Understanding Modulated RF With [W2AEW]

There was a time — not long ago — when radio and even wired communications depended solely upon Morse code with OOK (on off keying). Modulating RF signals led to practical commercial radio stations and even modern cell phones. Although there are many ways to modulate an RF carrier with voice AM or amplitude modulation is the oldest method. A recent video from [W2AEW] shows how this works and also how AM can be made more efficient by stripping the carrier and one sideband using SSB or single sideband modulation. You can see the video, below.

As is typical of a [W2AEW] video, there’s more than just theory. An Icom transmitter provides signals in the 40 meter band to demonstrate the real world case. There’s discussion about how to measure peak envelope power (PEP) and comparison to average power and other measurements, as well.

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Classifying Crystals With An SDR Dongle

When it comes to radio frequency oscillators, crystal controlled is the way to go when you want frequency precision. But not every slab of quartz in a tiny silver case is created equal, so crystals need to be characterized before using them. That’s generally a job for an oscilloscope, but if you’re clever, an SDR dongle can make a dandy crystal checker too.

The back story on [OM0ET]’s little hack is interesting, and one we hope to follow up on. The Slovakian ham is building what looks to be a pretty sophisticated homebrew single-sideband transceiver for the HF bands. Needed for such a rig are good intermediate frequency (IF) filters, which require matched sets of crystals. He wanted a quick and easy way to go through his collection of crystals and get a precise reading of the resonant frequency, so he turned to his cheap little RTL-SDR dongle. Plugged into a PC with SDRSharp running, the dongle’s antenna input is connected to the output of a simple one-transistor crystal oscillator. No schematics are given, but a look at the layout in the video below suggests it’s just a Colpitts oscillator. With the crystal under test plugged in, the oscillator produces a huge spike on the SDRSharp spectrum analyzer display, and [OM0ET] can quickly determine the center frequency. We’d suggest an attenuator to change the clipped plateau into a sharper peak, but other than that it worked like a charm, and he even found a few dud crystals with it.

Fascinated by the electromechanics of quartz crystals? We are too, which is why [Jenny]’s crystal oscillator primer is a good first stop for the curious.

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An SSB Transceiver On Only One Type Of Transistor

There are a multiplicity of transmission modes both new and old at the disposal of a radio amateur, but the leader of the pack is still single-sideband or SSB. An SSB transmitter emits the barest minimum of RF spectrum required to reconstitute an audio signal, only half of the mixer product between the audio and the RF carrier, and with the carrier removed. This makes SSB the most efficient of the analog voice modes, but at the expense of a complex piece of circuitry to generate it by analog means. Nevertheless, radio amateurs have produced some elegant designs for SSB transmitters, and this one for the 80m band from [VK3AJG] is a rather nice example even if it isn’t up-to-the-minute. What makes it rather special is that it relies on only one type of device, every one of its transistors is a BC547.

In design terms, it follows the lead set by other simple amateur transmitters, in that it has a 6 MHz crystal filter with a mixer at either end of it that switch roles on transmit or receive. It doesn’t use the bidirectional amplifiers popularised by VU2ESE’s Bitx design, instead, it selects transmit or receive using a set of diode switches. The power amplifier stretches the single-device ethos to the limit, by having multiple BC547s in parallel to deliver about half a watt.

While this transmitter specifies BC547s, it’s fair to say that many other devices could be substituted for this rather aged one. Radio amateurs have a tendency to stick with what they know and cling to obsolete devices, but within the appropriate specs a given bipolar transistor is very similar to any other bipolar transistor. Whatever device you use though, this design is simple enough that you don’t need to be a genius to build one.

Via [G4USP]. Thanks [2ftg] for the tip.

The BITX Transceiver Comes Of Age

There was a time when the idea of building your own single-sideband transceiver was too daunting for all but the most hardcore of amateur radio constructors. After all the process of creating SSB is complex enough in itself without adding the extra complexity of a receiver and the associated switching circuitry.

In 2003 an Indian radio amateur, [Ashhar Farhan], [VU2ESE] changed all that. His BitX SSB transceiver used a bidirectional amplifier design and readily available components such that it could be built by almost anyone using dead bug construction techniques for an extremely reasonable price.

Over the years since [Ashhar] first published his circuit, his design has been taken and enhanced, been presented in kit form, and extended to other bands by multiple other radio amateurs. Until now though it seems as though he himself has taken very little advantage of his work.

It is therefore with great interest that we note a new 40-meter BitX transceiver on the market from a company founded by the man himself. The transceiver itself is an Indian-assembled PCB with an updated circuit using a 12 MHz IF, varicap tuning, and large surface-mount components for easy modification. Just as with the original circuit, there is a full technical run-down of its operation should you wish to build one yourself. For a rather impressive $45 though you might wish to put down the soldering iron, it looks very much worth the wait for international postage.

