Posts on Dhiru's Notebook

Reversing the Huidu HD-R712 FPGA board

Fri, 27 Feb 2026 00:00:00 +0000

We are working on reversing the Huidu HD-R712 LED Display Full Color Receiving Card - a very cost-effective (~1000 INR) and widely available FPGA board.

We draw inspiration from the https://github.com/q3k/chubby75 work.

FPGA Blink Project Files 1

Random brain dump

$ sudo openFPGALoader --cable dirtyJtag --freq 10000 --detect
Jtag frequency : requested 10000Hz -> real 10000Hz
index 0:
 idcode 0x4014c35
 manufacturer anlogic
 family eagle d20
 model EG4D20EG176
 irlength 8

$ sudo openFPGALoader --cable dirtyJtag --detect
Jtag frequency : requested 6000000Hz -> real 6000000Hz
index 0:
 idcode 0x4014c35
 manufacturer anlogic
 family eagle d20
 model EG4D20EG176
 irlength 8

JTAG pinout:

 V
┌───────────────────┐
│ 1 3 5 7 9 │
│ 2 4 6 8 10 │
└───────────────────┘

9 => TCK

7 => TDO

5 => TMS

3 => NC (Not Connected)

1 => TDI

The pin mapping work was done using a DMM, the datasheet, and an optical magnifier.

The Polar Express - Efficient SSB Generation

Mon, 16 Feb 2026 00:00:00 +0000

Polar Modulation for the masses

We have been working on generating SSB signals using Polar Modulation.

Hardware stack: RP2350-Zero MCU board + Fast Si5351 module + AP63301 buck regulator (for 5W mode).

Please see https://github.com/kholia/PolarModulationSSB for more details.

The audio fidelity and general quality is ok'ish at the moment but it can only improve from here. We are yet to hookup the amplitude ("envelope") restoration part.

Motivation

Why should Guido, Hans, and FlexRadio folks have all the fun? ;)

PA0FRI Active Antenna Redux - The final version?

Thu, 12 Feb 2026 00:00:00 +0000

I recently worked on a PA0FRI Active Antenna design with fast BFR93A / BFR106 / BFR193 transistors.

Design

3D render:

Schematic:

/ [pdf]

Simulation Results

Simplest APRS Digipeater and iGate on MCU!

Sat, 07 Feb 2026 00:00:00 +0000

Description

We have built the simplest, power efficient and 'ready-for-solar' APRS Digipeater and iGate on a MCU (RPi Pico 2 W)!

Our existing KISSLink v1 BLE KISS TNC device is capable of running in standalone mode with an alternate firmware!

Goal(s): Our design prioritizes low power, reliability, and unattended deployment over flexibility.

And yes, we want to do this with cheap, widely available BaoFeng radios. This means a couple of things:

Wireless APRS interface for BaoFeng and other radios!

Thu, 29 Jan 2026 00:00:00 +0000

Description

We have built a Bluetooth-enabled and APRSdroid-compatible digital interface (KISS TNC) for less than 15 USD (for the fully-loaded make including cables). We call it the KISSLink v1.

This digital interface can be powered from the USB 5V or the inbuilt battery.

Schematic

/ [pdf]

RX path simulation (AF front-end)

APRS interface for BaoFeng and other radios

Sat, 17 Jan 2026 00:00:00 +0000

The design

Here is a "safe" APRS interface for BaoFeng and other radios.

Sample schematic:

/ [pdf]

Render

A VFM ADS-B receiver

Mon, 12 Jan 2026 00:00:00 +0000

Idea

Ismo recently shared the https://github.com/CoolNamesAllTaken/adsbee project which is pretty cool.

Challenges

The ADS-B (Automatic Dependent Surveillance-Broadcast) system uses a data rate of 1 Mbit/s (1 megabit per second) for its aircraft position and identification transmissions on the 1090 MHz frequency. This is too much for HOPERF CMT2300A and related transceiver chips unfortunately!

This got us thinking about the following VFM ADS-B RX chain.

Architecture

Here is a simple ADS-B RX circuit description.

Reasonable MCU ADC performance - STM32H562

Sat, 10 Jan 2026 00:00:00 +0000

Ismo (OH2FTG) has praised the STM32's ADC quality multiple times, and I finally decided to give it a go.

I usually stick with Waveshare RP2350-Zero boards, but the RP2350 ADC performance is limited to under 10 ENOB.

With the STM32H562RGT6, we're able to achieve ~13 ENOB using 16× hardware ADC oversampling, with potential headroom to push this even further.

By sampling the Si4732's SSB output using the STM32H562RGT6 ADC and exposing the audio samples to the host via a "virtual" USB UAC-2 device, we get the following RX results:

Alternate to PE4312 Digital Step Attenuator

Thu, 08 Jan 2026 00:00:00 +0000

The PE4312 is a 50Ω, 6-bit RF digital step attenuator available for around 2 USD. Pretty neat for implementing real digital AGC!

