Speaker board on top of the ATU board. Make sure battery power switch is still on OFF position!

  9. Insert QMX+ assembly with ABS solution installed into its enclosure, screw-in front and back panels of the enclosure.

  10. Switch Battery board's switch to the ON position.

  11. Carefully insert and screw-in QMX+ enclosure's top.

Ordering PCB's

I personally have a habit ordering PCB's from JLCPCB (again, I am not associated with them!). For the convenience, all 4 PCB's can be ordered in one order.

  1. ATU and Audio amp PCB. Fabrication files are here.
  2. Battery/Speaker PCB. Fabrication files are here.
  3. Order one of the versions of the front panel PCB (see fabrication links above).
  4. Order one of the versions of the rear panel PCB (see fabrication links above).

If you are ordering PCB's from JLCPCB:

  • for the front and rear panel PCBs from JLCPCB - select black PCB color.
  • for all PCB orders make sure for the option of "Mark on PCB" - select "Order Number (Specify Position)".

Group build manager (organizer)

Usually in group builds it supoposed to be the responsibility of a group build manager to:

  1. Order PCB's.
  2. Assemble kit bags.
  3. Upload the ATU firmware from this repo into the PIC16F1938 microcontroller.
  • Due to shipping restrictions, group build manager must not source and ship batteries, leaving their purchase for each individual participant.

Build configurations

There are two possible build configurations:

  1. All inclusive - ATU, battery, speaker (audio amplifier).
  2. ATU and speaker (audio amp) only.
  • For configuration (2) you do not need to order the Battery and Speaker PCB. If you decide later that you want o add a battery board - you can do that. It is a non-destrcutive mod.

Bill of Materials (BOM)

Discalimer: I am not associated with any supplier and do not receive any monetary or other benefit from referring to their products! I am using USA suppliers, other regions have better suppliers for BOM sourcing.

QMX+

ATU / Audio Amp PCB

  • U4: LM386N-4 Operational amplifier (Digikey part 296-43960-5-ND)
  • 1x8Pos DIP Socket for U4 (Digikey part A120347-ND)
  • J1: 1x10 pin 2.54mm Female pin Header Connector Extra Tall: https://a.co/d/21eQjdI
    • the 1x6 connector from the same Amazon kit will be used for JP102 on a companion board BOM
    • or Digikey part SSW-110-03-T-S-ND
  • J2: JST XH2.54 PCB mount male connector: https://a.co/d/9YMnd1q
    • The pigtail from the same kit will be used for the LED connection from the front panel.
    • Although the same part is mentioned here and for the front panel - you need to source only one item.
  • J3: 2-pin single row male pin header: https://a.co/d/2SuiWnt
  • JP102: two 1x2 pin 2.54mm Male pin Header Connector Extra Tall: https://a.co/d/2l7o6wW
    • These are sold in a bulk, you will have to cut 1x2 out of it. Effectively, we will end up having one 2x2 double row Extra Tall Connector.
    • Same strip is used for the Companion board BOM.
  • JP106: 1x3 3pin 2.54mm male pin Header Connector Extra Tall: https://a.co/d/2l7o6wW
  • JP302: 4-pin single row male pin header (Digikey part 664-G800W268018EU-ND)
  • JP501: 2x5 10-pin double row male pin header: https://a.co/d/dF83x28
    • cut 2x5 section from the strip.
  • SW1: PCB Mount Slide Switch THT Right angled (Digikey Part EG1917-ND)
  • RF_IN,RF_OUT: angled SMA connectors, PCB mountable: (Digikey part 931-1361-ND)
  • 1 x BN43-202 Binocular core for tandem match
  • 3 x T37-6 toroid core
  • 2 x T37-2 toroid core
  • 2 x T37-1 toroid core
  • 0.50 mm / AWG24 enameled inductor wire: https://a.co/d/7Qasw5C
  • PIC ICSP programming header: 5 Position Header Connector (Digikey part: S5480-ND)
  • 2 x SMA to BNC adapter: https://a.co/d/29J1TEH
  • 1 x BNC Male to Male jumper cable: https://a.co/d/121di1X

