It’s nice to see we hams, who I think suffer from a bit of an image as throwbacks in the larger maker community, get some recognition for the good stuff we’ve accomplished. Today on Hackaday, a nice article about Manhattan and Ugly construction was posted, with ample coverage given to the fact that a lot of the best exemplars of these techniques come from the world of amateur radio builders. I’m not certain about how others feel on this topic, but it seems to me that Hackaday is one of the preeminent blogs relating to our hobby, so I get quite excited when we get repped there.
Featured in this article are two names well-known in our circles, and guys that I’m proud to call my friends (although I have never personally met either in real life yet!). Todd VE7BPO, is renowned for his rigorous empirical work in circuit design, as well as his beautiful Ugly circuit creations. They feature one of his designs near the top of the article.
The other is Dave AA7EE, who is probably familiar to almost every reader, unless you just crawled out from living under a rock for the last decade. It’s not difficult to see why they chose Dave’s work for to illustrate Manhattan construction, as his is some of the best out there. Period. Also unsurprisingly, this is not the first time that Dave’s creations have made it to Hackaday.
Well done, gentlemen! Way to show the maker world at large that we’ve got relevant skills for the 21st century hacker community!
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.
I ended up having one leftover kit from the CC1 beta test and I thought that an experience builder might like to build it. There are a few minor mods to perform to the PCB, so it’s best suited for someone who feels comfortable with that. The (hopefully) final PCB spin is coming soon and will be slightly different, but this version works well, as AA7EE can attest to. I can offer the kit for a discount over the final CC1 retail price, and it’s currently available for 20 or 40 meters (although the final retail product will be available for more bands). Contact me at milldrum at gmail dot com if you are interested.
SOTA 12 Meter Challenge
I’m not subscribed to the SOTA reflector, but I saw a post on the VK3ZPF blog that there was an announcement on the reflector that there will be a SOTA 12 Meter Challenge. I think this is a great idea and I want to support it if I can. I haven’t made too many 12 meter QSOs, but when I have it seems like the DX has been pretty easy picking. When it’s open, the band seems quiet and the signals sound great. The plus for SOTA activation is that a resonant antenna is small and easy to pack.
My original plans for the CC1 were to only support up to 15 meters, but I think I may add 12 meters in order to support this initiative. The DDS in the CC1 is clocked at 50 MHz, so technically I should be able to output a 24.9 MHz signal, although I don’t know in practice how well this works at a frequency so close 0.5 Fc. If I can get it to work, I will release it as an available band on the CC1.
New PCBs Are Here!
Here is the latest beta PCB from the Etherkit, the CRX1 receiver! It is all-SMT construction, but I spread out the components a bit more than the CC1 and all of the parts are on one side of the PCB only. It’s VXO-tuned for the 40 meter band (a few kilohertz around 7.030 MHz) and is based on the Clackamas transceiver which I entered into the 2010 FDIM Challenge (which means it’s also a cousin of the CC1). This receiver has only discrete components (size 0805 resistors/caps, SOT-23 transistors), so it should be fairly easy to build. In other words, a good warm-up for the CC1. It also has a port for an external VFO, so it will be a platform for experimentation as well.
I’ll build this PCB up today and verify that it works, then get a few beta testers to confirm that all is well. Hopefully I can get this product onto market fairly quickly, with a low price. Stay tuned for more details as work progresses.
More Stuff For Sale!
I’ve added some new gear to my For Sale page that would be a great addition to the bench of any homebrewer. Please stop by and take a look!
For the first time in quite a while, I’ve taken a project from start to a complete finish in an enclosure. I wanted to have my prototype SSB QRP rig ready to take with me to Salmoncon, so I busted a move this weekend to tweak the last bits of the circuitry to my liking, build an enclosure, and get it properly mounted. You can see the results to the left. I have an assortment of Ten Tec enclosures on hand, but none of them were large enough to accommodate the bulky circuit board that I used, so I had to fabricate my own out of copper clad based on the WA4MNT instructions (such as AA7EE did with his wonderful CC-20 beta build). I would say that my mechanical construction skills are average at best, so it’s not the nicest looking enclosure, but I guess it’s OK for a first try (the perfectionist in me sees lots of flaws). The two-tone blue and grey doesn’t look too bad from a distance. Regardless of the aesthetics, the final enclosure is quite sturdy and will work well to keep the radio safe.
Here to the right, you can see the insides of the radio (sorry for the crummy photo, it was taken with my phone). The mainboard is the one laying horizontally and filling most of the room in the enclosure. To the left of the mainboard is the microcontroller/DDS board, standing vertically. Crammed in right in front of that, is the 4-digit LED frequency display and all of the other controls. Unseen and in the top cover, is a 1 watt, 8 ohm speaker. The LM380 AF amplifier can easily drive it to room-filling audio.