For half-the-price we can get the alternate Archiwave ARW637 or ARW621A ICs which work very similarly to PE4312!

References:

The best power supply for FieldOps

Tue, 06 Jan 2026 00:00:00 +0000

This short article describes a flight-safe power supply for FieldOps.

Component List

Simply get these:

USB QC/PD AFC trigger decoy board (9V)
USB QC/PD AFC trigger decoy board (12V)
USB QC/PD AFC trigger decoy board (15V)
Xiaomi Pocket Power Bank Pro 10000 33W

This one does 9V, 12V, 15V and 20V without any problems.

OR

A 65W USB PD power bank - not needed for 5 to 10W QRP FieldOps

Supporting HOPERF CMT2300A on Linux

Tue, 23 Dec 2025 00:00:00 +0000

What This Article Covers

This article presents a practical journey to add Linux support for the HOPERF CMT2300A Sub-GHz RF transceiver - starting from extracting register configuration tables out of vendor firmware, to building and testing a Linux driver on real hardware.

You'll learn:

How TP-Link's driver situation motivated this effort
How firmware was extracted and analyzed
How to build and load the custom driver on Raspberry Pi
How to verify real on-air packet RX

This is aimed at embedded Linux developers, reverse engineers, and RF hackers. It is not a beginner Linux kernel tutorial nor a full CMT2300A datasheet walkthrough - focus is on practical bring-up and reproducibility.

HFDY Active Loop - LZ1AQ loop clone

Sun, 09 Nov 2025 00:00:00 +0000

The HFDY Active Loop is working extremely well and that too from an indoor location in MK68! Pretty awesome ;)

Design

I am running the loop at 5V (via a regulated linear power supply) currently where it consumes slightly less than 65mA of current. The recommended voltage is 10V, which I will shift to soon.

Results

I am using Airspy HF+ Discovery SDR for this experiment.

Sustainable Radio Design V2

Fri, 07 Nov 2025 00:00:00 +0000

Design

We are finally going to build a QSD RX!

Here is the rough schematic I am thinking about:

References

MC1496 Information
HSDAOH on RP2350 (see internal_adc section)

This way we can continue using RP2350 instead of moving to something like STM32H5 immediately
PicoRX Simulations (also for DSP code)

Writing test cases for PCBs

Fri, 07 Nov 2025 00:00:00 +0000

This note demonstrates a small connectivity tester / check nets program for KiCad. This program allows doing checks like: Is the U1:8 pin connected to GND?

Motivation

Sometimes visual errors can creep in the schematic (and the PCB subsequently). This connectivity tester allows expressing the same connections in a non-visual way (with a different probability of making errors).

The ERC and DRC checks in KiCad work great but this non-visual test assertions provide another level of sanity checking.

Choosing a coax for HF field operations

Wed, 05 Nov 2025 00:00:00 +0000

Setup: Si5351 RF generator (@ 28 MHz) ➔ GSD-Hacks-v5 digital amplifier ➔ 7th order LPF ➔ {COAX-UNDER-TEST} ➔ Digital RF power meter ➔ Dummy load

Results

Results at 13.8V drain:

Coax Type	Power Reading
RG-58 (7 meters)	4.5W
RG-316 (7 meters)	3.9W
RG-188 (7 meters)	3.9W

Results at 15V drain:

Coax Type	Power Reading
RG-58 (7 meters)	5.4W
RG-316 (7 meters)	4.7W
RG-188 (7 meters)	4.7W

These measurement results seem to match the ones from Eric, WD8RIF.

Easy reproducible LPF filters

Sat, 01 Nov 2025 00:00:00 +0000

Here is the schematic for a standard 50Ω LPF for the 12-11-10m bands.

Designs

PCB Render:

Actual photo:

Performance

NanoVNA results of the PCB build:

Build Notes

These values come from RobG (https://hackaday.io/)

Shunt C: 100pF

Series L: 12T on T37-6 core, 11T on T50-6, making about 485nH

Shunt C: 180pF

Series L: 13T on T37-6 core, 12T on T50-6, making about 580nH

Shunt C: 180pF

Series L: 12T on T37-6 core, 11T on T50-6, making about 485nH

Shunt C: 100pF

Winding wire size: 27 SWG (is non-critical)

Note: We needed to reduce 1T (from the values specified above) when using the T50-6 cores. As usual, use a DE-5000 LCR Meter (or better) to know the exact values.

A proper single transistor LNA for HF

Tue, 28 Oct 2025 00:00:00 +0000

Note: This HF LNA design is inspired by PY2OHH designs and mcHF work.

Previous article: Single Transistor LNA for HF - it cut a corner when it came to output impedance matching ;)

Design

The idea that a single-transistor-preamp with 10 dB gain is more than enough for HF comes from Gajendra Kumar (VU2BGS). As a new "designer" I am often overwhelmed by the different possible design paths - so having guidance from an elmer becomes crucial.

