I’ve been working on getting the little bugs out of the Si5351 SSB rig and making improvements to the circuit. Since SSB QRP operating can be a bit more challenging than CW QRP ops, Dave AA7EE suggested that I think about a speech processor IC to use in place of the op-amp microphone amplifier. He directed me to the Elecraft K2 schematic, which uses an Analog Devices SSM2166. I poked around the Analog website a bit and found a sister IC called the SSM2167. It’s smaller, simpler, and cheaper than the SSM2166, which could make it perfect for this radio. I ordered a couple of samples of each from speakerxpert and they rush-shipped them here within a few days.
So today I got around to installing the SSM2167 in the 40 meter SSB radio, set the compression level to about 10 dB, and took a look at the transmitter waveform on my oscilloscope (I can still kind of see the screen if I get some light shining on it from the side). There is a single resistor which sets the compression level, and by jumpering around it, I can set the level to 0 dB. By comparing the waveforms with compression at ~10 dB and then off, I could tell that the average transmit power was increased quite a bit with compression on.
Next, I decided to check-in to the Noontime Net to see how it would work on the air and hopefully get an audio report. Luck would have it that net control Leslie N7LOB was very strong here, so I knew I should have no trouble checking in today. Also I was fortunate to have a strong signal from Lynn KV7L, the gentleman who donated the SA602s that are used in the radio. I’ve got a raw clip of my check-in below, which I hope to incorporate into a more polished video a bit later.
As you can tell from Lynn, 10 dB of compression might be a bit much for something like checking into a net. I changed the resistor to set compression at around 6 dB, which should be more appropriate for this type of use. It also sounds like some folks on the Noontime Net want to see some photos of the rig, so here are a few taken with my tablet. Not the best quality, but it should give you an idea of what it looks like until I can get my “real” camera back and take better photos.
Now that I think I’ve fairly well determined that the Si5351 is suitable for use in a ham radio transceiver, it seems like time to put thought into action and actually try to build one. Ever since discovering that the Si5351 can output multiple independent clocks from one IC, I thought it would be neat to use one output as a VFO and a second as a BFO. As I showed with my Grabber RX prototype, this is certainly a viable thing to do.
One type of SSB transceiver architecture that I’ve been experimenting with in the NT7S shack is one using an unidirectional IF for both the receive and transmit signal paths, as opposed to the bidirectional designs seen in radios such as the BITX. The Lichen transceiver seen in Chapter 6 of Experimental Methods in RF Design is a nice example of such a radio. In past experiments, I have switched the VFO and BFO signal paths using analog switch ICs. But I realized that when using the Si5351, all you would need to do to implement this type of architecture is to connect, for example, the CLK0 output to the first mixer and the CLK1 output to the second mixer, then swap the frequencies on each CLK output when switching to transmit.
With that in mind, let me present the block diagram of my implementation of this below:
The mixers are the ubiquitous 602/612 loved and hated by QRP homebrewers around the world. I’m not a huge fan of the 602, but it has a couple of things going for it in this application. First is that there are essentially two inputs and two outputs on the IC, which makes it very handy for this type of design. And while it has fairly atrocious intercept figures, it does reduce component count quite a bit. So you could consider this more of a cheap & cheerful radio for fun, not a design for work in seriously crowded conditions. The rest of the elements in the design are pretty much your standard circuits. Nothing too groundbreaking there. One thing I neglected to put on the diagram above is 10 dB attenuator pads on Si5351 outputs in order to get the ~3 Vpp output down to around the 300 mVpp that the 602 likes to see for oscillator drive.
So here’s the beautiful ugly mess on a piece of copper clad. This was originally a CC1 prototype board, but I decided to cannibalize it for this SSB rig since it already had the microcontroller and Si5351A, and because I was feeling too lazy to start from scratch. The radio build only took a couple of half-day sessions in the shack, and worked mostly as expected right off the bat. The T/R VFO and BFO swapping scheme worked perfectly, needing only a few extra lines of code to implement in the already-existing code. I ended up making my first QSO with the rig (5 watts transmitter output) checking into the Noontime Net and getting a S7-S9 report from net control. The second QSO was last night with fellow Oregonian, Joel KB6QVI, who was kind enough to give me a sked in order to check out how the radio was working on the air. Finally, I had a very brief QSO with Dave AA7EE, who gave me an inciteful audio report although we had a poor propagation path between us. Right now, I’ve got it back off the air to tweak a few thing, such as the audio response in the mic amp, but expect to get it back in working order for use at Field Day.