Here are some preliminary specs so you can get some idea of the performance:
Tuning range: 14.000 to 14.350 MHz (DDS)
IF BW: 2.3 kHz (3 dB), 6 crystal ladder filter
Current consumption: ~150 mA RX (not optimized for current yet)
TX Power: ~8 watts @ +13.7 VDC
MDS, IP3, etc.: not measured yet, see below
I haven’t measured any of the important RX specifications yet, but I’ll give you some subjective operating impressions. Compared to my IC-718, the sensitivity is very close. Maybe a few dB down but not much. Noise seems pretty good, a bit better than the IC-718. A rough guess of dynamic range and intermod distortion is that it is decent as well. Haven’t heard much in the way of distortion products or “crunching” in the pileups that I’ve tuned through. There’s no AGC, so you can listen to some pretty weak DX signals, then have the local guy replying really blast through but sound relatively clean. Since the architecture is based on ADE-1 mixers and low-noise MMIC IF amplifiers, it’s what you would expect. There’s no preamp, but that doesn’t seem to be much of a handicap on 20 meters. In fact, I think it would probably be counterproductive, especially since you probably aren’t working any stations that far into the mud that you need a preamp to hear them.
As I previously alluded to, my mechanical skills are a bit suspect at times, so I needed to have a test QSO with the radio once it was all buttoned up to make sure that it was working correctly. So I did a bit of tuning around at about 9 PM local and heard K2L, the South Carolina station for the Original 13 Colonies special event station, thumping my speaker off at well over S9. He was working stations at an easy clip with fairly short exchanges, so it was perfect for a quick test. I snagged him on the first call with an honest 59 report (at least I think it was honest…I heard him giving other stations lower reports so I assume I was really a 59) with approximately 8 watts PEP into my ZS6BKW at 30 feet. Mission accomplished!
It will be fun to take this rig to Salmoncon for some camping portable operation. I’ve never attended a Salmoncon before, but I think any of the attendees can use the special K7S callsign, so maybe I can do some CQing on 20 meters SSB with the short call and attract some stations. We won’t be up there until Friday evening, so I think we’ll miss the SOTA runs, but hopefully I can also get the radio out to a SOTA peak near here when I return. It might be too ambitious, but before Salmoncon I would also like to finish a 40 meter CW rig based on my Clackamas design that I entered into the 2010 FDIM contest. We’ll see if I can actually pull that off.
Stay tuned for more news on Salmoncon as it gets closer and hopefully I can get a video of the SSB rig on YouTube so that you can see it in action for yourself soon.
I don’t know exactly why, but I’ve had a bit of an obsession with the T32C DXpedition to Kiritimati since they got started a few weeks ago. Maybe because I found them easier to work than many of the DXpeditions that I’ve tried before. The fact that they are a very well-run operation has something to do with it, I’m sure. Whatever the reason, once I got a few contacts under my belt, I became driven to try to work them on all band slots practical for CW and SSB. I have a ZS6BKW antenna, so I can load it up from 10 to 80 meters. I figured 10 — 80 was a reasonable goal, but I knew the lower bands were going to be tougher since my antenna is only up at about 30 feet.
With the bands being as hot as they have been in the last month or so, it hasn’t been a great challenge to fill up the band slot chart for the most part. Almost all of the QSOs made over the last few days have been snagged within one or two calls (I also thank W9KNI’s book The Complete DXer for teaching me very valuable basic DXing skills). I will admit that I’ve been running 100 W output for these QSOs — with one important exception.
20 meters CW was one of the slots that I had not yet filled as of this morning (oddly enough, since that’s THE DX band). Over the last few weekends, I’ve been hacking away on the firmware to the CC-Series, trying to get the last major features up and working bug-free. Thanks to a request from AA7EE, I just implemented XIT on top of the RIT that was already in the firmware (speaking of Dave, go check out his even more impressive T32C QRP story). The nice thing about XIT is that it allows you to relatively easily work split stations like DX, even though there is no “official” dual-VFO capability in the rig. Since the XIT capability seemed to be mostly working correctly, I wanted to put the CC-20 on the air to try it out and be certain. The first station that I worked today with the CC-20 was K6JSS/KL7, operated by well-known Alaskan QRPer AL7FS. It was a simplex QSO, but it was nice to bust the mini-pileup with my first call. While continuing to work on CC-20 development, I monitored the DX cluster to see when T32C would show up on 20 meters. Sure enough, I ended up seeing him pop up on the cluster at about 0200 UTC. Time to put the CC-20 to the test.
I don’t have a valiant battle to describe. It took me about 10 calls to finally get him, although there weren’t a lot of people calling him. I suspect that the majority of my trouble in getting him was in zero-beating him with the unpackaged encoder knob. While in RIT or XIT mode, pressing in the tune knob toggles between the TX and RX VFOs. Trying to do that quickly when it’s not mounted on a chassis is tricky! Regardless, it didn’t take long until I heard the sweet sound of my callsign coming back to me across the vast Pacific Ocean. Two watts spanning 3600 miles to a tropical island in the middle of a huge ocean is pretty neat. This doesn’t rank in the annals of great QRP achievements, but it will always be a memorable QSO for me.
