mcHF Unit #1 / Update #2

So, some 50-60 hours of assembling later, we get something that looks like this:

IMG_1586
mcHF Unit #1 First Listen

The general purpose builder’s axiom:

  1. The things you expect to be hard turn out to be easy.
  2. The things that you expect to be easy turn out to be unexpectedly hard.

To that we could add a 2a: “…or they consume all of the available time”.

Being a noob with SMT, I thoroughly expected to be chasing solder faults for weeks. That didn’t occur. In fact, after quite a bit of experimentation, I haven’t found a single fault either in the receive or transmit path. I don’t know that everything is optimal yet, but all bands do seem to function.

(I did make a mistake on one of the PA transformers, but caught it and reworked it before adding the PA finals, which I only did after I knew everything else worked. Excepting the PA, I assembled the entire unit over the course of a few weeks. Many will build in stages, testing as they go. I chose not to. I can’t explain why…)

That doesn’t mean that bringup was flawless, however. What I did have issues with was tools and software. The basic bring-up is going to look like this:

Step #1: Basic power-up smoke-and-flame check. No smoke/flame/sparks? Proceed to…

Step #2: Get a bootloader into the processor’s flash.

Step #3: Using the bootloader, flash the operational firmware image.

Step #4: With functional firmware, work everything we can to check/fix faults.

Step #5: Parameterize operation for this specific unit. “Alignment”, but using data instead of an insulated screwdriver.

Then, we should be ready to radiate.

In practice, I ran into driver and connectivity issues that made the bringup a bit of a debugging exercise. Having witnessed others run into similar problems, instead of glossing over it, I’m going to write up a little more detail in some subsequent posts which I hope will be a useful resource for others. Look for those soon…

 

 

mcHF – unit #1 / update #1

When I started this project, I acquired 2 board sets; one to use as an everyday unit, and another to hack on. There is substantial potential in this design through software, and the cost per unit is reasonable, so obtaining a pair seemed wise. In these last few weeks, I’ve been assembling the first of the 2 units, the second to come later. That’s what this post is about.

Acquiring parts is the first task (unless you purchase the full kit from Chris; I elected not to). The project has origins in the UK, and the original Bill of Materials mostly references part numbers as sourced by Farnell/element-14 in Europe, with much of the remainder eBay sourced. Here in North America, most of the Farnell catalog is available through Newark/element-14. Yet, most of the BoM is fairly standard stuff available from other more familiar sources such as Mouser, where I sourced most of mine (and who I’m used to dealing with…heck, with Grant Imahara as a spokesperson, you have to be in good company…).

There are some exceptions and single source items, such as:

  • HY28B LCD displays – single source (have to come from China, required about 3.5 weeks via Singapore Post registered service). I ordered 3; one as a spare, because once these become unavailable, I’ll be well and truly stuck.
  • Si570 programmable oscillator – kind of the “heart” of this radio – this seems to only be available via DigiKey. I have not ordered just yet.
  • Mitsubishi RD16-HHF1 Power MOSFETs for the transmitter final amplifier. There are a small number of North American resellers of these, and they’re not all that cheap. Fakes appear to be very common on eBay.
  • Inductor cores – available via Amidon, Palomar, or others. Some, I already had in my possession.
  • The specific 3.5mm connectors specified for this PCB needed to come from Newark (using the Farnell numbers), no other equivalents appeared to match the footprint.

The photo above shows the state of the boards as I currently have them, with approximately 20-25 hours invested in assembly so far. Most assembly is complete with a few exceptions:

  • No display yet: I’m thinking of putting it in a socket, because of the damage that could be done if it needs to be removed. It connects using an uncommon 2mm pin pitch (instead of the typical 2.54mm/0.100″ header pitch). Sockets are available in that size, they’re just uncommon.
  • No encoders: I’d prefer to solve the display socket question first, because encoder shaft length might be tied to socket height.
  • No pushbutton switches on the UI. They’re backordered.
  • Have not wound the BPF/SWR inductors yet; I don’t have them all.
  • Do not have the finals yet, and I didn’t install the driver transistors yet; I think I’ll wait to get the receiver and UI working first.
  • No relays for the BPF.
  • I still need to get the Si570 oscillator. It will be difficult to solder correctly, so I’ve left off the nearby passives to make sure I have room to heat it well. Many builders report trouble soldering this 6-pin 5x7mm QFN part, which is not at all surprising; it was meant for wave soldering. So, I want to take some care with this.
  • No serial EEPROM on the UI yet. Early builds of the firmware didn’t use it, but newer ones do.
  • Not sure if I want to use the stock 30-pin header for the UI-RF board interconnect, or rig up something allowing more space between boards. They stack to 0.425″,which is just enough. However, I might want enough space between the boards for a metal sheet for RF quieting reasons, and that may require more space.
  • There are still some optional component value selections from recommended mods, which I need to make final decisions on.

