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Wideband Transmission #5

Latest CC1 Progress

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As you can see from the above photo, I have finished a significant portion of the digital side of the newest CC1 prototype and now I'm on to the receiver section. This weekend I finished my first pass of the audio chain and characterized the gain and frequency response of the chain. Next up is the design of the IF and front end of the receiver. This time I plan to do a much better job of characterizing the performance of entire radio, designing for specific critical receiver specifications, and iterating the design as necessary instead of holding on to dodgy performance from circuits.

Mixer Investigations and the Search for Better Dynamic Range

Since I decided to ditch the dual-gate MOSFET mixer front end, I've been considering what to replace it with. At first, I was thinking about using the ADE-1 for the mixer and product detector, but I've been intrigued with reading about H-Mode mixers over the last few weeks, which led me to the similar, but simpler KISS mixer by Chris Trask. That seemed like a good candidate for the CC1, with relative simplicity and better-than-average performance. Since good IP3 performance is the main characteristic of this mixer, I wanted to try measuring IIP3 at my own bench to see how it looked in a home made circuit with less than optimal parts and layout.

To get warmed up, I first attempted to measure the IIP3 of a few parts that I had on hand where I already knew IIP3 values to expect: the SBL-1 and the ADE-1. Using a DG1022 as the signal generators, my HFRLB as a hybrid combiner, and the DSA815TG, I was able to measure an IIP3 of +13 dBm for the SBL-1 and +17 dBm for the ADE-1, which is pretty much right on what other people have published.

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Here is my test setup for measuring the KISS mixer performance. I deviated from the circuit described in the KISS mixer white paper in a few ways. First, I used a TI TS5A3157 analog switch, as I didn't have any Fairchild FST3157 on hand. I also used a hand-wound trifilar transformer on a BN2402-43 core instead of a nice transfomer from a company like Mini-Circuits. I drove the KISS mixer with +3 dBm from a Si5351. My measurement of IIP3 for this variant of the KISS mixer came out to +27 dBm, which seems reasonable given the poorer components I was using. Conversion loss was 7 dB. I'm going to try to measure it again with an actual FST3157 and a Mini-Circuits transformer in the near future, so it will be interesting to how much that will improve the IMD performance.

But honestly, I probably won't need better than +27 dBm performance if this mixer is used in the CC1. Since the CC1 is meant to be a trail-friendly radio with modest current consumption, I don't think I want to include the high current amplifier needed after the KISS mixer to get maximum performance out of it. Which is kind of a shame, but I figure that I should be able to keep RX current to around 50 to 60 mA and still have a receiver with better IMD performance than your typical level 7 diode ring mixer receiver. Stay tuned for more details on the CC1 front end as they are worked out in the NT7S shack.

10 Meter Contest!

Yes, it's almost time for my favorite contest of the year: the ARRL 10 Meter Contest. Ever since I moved into the current QTH, it has been a bit of a tradition for me to operate the contest as SSB QRP only. By virtue of entering that least-liked category, it has been no problem to collect some modest wallpaper from this contest. That's fun, but my real goal is to beat my previous score. Last year, I think I did fairly well with 7490 using a stock IC-718 and my ZS6BKW doublet. So this year, I'm going to have to step up my equipment game in order to have a good chance of besting last years score. I'm thinking some kind of gain antenna is going to be a must. If I can get a Moxon or small Yagi up around 20 feet and use an Armstrong rotor, that should help give me a little more oomph than last time. We'll see if I can get something built in the less than 3 weeks before the contest.

Etherkit Rev B

You may have already seen it, but please allow me to direct your attention to my latest post on the Etherkit blog. For the tl;dr version: sorry to have been quiet on the business front so long, also sorry to have failed to do a good job keeping up on business communications, the OpenBeacon and CRX1 products are being sunsetted (I've reduced the price of my limited remaining stock of OpenBeacon to $29), new products and new initiatives are coming in the near future.

I wanted to mention a few more things that I neglected to say in that post. First, I also plan on releasing another revision of the Si5351A Breakout Board for sale as a kit. There are a few bugs to fix on the current version on OSHPark, but it shouldn't take me too long to get a new revision up there and ready for testing soon. I've also reduced the price of EtherProg to only $9, which should make it in line with other similar tools.