My solar powered WSPR beacon

Sun, 26 Oct 2025 00:00:00 +0000

My solar powered WSPR beacon is now active on the 12m band!

Tech Stack

Tech stack: Navitas 100W Solar Panel, Exide Solar Blitz 40AH battery, Skypearll Solar Charge Controller 30A, 200W 20A DC-DC CC CV Buck module (Robu) - set to output 7.5V, Waveshare ESP32-S3 Zero board, Si5351 with 0.5ppm TCXO, GSD-Hacks-v5 amplifier, DFRobot Gravity Digital 5A Relay Module

Photos of components involved (for reference):

Headless WSPR Monitoring System (2025)

Wed, 22 Oct 2025 00:00:00 +0000

Setup OS and SDR

Please use the latest Raspberry Pi OS 64-bit on RPi 4 or later.

Using a Raspberry Pi (<=3) is NOT recommended as it has quite a bit of power supply noise on the USB ports, which reduces the performance of the connected SDR.

Install dependencies:

sudo apt-get update

sudo apt-get install airspyhf \
 soapysdr-tools sox libsox-fmt-all wsjtx \
 pulseaudio-utils git vim fluxbox xterm tightvncserver

sudo apt-get install cmake pkg-config \
 libusb-1.0-0-dev \
 libasound2-dev \
 libairspy-dev \
 libairspyhf-dev \
 librtlsdr-dev \
 libsndfile1-dev \
 portaudio19-dev \
 libvolk-dev

Build airspyhf-fmradion SDR software:

Inbuilt band-hopping in WSJT-X 3.x

Sat, 18 Oct 2025 00:00:00 +0000

WSJT-X 3.x has inbuilt support for band hopping!

Results

RX results from an experimental version of DDX:

This is super useful for monitoring FT8 traffic on multiple bands.

References

The (now) poor quality, reliability and longevity of Luminous products

Sat, 18 Oct 2025 00:00:00 +0000

My old Luminous Zelio inverter (bought in ~2013) lasted for close to 8 years.

Trusting the Luminous brand, I installed two more Luminous Zelio inverters in year 2024 in two different homes.

Come year 2025 and both these Zelio inverters have conked off and that too in less than a year!

I guess they don't make the Zelio inverters the way they used to :-(

For now, I have shifted to Microtek Heavy Duty UPS 1750 and Microtek 1275 12V SW inverter models.

A Sustainable Radio Design?

Fri, 17 Oct 2025 00:00:00 +0000

Future radio receiver design ideas (from Ismo, Pete and other folks):

Antenna ➔ (BPF) ➔ BFR93A based pre-amp from mcHF project ➔ MC1496 (Mixer) ➔ 455 kHz IF ➔ Ceramic filter SMD (HCI) ➔ 'IF amplifier' (20-40 dB gain?) ➔ Overclocked Pico 2's ADC (3+ MSPS) ➔ Digital down-conversion and processing in digital domain ➔ Expose the processed audio samples over USB (Pico 2 acts as a sound card).

Benefits: This enables reception of SSB and CW signals! The 455 kHz IF with digital processing gives us the best of both analog selectivity (ceramic filter) and digital flexibility.

Emulating a full FT8 band for 'real'

Fri, 17 Oct 2025 00:00:00 +0000

This code generates a .wav file which emulates a fully-populated FT8 band!

Usage

This .wav file can then be played with rpitx on actual air (well on a dummy load) for receiver testing purposes.

rm mixed.wav; sox -m *.wav mixed.wav

sox mixed.wav -r 48000 sampleaudio.wav

Now play sampleaudio.wav using rpitx.

Testing

I have tested rpitx on Raspberry Pi Zero 2W TX'ing @ 14.074 MHz.

433 MHz CW signal source

Sat, 04 Oct 2025 00:00:00 +0000

For HF and amateur VHF bands our WiFi VFO works great.

But we didn't have a cost-effective UHF signal source until now…

Design

Thanks to Ismo (OH2FTG), we recently experimented with a HopeRF CMT2119A powered board called HOPERF RF module RFM119W-433S1.

Here is the CMT2119A powered board in action producing a CW (OOK) signal at ~433 MHz.

The stability is pretty good and a bit surprising considering that the board uses a 20ppm 26 MHz regular quartz crystal - not bad!

Making Manhattan constructions easier, better, cost-effective and almost tool-free

Sat, 04 Oct 2025 00:00:00 +0000

Instead of punching islands or using commercial pads (islands) or making traditional pads myself, I simply make use of small pieces of single-sided PCBs to create the pads / islands easily for my boards.

The Technique

This technique has a huge advantage over the punched islands or scored and divided boards techniques as it keeps the bottom ground plane perfectly 100% intact!

Also, it is almost a tool-free process to create the pads by breaking or cutting the single-sided PCBs. Single-sided prototyping boards also happen to be very reasonably priced.

