In my last post, I introduced my foolhardy campaign to homebrew a rig (receiver, transmitter, or transceiver) each month from November, 2020 to November 2021.
I’m already deep into the first one for November 2020. I don’t want to say too much about it in advance of its completion—it has a seasonal application—but here are a few pictures. [Move cursor onto image & click arrow to scroll]
What follows below is a list of the other projected members of the Twelve, along with a few comments on my current thinking regarding their features and design ideas. [Hover your cursor over underlined words or terms for a brief definition]
December 2020: WARC-SSB
This will be an single-sideband and CW transceiver for the 12 and 17 meters WARC bands. It will be my own design1 using my UDVBM-1 universal digital VFO/BFO based on an Arduino and an Si5351 clock generator. It will use termination-insensitive (TIA) IF amplifiers following the design by Wes Hayward W7ZOI and Bob Kopski K3NHI.2
Unlike many SSB designs such as the BITX family pioneered by Ashar Farhan VU2ESE3, the WARC-SSB will not use a bidirectional architecture. The balanced modulator, product detector, IF amps, and crystal filters will be built as separate modules, each with a shield can and SMA interconnections.
As of this writing, I am still noodling over the choice of IF frequency. Since I’ll be using an Si5351 for both VFO and BFO, and also using separate filters, I don’t even need to use the same IF. I probably will, though, since different IFs would require four crystal filters instead of just two.
It might seem like I’m really building two transceivers here and just putting them in a single enclosure, but the 12 and 17 meter sections will share a power supply—12VDC for the exciter/receiver circuitry and 24VDC for the finals—the audio sections (microphone and audio output), a switched-capacitor pre-selector/band-pass filter (on receive), and the transmit low-pass filter with a cut-off frequency of 26MHz. They’ll also share the unidirectional broadband TIA amps.
January 2021: 6U8A Regen
One purpose of the Twelve is to use many different technologies and construction methods, so at least one needs to use “thermionic valves” or, in American usage, vacuum tubes. This little tube-based regenerative receiver will be based on Forrest Cook W0RIO‘s Piglet Regen. I decided to name my version after its detector/amp tube to avoid confusion with Dieter “Diz” Gentzow W8DIZ‘s Pig Rig CW transceiver4 I build several years ago.
The W0RIO Piglet circuit shares an important feature with Charles Kitchen N1TEV‘s well-known high-performance design5: it uses a buffer stage between the antenna and the detector to minimize radiation back out the antenna—a common problem with regens.6 Kitchen‘s buffer was a grounded-base 2N2907 BJT transistor. Cook‘s Piglet (so named because it squeals so readily) used a grounded-grid buffer made from the triode section of the 6U8A. The pentode section is the “beating heart” of the receiver—its oscillator, its detector, and its audio amplifier rolled into one. RF from the buffer is fed into the control grid of the pentode, and receiver is tuned in the grid-leak circuit. “Throttling” is done by varying the positive bias on the pentode’s screen grid.
The Piglet was built for 5 to 10MHz reception. As such, its tuning rate is pretty fast. W0RIO‘s answer to that was to switch capacitors in parallel with the main tuning cap to re-scale the tuning range to a narrower segment. He also experimented with plug-in crystals to lock the tuning in even narrower. This had the additional effect of significantly increasing the overall gain of the receiver. I look forward to trying this myself.
February 2021: BITX-60
Unlike the WARC-SSB, this rig will pretty-much have a straight BITX bidirectional architecture except that it will use a TIA design for the bidirectional IF amps instead of the single-stage ones Farhan used. The audio circuits, balanced modulator/product detector, filters, and mixer will be straight BITX. Like the WARC-SSB, though, I’ll use my UDVBM for the VFO and BFO. I’ll also experiment with front-panel knobs to adjust both the frequency of the BFO and its phase relative to the suppressed carrier of the incoming sideband signal. This may improve the fidelity and clarity of voice reproduction. The BITX-60 will use 24VDC on the IRF510 final which will be mounted on a large heat sink with a 50mm cooling fan.
Since 60 meters is channelized, I’ll use a rotary switch to select the channel, and I’ll include a smaller knob on an encoder to vary the center frequency on channel 3 to prepare for prospective changes in the FCC allocation for that channel. Pete Juliano N6QW built this feature into his DifX transceiver in 20177.