To be bluntly honest, it has been a difficult year here on the Etherkit front because of multiple failures, some of which I must keep private for now. However, I have been buoyed by encouragement and help from friends and family, and I plan to redouble my efforts to make Etherkit the company that I envisioned when I founded it.

There will still be quite a bit more to announce in the near future, but now is not quite the time to reveal everything being worked on behind the scenes here. I will have more Etherkit news soon, so as usual, watch this blog for updates.

Thank you!

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Si5351A Investigations Part 7

Here's the post I know that a lot of you have been waiting for. Buzz around the Si5351 has been picking up at a pretty rapid clip over the last month or so, but a lot of homebrewers have been hesitant to use it in their designs because one critical parameter has not yet been measured: phase noise.

Phase noise measurements seem to be one of the least easily accessible to the typical ham homebrewer, but fortunately for us, we have in our ranks some engineers with access to excellent T&M gear that most of us would never be able to afford for our home workbench. Thomas LA3PNA was able to put me in touch with one such engineer, John Miles KE5FX. I don't know much about John, but I should, as it looks like he has developed the TimePod phase noise measurement device and the TimeLab analysis software (which is very slick, I must say).

John was generous enough to make a variety of phase noise measurements on the Si5351A Breakout Board that I sent him. Below, I present some plots of the phase noise measurement that were taken at various frequencies and under a few different conditions.

Before I get to a brief commentary, here are the plots. The first two plots were taken at 3 MHz, first with 2 mA output current then at 8 mA output current. Then you will find 10 MHz, 13.371 MHz (in both fractional and integer divider modes), 14 MHz, 100 MHz, and then a composite plot of all of the different traces.

3_MHz_2_mA 3_MHz_8_mA 10_MHz_powerup_default overlay_frac_int_mode_13mhz 14_MHz_CLK0_with_CLK1_at_0 100_MHz_CLK1_PLL_auto_calc_8mA overlay

I believe that the plots speak for themselves fairly well. If you compare these results to the receivers in the Sherwood Engineering receiver table, I think you'll see that the Si5351 acquits itself quite nicely for such an inexpensive part. Personally, I think the Si5351 is eminently usable for many receiver applications, except perhaps the most high-performance. Certainly for the price, it's going to be extremely hard to beat. I hope this motivates those sitting on the fence to decide if the Si5351 will meet their needs.

Finally, I would like to share a new video of the Si5351 in action, courtesy of prolific builder Pete N6QW. Here's Pete having the very first QSO with his new SSB QRP rig built using one of the Adafruit Si5351A Breakout Boards:

I would like to sincerely thank KE5FX for taking the time to make these measurements for the community and for allowing me to share them with you. If you have any ideas for critical phase noise measurements that aren't included here, let me know in the comments and perhaps we can get those made as well.

Edit: I failed to mention that these measurements were taken with a plain old 25 MHz ECS crystal as the reference oscillator. With a higher-quality reference oscillator, one would expect even better phase noise performance.

Si5351A Update

I don't have a ton of new updates for you from the NT7S bench, but I wanted to give you a heads up on an error on the Si5351A Breakout Board Rev B and let you know about some exciting stuff brewing on the Si5351 scene.

When I created Rev B of the Si5351A Breakout Board, I attempted to create a PCB footprint that would allow dual-use of both the standard 25 MHz ECS reference oscillator crystal, but also a 25 MHz Fox TCXO in the same footprint. It was almost a good plan, but somehow I overlooked one detail. On the TCXO, VCC is applied to pin 4 and ground is pin 2. Unfortunately, on the ECS crystal, those two pins seem to be internally connected, but I missed that. So if you want to use the ECS crystal with the board, you can simply cut the trace providing +3.3V to pin 4 of the footprint, and your Si5351 will work fine. Otherwise, the power rail will be shorted to ground and you will have an unhappy board. I apologize for that oversight and I will work on getting a corrected PCB up on OSH Park in the near future.

In happier news, it seems to me that interest in the Si5351 is finally starting to really gain momentum. I've had a fair number of ham homebrewers contact with inquiries about the Si5351 and sharing their experiences with the IC so far. Although I don't subscribe, I've heard that there is quite a bit of chatter on Farhan's Minima mailing list about the possibility of substituting the current Si570 for a Si5351. Given that the Minima is meant to be a minimalist rig, I think this makes a lot of sense. There even some blog posts from others coming out now. For example, the always entertaining Shack Nasties blog by M0XPD now has some blog posts about initial experimentation with the Si5351 in a transceiver. I would put Paul's blog in your feed reader if I were you, even if you are only interested in RF experimentation in general.

This should be a good upcoming time for the cheap and cheerful little clock IC. I'm going to be experimenting with it in the next CC1. It should work great, with one output for the VFO, one for the BFO, and the last for the TX drive. As always, keep an eye on the blog and my Twitter account for further updates.

Wideband Transmission #4

It's been a while since I've posted one of these. I understand that things have been fairly quiet over here in the last few months, so I wanted to let you all know that I'm not dead yet. I've actually been working on Etherkit a fair amount in the background, and that has been eating up most of my free work time. I know that things have looked stagnant, but please understand that I have been putting in time to revamp the business and bring some exciting new things to Etherkit. I have a few different, parallel projects going on right now. Soon I will commit to one of them and move forward on that, depending on how things pan out. I suspect I'll have more to say on the matter in less than a month on where Etherkit will be going in the future.

In related news, I've had a few people ask about what's going on with the CC1. I apologize for the CC1 being a huge bit of vaporware. To be frank, it has been the most frustrating project I've ever worked on, but I believe in it strongly enough to attempt to finish it. At this point, as much as I have had fun with the BF998, I believe that in order to make the CC1 the radio that I want it to be, I will have to abandon using the BF998 as mixers and switch to a balanced mixer design, most likely the ADE-1. I'm also looking into adding a small OLED display to the radio, which will also necessitate a large redesign to the mechanical layout of the radio (I'll probably end up doing the typical TFR design, such as the KX1, KX3, etc.). I'm also impressed enough with the Si5351A that I'm going to try using that as the new VFO and BFO. A brand new CC1 prototype is just getting started on the bench now, so it should be interesting to see how it works out. I'll post some progress photos and videos to my Twitter feed and the blog, as appropriate.

Thanks for hanging in there with me. It has been a real challenge to try to run a business while also being a full-time caregiver to my two boys. I would say that I haven't been very successful in doing both, so naturally, the business took the backseat. But now that my boys are getting older (Noah is 4 and Eli is 2.5, can you believe it?), I'm able to spend a bit more time during the day handing business. Things will be moving forward.

Goodbye to QRP Homebuilder

It's late at night here, but I wanted to write a short post, because this is very notable. I have unfortunately found out that the esteemed Todd Gale, VE7BPO took down his amazing site, the QRP/SWL Homebuilder. Todd's site has consistently been one of the best places on the web to get solid, entertaining, well-documented, and hype-free information on the RF circuits that we all love to build. The QRP Homebuilder has been the premier destination on the web for my favorite hobby for as long as I can remember.

Today's news is about as sad to me as when W7ZOI removed most of his RF experimentation materials as well. I could only hope to be half as talented as either of these two gentlemen, and we are all going to miss this most essential web site. I pray that some day soon we will find a new generation of experimenters who will be able to bring that same evidence-based RF work to the internet.

The good news is that all of that valuable documentation is not lost. Todd has graciously archived the last version of the site as a full-color PDF, with all of the schematics and colorful illustrations that you love. Todd is currently hosting the PDF on his server, but I wanted to mirror it here (with Todd's permission) in order to ensure that it has wider coverage.

Download the QRP/SWL Homebuilder PDF Archive

I'm not yet at liberty to discuss the circumstances of the decision that I have been told about, but I strongly believe that Todd himself will do that some day. I would like to thank Todd for his years of generous service and for blazing a trail in the RF experimentation community.

Edit: Good news! Todd already has a new site up and running, this time in the form of a blog. It currently only has a test post, but I would bookmark it and put it in your feed reader if I were you. Go forth and visit Popcorn QRP. I've added it to the blogroll. Best wishes on the new endeavor, Todd!

CRX1 Group Builds?