Overall, I’m pretty happy with the direction this radio is proceeding. If I can get all of the bugs worked out, this could be a pretty potent design. Not in the performance category, but in the cost and component count sense. I’m seriously considering whether it may be feasible to do crowdfunding for a run of kits if I can nail down the design well enough. I have come to believe that the Si5351 could be a game changer for ham radio HF and VHF radio designs.
The theme of this blog post is not lots of tedious work, but refinement leading to good results.
First off, let’s talk about the funny I2C address on the parts which I received from Mouser. Since Digi-Key has no order minimums and very inexpensive shipping available (in the form of USPS First Class mail), I ordered another batch of Si5351As from them so I could see if they would respond to the correct address of 0x60. Sure enough, once I received them and used the Bus Pirate I2C address scan macro, they came up on address 0x60. So it seems obvious that Mouser has some oddball parts; perhaps they were custom parts that inadvertently escaped Silicon Labs. I’m still waiting to hear back from Mouser about the issue, but in the meantime, I would recommend you order from a different distributor until they fix this problem.
I also decided last Friday to try to get my KiCad skills back in order and crank out a cheap and cheerful breakout board for the Si5351A. It didn’t take me too long to get back in the groove and design a small, simple PCB that would make it easier to prototype with the Si5351A. The board is 30 mm x 50 mm, with three end launch SMA connectors on the right edge and the power/I2C pins on the other side. I’ve also added wideband transformers (Mini-Circuits TC1-6X+) to the outputs to isolate them from the breakout board. Below you can see the OSHPark rendering of the board.
They will hopefully be here in about a week or so (one of the benefits of living in the same city as OSHPark). Assuming that they work as expected, there’s a chance that I may end up selling these as kits, so stay tuned if that interests you.
Now on to the best news. The last big question in my Si5351 investigations is whether it would be suitable for VFO usage in a standard amateur radio receiver, where it would have to be tuned rapidly. Having seen in a Silicon Labs application note that the Si5351 can be tuned glitch-free by locking the PLL to a fixed frequency and only changing the synth parameters of the attached multisynth, I set out to implement that in the Si5351 avr-gcc library.
Next, I ripped the AD9834 DDS and crystal BFO oscillator out of my last CC1 prototype and substituted the Si5351 for the VFO and BFO. Long story short, after a bit of tweaking, the part performed beautifully! I can crank the tuning encoder knob as fast as I possibly can, and I get no hint of any glitching or other tuning artifacts. The Si5351 has enough oomph to drive the BF998 dual-gate MOSFETs as well. Into a high-impedance, the drive level was over 4 Vpp, which is a decent drive level for that mixer. The only slight hardware change I had to make was to change the I2C pull-up resistors to 10kΩ and reduce the I2C clock speed down to about 100 kHz in order to reduce noise from the I2C line getting into the receiver. This change seemed to have no adverse affect on the tuning speed of the Si5351.
At this point, I believe I have investigated most of the main points that I wanted to look at when this first began. Wonderfully, the Si5351 appears to be a very suitable IC for use in all kinds of amateur radio applications. The multiple independent outputs is a superb feature, and has the potential to greatly reduce parts count and price in ham radio transceivers. I’m already thinking of many applications where this inexpensive, stable, and versatile IC can be used.
Even though the main objectives have been met, I’m still not done with this IC. I would like to look into further details, such as phase noise. I also have a lot of plans, such as building a new radio from scratch using the Si5351, possibly selling the breakout board mentioned above as a kit, and maybe even creating a more complete development board (which could be used as a wide-range VFO) by incorporating a microcontroller, LCD display, and encoder knob. Keep watching the blog for further updates.
I’m happy to report that the CRX1 40 meter receiver kit is now in full production and is available for purchase in the Etherkit Store for $40 (which includes all controls and connectors, you just add some wires and an enclosure). Allow me to quote from the product page:
The CRX1 is a simple VXO-tuned superheterodyne receiver for the 40 meter band, with tuning centered around the popular QRP watering hole frequency of 7.030 MHz. It is entirely constructed from surface mount devices in the easy-to-build 0805 (US) size for passive components and SOT-23 class semiconductors. The PCB is large and single-sided, which provides for uncramped construction and makes the CRX1 an ideal warm-up kit for the CC1 QRP transceiver (coming soon). The CRX1 is not just meant to be a novelty to be tossed aside after construction. All of the support circuitry for muting, T/R, and sidetone is included, so it can be paired with virtually any transmitter which uses grounded keying. There is also a port for an external VFO to enable further user experimentation.
All controls and connectors are included with this kit, so you just need to supply an enclosure and a few knobs to finish the job!