Why not use a single knob for the VFO, the BFO, and the BFO phase and just use a menu and the encoder button to step through the functions? The answer is: because I don’t want to, and I don’t need to, either. Sorry, but I hate multi-function controls like that. I can tolerate them when front-panel space must be conserved for a very-good reason (as on a small field rig), but this BitX60 will stay in my shack at my operating position and there is enough space for a few more knobs (for crying out loud!). By the way, I put rotary encoders, manually-operated switches, and the LCD display on the same I2C bus as the Si5351 anyway (using PCF8574-based 8-bit expanders), so I’m not “wasting” Arduino pins, either. In fact, unless I want an analog input or PWM output, I use just two I/O pins on the Arduino (SDA1 and SCL1) for everything.
March 2021: Beacon 6
As the name implies, this will be a 2-channel, 6-Meter CW automatic-beacon transmitter. It will be built using nothing but discrete components. Its RF sources will be home-brewed ovenized crystal oscillators running at 50.060 or 50.080 MHz, the two FCC-mandated beacon frequencies for 6-meters. No means known to me personally to maintain oscillator accuracy and stability will go unused. In the end, this will come down to thermal stability. Ovenizing the crystal will be a big part of that, but even maintaining the stability of those is not a trivial matter. Since I’m determined to use only discrete components, I can’t use op-amp ICs for some kind of PID feedback mechanism, and I’m not going to homebrew op amps! It may be within reach to work-up a simple differential amp circuit that would do the trick using a thermistor, thermocouple, or diode as a sensor.8
I’ll be operating the beacon on a half-wave end-fed antenna oriented vertically. It will automatically transmit my call sign, grid square, power level (5W barefoot), and Zulu time every minute at 13 wpm.
Hold on, you say, how will I do that without using something digital to automate those transmissions? Well, here’s my loophole: I’ll built the Beacon 6 as a CW-only transmitter, with a jack for plugging in a key in the usual way. It’s possible, in fact, that if I provided the rig with some frequency agility by switching in parallel capacitance (fixed or variable), I could use it as an ordinary VXO CW transmitter—and now that I think of it that’s a damn good idea! Naturally, though, I can also plug in an automated keyer in place of a manual one without changing the character of the rig at all. How’s that for fast talking?
April 2021: TAK-20
I’ve had a TAK-xx rig on my todo list for a long time. The original TAK-40 was a design by Jim Veatch WA2EUJ that won him first prize in the 2008 ARRL Homebrew Challenge contest.9 The challenge was to design and build a transceiver for both CW and SSB to operate on 40 meters with at least 5W PEP. That doesn’t sound so hard, does it? Here was the big catch: it had to be designed to use all-new-and-available parts (nothing from the junk box or hamfest), and it had to cost less than $50USD (not including the power supply or other supplies such as wire, screws, etc.). Veatch‘s primary means of accomplishing that was to go with integrated circuits and digital control as much a possible.
For my version for 20 meters, I’ll take the integration one step further: WA2EUJ used a varactor-tuned VFO with the control voltage coming from a DAC driven by a PIC MCU and a rotary encoder. I will dispense with the VFO, the DAC, and the PIC and go straight to a three-channel Si5351A clock generator driven by an Arduino Nano. I’ll likewise not use his crystal-controlled and varactor-tuned BFO, but instead employ one of the Si5351 channels.
I’ll keep all the rest of the original TAK architecture intact: 74HC125 tri-state buffers for TX/RX signal steering, NE612 double-balanced mixers, a MC1350P for IF amp and AGC , a six-pole crystal filter, and TL084 op amps for various purposes, including audio. Lastly, I’ll keep the IRF510s he used for the driver and final amp (he used a 510 for the driver simply because it was the cheapest suitable device he could get at the time). I will have to come up with all-new software for the Arduino to take over the tasks Veatch assigned the PIC, but that’s just par for the course.
May 2021: Binaural-30
Here’s another name for a rig that is mostly self-explaining. It’ll be for 30 meters, and since there’s no phone (AM, SSB, or FM) allowed on that band, this will be a CW-only transceiver. The transmitter section will be a little unusual but hardly unknown: a super-VXO for frequency agility between 10.100 and 10.030MHz, a span of 20KHz.10 To maximize stability, I’ll use the ovenizing techniques to be developed for my Beacon-6, and I’ll use grounded-base and emitter-follower buffer stages after the VXO for a nice, chirp-free signal. The VXO will be left running whenever the rig is turned on, and keying will take place in the last buffer stage.
