Crystal Radio Improvements

Previously I made a basic crystal radio, since then I’ve made a number of design improvements.

Crystal Radio Schematic

Multiple Bands

There is only a few medium wave stations where I live so I decided to add shortwave as well, to achieve this I used a rotary switch and a 7uH inductor, this is wound on a T50-2 iron oxide toroid, this ensures a high Q factor that would be difficult to achieve with an air core, Unfortunately it’s nearly impossible to tune as it covers near enough the entire shortwave band, so a bit of a failure on my part.

Antenna Coupling

Originally I used a fixed 10pF coupling capacitor, I have since replaced that with a 35pF variable trimmer capacitor, I find around 25-30pF to be optimal, although it’ll depend upon your antenna and how selective / sensitive you want it.

Audio Amplifier

To make listening more comfortable and improve reception of weak signals I made an audio amplifier, this can be switched in with a DPDT toggle switch and is powered from four AA batteries, this is capable of driving a 8 ohm loud speaker at a modest volume.

The circuit is nothing special but works quite well, care needs to be taken with the input wiring to avoid hum, shielded or coaxial cable is best.

Case

This time I decided to make something half decent looking, I glued together some scrap MDF sheet to make a base and front panel, I then applied walnut wood veneer to the front and varnished it, on the front I mounted two 3.5mm jacks, one for crystal earphones and the other the amplifier output, the tuning capacitor, DPDT toggle switch, 1 pole 12 way rotary switch and the volume and gain pots.

On a piece of brass sheet I have a BNC connector for the antenna input, I made a bit of a mess of the veneer during construction but oh well, lesson learned, don’t drill wood veneer.

Results

Adding an audio amplifier really boosts what can be received, another thing I have considered is adding a LNA (Low Noise Amplifier) as the RF front-end, however at this point it would make more sense to use a different radio technology.

Overall I’m quite pleased with it but there is definitely room for improvement, but for now I’m done with crystal radios, my next attempt will likely be a regenerative or perhaps superheterodyne radio.

Making a Crystal Radio

Crystal Radio Schematic
Click for full size

A crystal radio is a radio designed for receiving audio (voice) broadcasts, it was invented around the beginning of the 20th century and became extremely popular in the 1920’s and 1930’s, allowing millions of people to access radio broadcasts that otherwise would have been prohibitively expensive, the majority would have been self constructed sets rather than commercial devices, this sparked a huge interest in radio and electronics and ultimately was the catalyst for the rise of commercial radio.

The reduced cost of vacuum tubes and increased reliability led to the downfall of the crystal radio, however it continued to see sporadic usage and has had numerous revivals to the present day, the ease of construction, low cost and no need for a power source means it still sees usage in poor countries and is a popular project for electronics and radio hobbyists.

Crystal radios are primarily designed to receive Amplitude Modulated (AM) broadcasts, although examples have been made that can receive Frequency Modulated (FM) broadcasts, the most common band used is the medium wave broadcast band which roughly spans 530 to 1,700 kHz.

Theory of Operation

While there are many variations in design all crystal radios consists of four main blocks, the antenna, tuner, detector and speaker.

The antenna is chosen to receive radio waves as efficiently as possible, for medium wave AM band a monopole, loop or ferrite rod antenna is a common choice, there are two options for connecting the antenna to the tuner, magnetic or capacitive coupling, I opted for the latter which is the purpose of C2.

The tuner in the majority of sets consists of a fixed inductor (L1) and a variable tuning capacitor(C1), the tuning capacitor needs a value of at least 500pF to cover the entire medium wave band, for inductance a value between 200uH and 250uH is often used, this forms an LC tank circuit which resonates at a specific frequency, given by the equation:

$$ f_0 = \frac {1}{2\pi\sqrt{LC}} $$

Solving for inductance gives the equation:

$$ L = \frac {1}{4\pi^2Cf^2} $$

It's preferable to use the lowest inductance possible as longer coils tend to have greater resistance which reduces the Q (quality) factor of the coil, however since Q is tied to bandwidth too much can also be an issue.

In my case for the medium wave band I decided on 220uH inductor and a 720pF tuning capacitor I had in my parts bin, you will most likely want to wind your own inductor as commercial inductors of this value normally use ferrite cores which can introduce losses, it may work fine but I haven’t tested it, in any case using an air core coil is traditional.