Frequency Range: Approximately 7.030 to 7.034 MHz (at +13.7 VDC power supply)
IF Bandwidth: Approximately 400 Hz
Current Consumption: 25 mA (at +13.7 VDC power supply)
Power supply: +9 VDC to +14 VDC
MDS: -123 dBm
3rd Order IMD DR: 84 dB
IF Rejection: 74 dB
Image Rejection: 67 dB
PCB dimensions: 70 mm x 100 mm
Antenna Connector: BNC
DC Power Connector: 2.1 mm barrel jack
Phone Jack: 3.5 mm stereo
Key Jack: 3.5 mm stereo
Reverse polarity protection
Muting, sidetone (user enabled), T/R switch, external VFO port included
40 Meters – 7.030 to 7.034 MHz
The CRX1 is a fun little receiver to build and is a great kit to get your feet wet with SMT construction!
On a side note, I’ve established an IRC server on my Raspberry Pi for Etherkit and it has been working great for the last month or so. Please do stop by for tech talk (and other occasional diversions) on channel #etherkit at irc.recursiv.com.
This is the first in a series of blog posts covering a wide variety of topics. In the past, I have used Twitter for my microblogging needs. For a variety of reasons, I’m on a Twitter hiatus right now, so I’ll be using this series to convey some of the disconnected (and possibly connected) random thoughts that I feel I need to get out there. I don’t think I’ll be abandoning Twitter completely, but I will be reworking the ways in which I use it once I come back.
I’m also in the process of disconnecting completely from Google, so I wanted to give fair warning to those who correspond with me via my Gmail account that I will be abandoning that service very soon. I’ve already deleted my Google+ profile, and will be deactivating the rest shortly. I’ll probably describe my rationale for this later, but keep in mind that I’ve been a Google customer data mine for nearly a decade, so this is not something that I undertake lightly. I’ll try to get alternate contact information to those of you who regularly correspond with me.
It is an age of new beginnings.
With the introduction out of the way, let’s get down to the good stuff. Above, you can see the latest project on the Etherkit bench. It’s a re-work of the receiver from the Clackamas transceiver (the rig that I submitted to the 2010 FDIM 72-part challenge). I’ve decided to make this receiver into a cheap & cheerful little kit to get people warmed up for building the CC1. It’s currently for 40 meters only, is a superhet, and is VXO tuned (covers 7.030 MHz plus a bit more). It is 100% discrete component (you can see a TDA7052 IC above, but I’ve abandoned it for a different AF amp) and will be SMT construction. The receiver itself is pretty simple, but you can see there’s a fair bit of other circuitry on there. That stuff is mute and sidetone circuits. It’s easy enough to design a standalone receiver, but most of them will probably just gather dust after being built unless they can interface to a transmitter easily. With this extra circuitry, you can just split off your transmitter’s key line and connect it to this receiver to have built-in muting and sidetone. My goal is to make this project cheap and fun to build. I’ll be fast-tracking this one so I can get back to the CC1 soon.
Oddly enough, another project from the FDIM Class of 2010 is also coming out soon. As spotted on The QRPer, the Cyclone 40 transceiver is based on the rig that Dave Cripe, NM0S submitted as his 2010 FDIM 72-part challenge entry. I recall that the rig had a very unique design and that the specs were impressive. Dave’s a great designer, so be sure to buy one to get a rig unlike anything else you’ve seen before and to support 4SQRP.
Choking off the Internet firehose that I had previously directed at me has allowed me to devote a bit more time to enjoyable activities that I’ve neglected, one of those being reading. I’m currently enjoying a book I’ve had on my shelf for a while now called Seeing in the Dark by Timothy Ferris. It’s billed about being about amateur astronomers, but it does get into the professional side quite a bit as well. It’s a good read and very entertaining, and I can’t help but see a lot of parallels between amateur radio and amateur astronomy.
That’s a great segue to the final item, which is a bit of fun from our favorite Canuck astronaut, Cmdr Hadfield. He’s leaving ISS in a few days and just released a surprisingly touching (although obviously light-hearted) rendition of Space Oddity by David Bowie (one of my guilty favorites). Cmdr Hadfield may not be on the level of Neil Armstrong or Yuri Gagarin, but he’s definitely making a play for Coolest Astronaut Ever.