The future of DDX - 2025 version

Sat, 04 Oct 2025 00:00:00 +0000

Shipping hardware internationally is a hard, labor intensive, and overall a frustrating process - especially more so these days.

Here is our plan to supply the DDX to customers:

Make the hardware files free / low-cost. The users will be able to order fully assembled boards from JLCPCB or other vendors on their own.
Required a small licensing fee for the software firmware part. This is how we get to keep the hobby self-sustaining!

Another cool SiC part for HF amplifiers

Mon, 29 Sep 2025 00:00:00 +0000

I recently spotted the Tokmas CI7N170SM TO-247 part on LCSC. It seems like a pretty neat part for building non-QRP HF amplifiers!

This could be a better part for our Baby QRO amplifier.

Datasheet Excerpts

The full datasheet is available here.

Comparison

In comparison, here is what a professional RF part (MRF300AN) looks like:

That 272W maximum power dissipation figure is crazy good but switching characteristics are not that great (fast).

Debugging gaming pads on Linux

Mon, 29 Sep 2025 00:00:00 +0000

While running https://github.com/fhoedemakers/pico-infonesPlus, I found that my SNES gaming pad was not fully supported.

Specifically, the UP/DOWN and LEFT/RIGHT keys were not working.

Let's debug this a bit:

Plug in the gaming pad on a Linux box and run the following command (hidraw5 will need to be changed as needed):

$ lsusb
...
Bus 001 Device 063: ID 0810:e501 Personal Communication Systems, Inc. SNES Gamepad

$ sudo hexdump -C /dev/hidraw5
...
00004a50 01 80 80 7f 7f 0f 00 00 01 80 80 7f 00 0f 00 00 |................|
00004a60 01 80 80 7f 00 0f 00 00 01 80 80 7f 00 0f 00 00 |................|
*
00004a80 01 80 80 7f 7f 0f 00 00 01 80 80 7f 7f 0f 00 00 |................|

This is what I see when pressing the UP key.

FT8 Decoding Challenges on Android

Mon, 29 Sep 2025 00:00:00 +0000

Here is the FT8 WAV test file.

On an AMD64 machine:

1 second using the fast decode settings.

We were able to get the MSHV's FT8 engine to work on Android, thanks to the work done by https://github.com/sannysanoff/SDRPlusPlusBrown folks.

Around ~4.5 seconds to decode the same file.

This is why we can't really have full-blown realtime FT8 decoder(s) on Android just yet!

Idea: But we can surely use this full-blown FT8 decoder in our FT8 Decoder app which has no realtime requirements!

Success with 2m WSPR!

Thu, 25 Sep 2025 00:00:00 +0000

OCXO's are awesome - this is what I learned while trying to get WSPR working reliably on the 2m band.

Hardware

Here is all you need for reliable WSPR'ing on the 2m band:

A RAW OCXO "can" works fine too!

Note: This modded Si5351 board image comes from SimonsDialogs. Essentially we are modding the CLK2 output port to become an input port which accepts the OCXO's output signal.

Black Box output characterization of CD2003 DCR receiver

Sun, 21 Sep 2025 00:00:00 +0000

Circuit: DDX-Commercial-7

Antenna: Small jumper cable attached

Initial Results

10m: 36 dB on WSJT-X audio meter, on quiet and also with nearby beacon on !!!

12m: 36 dB on audio meter, on quiet and also with nearby beacon on !!!

15m: 46 dB on audio meter on quiet, 65 dB with nearby beacon on - OK

20m: 44 dB on quiet, 65 dB with beacon on - OK

40m: 40 dB on quiet, 60 dB with beacon on - OK

Running Vivado 2025.1 on Ubuntu 25.04 (plucky)

Sun, 21 Sep 2025 00:00:00 +0000

Notes to get Vivado 2025.1 running on Ubuntu 25.04 (plucky) Linux distribution.

Original reference: QMTech XC7Z020 Notes

Setup

Install dependencies:

sudo apt-get update

sudo apt-get --no-install-recommends install \
 bc binfmt-support bison build-essential ca-certificates curl \
 debootstrap device-tree-compiler dosfstools flex fontconfig git \
 libncurses-dev libssl-dev libtinfo6 parted qemu-user-static \
 squashfs-tools u-boot-tools x11-utils xvfb zerofree zip

Hack deps a bit:

sudo ln -s /lib/x86_64-linux-gnu/libtinfo.so.6 /lib/x86_64-linux-gnu/libtinfo.so.5

You can now go ahead and run the Vivado installer.

Single Transistor LNA for HF

Sun, 21 Sep 2025 00:00:00 +0000

Note: This HF LNA design is inspired by Charlie Morris ZL2CTM's prior work.

Design

It seems even MMBT2222A should work for building a HF LNA!

WSPR Decoding Challenges

Sun, 21 Sep 2025 00:00:00 +0000

The wspr_spread work is pretty awesome.

Doppler Spread

It helped us debug why our TCXO-powered-WSPR beacon was pretty decent on 4m band but flaky on 2m.