The detector (D1 & C3) is used for demodulating (extracting) the audio from the RF carrier, back in the day this was an actual lump of crystal such as galena or iron pyrite, the ‘cat’s whisker’ would be adjusted over the surface until a sensitive spot was found, various alternatives have also been used, for simplicity I went with a 1N34A germanium diode (alternative 1N270), the diode choice is very important, germanium starts to conduct as low as 0.1V, I tried a common silicon 1N4148 which gave very poor sensitivity, a schottky diode may be a viable alternative here, the value of the capacitor is not critical, 1nF worked for me.

Finally for the speaker I used a high impedance piezoelectric earpiece, these have an extremely high impedance, so much so that a 100k resistor (R1) is required to provide a suitable discharge path, traditionally a more conventional high impedance speaker would be used giving an impedance around 3k to 10k, these are still available from places like ebay albeit more expensive.

Assembly

A crude but functional crystal radio

For designing the inductor I used the excellent free program Coil32 which I highly recommend you check out, this gave me the number of turns required.

Winding the coil is a bit of an art in itself and can only be learned through experience, I typically use a wax coated cardboard tube, wind the coil as neatly as possible, then coat it with more wax to secure it, this has the advantage over varnish that it sets hard right away, in any case the value is not super critical so there is no need to worry if you do not have an LCR meter handy, go with the calculated number of turns and add a few more for luck.

I mounted the coil and tuning capacitor on a piece of scrap wood, since this is so simple I decided against using a PCB and simply wired it point to point, I made provision for swapping the detector parts using female machine pin headers so I could experiment.

I plan on remaking it much nicer at some point, there is many good examples made by Dave Schmarder.

Testing

Having a strong AM station nearby is pretty much required, you will have trouble receiving weaker stations, although with a good antenna it should be possible, I had no problems receiving a 2kW station located about 3km away even inside the house with a cheap monopole, some European countries no longer broadcast medium wave so you may have more difficulty there.

For a test signal I used my TinySA with 1kHz AM modulation, a signal inserted at -7dBm was clearly audible and was detectable as low as -23dBm, although I noticed a decrease in sensitivity at the low end of the band likely because Q is frequency dependent.

Improvements

The nice thing about crystal radios is there is a lot of things you can do to improve them, such as adding an audio or RF amplifiers, different bands, different detectors, different coil winding methods, audio transformers and so on, so making one is definitely worth the time.

Useful Linux Utilities 2020

There are a number of very useful tools that people may not be aware of that can be a significant boost to productivity in your day to day usage of Linux, or just plain cool, this article will cover some of the more interesting ones I have come across, all of these are completely free.

If you find any of these useful to you or want to suggest something for a future article please leave a comment.

File

While regular users of the Linux terminal are probably already aware of this tool it’s hard to understate how helpful it can be at times, the file command simply looks at a file and tries to determine what it actually is, this can be very useful if there is no file extension or you suspect a corrupted file, this should be built into your shell so no need to install it.

Using it is very easy, just type file followed by the name of the file you wish to check, it will then display the detected file type.

qBittorrent

qBittorrent

One of my favorite torrent clients, provides all the required features without any additional rubbish, it’s designed similar to uTorrent which was a once very popular torrent client, which is now essentially spyware, qBittorrent is completely open source with active development, it’s also available for multiple operating systems.

One handy feature is an included torrent search engine, however it does tend to produce fake results so I’d still advise manually checking them on a trusted website.

Flameshot

Flameshot is a very useful tool for taking screenshots, it provides features such as area selection, annotation and image upload (currently imgur only), all the screenshots in this article and probably most on this website are taken with it.

It still has some way to go though before it can match the best Windows tool for screenshots ShareX, still with it being under very active development I’m looking forward to seeing where it goes.

KeePassXC

It continues to surprises me that there are many people out there still failing to make use of password managers, they’re such a massive boost to security and convenience that I consider them to be essential software.

KeePassXC is a modern fork of KeePass, it’s completely open source and has been trusted by many, including myself for a long time, unlike some password managers it stores your encrypted passwords completely offline, as such it provides a high degree of privacy and security.

OBS Studio

Open Broadcast Software Studio is a very versatile tool for recording and streaming video, it’s capable of accepting numerous inputs such as your desktop, games, capture cards, webcams and so on and includes a complete audio mixer, even though it’s free and open source this is easily professional level software with extensive capabilities.

