Radio Hacks

1327 Articles

Making PCB Strip Filter Design Easy To Understand

October 28, 2024 by 4 Comments

We’ve always been fascinated by things that perform complex electronic functions merely by virtue of their shapes. Waveguides come to mind, but so do active elements like filters made from nothing but PCB traces, which is the subject of this interesting video by [FesZ].

Of course, it’s not quite that simple. A PCB is more than just copper, of course, and the properties of the substrate have to be taken into account when designing these elements. To demonstrate this, [FesZ] used an online tool to design a bandpass filter for ADSB signals. He designed two filters, one using standard FR4 substrate and the other using the more exotic PTFE.

He put both filters to the test, first on the spectrum analyzer. The center frequencies were a bit off, but he took care of that by shortening the traces slightly with a knife. The thing that really stood out to us was the difference in insertion loss between the two substrates, with the PTFE being much less lossy. The PTFE filter was also much more selective, with a tighter pass band than the FR4. PTFE was also much more thermostable than FR4, which had a larger shift in center frequency and increased loss after heating than the PTFE. [FesZ] also did a more real-world test and found that both filters did a good job damping down RF signals across the spectrum, even the tricky and pervasive FM broadcast signals that bedevil ADSB experimenters.

Although we would have liked a better explanation of design details such as via stitching and trace finish selection, we always enjoy these lessons by [FesZ]. He has a knack for explaining abstract concepts through concrete examples; anyone who can make coax stubs and cavity filters understandable has our seal of approval.

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Turning A Quansheng Handheld Into A Neat Desktop Transceiver

October 28, 2024 by 11 Comments

The Quansheng UV-K5 is a popular handheld radio. It’s useful out of the box, but also cherished for its modification potential. [OM0ET] purchased one of these capable VHF/UHF radios, but got to hacking—as he wanted to use it as a desktop radio instead!

This might just sound like a simple reshell, but there was actually a bit of extra work involved. Most notably, the Quansheng is designed to be tuned solely by using the keypad. For desktop use, though, that’s actually kind of a pain. Thus, to make life easier, [OM0ET] decided to whip up a little encoder control to handle tuning and other control tasks using an ESP32. This was achieved with help from one [OM0WT] and files for that are on Github. Other tasks involved finding a way to make the keypad work in a new housing, and how to adapt things like the audio and data module and the speaker to their new homes.

Despite the original handheld being much smaller than the case used here, you’d be surprised how tight everything fits in the case. Still, the finished result looks great. We’ve seen some other adaptable and upgradable ham radio gear before, too. Sometimes custom is the way to go! Video after the break.

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A New Chinese Radio Breaks Cover, Is It Worth It?

October 26, 2024 by 20 Comments

Scanning the firehose of new electronic kits and modules coming from the usual Chinese suppliers can be a rewarding experience, as sometimes among the endless breakout boards comes an item that looks interesting enough to try. As an example there’s a receiver kit being given a quick review by [Tech Minds], offering AM and HF multi-mode, FM broadcast, and air band alongside what appear to be digital streaming features.

Looking at it, though all the RF part is hidden under screening cans we’re guessing it might contain one of the Silicon Labs all-in-one receiver chips, but the whole appears to deliver a useful receiver with a comprehensive interface. The review isn’t quite technical enough so we can’t glean a lot more, but it looks as though it could be useful. We’d be tempted to snag one for review, but since with very few exceptions we pay for the stuff we review, it’s a mite expensive at $50+ for yet another radio.

There’s an ongoing question with all these cheap kits and modules though, first of all where did the design come from and are we freeloading on someone else’s hard work, but then whether or not what you’re getting is a knock-off using defective semiconductors or with bean-counting parts removal degrading performance. We’re guessing more will come out about this radio in due course, and we can all make our own judgement. Meanwhile this one can be found on AliExpress or Banggood, so take a look and see if you’re tempted.

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RF Detector Chip Helps Find Hidden Cameras And Bugs

October 26, 2024 by 6 Comments

It’s a staple of spy thriller movies, that the protagonist has some kind of electronic scanner with which he theatrically searches his hotel room to reveal the bad guys’ attempt to bug him. The bug of course always had a flashing LED to make it really obvious to viewers, and the scanner was made by the props department to look all cool and futuristic.

It’s not so far-fetched though, while bugs and hidden cameras in for example an Airbnb may not have flashing LEDs, they still emit RF and can be detected with a signal strength meter. That’s the premise behind [RamboRogers]’ RF hunter, the spy movie electronic scanner made real.

