Shortwave on Dhiru's Notebook

HAM Radio Is NOT Just for Talking

Mon, 04 May 2026 00:00:00 +0000

It's a Training Ground for Engineers (And We've Been Ignoring It)

Let's drop the nostalgia and say something uncomfortable:

If you think ham radio is just people talking into microphones, you're not just wrong - you're overlooking one of the most hands-on, intellectually rigorous engineering playgrounds still accessible to individuals.

Because amateur radio isn't about conversation.

It's about understanding how information survives reality.

And reality is hostile.

Signals Don't Care About Your Abstractions

Modern software engineers live in a world of clean abstractions: APIs work (until they don't), packets arrive (until they don't), networks are "just there."

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:

HFDY Active Loop - LZ1AQ loop clone

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

The HFDY Active Loop is working extremely well, even from an indoor location in MK68.

Design

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

Results

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

Future work

It would be very interesting to compare this HFDY Active Loop against the PA0FRI Active Antenna.

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)

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 available design paths, so guidance from an elmer is crucial.

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.

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).

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

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

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 guidance from an elmer is crucial.

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

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 that 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) use.

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

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: