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.
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.
A little while ago, I got a hankering to work on a SSB transceiver. It's something that I've never homebrewed before, and it seemed it like it might be fun to tackle. The BITX20 seemed like an obvious choice, and W7ZOI recently published an improved bidirectional amp which would be nice to try in the rig. But I'm one who likes to try stuff that's a bit off the beaten path, so I decided to try my hand at something a bit different.
VU2PEP has a lesser-known SSB design on his website, that's a dual-band transceiver. Besides having 20 and 40 meter capability, it also has a different topology than the BITX series. Instead of reversing the flow of the signal to generate a SSB signal, this design sends the RX and TX signal in the same direction through the IF. Take a look at the schematics to get an idea of what I'm talking about.
I decided to make a "remix" of this design. The basic topology is the same, but most of the circuits are revised. The IF was moved to 4.9152 MHz, and the VFO is heterodyne-style to provide a ~19.12 MHz LO signal. My version is only for 20 meters. The front end has a preamp added and uses a cascode JFET mixer instead of a single JFET. So far, the RX strip and VFO is complete (although I might change the VFO because of some birdie problems), but the transmit amplifiers haven't been built yet. I got a good chance to work out the RX during Sweepstakes. Check out my YouTube video below to hear me describe the circuit so far and listen to the receiver on SS.
Disclaimer: For those who don't know, I'm an employee of Buddipole, and I do speak quite a bit of my positive experiences with some Buddipole products in this post.
Yes hams, it's that time of the year again. Field Day, the Super Bowl of the ham radio world. I haven't had the best track record of participating in Field Day over the years, due to a few different factors. The largest stumbling block is the nasty allergies that I get during late spring, which usually end up peaking in intensity right around the end of June. The other problem is that I've never been a big fan of the big-time organized local clubs. I won't go in to the reasons for that (you can dig back in the blog if you are really interested), other than to say that in my experience they are not the kind of places that I find interesting.
Now that I own a house with a proper backyard, I feel like I now have the option to participate in Field Day by setting up out back, so that I can duck inside if my allergies get too out of control. It also helped that I recently started taking some new meds, which have helped to control the allergies quite a bit better than anything else so far. So I was more than happy to give FD a go this year, even though it wasn't going to be more than a backyard adventure.
Given the recent development of my employment with Buddipole, and the demise of my main station random wire antenna in a recent spring storm, it only made sense to deploy the Buddipole. I could have dragged out the IC-718 sitting idle in the shack and paired it with my very heavy 35 Ah gel cell, but I was feeling up for a bit of a challenge. I settled on using the FT-817, and considered pairing it with my recently constructed 20 watt linear amp, but I realized that running 20 watts would give me the same power multiplier as running 100 watts would. So I figured, why not take the dive and go QRP for the entire event? Not only that, but why not make SSB the main mode of operation? This was appealing to me not only because I am a QRPer at heart, but also because it would push my limits, and give me something new to try.
I've run into my share of hams who think that QRP is the devil's handiwork, and that anyone running less than 100 watts is inflicting undue hardship on the poor receiving station. While I know that a QRP signal does have a more difficult time being heard (especially SSB), I also know that there have been plenty of times when the receiving station would have had no idea that I was running QRP unless I told them (and many times, I won't tell them). The fact is, if you can hear me well enough, you'll answer me. If not, you won't. Yes, I get less contacts running QRP. But if the conditions are too painful for the other station, they will just not answer me or will politely cut it short. I especially feel absolved of any guilt running QRP SSB on Field Day because of the whole nature of the event. The concept is to test how well we do under less-than-ideal conditions. Quoth the rules (emphasis mine):
2. Object: To work as many stations as possible on any and all amateur bands (excluding the 60, 30, 17, and 12-meter bands) and in doing so to learn to operate in abnormal situations in less than optimal conditions. A premium is placed on developing skills to meet the challenges of emergency preparedness as well as to acquaint the general public with the capabilities of Amateur Radio.
The great thing about using the Buddipole was the ability for me to use it in conjunction with the frequency agility of the FT-817 to hop around the bands. Yes, it does take a bit of time to change bands, which is not quite as fast as using a multiband doublet with a tuner. However, with just a bit of practice, you get to know what setting sare needed to resonate your antenna on any band and can reconfigure and tune it in a matter of a few minutes. Given that I decided to run QRP SSB, I needed every bit of power I could get, so I was glad to not have a lossy tuner in the way.
Given the somewhat last minute nature of my decision to play in Field Day, I didn't have a way to power a notebook PC with a battery, so I settled on the old standby of paper logging. Since I decided to stay strictly search & pounce, it wasn't a big deal to paper log. The biggest pain is in dealing with dupe avoidance, but I figured that I wouldn't have to worry about that too much since I would be racking up huge QSO counts.
The only thing left to nail down at this point was power. I knew that I wanted to try out our brand new A123 lithium nanophospate battery technology that we are ramping up at Buddipole. If you don't know about this battery technology yet, prepare to be blown away when we officially roll these out. This technology has been used in the R/C hobby for a few years, and is just now making it's way into amateur radio use. It also happens to be the same technology used in the upcoming(?) Chevy Volt plug-in hybrid vehicle. It would take too long to list all of the advantages of this technology here, but the amazing flat discharge curve, long life, very quick charge time, and incredible safety are all reasons why I'm confident that this will be the dominant battery technology in the portable/pedestrian mobile ham circles within the next few years. The particular pack that I was using is a 3S1P configuration, which means 3 cells in series, one parallel set (we also have 4S1P and 4S2P packs). Each cell is 3.3 V nominal, so this pack is rated at 9.9 volts, which is perfect for use with the FT-817. A **1P pack has a capacity of 2.3 Ah, which I figured would give me at least a few hours of operating time.