Battery/Speaker PCB

  • U4, U5, U7 - 18650 battery holder (THT) (Digikey part 36-1043-ND)
  • U8: 1xBMS battery charger/protection board https://a.co/d/gX6wQ45
    • Sometimes one vendor is unavailable, other comes in. But these parts are generally are always available. Make sure to source 3S 40A 12.6V model!
  • 3x18650 Lithium Batteries. 18650BatteryStore.com part number INR18650-25R.
    • These are original Samsung 25R 18650 2500mAh 20A Batteries. Not problematic ones from Amazon and a such.
    • Alternative from Digikey, part number 1568-1488-ND
  • SW1: PCB Mount Slide Switch THT Right angled (Digikey Part EG1917-ND)
  • J1: 1x10 pin 2.54mm Male pin Header Connector Extra Tall: https://a.co/d/2l7o6wW
    • These are sold in a bulk, you will have to cut 1x10 out of it. Do not worry, we use some for the ATU Mount PCB as well.
  • JP102: 2x3 6pin 2.54mm connector, long needles: https://a.co/d/4Ca8vJi
    • For JP102 we need 2x2 female connector. But again, I could not source one with long needes. So, I just cut two side needles leaving plastic part intact.
  • JP106: 1x6 6pin 2.54mm Female Socket Long needle stackable header: https://a.co/d/21eQjdI
    • For JP106 we need actually 3-pin connector. However I could not source one with long needles. So, I just cut 3 pins. Leaving the plastic though intact!
  • LS1: Speaker 2W 8Ohm 28mm: https://a.co/d/bBaHMG7
    • or Digikey part 102-3850-ND
  • Power supply/charger for batteries: https://a.co/d/hriKC1F
    • It is very important to use this recommended power supply for the best charging experience and from the safety perspective! The BMS module used in battery board is not a charger. Its purpose is to manage balanced battery charge and discharge.
  • U1: Mini-Voltmeter: https://a.co/d/epVwKYk

Front Panel

Digikey part list

For the ordering convenience, below is the part list from Digkey for one build. List contains the vast majority of parts that can be sourced from Digikey except for some minor parts, like few pin headers and BMS battery charger. https://www.digikey.com/en/mylists/list/WN7WP7HZ7G

Alternative US sourcing option

If you are located in US, prefer brick & mortar style shopping and in addition are lucky enough to live near one of many Microcenter stores - it carries many if not all parts in the part list either individualy or in a variety of sets. Look at the Maker section of the store, prices are lower or competitve to Amazon. It may be worth paying a visit to the store, if not for the parts, but to replenish the BAWLS stock for sure 😄

Approximate cost estimate

Below is a rough estimate (with most pessimistic unoptimized assumption) for few configurations based on March,8, 2025 simulation of JLCPCB ordering plus US shipment and, Digikey part list cost. Estimation is based on a minimum batch of 5 PCB order and can be significantly lower with higer batch size and occasionally available coupons. With current inflation rates and tariff inconsistencies in a few months these estimates might be well outdated.

  • ATU/Audio PCB: $208 per 5
  • Battery/Speaker PCB: $10 per 5
  • Front Panel with SMD LED: $20
  • Rear Panel PCB: $7
  • Shipment to US: $38
  • Tax: 16$
  • Total per 5 PCB of each and shipment: $284
  • Total per set of 4 PCB's of each type: 284/5 = approx. $57
  • Total other parts per 1 build: approx $54 + shipment.
  • Grand Total per 1 build: $111 max.

Detailed Build Instructions

Can be found here.

ABS V2.0 Release notes

ABS ATU PCB

  • ATU Schematic was improved by eliminating an ATMEGA MCU
  • 6-layer ATU PCB with better signal isolation and RFI reduction
  • Simplified assembly process. ATU requires only inductor windings and few connector soldering
  • Added a capability of using SMA connectors for QMX+ integration
  • Portion of Stockton bridge elements moved closer to the MCU to improve the quality of analog forward and reverse power measurement signals
  • Improved SWR on 6m and 10m bands

ABS Audio Amplifier/Speaker circuit

  • ATU and ATU Mount PCB are combined into a single ABS ATU PCB with all SMD components
  • Audio amplifier schematic was imprioved resulting in a better sound
  • Audio aplifier is powered through 12V rail improving dynamic range and noise reduction
  • Speaker matching circuit accomodates 4, 8 and 16 Ohm speakers

ABS Battery/Speaker PCB

  • Fully redesigned allowing the use of a standard 11mm clearnce between ATU and Battery PCB
  • Standard length pin headers and female sockets used in the design simplifying the build process
  • Added an on-board voltmeter

Front Panel Modification

  • Increased pad sizes for control button and front LED wire connection easing the soldering.

Rear panel

  • Redesigned to accomodate SMA connectors and voltmeter controls.

Known issues

  • ATU-100 design used for the ABS underperforms on 6m band. If using an ATU on a 6m band is absolutely important for you - build the ATU with SMA connectors. This way when using 6m - ATU can be unplugged from QMX+. Then you can either use a resonant antenna or look for a commercial ATU solution.

Some future work:

  • Design ATU based on Dave's (N7DDC) ATU-10 schematic using latching relays.

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Companion PCB's to add ATU, internal battery with charger and a speaker to QRP Labs QMX+ transceiver

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