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May 2023 Update
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Help decide what's next!
The 2023 Customer Interest Survey
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I don't know about you, but when someone actually asks for a piece of my mind I always jump at the chance. Here's your chance to let us know what you think. The 2023 MDRF Customer Interest Survey is now open and ready for your responses.
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What kinds of things in amateur radio are you interested in? What parts of a rig would you rather build and which to buy? What are your favorite bands and modes of operation? What kinds of tools and equipment do you have for your homebrewing? Answers to these questions (and more) will guide MDRF as we plan for future offerings.
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It will take about ten minutes to consider and respond to the questions. No identifying information will be collected or stored, so the survey is completely anonymous. You can access the survey from the menu at the top of the MDRF website, or use this direct link:
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Please complete the survey only once, but do share the link with as many friends and fellow club members as you can.
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Time for an inflation buster!
Lower Prices for QER SSB Filters
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A crystal ladder filter narrow enough to suppress the opposite sideband for SSB reception and transmission is the toughest nut to crack for a homebrewing radio amateur. The quasi-equiripple design pioneered by David Gordon-Smith, G3UUR, makes this task easier, but nothing aside from expensive manufacturing processes can make for a plug-'n-play filter. Even then, the need to carefully match input and output impedances (to minimize a rippled passband) requires a cut-and-try approach for satisfactory results.
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Previous versions of the Mostly DIY RF QER filters included on-board bifilar transformers intended to make that task easier. Paradoxically, though, their fixed transformation ratios frequently made the task harder for many users. So the latest version of the QER PCB does not include provisions for transformers, leaving the means of impedance matching with the homebrewer (where it always was anyway). These means include multi-filar transformers, conventional ratio transformers, or (and usually easier) L-match networks of capacitor and inductor.
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The best news is that the filters are now available at lower prices for the kit (down from $24.95 to $19.95) and assembled-and-tested versions (down from $49.95 to $39.95).
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The new PCBs are on their way from the fab house, so the lower prices will take effect on June 1st. At that time, new user's guides will be available on the website to walk you through the impedance-matching process using either a VNA, an oscilloscope and signal source (can be homebrewed), or a sensitive power meter (can also be homebrewed) and signal source. There's more than one way to bake ham, after all.
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Three different ways to
Protect Yourself with the PWR-1
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Most of us have been there. For whatever reason, and in fact contrary to all reason, you’ve reversed the polarity of your power connection and now one, some, or maybe all of the active devices in your homebrew rig–transistors mostly (including those built into ICs)–are toast.
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All of us have been somewhere else, too: the “undiscovered country” of noise conducted through our power supplies. Because it’s very uncommon to shield the power cables we connect to our rigs, a lot of noise is also picked up in them, fed into our power inputs, and then bounces around inside our sensitive circuitry. What’s more, we often generate noise inside our gear, commonly from digital devices such as Arduinos, displays, rotary encoders, and the like. In short, we’re happier when we can either eliminate or reduce noise sources–certainly those over which we have some control.
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This is where the PWR-1 comes in. Its P-Channel MOSFET instantly shuts off power if polarity has been reversed, and its low-pass and common-mode filtering keeps noise down to a tolerable level. Some circuits–such as a direct-conversion receivers–are susceptible to common-mode AC hum. The PWR-1 suppresses that to inaudible levels.
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The PWR-1 has one other optional function: it can sense the total current draw through it, sending an analog signal that can be read by the ADC input of an MCU (Arduino, Xiao, etc.). This is done with a Hall-effect sensor, so full voltage and current are available.
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The PWR-1 will be available in three versions: one with just the fuse and reverse-polarity protection, one to also include noise filtering, and one for the whole . . . enchilada (pictured above). Each will be available only as assembled and tested units.
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Available on the summer solstice (June 21st)
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From the wizard of Newbury Park!
The Pssst Transceiver Kit
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Sometimes you just want to put something together and have it work, you know? No futzing with isolation pads, superglue, and blank copper-clad, no dead-bug make-shifts, no ugly, ugly, ugly component acrobatics. Sometimes, a nice and orderly printed-circuit board that's just like uptown, along with sorted and clearly-labeled components and step-by-step instructions, can provide respite from the terrors and risks of scratch-built homebrewing. Just once in a while, mind you.
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Here's a dandy kit that can get you on 15, 17, or 20 meters pretty quickly, is fairly simple to put together (only eight transistors), and is small enough to take on a trip. At the same time, its modular architecture makes it also an experimenter's platform. It's not a single PCB and a mess of components. Each circuit block is its-own module which you can swap out for a different one you scratch build later on.
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Why would you want to do that? Suppose, for instance, you want a narrower passband for the SSB filter (maybe even narrow enough for CW use). Likewise, you might want a wider or narrower front-end bandpass filter, or a different frequency response for the mic amp. Or, how about an active or triple-balanced diode-ring mixer for the product detector, or maybe higher gain in the RF amplifier on receive? Because the circuit modules in the Pssst just plug into a motherboard, you can unplug one and put another one in.
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Of course, you can do this to change bands as well. All you need to do is to swap out the front-end band-pass filter and you can put the rig on 15 or 17 or 20 meters (along with changing a jumper on the digital VFO/BFO board).
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The Pssst was designed and originally built by Pete Juliano, N6QW (Pete's Simple Single-Sideband Transceiver). Rather than use bidirectional circuits for many of the blocks, he relies on inexpensive relays to "steer" the modules from receive to transmit modes. Each active module uses a single transistor for gain (except for the final amp which uses three), and in that way the Pssst is a minimal design that, because of its modular architecture, can be made as complex and as elaborate as the experimenter wishes.
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The Pssst is designed for a nominal output of 5 Watts on 20M when fed with 12VDC. By feeding the final amp with a higher voltage and providing some active cooling (from a three-dollar "pancake" fan), output can be increased to beyond 15 Watts.
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In addition to complete and detailed kit instructions, the Pssst design has an existing Groups.io "reflector" forum for the exchange of ideas and questions. The kit will be available in two basic versions: with or without enclosure panels and hardware.
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Available on the 150th birthday of Lee DeForest, the inventor of the Triode (August 26th)
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Buy on Tindie!
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Help support the DIY movement by buying Mostly DIY RF products on Tindie, a platform for the sale of small-scale, open-hardware and other electronics-related materials. You might want to look around at the other goodies available there. Click on the logo below to browse their offerings.
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Use the icon below to follow Mostly DIY RF on Instagram!
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