As a mild winter turns into an unusually nice spring here in Beaverton (last week we had multiple days with clear skies and highs in the upper 70s °F), a young ham’s thoughts turn to portable activations, Field Day, SOTA, and the like. I’ve been looking forward to this summer for the opportunity to take the CC1 out in the field, but I may not get to be quite as adventurous as I hoped. Last winter, I slipped in a wet patch on the concrete in the garage and hurt my knee. As a typical guy, I didn’t go to the doctor to have it checked out, I decided to “walk it off”. It did heal, but not completely. So I finally gave in and saw my doctor about it a few weeks ago. She strongly suspects a torn meniscus, and ordered an MRI to confirm it. Unsurprisingly, my insurance company denied coverage on the MRI, instead expecting me to do a bunch of physical therapy based on at best a guess on what the problem is. Coming from a technical background such as mine, this boggles my mind. When you have a problem and you have the tools to make a measurement, you make the measurement to see what’s wrong, not just take a course of action based on a guess! I understand that money is the driving factor behind this decision, but it still seems like a waste of resources for both myself and the insurance company. Not to mention that I don’t have the faith in the efficacy of physical therapy that consensus medicine does.
So now I have to decide whether to shell out beaucoup bucks on physical therapy that probably won’t do anything other than siphon money from our family to their coffers. I’ve looked at many recommended loan options in the meantime and if that fails to miraculously heal the non-specific “knee pain” referred to by the insurance company, then I guess I get the privilege of paying for the MRI that I should have had in the first place.
I’m completely fed up with politics, so I have no desire for a political battle in my comments. I’m quite aware of the history of employer-provided health insurance in the US, and the effect of government distortions in the medical marketplace. There’s plenty of blame to be handed out all around, so let’s just leave it at that.
Anyway, I may not get to do any SOTA summits this year (except for perhaps a super-easy one such as Cooper Mountain right on the outskirts of Beaverton), but hopefully I can at least get out with the CC1 for portable ops to the park or while camping.
Speaking of the CC1, it’s at a bit of a lull in its development right now. I’m waiting for all of the beta builders to complete their construction so I can be sure that I have all of the major hardware bugs worked out (which looks tentatively promising right now). I still have quite a bit of firmware coding to work on, then I’ll be ready for the next (and hopefully last) PCB spin. With any luck, that should come in about 8-10 weeks.
In the meantime, I want to work on some side projects, and perhaps some opportunities to raise more capital to fund CC1 development. In that regard, I’ve been looking at a neat part recently. It’s a MEMS VCXO from SiTime called the SiT3808. What’s cool about this part is that it has linear voltage tuning, so that you don’t have the uneven tuning response like you would from a varactor-tuned VCXO. The phase noise on the spec sheet also looks very good. I ordered some samples for 7.030 MHz and 28.060 MHz and breadboarded them to test the frequency stability. It was nothing short of amazing. The 7.030 MHz part had a long term drift of 5 Hz in 1.5 hours. The 28.060 MHz part drifted only about 20 Hz in 2 hours. That’s pretty spectacular for CW use.
Since the 28 MHz part was so stable, I created a QRP transmitter for it by adding on a keying circuit and a couple of BD139 amplifiers. It outputs a very clean and stable 2 watt signal and has a tuning range of about 20 kHz. I also was fairly easily able to create a TX offset circuit, so that the transmitter can be paired with a direct conversion receiver (which I plan to do soon). Since tuning is linear, the offset is the same anywhere in the tuning range, unlike a typical varactor-tuned crystal oscillator.
I’ve been thinking about a way to introduce these parts to the ham community, since I don’t believe that I’ve seen them mentioned by any homebrewers or used in any kits. Last week on the qrp-tech listserv, K7QO proposed a group build of the venerable NE602/LM386 direct conversion receiver (this one from chapter 1 in Experimental Methods in RF Design). Since this design is so well known, it seems like a “remix” of this design using the SiT3808 as the local oscillator might be a fun way to spread the word about the product. I breadboarded a version with the 7.030 MHz SiT3808 sample, which you can see below (the SiT3808 is in the upper-right corner, and it obscured by the tuning pot wiring).
It works exactly as expected. Wide open band signals directly dumped down to baseband, and a nice, stable LO. This particular SiT3808 part number only tunes about 4 kHz, but I will be able to get parts with a greater tuning range. I’m consulting with SiTime right now about bulk pricing, and hopefully I’ll be able to do a kit run of at least 100 of these bad boys in the near future. Let me know in the comments if this is something that may interest you.
So that’s my big rant for the day. Stay tuned for further updates on all of these projects in the near future.
Last night after the rest of the family was in bed, I was hacking on the CC1 firmware to add the BFO calibration routine so that I could get an accurate readout of my receive frequency. After successfully completing that task at the late hour of 0130, I decided to cruise 40 meters to see what was going on. Normally the best time for 40 meter DX at my QTH seems to be from about 0200 or so until sunrise, so I thought I might catch something.
