HF-PA-v2

VU3CER's Class-E HF PA for https://github.com/kholia/Easy-Digital-Beacons-v1 project for 20m band and up. It has (optional) software-controlled variable PA Output Power.

Supported bands: 80, 60, 40, 30, 20, 17m, and more bands with switchable 'LPF Module' board.

(July 2021 Update): While this HF PA works as well as the uSDX V1.02 PA and the QCX+ PA (they all use the same design!), we prefer our new HF-PA-v3 system PA for its robustness. If you need a 3W+ @ 14 MHz with high efficiency, this Class-E HF PA design (HF-PA-v2) is the best one ;)

Constraints for the initial PCB prototypes for validating the design:

• PCB is to be homebrewed (laser printer, toner tranfer using iron, etching via FeCl3)

• PCB is single-sided. Only one layer is available for routing.

• BS170 MOSFETs need to be on an edge to allow usage of heatsinks.

• My external PA150 HF Linear Amplifier needs 2W minimum to function.

Input: Few milliwatts is fine. Note: Si5351's output is around 8-10mW.

Output: Full-power 3.2W+ @ 13.3v (4S LiFePo4) for 20m band (14.074 MHz) with around 45-55% efficiency OR Safer 2W with reasonable PWM setting for digital modes!

Note: All screenshots are clickable and zoomable.

Note 2: Active cooling (fan) is recommended for digital modes! You have been informed ;)

Schematic:

The HF PA has over-voltage ("High-SWR") protection via a 47v zener power-dumping diode.

PCB renderings:

Socketable version (recommended):

Testing the Triple-Mode PSU + LPF 20m + 3xBS170 @ 13.8v:

LPF schematic (from uSDX PCB by WB2CBA):

Safe power supply module for the PA. It has over-current protection.

Note: This 3D rendering is only published to help with the manual layout work on Zero-PCBs.

Note 2: Various sub-circuits were simulated in LTspice prior to implementation.

Sample Code

• https://github.com/kholia/uSDX_Beacon

• https://github.com/kholia/Easy-Digital-Beacons-v1

O(Current consumption)

The ESP8266 usually draws a peak current of about 250mA after it wakes up and then more or less constantly draws around 70mA before it goes back to sleep.

DS3231 -> 5mA

Si5351 -> ~50 to 100mA

Upper bound -> 1.4A maximum.

BOM

• 1 x SN74ACT00N (TI)

• 3 x BS170 (ON Semi)

• 1 x 7805 Voltage Regulator TO-220 (STMicroelectronics)

• 1 x 7806 Voltage Regulator TO-220 (STMicroelectronics)

• 1 x 1N5822

• 1 x 1N5368B (47V 5W Zener Diode)

• 2 x 0.2 Ohms - 3W Current Sensing Resistor

• 2 x 1k Ohm - 0.25W Metal Film Resistor

• 220uF 25v Electrolytic Capacitor

• 5 x 100nF (104) Ceramic Capacitor

• 1 x 10nF (103) Ceramic Capacitor

• 1 x BD140 Transistor

• 1 x TIP42 Darlington Transistor

• 3 x T37-6 - Yellow Toroid, 1 x T37-2 - Red Toroid (LPF)

• 2 x 180pf, 2 x 390pf, 1 x 30pF NP0 Ceramic Capacitors (LPF caps, Kemet)

• 3 meters - Copper Magnetic Winding Wire (24 AWG - 25 SWG)

• Misc: Connectors, Zero PCB, Various Consumables

• Tools: LCR-T4 Meter (for measuring things), RF Power Meter

Tip: Buy in bulk for better pricing, and for getting spares for the "junk box".

20m LPF Module Details

• L1 - T37-6 / 16 turns
• L2 - T37-6 / 17 turns
• L3 - T37-6 / 16 turns
• L4 - T37-2 / 10 turns
• C1 - 180pf
• C2 - 390pf
• C3 - 390pf
• C4 - 180pf
• C5 - 30pf

Borrowed from QCX manual and uSDX WB2CBA PCB documentation.