Doppler spread value on 70 MHz:

... 70.0924994 VU3CER MK68 23 0 0.29 1 1 0 1 44 1 810 0.517

Now see the problem on 144 MHz:

... 144.4905417 VU3CER MK68 23 -3 0.12 1 1 0 1 39 1 810 0.865

WSPRing on higher bands

Sat, 30 Aug 2025 00:00:00 +0000

Our WSPR beacon design works fine even on the 4m band (~70 MHz) . The key is to use a 25 MHz high-quality TCXO, like the 25 MHz HCI 0.5ppm TCXO!

Results

Challenges

2m WSPR is still out of reach for now - see the following sporadic decodes.

Of course, the next challenge is to get 2m WSPR beacons working 100% reliably at a low cost.

Notes on coupled inductors

Sun, 17 Aug 2025 00:00:00 +0000

The usage of ready-made coupled inductors in RF designs was pioneered by Jim Veatch in his award-winning RF amplifier designs.

Applications

For Baby-QRO applications, we can use Wurth 744851330 coupled inductor. For 5W / 10W RF amplifier applications, we can use Bourns SRF1260A-4R7Y coupled inductor.

Recently we were able to utilize very cost-effective YJYCOIN YPRH1207C-4R7M Chinese coupled inductor with excellent results.

With our current Digital Amplifier designs, this Chinese coupled inductor works even at ~75 MHz.

Initial success with cost-effective 6m WSPR + 2m FT8 beacons

Sat, 16 Aug 2025 00:00:00 +0000

Our 6m WSPR beacon design works fine now. The key is to use a 25 MHz high-quality TCXO, like the 25 MHz HCI 0.5ppm TCXO!

2m WSPR is still out of reach for this VFO design - see the following drifty screenshots:

While WSPR is no good, 2m FT8 works pretty fine!

Checking Zoom latency externally

Fri, 08 Aug 2025 00:00:00 +0000

Here is a handy script that I often use to check the quality of the Zoom connection. It measures TCP latency instead of the usual ICMP stuff (which is often blocked).

#!/usr/bin/env python3
"""
TCP Ping Test (defaults to port 80, 10000 packets)

Usage: ./tcpping.py host [port] [maxCount]
- Ctrl-C Exits with Results
"""

"""
pip3 install matplotlib numpy

python3 ./tcp_ping_grapher.py 115.114.56.202 443 100

python3 ./tcp_ping_grapher.py teams.microsoft.com 443 100
"""

import sys
import socket
import time
import signal
from timeit import default_timer as timer

# https://matplotlib.org/examples/animation/animate_decay.html
import numpy as np
import matplotlib.pyplot as plt
import matplotlib.animation as animation

host = None
port = 80

# Default to 10000 connections max
maxCount = 10000

## Inputs

# Required Host
try:
 host = sys.argv[1]
 # host = "115.114.56.202"
except IndexError:
 print("Usage: tcpping.py host [port] [maxCount]")
 sys.exit(1)

# Optional Port
try:
 port = int(sys.argv[2])
 # port = 443
except ValueError:
 print("Error: Port Must be Integer:", sys.argv[2])
 sys.exit(1)
except IndexError:
 pass

# Optional maxCount
try:
 maxCount = int(sys.argv[3])
except ValueError:
 print("Error: Max Count Value Must be Integer", sys.argv[3])
 sys.exit(1)
except IndexError:
 pass

# Pass/Fail counters
passed = 0
failed = 0

def getResults():
 """ Summarize Results """

 lRate = 0
 if failed != 0:
 lRate = failed / (count) * 100
 lRate = "%.2f" % lRate

 print("\nTCP Ping Results: Connections (Total/Pass/Fail): [{:}/{:}/{:}] (Failed: {:}%)".format((count), passed, failed, str(lRate)))

def signal_handler(signal, frame):
 """ Catch Ctrl-C and Exit """
 getResults()
 sys.exit(0)

# Register SIGINT Handler
signal.signal(signal.SIGINT, signal_handler)

def work(t=0):
 passed = 0
 failed = 0
 count = 0
 maxCount = 3200
 # Loop while less than max count or until Ctrl-C caught
 while count < maxCount:
 # Increment Counter
 count += 1
 success = False
 # New Socket
 s = socket.socket(
 socket.AF_INET, socket.SOCK_STREAM)

 # 1sec Timeout
 s.settimeout(1)

 # Start a timer
 s_start = timer()

 # Try to Connect
 try:
 s.connect((host, int(port)))
 s.shutdown(socket.SHUT_RD)
 success = True

 # Connection Timed Out
 except socket.timeout:
 print("Connection timed out!")
 failed += 1
 except OSError as e:
 print("OS Error:", e)
 failed += 1

 # Stop Timer
 s_stop = timer()
 s_runtime = "%.2f" % (1000 * (s_stop - s_start))

 if success:
 print("Connected to %s[%s]: tcp_seq=%s time=%s ms" % (host, port, (count-1), s_runtime))
 passed += 1