The receiver section will be a little more unusual, though again not unknown: it will use a Tayloe detector for quadrature “I” and “Q” binaural audio output.11 By separating the audio into two streams, one ninety degrees off phase from the other, the human psychoacoustic system perceives sounds of different pitch (such as CW signals at different frequencies as heard within the passband of a receiver) as taking a physical location in three-dimensional space.12
Exploiting this characteristic of the “meat computer” we have in our heads can help us to separate one CW signal from another in a crowded band. There are other ways to separate the signals by narrowing the passband, by using switched-capacitor audio (SCAF) filters to process the audio, or using DSP. I want to try the binaural IQ method. Those who have say it’s an eerie experience hearing the signals moving around inside your head when listening with headphones.
June 2021: μBITX Fielder
This will be an almost-straight μBITX design13 for 160 through 10 meters, except that I’ll use my own Si5351/Arduino system (the UDVBM-1) and firmware, and I’ll build it in shielded modular form using circuit boards I lay out myself. As the rig’s name implies, it will be for use in the field rather than in the shack. I already have an enclosure for it: a U.S. Army field crystal case I’ve had kicking around for several years. Once used for FT243 crystals, it is built in two halves, with the bottom half serving as the lid for the top.
After removing all the felt padding, I’ll put the electronics in the top half (including a small antenna “tuner” and 49:1 balun) and use the bottom half for a LiPo battery pack and to store a code key, microphone, end-fed antenna wire, a few carefully-chosen tools, and spare parts such as fuses and replacement IRF510s. How will I replace the MOSFET finals in the field? They’ll be installed in a shielded module with their tabs screwed to the side of the field case and their leads clamped in three-pin terminal blocks. For replacement, I’ll just unscrew them. I’ll decide later if I need to do something similar with the 2N3904 drivers.
I have no illusions this rig will be useful for hiking or backpacking. The empty field case alone weights three pounds, and it’s about eleven-inches long and almost five-inches tall. As you’d expect of anything Army issue, it’s built like a brick . . . hamshack. With the electronics, the battery pack, and the accessories, the rig could approach ten pounds. It might be usable for a SOTA activation if the walk from the car to the summit isn’t too far.
July 2021: GS-1 SDR
This rig will be about as close to the bleeding edge of radio technology as I ever care to get. This will be an SDR “homebrew” in a denotational sense only, i.e., I’m “building” it at home. It’s really more of a “system integration” at home, though, since I’m putting systems together that are already available on the market and that have many other applications. The heart of the GS-1 will be the Great Scott HackRF unit.14
This device is capable of both receive and transmit on 160 meters through the 6cm (5650-5925GHz) bands, though for TX it serves only as an exciter. It will need a separate linear amplifier(s) and switchable low-pass filters. I have heard that the HackRF is slow switching between RX and TX, so I may want to use a separate RTL dongle for receive. I’ll use SDR# (SDR “Sharp”) for software running on an embedded Raspberry Pi.
August 2021: AM-80/160
And now for something at almost the other end of the radio-technology timeline, a tube-based transceiver for 80 and 160 meters AM phone. The AM-80/160 will take up to about 100 Watts of input power into a pair of 807s, 811s, 813s, 6146s, or 6JS6Cs, whichever is available at a good price as new-old stock. I have some of those used in my collection already, and I might settle on a pair if they test strongly enough. Everything in this rig will be tube driven, except for the VFO: that will be my UDVBM (Si5351/Nano based). I’ll probably also use it for a BFO as that might come in handy if I want to use the rig for CW or LSB. The mic amp will use something like a 6U8A or 6EA8, the IF amps and mixers will use 6BA6s for similar, and the speaker output will be a single-ended 6L6. I’ll be drawing heavily on old ARRL Handbooks for design fragments . . . and maybe even a complete design. I can’t say I’d turn one down should it offer itself.