OBS is capable of streaming to most (all?) major platforms including YouTube, Twitch and Facebook, it’s very easy to setup and use making it both suitable for beginners and professionals alike, if you need this kind of software I can’t recommend it enough.

Gufw

Gufw is a graphical front end to the ufw firewall, which itself is a front end to iptables the Linux firewall, setting up a firewall can be a time consuming process if you’re not experienced in doing so, Gufw provides a nice user friendly way to setup and configure a Linux firewall which will help enhance your security with very little effort, it may not be exactly feature packed but it certainly does the job.

If you don’t already have a firewall setup I would strongly recommend trying this.

Raw Therapee

Raw Therapee is a powerful raw photo processor that is of great value to both professional and amateur photographers, it provides a huge selection of tools for getting the highest quality photos possible from your camera.

It has a very well designed and easy to use interface that puts many commercial tools to shame, combined with being open source and actively developed this is a must have tool for any photographer.

Steam Deck Update

A few days ago Valve in a somewhat unusual move posted a partial teardown video of the Steam Deck, in particular showing off the battery and M.2 SSD, although the video was filled with various amusing warnings such as “taking out the screws will permanently weaken it”, which as any competent person will know is essentially bullshit, still I can’t blame them for it, as your average user has the intellect of a baked potato and shouldn’t be encouraged.

The overall design and build quality seems very good, in particular the controls appear to be modular which is going to make replacement easy, Valve also suggest they will be providing replacement parts, although this remains to be seen, I have no doubt there will be numerous third party options in any case.

Updated FAQ

Valve also posted an updated FAQ on the Steam Deck website, some things of particular note are it can be used as a game controller and includes a decent 1.5m USB-C charging cable, the screen is also 10 finger multitouch (although I have no idea why you’d put 10 fingers on it), the rest of it is fairly obvious stuff such as dual boot support, etc.

Developer Release

Valve have also been shipping early units to a number of game developers, as such there is a decent bit of game footage floating around on Twitter, it has been confirmed by at least one developer that a five hour battery life can be expected from a moderately demanding game, this is a good sign that most players will squeeze at least 4 hours out of it and much more with light games.

Conclusion

We’re now under three months before the first release units ship, I’m hoping more details are released soon about Steam OS as I have yet to see the anti-cheat improvements promised for EAC and Battleeye, it would also be interesting to try out the new interface which will eventually replace the big picture mode.

If you’ve not already reserved then you’re pretty much out of luck, most if not all regions have slots later than Q2 2022.

Steam Deck – The Future of Portable Gaming?

Valve Corporation (aka Valve Software), the makers of the popular Steam gaming platform announced the Steam Deck a portable gaming handheld on the 14th July 2021, reservations were opened on the 15th for a small fee, first batches are expected to ship in December 2021, although most people will probably receive theirs in early to mid 2022, reservations are currently only open to select countries and require a previously active Steam account, this is clearly in an effort to deter scalping which has plauged the GPU market.

Spectifications

The specifications of the Steam Deck have generated a lot of interest, it uses a 64 bit x86-64 CPU made by AMD using the Zen 2 architechture with 4 cores and 8 threads, this is only one generation behind the current Zen 3, this includes the RDNA 2 APU which has been proven to be very capable at running most modern games at or above 60 fps at 1080p.

Combined with 16GB of LPDDR5 RAM it’s expected to out perform nearly all current gaming handhelds, as with many of Valve’s previous products they are likely to be selling this at close to a loss, since the majority of their income comes from the Steam platform rather than the hardware itself.

It features a 7 inch LCD IPS display with touch, which is optically bonded to the front glass, some have questioned why it does not use an OLED display, but given how low they are pushing the price already I would say this is expected, given it’s an IPS panel it will still look great, the display resolution is 1280×800 giving it a 16:10 aspect ratio, this may seem a bit low resolution, but it’s a sensible tradeoff, RDNA 2 may be powerful but resolution is still a big framerate killer, an external monitor can be connected via USB-C DisplayPort if you really want a larger display.

Other features include a 6-axis IMU, bluetooth 5.0, dual band WIFI. stereo microphone and stereo speakers, connectivity includes a 3.5mm headphone/headset jack and a USB-C 3.2 Gen 2 port.

Battery Life

Valve have stated that it will last between two to eight hours from the internal 40Wh battery, this is more or less what I expected, ultimately how long you get depends on the games you play, very intensive games will naturally drain it faster than a simple game.