 # Sleep for 1sec
 if count < maxCount:
 # time.sleep(0.5)
 # time.sleep(1)
 time.sleep(2)

 t += 2
 yield t, float(s_runtime)


# Output Results if maxCount reached
# getResults()
def data_gen(t=0):
 cnt = 0
 while cnt < 1000:
 cnt += 1
 t += 0.1
 yield t, np.sin(2*np.pi*t) * np.exp(-t/10.)


def init():
 ax.set_ylim(0, 128 * 3)
 ax.set_xlim(0, 300)
 del xdata[:]
 del ydata[:]
 line.set_data(xdata, ydata)
 return line,

fig, ax = plt.subplots()
line, = ax.plot([], [], lw=2)
ax.grid()
xdata, ydata = [], []


def run(data):
 # update the data
 t, y = data
 xdata.append(t)
 ydata.append(y)
 xmin, xmax = ax.get_xlim()

 if t >= xmax:
 ax.set_xlim(xmin, 2*xmax)
 ax.figure.canvas.draw()
 line.set_data(xdata, ydata)

 return line,

ani = animation.FuncAnimation(fig, run, work, blit=False, interval=10,
 repeat=False, init_func=init)
plt.show()

Usage:

WiFi VFO, beacon and signal generator

Sat, 05 Jul 2025 00:00:00 +0000

We make heavy use of Easy-Digital-Beacons-v1 for testing RF amplifiers.

This single board is a versatile WiFi VFO and FT8 / FT4 / WSPR beacon.

You can also use our CW-SigGen project to generate a suitable test signal.

New RF parts and new promises - part 2

Sun, 15 Jun 2025 00:00:00 +0000

Tokmas CID9N65E3 rocks!

Performance

It is CRAZY how efficient this GaN FET is in TO-252 (DPAK) package. It generates 5W @ 28 MHz with 13.8V at drain without even warming up! Close to 4W @ 50 MHz with 12.0V at drain. 5W+ @ 50 MHz with 13.8V at drain. 11W+ @ 50 MHz with 20V at drain.

It even produces ~3W at 70 MHz with 13V at drain - w00t!

The poor quality, reliability and longevity of MOONDROP products

Sun, 15 Jun 2025 00:00:00 +0000

I had bought two pairs of MOONDROP Aria 2 IEMs after auditioning them at a Headphone Connect event.

After a few months of usage, one of the Aria 2 earphones lost audio in the left earpiece. We got it 'serviced' under warranty from Headphone Zone.

After a year of almost no usage, the other pair of Aria 2 IEMs lost audio in one of the earpieces too!

I have never seen this poor quality, reliability and longevity before!

Fast(est) gate drivers in the West

Tue, 03 Jun 2025 00:00:00 +0000

I recently found some FET gate drivers which are quite fast!

The Drivers

Wuxi Maxinmicro MX1025D - Favorite!
BD2311NVX-LBE2 from ROHM Semiconductor
TI LMG1020
Tokmas LMG1020YFFR

Usage

They are perfect for driving the fast Tokmas GaN FETs that we recently discussed on this site.

Our 'workhorse' gate driver for the recent experiments has been the Onsemi's NCP81074ADR2G in a friendly SOIC-8 package.

And we have shifted to MX1025D gate driver in our latest amplifier designs.

Debugging / reversing Firebase gRPC traffic with mitmproxy

Wed, 16 Apr 2025 00:00:00 +0000

Recently, I was stuck in figuring out how the Firebase gRPC calls worked and how I could generate, modify, and replay them. Trapping and modifying the existing gRPC traffic was not working too well. Finally, I took a step back and spent some time on learning how to build and debug simple Firebase applications. This approach helped me tremendously and I was able to make further progress with my original task in almost no time.

Ideas for a 2m (144 MHz) WSPR / FT8 beacon

Tue, 15 Apr 2025 00:00:00 +0000

I am posting an early design sketch of a 2m WSPR beacon.

Key Points

25 MHz HCI 0.5ppm TCXO powering the Si5351 module instead of the 26 MHz TCXO. If this fails, we can use a 10 MHz OCXO instead (a bit out of spec but works fine).
Tokmas CID10N65F GaN FET might work @ 144 MHz as the 'final'. If not, use Mitsubishi RD15HVF1-501 MOSFET as backup.
2SK3475 as the driver with variable DC bias at the gate
The whole VCC to this amplifier will be PTT switched
Ideally, we would want to keep the driver stage linear but the final stage as switched (Class C/D) Alternate: Perhaps by DC coupling the Si5351 input to 2SK3475, we can avoid the need for DC gate bias
The "RFC" (bifilar coil still needed?) part will need to be figured out for VHF!

Status

Results: To be built and tested soon!

Easily verifying certificate chains

Mon, 14 Apr 2025 00:00:00 +0000

Here is a quick script to verify that the certificate chain is valid and will work.