And what will I use for the “heavy iron”,” you may ask? To an extent, that will depend on the tubes I use for the finals. I’m not too keen on exceeding around 750VDC by much for the plate supply, and even that is enough to scare me straight. I may look into a diode-capacitor voltage “multiplier” as an option, though I don’t know about current capacity or voltage regulation with one of those.15
If it turns out I need to settle for lower input power because of self-imposed limits (cost of the power transformer being the main one), that would be okay. 50 Watts instead of 100, for instance, would only be worth a half S-unit, and it’s not like this will be a primary or constantly-used rig anyway. I don’t really even know how many AMers there are in my neck of the woods in the first place. Maybe I should find out.
September 2021: Kitchen Regen
Of course I already have a regen project on the list, but the coverage of the 6U8A Regen ends at 30 meters. The Kitchen Regen will pick up at 31 meters and go all the way to 10 meters. And, no, this will not be a rig I’ll use while cooking. The name comes from Charles Kitchen N1TEV, widely esteemed as the foremost authority on this now-ancient but still very-cool receiver technology. I’ll be using his all-solid-state design for the High-Performance Regenerative Receiver I mentioned above in connection with W0RIO‘s Piglet Regen, and that I’ve cited below in Ref. 5.
Unlike the 6U8A Regen which controls (“throttles”) regeneration by changing the bias on the pentode screen grid (sometimes called “electron coupling”) , Kitchen‘s design uses a variable capacitor to adjust the degree of coupling between the detector/oscillator and the feedback signal from the “tickler” coil. Throttling by this method allows for greater stability in both the tuning and the level of regenerative feedback. By the way, Kitchen provides a concise historical overview of the development of the regen receiver—beginning with E. Howard Armstrong‘s invention in 1914—and receiver topologies in general (regens, D-Cs, and heterodynes). I recommend reading Ref. 5 to learn more.
To get the frequency agility I’m looking for, I’ll make up several plug-in coil units (each with the three front-end coils on a single PVC coil form) to plug into octal sockets. To maximize the “cool” factor, I’ll mount the coil and the variable capacitors (main tuning, fine tuning, and throttle) in the open, using clear plastic for the front panel. I’ll mount the capacitors as far back from the panel as possible and use long plastic shafts from the biggest-damn knobs I can find. This will prevent any hand-capacitance monkey business.
October 2021: 2M-SSB
The capstone for this year-long campaign will be a rig for which I’m least prepared in terms of knowledge or prior experience. But like many Hams, I’ve long-since become bored with 2-meter FM—at least the handy-talkie and repeater type. It’s handy and useful sometimes, but it’s no longer fun.
Sure, I can whip out my cheap-as-dirt Baofeng and talk to everyone listening along a more-than three-hundred-mile front between southwest Washington and northern California. Meh. I can also talk to anyone on Planet Earth by pulling out my cell phone—a state-of-the-art SDR radio and multi-core computer to boot. Also meh. Don’t get me wrong, I do dutifully contribute funds to a few regional repeater systems, mainly because of amateur radio’s (and therefore my) public-service obligations. That’s just it: it’s an obligation, not fun.
So I’d like to do something different and fun with VHF and UHF, maybe as half-way houses for eventual microwave activity. It’s my impression that there’s not a lot of CW and SSB being done on 2 meters, and I’m just anti-social enough to find that attractive. I have visions of doing SOTA activations and making other mountain-top QSOs at five Watts using a light-weight but many-element Yagi ten-feet long when it’s assembled, or tossing a twin-lead J-Pole up in a tree while I lounge in a campsite and chatter away on CW with some other Ham up on a peak. Doesn’t that sound like a blast?
- The first is that I’ll most-definitely be using digital means of signal generation and control. I think I can use an Si5351 for that, but I may need to do my own PCB layout for it if the ones currently available are not suitable for reliable VHF operation.
- I don’t think I can use the filter method to suppress the carrier and opposite sideband. I think that’s okay because I ought to be able to use quadrature instead, made easier by the multi-channel Si5351.
- I don’t think I can use any of the easy-going construction methods such as “ugly” or “Manhattan.” I do think I’ll need to use careful RF-layout methods using four-layer PCBs with impedance-controlled striplines and inner-layer ground and power planes.
- I don’t think I can use or will even need toroids for filter inductors. Most of the inductors will be in nano-Henries and air-core coils will do the job. Actually, it’s possible there’s no stable core material for VHF anyway.