Scanning below 7.030 MHz, I came across a very loud station. I figured it was somebody in CONUS, but decided to listen for an ID just in case. It actually turned out to be PJ2/K8ND in Curaçao. Not exactly rare DX, but it’s still quite a ways from my QTH and it’s a new one for me. So I figured I would take a crack at it with the CC1. Long story short, I set the CC1 in XIT mode and after an hour of trying, my 3 watt signal finally managed to crack the JA-wall. I was pretty excited! Not exactly a heroic snag in the annals of DXing, but it was a good one for me. My single HF antenna is a ZS6BKW only up about 30 feet, so busting a 40 meter pileup to a station 6000 km away made my night. My first DX contact on the CC1! Even better, I woke up to find that the FB op uploaded his log to LoTW immediately, and I’ve got +1 to my DXCC count.
A brief post to show you the CC1 prototype, now inside of its aluminum enclosure. This is the actual enclosure that will be used for production, but I will have the end caps custom cut and silkscreened, so you won’t have to do it yourself. Pardon my questionable metalworking skills, and please note the the production tuning knob will be different (a bit smaller so as to not interfere with the LEDs). At least this will give you some idea of what the final product will look like. The dimensions of the enclosure is 70 x 100 x 29 mm (or 2.75 x 3.93 x 1.14 inches). The first photo shows a size comparison with a standard deck of cards. The weight is 190 grams (6.7 oz).
After the latest circuit tweaks, everything is looking very good with this beta test. I will have more news for the beta testers in the near future. Exciting!
Two days ago, I received my pack of 10 CC1 prototype PCBs from Seeed Studio. The excitement was too much, so I immediately started building the first CC1 prototype as soon as my wife got home from work. Not surprisingly, I didn’t go to bed until I completed the build, sometime around 3 AM. I knew it was futile to even try to sleep, as I’d just lie in bed wondering if I had messed something up with the circuit. The radio seemed to pass all of the basic checks early that morning, but had a few oddities that needed to be worked out.
Yesterday, I was able to tweak some component values and got almost everything in line with my Manhattan-built prototype. I could hear a good rush of band noise as the antenna was connected, signals were coming in, and there was a stable 3 W CW output from the transmitter. Everything was looking great, but by the time the radio was ready to go QRV, 40 meters was closed and I was dead tired anyway.
Tonight, I tried to make a first QSO with AA7EE, but 40 meters had already gone long by the time I was able to make it to the radio at 6 PM, and Oakland was well out of the skip zone. There were a lot of signals from Rockies and east on the band, so I cruised a bit looking for a CQ. No luck finding anybody CQing, so I found a clear spot just above the QRP watering hole and called CQ with the CC1 keyer memory. Right off the bat, I got a call from WA0JLY! We gave each other 559 reports, but he actually came up to 579 by the end of the QSO. It was a very short QSO, as just as we exchanged reports, I was called away to help with our 10 month old son Eli. So I apologize Denny for the cutting the QSO short and for my shaky fist! Earlier today, I made some special QSL cards to commemorate the occasion and WA0JLY will get the first one. I do plan on getting more on-air time with the CC1 over the next few months, something that I’ve set aside far too much while I’ve been doing design.
So the initial verdict for this CC1 beta test is looking good. I will be getting in touch with the original beta testers soon and soon after that will contact those who requested to be in on the next beta (if you are one of those people and you don’t hear from me soon, feel free to contact me). As I’ve been saying recently, I’m cautiously optimistic about this board spin. I hope that I will be able to deliver a good product to my beta testers that has all of the original bugs eliminated.
I’ve had a lot of people ask for details about the CC1 and I forgot that it has been a while since I’ve last reviewed the details about the rig on the blog. So here’s a quick list of specs. Please keep in mind that this is strictly preliminary and subject to change for the release version.
Monoband CW QRP transceiver kit
DDS VFO (AD9834), full band coverage
Mostly SMT construction (0805 resistor/capacitors)
Initial available bands: 40, 30, 20, 15 (probably will add 80 and 17 if there is demand)
ATmega328P microcontroller with built-in keyer and straight key mode, audio frequency annunciation, RIT/XIT, voltage supply readout, breakout headers to UART, I2C, ADC, GPS port for WSPR transmission (and hopefully APRS over PSK63)
TX output power: 3 W
RX current: ~40 mA
TX current (13.7 VDC, 3 W): ~370 mA
MDS: -125 dBm
IF rejection: 86 dB
Image rejection: 95 dB
Two-tone, 3rd order IMD dynamic range: 75 dB
PCB dimensions: 70 x 99 mm
Custom matching aluminum enclosure measuring 70 x 100 x 25 mm will be included