Being at a bit of a disadvantage in the "contest", I wanted to pick up some extra bonus points, so I remembered the 5 watt Harbor Freight solar panel that I had gathering dust in the closet. Using that in conjunction with my half-depleted 7 Ah gel-cell, my power strategy was fully formed in my mind. During the sunny part of the day (my backyard is on the north side of the house and is fairly narrow, so it doesn't get a ton of sunlight) I would use the solar panel/gel cell combo, then switch to the A123 pack when there wasn't anymore sunlight to be had at the station.
Given the set up that I described, it looked like I would fall into the 1E class for the event. Given a very strict reading of the rules, it seemed like I might have been able to claim 1B Battery, but in the spirit of the event, 1E was the appropriate choice.
I wasn't able to start operating right at 1800 UTC due to some chores that needed to be completed first before play time. When I did get going, I started on 20 meters with the Buddipole in vertical dipole configuration and quickly started to get QSOs in the log. As I mentioned earlier, my strategy was strictly search & pounce, choosing only the loudest stations to try to work. For the most part, it was a successful strategy. I was able to work just about everyone that I heard at a S5 - S7 signal level or better.
Once the afternoon wore on and 20 meters started heating up, the pileups started to heat up as well. I found that it was getting harder and harder to be heard as I was the little fish in the big pileup. So by mid-afternoon, I started working my way up the bands. By jumping to 15 meters (then 10, and eventually 6) was the band was starting to open, I was able to stay ahead of the really competitive pileups. One of the coolest things about the operating was the feeling of riding the QSB like a wave up and down; waiting for a crest in the propagation to strike fast with my callsign. It could have all been in my mind, but it did seem to help to operate like this.
As the sun started to set behind the neighborhood houses, a good sporadic E opening hit the West Coast and I was able to get some nice 6 meter and 10 meter QSOs out to about 1000 miles or so. I had big plans for staying up late after dark to operate, but by the time that dusk fell on Beaverton, I was totally exhausted. So I laid down on the sofa and set the alarm on my iPhone to wake me in a few hours. Not surprisingly, I must have turned off the alarm in my sleep, because the next thing I remember is that it was 5 AM the next morning.
A bit disappointed, but feeling renewed, I put on a pot of coffee and decided on my strategy for the morning. It seemed obvious to give the lower bands a shot, since the propagation was bound to be best there and I hadn't worked them the day before. So the Buddipole was reconfigured as a Versatee Vertical with the low band coil, and the power was supplied by the A123 pack. Once I got going again around 7 AM, I was shocked at how well I was doing on 75 meters. The puny 5 watt signal from the FT-817 into the Buddipole had some good mojo, as I got multiple unsolicited "great signal" reports from the stations that I contacted (many of them VE7s). In my QSOs on the previous day, it was obvious that I was a QRP station, often needing multiple calls to bust a small pileup and sometimes needing a repeat or two. But both 75 meters and 40 meters were working remarkably well for me. The call got through on the first try nearly every time, and almost no fills were necessary. It truly felt like I was running 100 watts.
After a morning of fun, I had to go QRT for the day in order to complete some other chores that I had put off for far too long. It was a bit tough to tear myself from the station, but responsibility trumps fun, even if you try to put it off for as long as you can.
Before I started operating, I thought that 50 QSOs would probably be a reasonable goal to shoot for as a QRP SSB station. As it turns out, I got really close; with a final tally of 49 QSOs, all of them SSB. Twelve of those QSOs were on solar power, so I qualified for the 100 point alternate power bonus. Since I was on emergency power the entire time, I also got 100 points for that. Given my 5 watt power limit and 100% emergency power status, I qualified for a power multiplier of 5. I also managed to copy the special W1AW bulletin for 100 points, and plan to submit my log via the web for another 50 points. If I did the arithmetic correctly, that should give me a final score of 595 points.
I also want to make note of the performance of the A123 battery pack. I started the event by charging the pack to a full charge with my Cellpro Multi4 charger. Although I did the majority of my operation timewise on the solar panel, by far I had the most QSOs with the A123 pack. According to my rough log calculations, I used the A123 pack for over 3 hours of operating time and logged 37 QSOs with it. When I returned the pack to the charger after Field Day, the charger reported 19% of the charge was left (the voltage display of the FT-817 never dipped below 9.6 V the entire time I was operating with the A123 pack). The next charge only took 38 minutes to get me back to 100%, and ready to go again. The 3S1P pack only weighs about 8 oz. and gave me a ton of operation time, much more than I expected. It sure blows away the much heavier and bulkier 5 Ah gel cell that I usually use with the FT-817. Ask the Goathiker, he'll tell you how great these things are.
I could wax poetic about the event, but I think you get my feelings about the thing by now. I'll just end by saying that this was my best Field Day by far, and that I had more fun with QRP SSB than I thought possible. I have a great appreciation for the excellent ops that put up with my peanut whistle, and learned a lot more about how capable a QRP SSB station can be.