I'm pretty happy with the way that the CRX1 turned out, but understandably I haven't sold a ton of them because 1) they are a SMT kit and 2) the tuning range is a bit limited. However, it's a stable and sensitive CW receiver and it's pretty fun to build as well.

There are still PCBs and a fair number of components left to kit another batch of CRX1s, but I would need to order more components in order to complete a 2nd batch of kits. I'd hate to see these parts sitting around, so I have a potential proposal that I'd like to use to gauge interest for ordering those other components.

I believe these would be great as a group build project for those who have built through-hole kits in the past but want to try their hand at SMT. The circuit board is not cramped and the passives are almost all 0805, so they are not too small. So of there are any of you interested in ordering a batch for a group build (whether for a few friends or for a club) then email me at milldrum at gmail dot com. I can arrange for a bulk discount over the current $30 retail price. The discount will be based on the number ordered.

Finally, wanted to show you a very quick demonstration of the receiver to those of you who haven't seen it in action before. Take a peek at this video to see it listening to 40 meters.

I could probably work out something on the OpenBeacon as well, if you think your group would prefer to do that instead. Just send me an email to the above address.

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Si5351A Breakout Board Update

I've had a good response to the Si5351A Breakout Board when it was posted on Hackaday last month. There have even been a few folks who went through the trouble of ordering PCBs from OSHPark so that they could build their own copies of the board for experimentation. One of them, Tom AK2B, even constructed a complete receiver using the Si5351A Breakout Board and the RF Toolkit modules from kitsandparts.com. Check out the link to the nice-sounding audio in the embedded tweet below.

When the link to the Breakout Board was posted on Hackaday, I wasn't even sure that anyone would be interested, so the design was not as robust as it should have been for public use. But thanks to some suggestions from Tomas OK4BX and some of my own ideas, I've created a Rev B Breakout Board that has a number of improvements.

Si5351A Breakout Board Rev B
Si5351A Breakout Board Rev B

I increased the size of the board by 10 mm on the short side in order to accommodate some new circuitry. I could have kept the board the same size and put the new components on the back side of the board, but I thought it would be better to keep everything on the front. Thanks to Tomas' suggestion, I added simple MOSFET I2C level conversion so that the Si5351A can be properly interfaced with a 5 V microcontroller. I also added a 3.3 V LDO regulator and jumper blocks so that the I2C interface voltage and the 3.3 V source can be selected. The traces from the Si5351A to the output transformers were also screened with vias, which improved crosstalk between outputs by about -6 dB. I also increased the pad size for the SMT crystal in order to make it easier to hand solder. In addition, I added a provision for the crystal footprint to double as a footprint for a TCXO. So far, the crystal works fine, but I haven't ordered the TCXO yet in order to verify that it works as well, but I don't think there will be any problems as long as the crystal is working.

As I anticipated from a previous post, Adafruit has released their own version of a Si5351A breakout board. It looks like they use the same I2C level conversion scheme as my board, but that is where the similarity ends. The Adafruit board seems to be geared to using it strictly as a clock generator, where the Etherkit board is designed to be used in RF applications by providing output isolation via broadband transformers and screening of the output traces. The Etherkit board also has more flexible options for using the board in 5 V or 3.3 V environments.

You can order the new board from OSHPark here, and find the documentation for it on GitHub.

I need to do a bit more testing to ensure that everything is working as it needs to, but so far the preliminary tests look great. Assuming that everything with the new board checks out, there's a decent possibility that I will kitting at least one batch of these boards for sale. Stay Tuned.

Si5351A Breakout Board Documentation

I appreciate all of the interest in the Si5351A Breakout Board that I have available on OSHPark. I apologize for not having this available sooner, but here is a GitHub repository which hosts the KiCad design files and a PDF of the Breakout Board schematic, which lists the part numbers for the reference oscillator and the output transformers so that you can order your own. Also the few passives on the board are size 0805.

This, along with either the avr-gcc library or the Arduino library, should get you going in generating all kinds of clocks and local oscillators. While this board seems to work fine in interfacing with the 5V Arduinos that I have, I worry that comms might be iffy, so I'm going to add simple MOSFET-based level conversion to the next iteration of this board. Keep an eye on the blog for further developments in this area.

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For Noontime Net

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 Analog 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.

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Emanations from Amateur Radio Station NT7S