Dhiru's Notebook - Articles by Dhiru Kholia

Testing small power supplies

Tue 18 February 2025 By Dhiru Kholia

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.

You can stress-test power supplies using …
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Reimagining the 'Tangara' music player

Sat 15 February 2025 By Dhiru Kholia

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 …
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Easy WSPR Encoder

Fri 14 February 2025 By Dhiru Kholia

The Easy WSPR Encoder can be accessed here.

Update: You may find this software more useful.
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100mW WSPR beacon (2025)

Fri 14 February 2025 By Dhiru Kholia

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

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

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

Power consumption: Before RF generation starts -> 20mA …
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Budget RF Lab for HF

Thu 13 February 2025 By Dhiru Kholia

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

We maintain this documentation here.

Have fun! :-)
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Easy FT8 Encoder

Thu 13 February 2025 By Dhiru Kholia

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: https://pengowray.github.io/ft8play/ is crazy good!
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RSP1 Clone SDR Notes (2025)

Thu 13 February 2025 By Dhiru Kholia

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

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 …
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Easy reproducible TX-BPF filters

Mon 10 February 2025 By Dhiru Kholia

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

10m TX-BPF:

Results of the PCB build:

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 …
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Ubuntu Going Downhill
Sun 09 February 2025 By Dhiru Kholia
I am a bit late to realize that Ubuntu is going downhill and has been for a while.

Here are a couple of things 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 …
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250mW WSPR beacon (2025)

Sun 09 February 2025 By Dhiru Kholia

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

3D render:

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

Results: To be built and tested soon!

Time to build: Less than 20 minutes
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