This is my first exposure to SMT assembly at this level; I’ve done minor rework to SMT before, but never assembly on this scale.

For assembly, I’m using a simple temp-controlled soldering station with a fine-point conical tip for most assembly (using .015 67/33 flux-core solder wire), and it’s working fine for most things. It took a little practice to get good quality joints, starting with the larger pitch SO-x chips, working my way up to the 100-pin LQFP CPU. That one took about 60 minutes to pin down clean one pin at a time (I didn’t like the drag method myself). I did bridge a few pins, but they cleaned up OK.

A friend lent me an unused hot air pencil for rework; I haven’t needed to use it so far. For unit #2, I may use it for some of the assembly.

Of course, I haven’t seen the unit run yet…until I do, no claims about my quality of workmanship…

I should note, it’s certainly not a project for a first-time builder, although it could be accomplished by a first timer with a little coaching, I think. It is time consuming, and there is potential for difficult-to-detect/correct mistakes in many places. However, if you’ve built a few things before, you’re patient, and are ready for a challenge, it’s not so bad. The boards were laid out with room to spare in most places, and most of the passives are 0805 dimension; not too small for manual placement. In the future, SMT is what we’ll be doing for most everything; learning to deal with it is just going to be a requirement.

More to come after I make some decisions, and finish a few other tasks. Until then…

 

mcHF – a.k.a. what I wish I’d done

90 years ago, amateur radio operators built all their own stuff. There wasn’t any other way; no one would or could do it for you, and one really had to be committed to build a station with the technology of the day, not to mention the costs involved. You had to understand how every component worked, and how to make a radio “system” work with minimal to nonexistent test equipment.

After WWII, more commercial gear became available, and useful stations could be cobbled together using surplus military gear. An operator didn’t have to build from scratch anymore, but they did still have to understand their gear in detail so as to make it work within their legal operating bands.

Kits were still an option into the 60s and 70s, as tube gear transitioned into the semiconductor age. Perhaps an operator didn’t understand how the equipment worked at the outset, but by building it, he would at the end. Kits are a difficult business model, however. If your customers have trouble putting your products together, it will cost you in terms of technical support, and in terms of reputation. Because of this, and perhaps because of attention span compression in the modern age, kits come and go.

From the 70s into the 80s, amateurs who built their own gear (and who truly understood their own gear) became increasingly rare. So many simply purchased commercial gear and became “appliance operators” as the options declined. More educated and motivated operators might fix broken gear as a way to build a station cost-effectively. Into the 90s, the transition into higher levels of silicon integration and surface-mount technology made the equipment nearly unserviceable except for the most committed folks.

In the early 21st century, though, bright spots are entering. The internet makes all sorts of information accessible to anyone that wants to look for it. Open source software (where the source code and licensing are available to anyone that wishes to work with it), and the culture that came with it, opened the door to open source hardware. EDA/design tools are now sometimes available for free, whereas they used to cost monumental amounts. In short, for those that wish to invest themselves into Making Their Own Stuff, it is now possible in ways not possible before. Still, it does require an investment of self to succeed.

Example: mcHF, started by Chris, m0nka, in the UK, and supported by a cast of others. They’ve designed a small, SDR centric HF rig that you can build if you’re willing to invest yourself a little. The design is released under non-commercial usage constraints, and PCBs are available for nominal cost. In short, it’s a reasonable way to get exposed into the current state-of-the-art in “smart” radio technology.

I’ve been watching the project for several months now, and finally decided to dive in, with 2 pairs of boards (one pair for a working radio, one to hack on), arrived yesterday:

IMG_1522
mcHF RF and UI Boards

Design-wise, this is the kind of project that, if I had the time, I’d love to have undertaken myself. On the other hand, my engineering background is more software and systems with a little RTL thrown in; even though I understand how the hardware works, I’m not sure I’m up to designing one from scratch with this technology. Troubleshooting/modifying/improving it, however, may help me learn enough to cross that design threshold. Besides, it looks like fun.

What’s compelling about mcHF is that it’s an SDR design; that is to say that the modulation/demodulation/filtering (all the “magic” radio stuff) is done in software instead of captive hardware. This does two things; it reduces the cost and complexity, while enabling changes or improvements in functionality without requiring hardware redesign.

(Ironically, I spend a lot of my professional time with software, and I dabble in this space because I want the distraction of playing with hardware, not software. Go figure…)

I suspect that the future of HF operating is really in digital modes; the really interesting and useful future things will happen in digital, and this is just the kind of open platform to make hacking in this space possible.

So, I’ll try to work on one (actually two). Watch this space…