% cat verify-cert-key.sh
#!/usr/bin/env bash

certFile="${1}"
keyFile="${2}"
caFile="${3}"
certPubKey="$(openssl x509 -noout -pubkey -in "${certFile}")"
keyPubKey="$(openssl pkey -pubout -in "${keyFile}")"

if [[ "${certPubKey}" == "${keyPubKey}" ]]
then
 echo "PASS: key and cert match"
else
 echo "FAIL: key and cert DO NOT match"
fi

openssl verify -CAfile "${3}" "${1}"

Reimagining the 'Tangara' music player - Part 2

Fri, 11 Apr 2025 00:00:00 +0000

Tangara is a pretty awesome project!

It recently inspired us to build a similar FOSS DAP product but at a much lower cost of <= 40 USD. Our initial tech stack: RP2350-Zero, PCM5102A 32-bit 384kHz DAC, Burr-Brown OPA1662 (specified for 3.3v) as the unity gain buffer and headphone driver, no explicit DC-DC converters anywhere, microSD card, everything will be a module if possible

We quickly got this prototype working on a breadboard and discovered some limitations:

Ideas for a 6m WSPR beacon

Thu, 10 Apr 2025 00:00:00 +0000

I am posting an early design sketch of a 6m WSPR beacon.

Key Points

25 MHz HCI 0.5ppm TCXO powering the Si5351 module instead of the 26 MHz TCXO. If this fails, we can use a 10 MHz OCXO instead (a bit out of spec but works fine).
Tokmas CID10N65F GaN FET should work @ 50 MHz
TI UCC27614 or Onsemi NCP81074 gate driver

Status

Results: To be built and tested soon!

My WSPR beacon results - April 2025

Thu, 10 Apr 2025 00:00:00 +0000

This ~1W to ~5W WSPR beacon runs continuously on the 10m band. It handles extreme environmental temperatures pretty well (it is 42°C plus here).

Our article on this beacon's design and operation will appear in the May/June 2025 issue of the QEX magazine soon.

References

New RF parts and new promises

Thu, 20 Mar 2025 00:00:00 +0000

Ismo (OH2FTG) recently introduced me to a bunch of Tokmas RF parts. Out of these, the Tokmas CID10N65F GaN FET stood out. It seems to have a lot of potential (for HF + 6m) at a very low price point.

This RF MOSFET part can be purchased from LCSC.

It seems Tokmas CID10N65F has the potential to completely replace the RD16HHF1 part from Mitsubishi Electric!

Datasheet

Datasheet excerpt:

1W WSPR beacon @ 5V (2025)

Fri, 14 Mar 2025 00:00:00 +0000

I have designed, built and tested an all-HF WSPR beacon which produces 1W @ 5V and is rugged and cost-effective.

Results

Power consumption: Around 420mA @ 5V.

Cost

Cost: Around 500 INR.

Time to build

Time to build: Less than 30 minutes.

Files

The files for this project are published here for personal (non-commercial) usage.

For a 5W (QRO) WSPR beacon, please hold on for our upcoming QEX magazine article ;)

Testing small power supplies

Tue, 18 Feb 2025 00:00:00 +0000

I found this 60W Electronic Load to be quite useful for testing small power adapters and supplies.

While it is possible to homebrew an adjustable electronic load we recommend getting this electronic load module or a better-but-costlier one like the UNI-T UTL8212+ electronic load.

Observations

You can stress-test power supplies using this electronic load quite easily and conveniently.

It turns out that the Orange branded 12V 2A or 3A adapters from Robu are of really poor quality. The output voltage drops to less than 2V when the load current is increased to around 1A. This is NOT the first time that the Orange branded stuff has turned out to be of poor quality. In the end, you get what you pay for.

Reimagining the 'Tangara' music player

Sat, 15 Feb 2025 00:00:00 +0000

Tangara is a pretty awesome project - no doubts about it. I found this review of Tangara's design pretty interesting and educational.

It has inspired us to build a similar FOSS DAP product but at a much lower cost of 40 USD (that being the launch price of Sansa Clip in year 2007). The idea is to deliver '90% of the value' of Tangara in a slightly smaller (but fatter) and more cost-effective package.

100mW WSPR beacon (2025)

Fri, 14 Feb 2025 00:00:00 +0000

I have built probably the easiest, reasonably rugged and most cost-effective 100mW WSPR (or FT8) beacon.

The Build

Here is my quick and dirty build with whatever I had lying around:

We have replaced the traditional expensive Mini-Circuits transformer with a cost-effective Bourns coupled inductor.

Analysis

Power consumption: Before RF generation starts ➔ 20mA @ 5v. After RF generation starts ➔ 52mA @ 5v. So the power input consumed in the RF generation process is more than 150mW it seems (which is good).

Easy WSPR Encoder

Fri, 14 Feb 2025 00:00:00 +0000

The Easy WSPR Encoder can be accessed here.

