Tag Archives: Radio

Bandpass Filters from the CNC Mill

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A bandpass allows a certain electrical signal to pass while filtering out undesirable frequencies. In a speaker bandpass, the mid-range speaker doesn’t receive tones meant for the tweeter or woofer. Most of the time, this filtering is done with capacitors to remove low frequencies and inductors to remove high frequencies. In radio, the same concept applies except the frequencies are usually much higher. [The Thought Emporium] is concerned with signals above 300MHz and in this range, a unique type of filter becomes an option. The microstrip filter ignores the typical installation of passive components and uses the copper planes of …read more

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City of Tacoma Fined $300,000 For Witholding Stingray Surveillance Data

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Both Cyrus Favrivar of Ars Technica and Kate Martin, writing for The Tacoma News Tribune, have reported (Ars, Tribune) that Judge G. Helen Whitener has rebuked the Tacoma Police Department’s for their apparent decision to not produce the surveillance… Continue reading City of Tacoma Fined $300,000 For Witholding Stingray Surveillance Data→

These Capacitors are a Cheap Gimmick

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If you search through an electrical engineering textbook, you probably aren’t going to find the phrase “gimmick capacitor” but every old ham radio operator knows about them. They come in handy when you need a very small capacitor of unknown value. For example, if you are trying to balance the stray capacitance in a circuit, you might not know exactly what value you need, but you know it won’t be very much. That’s when you want a gimmick capacitor.

A gimmick capacitor is made by taking two strands of insulated wire and twisting them together; the length and the tightness …read more

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Silicon Bugs In The FTDI FT232R, And A Tidy RF VCO Project

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[Scott Harden] wrote in to tell us of some success he’s having using the FT232 chip to speak SPI directly from his laptop to a AD98850 digital signal generator. At least that was his destination. But as so often in life, more than half the fun was getting there, finding some still-unsolved silicon bugs, and (after simply swapping chips for one that works) potting it with hot glue, putting it in a nice box, and putting it up on the shelf.

In principle, the FTDI FT232 series of chips has a bit-bang mode that allows you to control the individual …read more

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Understanding a MOSFET Mixer

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A mixer takes two signals and mixes them together. The resulting output is usually both frequencies, plus their sum and their difference. For example, if you feed a 5 MHz signal and a 20 MHz signal, you’d get outputs at 5 MHz, 15 MHz, 20 MHz, and 25 MHz. In a balanced mixer, the original frequencies cancel out, although not all mixers do that or, at least, don’t do it perfectly. [W1GV] has a video that explains the design of a mixer with a dual gate MOSFET, that you can see below.

The dual gate MOSFET is nearly ideal for …read more

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A Guide To Audio Amps For Radio Builders

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For hams who build their own radios, mastering the black art of radio frequency electronics is a necessary first step to getting on the air. But if voice transmissions are a goal, some level of mastery of the audio frequency side of the equation is needed as well. If your signal is clipped and distorted, the ham on the other side will have trouble hearing you, and if your receive audio is poor, good luck digging a weak signal out of the weeds.

Hams often give short shrift to the audio in their homebrew transceivers, and [Vasily Ivanenko] wants to …read more

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VCF East: SDR on the Altair 8800

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You’d be forgiven if you thought software defined radio (SDR) was a relatively recent discovery. After all, few outside of the hardcore amateur radio circles were even familiar with the concept until it was discovered that cheap USB TV tuners could be used as fairly decent receivers from a few hundred MHz all the way up into the GHz range. The advent of the RTL-SDR project in 2012 brought the cost of entry level SDR hardware from hundreds of dollars to tens of dollars effectively overnight. Today there’s more hackers cruising the airwaves via software trickery than there’s ever been …read more

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Restoring A 1930s Oscilloscope – Without Supplying Power

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We’ve all done it: after happening across a vintage piece of equipment and bounding to the test bench, eager to see if it works, it gets plugged in, the power switch flipped, but… nothing. [Mr Carlson] explains why this is such a bad idea, and accompanies it with more key knowledge for a successful restoration – this time revitalising a tiny oscilloscope from the 1930s.

Resisting the temptation to immediately power on old equipment is often essential to any hope of seeing it work again. [Mr Carlson] explains why you should ensure any degraded components are fixed or replaced before …read more

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Fail Of The Week: Never Assume All Crystals Are Born Equal

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You should be used to our posting the hacks that didn’t quite go according to plan under our Fail Of The Week heading, things that should have worked, but due to unexpected factors, didn’t. They are the fault, if that’s not too strong a term, of the person making whatever the project is, and we feature them not in a spirit of mockery but one of commiseration and enlightenment.

This FOTW is a little different, because it reveals itself to have nothing to do with its originator. [Grogster] was using the widely-available HC-12 serial wireless modules, or clones or even …read more

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An FM Transceiver From An Unexpected Chip

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The Si47xx series of integrated circuits from Silicon Labs is a fascinating series of consumer broadcast radio products, chips that apply SDR technologies to deliver a range of functions that were once significantly more complex, with minimal external components and RF design trickery.  [Kodera2t] was attracted to one of them, the Si4720, which boasts the unusual function of containing both a receiver and a transmitter for the FM broadcast band and is aimed at mobile phones and similar devices that send audio to an FM car radio. The result is a PCB with a complete transceiver controlled by an ATmega328 …read more

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