- I do think I may need to use helical resonators for band-pass and low-pass filtering, and maybe for LO coupling. If so, I don’t think I’ll buy them. I’ll try to make them instead. I have some machinist and metal- fabrication skills, which even includes electroplating silver on the helices and shield cans. By hell! If I can pull off homebrewing helical resonators then that ought to earn me a Bad Hombre patch for my ARRL ball cap!
- I think I’ll limit the rig to those segments of the 2-meter band plan for CW and “weak-signal” use: 144.05-144.10 (general CW and weak signals), 144.10-144.20 (EME and weak-signal SSB), and 144.200-144.275MHz (general SSB operation).
- Whether or not keeping the rig within that 225KHz segment will have any advantages is something I don’t think I can say at this time. At a minimum, that’ll allow for some very-tight front-end filtering, and when it’s cold outside, squeezing through a narrow portal is better than swinging open a 4MHz-wide barn door.
That’s about all I have so far on this long-shot of a homebrew rig. Fortunately, I have nearly a year for lots of research and noodling.
November 2021: Fabricante 13
October’s rig, the 2M-SSB, will be the twelfth one in this series, so the Fabricante (trans.: “maker”) 13 will be a bonus rig to be completed as the campaign began—during my birthday month. I don’t have many concrete ideas yet. I’ve thought about a receiver dedicated to the 5 and 10MHz WWV frequencies with ultra-tight front-end filtering. I’ve also toyed with the idea of going primordial with a artfully-designed and finely-wrought crystal set for the commercial AM broadcast band—that 1100KHz-wide wasteland filled with holy rollers, conspiracy theorists, and assorted kindred crackpots. But hey, that’s where broadcast radio began and where it reigned for decades until it moved its headquarters (and all its bad habits—high advertising-to-music ratios and bucket-mouthed DJs) to FM by the 1980s.
If you all have any ideas for the Fabricante 13, let me know. QSL?
1. Almost no one’s designs are completely their “own.” What they do is to put bits and pieces together they learned from someone else. How one does that and synthesizes those bits may be unique, advanced, and even revolutionary (mine are none of those things), but it is all built on “prior art” (https://en.wikipedia.org/wiki/Prior_art)
2. Wes Hayward & Bob Kopski, “A Termination Insensitive Amplifier for Bidirectional Transceivers” (2009). http://w7zoi.net/bidirectional_matched_amplifier.pdf
3. Ashar Farhan, “BITX–An easy to build 6 watts SSB transceiver for 14MHz” (2004). https://www.vu2ese.com/index.php/2020/06/18/bitx-an-easy-to-build-6-watts-ssb-transceiver-for-14mhz/. See also https://www.hfsignals.com/
5. Charles Kitchen, “High Performance Regenerative Receiver Design” QEX (1998). http://www.arrl.org/files/file/Technology/tis/info/pdf/9811qex026.pdf
6. Doug Adams, “Regenerative Radio Receivers” (2012). http://large.stanford.edu/courses/2012/ph250/adams1/; Eddie Insame, “Designing Super-Regenerative Receivers” (2002). http://www.eix.co.uk/Articles/Radio/Welcome.htm; and Rodney Champness, “Behind the Lines: A Short History of Spy Radios in WW II” (1998). http://messui.polygonal-moogle.com/valves/SC199809.pdf
7. ARRL News, http://www.arrl.org/news/view/arrl-asks-fcc-to-allocate-new-5-mhz-band-retain-channels-and-current-power-limit & Pete Juliano, “A New line of Transceivers: DifX” (2017). http://n6qw.blogspot.com/2017/03/a-new-line-of-transceivers-difx_23.html
8. For example, see Alan Wolke W2AEW, “#193: Back to Basics: the Differential Amplifier . . .” YouTube video, https://www.youtube.com/watch?v=mejPNuPAHBY.
9. Jim Veatch, “The TAK-40 SSB CW Transceiver” QST (May 2008). http://www.arrl.org/files/file/QST/Homebrew%20Challenge/HBC%201%20Winner-WA2EUJ.pdf
10. See Peter Parker VK3YE experiments with super-VXOs: https://www.youtube.com/playlist?list=PLIe6EGOjQefd00TojphLIxC-eaLOdkPq1
11. Dan Tayloe, “Ultra Low Noise, High Performance, Zero IF Quadrature Product Detector and Preamplifier” (2013). Handout for Northern California QRP Club presentation. http://www.norcalqrp.org/files/Tayloe_mixer_x3a.pdf