BOM + Equipment Sources

• https://www.semikart.com/ (BS170, NP0 LPF caps - Kemet and others, Aavid DIP-14/16 Heat Sinks)

• https://www.semikart.com/search/SN74ACT00N

• https://robu.in/product/0-2-ohm-3w-surface-mount-sense-resistor-pack-of-3/

• https://www.electronicscomp.com/

  • BS170, regular caps, ST voltage regulators

  • TIP42, BD140

• https://www.electroncomponents.com/ (transistors, connectors, consumables, misc)

• https://www.sunrom.com/ (regular ceramic caps)

• https://projectpoint.in/

  • Transistors, regular caps, voltage regulators, MFR resistors, misc

  • Copper Magnetic Winding Wire

• https://www.bhagwatilightingindustries.com (Thermal Adhesive Paste)

• https://www.sunrom.com/p/254mm-40x1-female-socket-strip-machine-round-pins

  SIP Sockets 1A

• eBay (gr_makis) - Toroids

• LCR-T4 LCR Meter

Notes

• The CDIL 2N3904 TO-92 transistor has CT2N 3904 LS marking on it.

  CT -> Continental... Device India Ltd (CDIL)

• Burnt BS170 MOSFETs typically have their Drain and Gate shorted (Pin 1 and Pin 2 respectively).

• Use SIP sockets to avoid accidentally killing the MOSFETs via ESD (during probing, soldering, etc).

• PCB test: Remove the MOSFETS (keep everything else connected) and measure the resistance between the Gate Pin and Ground. It should show OL (Open Line).

Tips

• BS170 MOSFETs are very sensitive with regards to ESD and high soldering temperatures.

  Use best practices when dealing with BS170 MOSFETs and perhaps always ;)

References

• https://github.com/kholia/uSDX_Beacon
• https://github.com/agustinmartino/wsjt_transceiver
• http://hyse.org/pdf/www.aoc.nrao.edu/~pharden/hobby/_ClassDEF1.pdf
• http://hyse.org/pdf/www.aoc.nrao.edu/~pharden/hobby/_ClassDEF2.pdf
• http://thestone.zone/radio/2020/12/13/multi-watt-amplifier.html
• http://thestone.zone/radio/2020/12/18/gate-driver-amplifier.html
• http://thestone.zone/radio/2021/01/14/capacitors.html
• http://thestone.zone/radio/2021/01/16/minor-enhancements.html
• https://www.g0kla.com/scpa/SimpleCheapPA.php
• https://www.linkedin.com/pulse/rf-pcb-design-rules-manufacturing-process-lisa-chu/
• http://thestone.zone/radio/2021/06/04/attenuator.html
• http://thestone.zone/radio/2021/06/05/power-amplifier.html
• https://on7dq.blogspot.com/2020/12/qcx-mini-measurements.html
• https://www.random-science-tools.com/electronics/dBm-Watts-volts.htm
• https://www.mitsubishielectric.com/semiconductors/php/oSearch.php?FOLDER=/product/highfrequency/siliconrf/discrete
• http://www.carnut.info/WSPR_Tx/WSPR_Tx.htm
• https://sites.google.com/view/andy-g0ftd/iron-fist-transmitter
• https://www.dj0abr.de/english/technik/dds/pa.htm
• https://www.qsl.net/py2ohh/
• https://hf5l.pl/en/transceiver-usdx-with-arduino-nano/#

Credits

• MTR5B schematic
• PFR-3 design
• Dan Tayloe, N7VE (NC2030 PA design)
• Hans Summers (QCX+)
• Guido PE1NNZ (uSDX)
• WB2CBA (uSDX PCB)
• Tom (AK2B)
• Various uSDX folks
• Chris (G0KLA / AC2CZ) - over-current protection