At the rear of the device is an ESP32, but the front end is an AD8317 RF detector chip. This is an interesting and useful component, in that it contains a logarithmic amplifier such that it produces a voltage proportional to the RF input in decibels. You’ll find it at the heart of an RF power meter, but it’s also perfect for a precision field strength meter like this one. That movie spy would have a much higher chance of finding the bug with one of these.

For the real spies of course, the instruments are much more sophisticated.

Silent Antenna Tuning

October 23, 2024 by 56 Comments

If you want to deliver the maximum power to a load — say from a transmitter to an antenna — then both the source and the load need to have the same impedance. In much of the radio communication world, that impedance happens to be 50Ω. But in the real world, your antenna may not give you quite the match you hoped for. For that reason, many hams use antenna tuners. This is especially important for modern radios that tend to fold their power output back if the mismatch is too great to protect their circuitry from high voltage spikes. But a tuner has to be adjusted, and often, you have to put a signal out over the air to make the adjustments to match your antenna to your transmitter.

There are several common designs of antenna tuners, but they all rely on some set of adjustable capacitors and inductors. The operator keys the transmitter and adjusts the knobs looking for a dip in the SWR reading. Once you know the settings for a particular frequency, you can probably just dial it back in later, but if you change frequency by too much or your antenna changes, you may have to retune.

It is polite to turn down the power as much as possible, but to make the measurements, you have to send some signal out the antenna. Or do you?

Several methods have been used in the past to adjust antennas, ranging from grid dip meters to antenna analyzers. Of course, these instruments also send a signal to the antenna, but usually, they are tiny signals, unlike the main transmitter, which may have trouble going below a watt or even five watts.

New Gear

However, a recent piece of gear can make this task almost trivial: the vector network analyzer (VNA). Ok, so the VNA isn’t really that new, but until recently, they were quite expensive and unusual. Now, you can pick one up for nearly nothing in the form of the NanoVNA.

The VNA is, of course, a little transmitter that typically has a wide range coupled with a power detector. The transmitter can sweep a band, and the device can determine how much power goes forward and backward into the device under test. That allows it to calculate the SWR easily, among other parameters.

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Save A Packet, Use Cheap Co-Ax!

October 21, 2024 by 58 Comments

Anyone who works with radio transmitters will know all about matching and impedance, and also about the importance of selecting the best co-axial cable connecting transistor and antenna. But here’s [Steve, KD2WTU] with a different take, he’s suggesting that sometimes a not-so-good co-ax choice can make the grade. He’s passing up expensive 50 ohm cable in favour of the cheap and ubiquitous 75 ohm RG6 cable used in domestic TV and satellite receiver installations.

Fighting that received wisdom, he outlines the case for RG6. It’s cheap and it has a surprisingly low loss figure compared to some more conventional choices, something that shouldn’t be a surprise once we consider that it’s designed to carry GHz-plus signals. Where it loses is in having a lower maximum power rating. Power shouldn’t be a problem to a shoestring ham for whom 100W is QRO. Another issue is that 75 ohm coax necessitates a tuner for 50 ohm transmitters. It also has the effect of changing the resonance of some antennas, meaning a few mods may be in order.

So we’re convinced, and with the relatively QRP shack here we can’t see RG6 being a problem. Maybe it’s something to try in out next antenna experiment. Meanwhile if you’re interested in some of the background on co-ax impedance choices, we’ve been there before.

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Forget Flipper, How About Capybara?

October 20, 2024 by 23 Comments

One of the hacker toys to own over the last year has been the Flipper Zero, a universal wireless hacking tool which even caused a misplaced moral panic about car theft in Canada. A Flipper is cool as heck of course but not the cheapest of devices. Fortunately there’s now an alternative in the form of the CapibaraZero. It’s a poor-hacker’s Flipper Zero which you can assemble yourself from a heap of inexpensive modules.

At the center is an ESP32-S3 board, which brings with it that chip’s wireless and Bluetooth capabilities. To that is added an ST7789 TFT display, a PN532 NFC reader, an SX1276 LoRa and multi-mode RF module, and an IR module. The firmware can be found through GitHub. Since the repo is nearly two years old and still in active development, we’re hopeful CapibaraZero will gain features and stability.

If you’re interested in our coverage of the Canadian Flipper panic you can read it here, and meanwhile if you’re using one of those NFC modules, consider tuning it.