During some discussions with AA7EE regarding a seeming lack of 20 meter propagation between us at any time right now, we both decided to do a bit of research into what was even feasible according to predictive software. Dave went to the VOACAP web service from OH6BG to get some nice plots which showed that indeed it would be nearly impossible for us to make a 20 meter QSO right now.
The web site is nice, but being a Linux nerd, I wanted to see if I could find comparable software for my PC. A small bit of searching led me to VOACAPL from HZ1JW, and the matching package pythonProp, which gives a GUI frontend to the CLI VOACAP interface.
The installation of the VOACAPL software is quite easy if you are using Ubuntu. Just download the .DEB file and install using your favorite package manager. Installing pythonProp is a bit more involved, since there are a fair number of dependencies to install first, but as long as you closely follow the instructions on the website it shouldn’t be much of a problem.
If you are like me and the thought of tackling VOACAP through the command line was a little bit daunting, then the voacapgui tool (in the pythonProp package) is just what you are looking for. The GUI has three main tabs for interacting with the program: one for the site information (transmitter and receiver QTH, antenna, and power), one tab to execute point-to-point channel analysis, and one for generating area propagation maps.
As you can see above, the P2P tab can get you a nice plot of the probability of making a QSO over a certain path with the specified antennae and power levels. And since this is a Linux port of the program that Dave used on the web, the data we got back was nearly identical. No 20 meter QSOs for us right now.
Here you can see an area map showing circuit reliability for 7 MHz at 0300 UTC during Oct 2011 using 5 watts. That doesn’t look very good! (Sometimes I wonder if the predictions for low power are a bit out-of-whack. This software was originally written for VOA, so I wonder if it’s really calculating the reliability for a 5 W AM signal. I am a total novice at this, so I expect some VOACAP expert will probably put me some knowledge on this, as the kids say).
Any way, it’s a neat package to play around with if you have a Linux box. Many thanks to HZ1JW for taking the time to port VOACAP over to Linux in a easy-to-use package.
Sure enough, I made a mistake. Had I read the documentation more thoroughly, I would have seen that parameter Required SNR was set to a default suitable for SSB. At least I was onto the right idea a few paragraphs above. Here’s the same area plot as before, but with the Required SNR set for a suggested value of 24 for CW operation.
Here it is, the first CC-Series beta unit completed by someone other than me! As is obvious by glancing at the photos, Dave AA7EE has done a magnificent job of assembling the CC-20, as well as creating a custom enclosure for the radio out of red copper clad using the WA4MNT technique. There’s really not much more for me to add, except to tell you to get yourself over to Dave’s blog to check out his story about the build and to see more shiny photos.
As I’ve previously noted, the VRX-1 is a nifty little basic direct conversion receiver, but it has some shortcomings that could be problematic under certain circumstances. Here’s a story of one of those issues and the cure that was found.
Dave AA7EE purchased and built a VRX-1 kit a while ago but was never fully satisfied with the performance due to an annoying 60 Hz hum. He and I had briefly traded comments on the topic via Twitter, but I never really seriously took the time to think about it until just recently. Dave had built and placed a peaked lowpass audio filter into the receiver thinking that would help with the hum, but unfortunately it did virtually nothing to help with it.
I was a bit surprised to hear of the hum problem, since I had never encountered any significant amount of hum, nor had I had other complaints of hum. The eureka moment came when Dave had mentioned that the hum went away when he disconnected the antenna, or it decreased in signal strength when he moved away from his home. I had assumed that the hum was a glitch in his audio circuitry, but this reminded me of the problem known as common mode hum. The best description of this phenomena is found on pages 8.8 – 8.9 of Experimental Methods in RF Design, but I can provide a brief overview. Common mode hum is the result of the LO leakage getting out of the antenna port, modulated by a mains power supply (like an old-fashioned model with rectifiers), and then re-received by the radio.
Due to the simple, single-ended mixer design in the VRX-1, I knew that LO-RF isolation was very poor. So the first suggestion to pop in my mind was to tell Dave to try a common-gate JFET preamp on the front end. Although these type of mixers have modest gain, they have a low noise figure, and even more importantly for us, excellent reverse isolation (on the order of 30 dB). This should be enough to kill any significant amounts of LO leakage.
Dave built a circuit from master homebrew experimenter, Todd VE7BPO. It’s the last circuit on this page, and it looks rock-solid. A double-tuned circuit on the front and a single-tuned circuit on the output. Sure enough, that ended up doing the trick. Rather than trying to reinterpret Dave’s thoughts, go visit that last link, then watch his YouTube video so you can hear the results for yourself:
I’m really pleased to hear that Dave’s annoying problem is finally fixed. This makes me wonder, in retrospect, whether I should have just designed in a preamp to the VRX-1. It certainly isn’t needed for noise figure purposes, but as you can see it can make a huge difference with those who might have problems with hum. There’s also a well-documented problem of a loud impulse generated when the antenna is connected or disconnected during operation. I suspect at the reverse isolation of the preamp would also help this. Hindsight is certainly 20/20. If there is ever a VRX-2, then you can bet that it will get a stock common-gate preamp.