Last night, I had the very first 2x CC1 QSO with Dave AA7EE on 40 meters. Rather than try to blather about it, I'll let the video do the talking. Needless to say, we were both quite stoked!
First CC1-to-CC1 QSO
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Tag Archives: AA7EE
SSB In A Box
Unnamed SSB QRP Rig
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.
SSB Rig Guts
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.
Two Watts Across the Pacific
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.
VOACAP For Linux
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.
Update
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.
That looks better!
The First Wild Beta
AA7EE CC-20 Beta 1 Interior
AA7EE CC-20 Beta 1
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.
Curing Common Mode Hum in the VRX-1
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.
That Which Does Not Kill Us
I feel pretty guilty that I've let the blog content slide in 2011. As you can imagine, between having a near-toddler cruising around the house, doing a major redesign of a QRP transceiver, and trying to bootstrap a new small business, free time is at a premium (and my wife and kid owns what little there is). The least that I can do is give you a quick glimpse into the progress with the radio.
If you don't follow me on Twitter, you probably don't know any of the details of my progress with the CC-Series radio. After advancing the design of the radio to a point where I thought it was production-ready (two PCB turns, lots of design review and tweaking), I ended up failing pretty miserably in the end. The problem was with a subtle, but noticeable pull on the free-running VFO on transmit (which was not present on the prototype). I spent close to 2 months attempting to troubleshoot that one little problem, but sadly it ended up defeating me. Perhaps "defeat" isn't the correct word. There was a part of me that wanted to keep stubbornly trying until I tackled the problem (ask poor Jennifer about my stubbornness). But I had to look at the issue realistically, from a business point-of-view. I had no idea if it would take me a few more days or many more months to solve my problem. So in the interest of trying to save my fledgling company, which hasn't even made it out of the nest, I made the difficult decision to temporarily abandon the CC-Series development.
Instead, I decided that I would take on a similar project: revamping my minimalist entry in the 2010 FDIM Challenge (the 72 part rig). It started as just a few upgrades, but quickly spun into a new project of its own. When the VXO scheme that I wanted to try didn't work out as I had hoped, I decided that I would bite the bullet and add a DDS to the project. I planned on reworking the CC-Series with a DDS anyway, so this would be a good way to learn how one works. In order to make the rig worthy to be sold to other people, I kept incorporating changes and features from the CC-Series. I also leveraged my firmware from the CC-Series, which made it easy to get up to speed with the new radio fairly quickly. By now, the rig resembles what I intended the CC-Series to be in the first place.
The new CC-Series?
A few nights ago, I made my first QSO with the rig with W7GVE in AZ. We had a nice little chat and he let me know that I had a little bit of chirp on my signal. Right after I signed off with Ed, I got a really pleasant surprise. Who else but the great father of us QRP homebrewers, W7ZOI! He dropped in to give me a quick "hi" when he heard me on the QRP watering hole of 14.060 MHz. According to my (admittedly incomplete) log on my PC, this was my first QSO with Wes. It was a great thrill, but unfortunately I missed about 25% of his transmissions because I was too nervous to copy CW well. I fully admit that my CW is still lousy, and my comprehension drops off the cliff when the other guy is going greater than about 15 WPM and I'm jittery.
I made some tweaks to the transmitter (and torched some finals in a spectacular, fireworks fashion), then managed to make a sked with one of my partners in crime, AA7EE. It was a rough QSO, especially for me, but we exchanged signal reports so it counted (20 meters at 2200 local on a short path between us is not conducive to communication). Better yet, Dave reported that the signal was rock-solid and chirp-free.
So where do we stand now? I want to do a little more on-the-air testing, then I'm going to start laying out the PCB. The last time I ordered prototype PCBs from my vendor, they were very high-quality, but the turn around time was less than desirable (nearly 3 weeks). This time, I'm going to see if I can lay out the board with minimum vias (probably not going to happen). If I can do that, I might be able to make my own board with the toner transfer method. If not, then I'm going to look into a vendor that can give me boards with more alacrity, at least for the prototypes.
It's been frustrating, but it's also forced me to refine all of the circuits in my radio in order to make them as bulletproof as possible. As long as I can get this puppy to market, then it will have been worth the heartache.
Update
Last night, I had another QSO with AA7EE so that he could record my transmissions and send me back the recording for evaluation. We had talked about meeting sometime after dinner, but set no specific time. Right around 1900 local, I fired up the rig on 14.060 MHz and was just getting ready to send a tweet to Dave to see if he was around. Within about 30 seconds of turning on the rig, I heard someone calling CQ on the watering hole frequency. Sure enough, it was AA7EE. I established contact and we had a quick little chat. Thanks to Dave's generosity, I've posted his recording of the QSO below. The QSB was bad on my end, but as you can hear from the recording it wasn't very bad on his end. Even though the signal was weak, the note from the rig sounds clean, stable, and chirp-free. Be sure to stick around to the end of the recording for a few moments of commentary from Dave himself.
AA7EE-NT7S - 0217 - 24 May 2011
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