20m

2 Articles

Traditional Analogue And An FPGA Make This Junkbox HF Receiver A Bit Special

August 20, 2021 by 2 Comments

We will have all at some point seen a fascinating project online, only to find not enough information to really appreciate and understand it. Such a project came [Bill Meara]’s way over at the SolderSmoke podcast, and he was fortunately able to glean more from its creator. What [Tom] had made from junkbox parts was a fairly traditional analogue receiver for the 20m amateur band which would be quite an achievement in itself, but what makes it special is its use of an FPGA to augment the analogue tuning.

A traditional analogue radio has a local oscillator which is mixed with the signal from the antenna, and an intermediate frequency of the difference between oscillator and desired signal is filtered from the result and amplified. The oscillator on older receivers would have used a free running tuned circuit, while a newer device might use a phase-locked loop to derive a stable frequency from a crystal.

What [Tom]’s receiver does is take a free-running traditional receiver and use the FPGA as a helper. It has a frequency meter that drives the display, but it also uses the measured figure to adjust the oscillator and keep it on frequency. It has two modes; while tuning it’s a traditional analogue receiver, but when left alone the FPGA stops it drifting. We like it, it’s definitely a special project.

We’ve featured a lot of radio receivers over the years, and this certainly isn’t the only one that’s a bit unconventional.

Clock Radio Receives Upgrade

May 5, 2019 by 8 Comments

Before everyone had a cell phone alarm to wake them up in the mornings, most of us used clock radios that would faithfully sit by our beds for years. You could have either a blaring alarm to wake you up, or be gently roused from slumber by one of your local radio stations. These devices aren’t as commonly used anymore, so if you have one sitting in your parts drawer you can make some small changes and use it to receive radio stations from a little further away than you’d expect.

This Panasonic clock radio from [Ryan Flowers] has several upgrades compared to the old clock radio hardware. For one, it now can receive signals on the 7 and 14 MHz bands (40 and 20 meters). It does this by using separate bandpass filters for each frequency range, controlled by a QRP Labs VFO kit which can switch between the two filters automatically once programmed. The whole thing is powered by 8 AA batteries, true to form with a clock radio from the ’90s.

[Ryan] notes that his first iteration was a little quiet but he’s now able to receive radio stations from as far away from Japan with this receiver. Even without a license, you can make these changes and listen in to stations from all around the world, as long as you don’t start transmitting. If you want to make a small upgrade from this clock radio though, it’s not that hard to get into.

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