We don’t often feature commercial product launches here on Hackaday, though we are besieged by people trying to persuade us to do so. So why this one? When the creator of a design that has been as significant as the BitX has been to its community of builders releases a new version it is newsworthy in itself, and if they are commercializing their work then they deserve that reward.

We’ve featured the BitX here in the past, with a rather impressive dead-bug build, and a look at a multiband version. We’re sure that this design thread has more to deliver, and look forward to more.

Thanks [WB9FLW] for the tip.

The Minima Is An All-Band HF Transceiver For Under $100

If you have ever browsed an amateur radio magazine you could be forgiven for receiving the impression that it is a pursuit exclusively for the wealthy. Wall-to-wall adverts for very large and shiny transceivers with hefty price tags abound, and every photograph of someone’s shack seems to sport a stack of them.

Of course, this is only part of the story. Amateur radio is and always has been an astonishingly diverse interest, and away from the world of shiny adverts you’ll find a lot of much more interesting devices. A lot of radio amateurs still design and build their own equipment, and the world of homebrew radio is forever producing new ideas.

One such project came to our attention recently, the Minima, an all-band HF SSB transceiver. It’s an interesting device for several reasons, it uses readily available components, it’s an impressively simple design, and it should cost under $100 to build. This might sound a little far-fetched, were it not from the bench of [Ashhar Farhan, VU2ESE], whose similarly minimalist BITX single band SSB transceiver set a new standard for accessible SSB construction a few years ago.

The circuit shares some similarities with the tried-and-tested BITX, using bi-directional amplifier building blocks. The mixers are now FETs rather than diodes, the intermediate frequency has moved from 9MHz to 20MHz, and the local oscillator is now an Arduino-controlled clock generator. The whole thing is designed to be built dead-bug-style if necessary, and two prototypes have been built. We’d expect this design to follow a similar evolution to the BITX, with the global community of radio amateurs contributing performance modifications, and no doubt with some kit suppliers producing PCBs and kits. We think this can only be a good thing, and look forward to covering some of the results.

We’ve featured [Ashhar]’s work here at Hackaday before, when we covered a BITX build. if you’re left wondering what this amateur radio business is all about, we suggest you have a read of [Bill Meara]’s guest post on the subject.

Thanks [Seebach] for the tip.

Two Guys, A Hotel Room And A Radio Fire

Can you build a HF SSB radio transciever in one weekend, while on the road, at parts from a swap meet? I can, but apparently not without setting something on fire.

Of course the swap meet I’m referring to is Hamvention, and Hamvention 2016 is coming up fast. In a previous trip to Hamvention, Scott Pastor (KC8KBK) and I challenged ourselves to restore tube radio gear in a dodgy Dayton-area hotel room where we repaired a WW2 era BC-224 and a Halicrafters receiver, scrounging parts from the Hamfest.

Our 2014 adventures were so much fun that it drove us to create our own hacking challenge in 2015 to cobble together a <$100 HF SSB transceiver (made in the USA for extra budget pressure), an ad-hoc antenna system, put this on the air, and make an out-of-state contact before the end of Hamvention using only parts and gear found at Hamvention. There’s no time to study manuals, antennas, EM theory, or vacuum tube circuitry.  All you have are your whits, some basic tools, and all the Waffle House you can eat.  But you have one thing on your side, the world’s largest collection of surplus electronics and radio junk in one place at one time.  Can it be done?

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RPiTX Turns Rasberry Pi Into Versatile Radio Transmitter

Since the discovery that some USB TV tuner dongles could be used to monitor radio waves across a huge amount of spectrum, the software-defined radio world has exploded with interest. The one limiting factor, though, has been that the dongles can only receive signals; they can’t transmit them. [Evariste Okcestbon, F5OEO] (if that is his real name! Ok c’est bon = Ok this is good) has written some software that will get you transmitting using SDR with only a Raspberry Pi and a wire.

There have been projects in the past that use a Pi to broadcast radio (PiFM), but this new software (RPiTX) takes it a couple steps further. Using just an appropriately-sized wire connected to one of the GPIO pins, the Raspberry Pi is capable of broadcasting using FM, AM, SSB, SSTV, or FSQ signals. This greatly increases the potential of this simple computer-turned-transmitter and anyone should be able to get a lot of use out of it. In the video demo below the break, [Evariste] records a wireless doorbell signal and then re-transmits it using just the Rasbperry Pi.

The RPiTX code is available on GitHub if you want to try it out. And it should go without saying that you will most likely need an amateur radio license of some sort to use most of these features, depending on your locale. If you don’t have a ham radio license yet, you don’t need one to listen if you want to get started in the world of SDR. But a ham license isn’t hard to get and at this point it shouldn’t take much convincing for you to get transmitting.

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