Update: You may find this software more useful.

Budget RF Lab for HF

Thu, 13 Feb 2025 00:00:00 +0000

Bharath and I have written our thoughts on building an RF lab on a budget. It is geared towards homebrewers and new amateur radio operators.

Budget RF Lab Documentation.

Have fun! :-)

Easy FT8 Encoder

Thu, 13 Feb 2025 00:00:00 +0000

The Easy FT8 Encoder can be accessed here.

In the near future, we want to add the K1JT's original FT8 encoder functionality as well.

Update: FT8Play is crazy good!

RSP1 Clone SDR Notes (2025)

Thu, 13 Feb 2025 00:00:00 +0000

Notes to get RSP1 working on Linux and macOS using FOSS drivers (2025)

Prerequisites

Please use a mainstream Linux distribution like Ubuntu 24.04 LTS (or later) or the latest Raspberry Pi OS.

Using a Raspberry Pi is NOT recommended as it has quite a bit of power supply noise on the USB ports, which reduces the performance of the connected SDR.

Linux Setup

On Linux, add the following lines to the /etc/modprobe.d/blacklist.conf file

Easy reproducible TX-BPF filters

Mon, 10 Feb 2025 00:00:00 +0000

Some weeks back, we published our designs for building reproducible TX-BPF filters easily.

Designs

10m TX-BPF:

Results of the Dhiru's Manhattan build:

Results of the PCB build:

Why use BPFs?

While many amateur radio operators focus solely on antenna optimization, the significant benefits of TX-BPF filters are often overlooked or under-discussed in the hobby! Even with HOA antenna restrictions, you can still optimize your station's performance through proper TX-BPF filtering.

250mW WSPR beacon (2025)

Sun, 09 Feb 2025 00:00:00 +0000

I am building an easy-to-use and cost-effective WSPR pHAT for Raspberry Pi Zero 2 W.

Design

3D render:

We have replaced the traditional expensive Mini-Circuits transformer with a cost-effective Bourns coupled inductor.

Status

Results: To be built and tested soon!

Time to build: Less than 20 minutes

Ubuntu Going Downhill

Sun, 09 Feb 2025 00:00:00 +0000

I am a bit late to realize that Ubuntu is going downhill and has been for a while.

Why?

Here are a couple of things I have noticed about Canonical/Ubuntu:

Forced paid updates even for active life OS versions
Series of bad decisions (Mir, Unity, Upstart, Snaps) causing pain all around
Inflicting slow and buggy snap applications on their users. Not listening to feedback from users - Firefox Snap is really slow to launch, especially on older computers.

My PA0FRI Active Antenna

Sat, 08 Feb 2025 00:00:00 +0000

My homebrewed PA0FRI Active Antenna is working well from a very physically constrained location.

Design

3D render:

Schematic:

Results

The antenna is connected to a RSP1 Clone SDR which is running custom FT8-band-hopping software. I am using a SOLID 4-Way 5-2400 MHz RF splitter to connect multiple SDRs to the same active antenna. NB: Plug in 75-ohms dummy loads (terminators) on the unused ports of the RF splitter - MX-282 / MX-280 75-ohms dummy loads work fine.

Baby-QRO RF switching amplifier

Fri, 31 Jan 2025 00:00:00 +0000

Sometimes we all need a bit of QRO - Life's too short for QRP sometimes. So we give you the Baby-QRO switching amplifier!

This Baby-QRO switching RF amplifier design is inspired by the wonderful Single NXP MRF-101 Eval Board project by Jim Veatch. Thank you Jim!

Instead of using the expensive MRF101 MOSFET, we use fast SiC MOSFET(s) from Wolfspeed / SUPSiC.

Design

3D render:

Actual picture:

Easy Taint Tracking - Finding Heartbleed in 2024

Fri, 01 Nov 2024 00:00:00 +0000

Aim

Finding 'Heartbleed' class of bugs with taint analysis.

Background reading: https://heartbleed.com/

Motivation

While Coverity is now able to detect this bug, we wanted to evaluate the state of open-source security tooling in 2024.

Have we been able to reduce the cost of finding such bugs after all these years?

The Idea

Can we find an execution path from the tainted data in the n2s function to sensitive functions?

Since n2s typically operates on network received bytes, it can serve as a taint source.

My solar powered website

Fri, 01 Jan 1999 00:00:00 +0000

This notebook (aka 'blog') is powered by free solar energy!

I was (and am) inspired to start writing again by reading this excellent article by 'LOW←TECH MAGAZINE'. Imitation is the sincerest form of flattery…

Tech Stack

Tech stack: Navitas 100W Solar Panel, Exide solar charge controller (10A), Exide Solar Blitz 40AH battery, 200W 20A DC-DC CC CV Buck module (Robu), Cuzor Mini Pro RouterUPS (12V), LM2596S DC-DC 24V/12V to 5V 5A Step Down USB module, Raspberry Pi Zero 2W