For charging and for continuous power it specifies a USB-C 45W PD3.0 power supply, which will likely be included with it, one thing that remains to be seen is if they offer replacement batteries, lithium batteries degrade over time so this could be an important consideration.

Steam Deck as a PC

Valve are advertising the Steam Deck as a portable PC, in many ways this is true as it is capable of doing anything a PC can do, to facillitate this Valve will be releasing an official dock for it which includes DisplayPort 1.4, HDMI 2.0, Ethernet, one USB 3.1 port and two USB 2.0 ports.

It can be connected to any monitor or TV up to 8k resolution, although if intended for gaming you should not exceed using it on a 1440p monitor as it may struggle to maintain a playable FPS, resolution scaling is an option for higher resolution monitors, although I tend to find this degrades image quality significantly.

It’s hard to say for sure how well it will perform in this scenario, we will need to wait for benchmarks to be sure, but certainly if you don’t have a PC or your PC is very slow this may be a viable solution.

Input

On the front, the Steam Deck has two analog joysticks with capacitive touch sensing, eight buttons, two trackpads (which Valve note are 55% more responsive than the Steam controller ones); on the top are two bumper buttons and two analog bumper buttons along with the power and volume buttons, on the rear there are four grip buttons, this gives a total of at least 20 assignments which can be adjusted with Steam input.

This should be sufficient for many games, but if you need more then using the USB port or Steam dock with additional controllers is an option.

Storage

The Steam Deck is available in three tiers, the bottom has 64GB of eMMC storage, the middle has a 256GB NVMe SSD and the top has a 512GB NVMe SSD, it has been revealed that it uses a standard M.2 2230 socket, so upgrading your memory should be possible, Valve seemed reluctant to advertise this as it opens the possibility of buying a low tier version and adding your own SSD, which is cheaper.

Because 64GB is such a small amount of storage I would not recommend it unless you plan on adding your own storage, it might do for some more basic games, but if you want to play large AAA games it will quickly become unworkable with some games exceeding 64GB as it is.

All versions also support additional storage via micro SD card, although this is typically quite slow making it the least desirable option, while we don’t have full specs yet it’s reasonable to assume that eMMC will achieve 300-400MB\s, NVMe 2000MB\s or greater, a good UHC-I SDXC card will give at best around 120MB\s.

Another final option is connecting external storage via the USB 3.2 Gen 2 port, although this kind of defeats the main point of the Steam Deck being portable.

Pricing

steam deck prices

The lowest tier version currently costs £349, the mid tier £459 and the top tier £569, this is extremely good pricing for the hardware you’re getting, the nearest competitor in performance would be the GPD Win Max which is around £584, but it’s not really comparable .

The highest teir is not really that great value for money, so I would suggest going for the mid tier, if you’re willing to install a SSD then the low tier is overall an excellent choice.

Software

The Steam Deck will be releasing with a new Steam OS 3.0, this time based on Arch Linux, along with the KDE Plasma desktop environment, this is not currently available but I’m hoping they will release this before the Steam Deck starts to ship.

Steam Deck does not place any restrictions on your software, you’re free to essentially do whatever you like, including installing other operating systems, although given hardware support this mostly means Windows or other Linux distributions, although I’m sure people will have fun getting obscure OS’s working on it.

This opens a lot of options besides your Steam library, certainly I expect emulators will become a popular choice allowing you access to many thousands of games, using alternative stores like Epic Games is also an option if you so desire.

The Steam Deck is fully capable of running most Windows only games using Proton, it’s not perfect but it works in most cases, the only real problem at the moment is that Proton will not work with some anti-cheat software, Valve have already confirmed that BattleEye and EAC will have support ready by launch but other anti-cheat software remains uncertain.

Suitable for Casual Users?

This remains a big question, and generally I would say no, even with the increasing support for Windows games there will be people frustrated at it for not running certain games, or software, at the end of the day it’s still running Linux and some Linux knowledge is preferable to get the most out of it.

Installing Windows is of course an option, but for casual users this may present too much of a problem, it would have been nice to see Valve offer a choice of operating system, maybe they will, it remains to be seen.

Overall Verdict

Overall while there are still many unanswered questions, what we have seen so far is quite promising, we will likely get more details as we get closer to launch, for now you should reserve it as soon as possible before stock runs out or you end up waiting a long time, reservation is only £4 and you can get it refunded if you change your mind.