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Posts Tagged ‘Soldering’

Spectrum Analyzer Aluminum Frame

April 11th, 2012 5 comments

Beautiful new frame for my SA

I haven’t posted for a while.  I’m sorry.  I was being selfish.  I’ve made fantastic progress on my spectrum analyzer build, and it’s so much fun that I haven’t had the will to pull myself away and post about it.

Also, completely unrelated to the build, I’ve experimented with a service called “Cloudflare” as a way to make my site more resilient.  It doesn’t, it’s MUCH worse.  I’m not happy with it at all.  I’ve shut it down, so hopefully once the DNS changes propagate it’ll be more stable.

Anyway, back to topic.  The last post about the analyzer was about the ChipKit digital logic controller.  That was going very well, so well, in fact, that I was able to finally diagnose an intermittent connection problem between modules.  Intermittent problems are always the worst, especially when you don’t trust other components in the system.  The reason this is relevant to the discussion at hand is that the problem only manifests when one of the connectors has pressure one one side.  I needed a reliable way the hold all the modules in fixed positions.

Since beginning this project, I’ve been inspired by the way that two people built their analyzers. Hans’ is probably my favorite.  I took the image below from his photo album in the Yahoo Spectrum Analyzer group.

I love how clean and organized it looks.  Much different than most of the others out there.  His frame has holes that go all the way through the frame, and he has a back cover that screws on.  His coax cabling is made of right-angle soldered-on connectors with what looks like RG-405 hard pipe.

Another inspirational build is Sants.  This image is also scraped from the Yahoo group.

Sant's build

This build is most probably the closest to mine.  The pockets, or wells, for the component side of the boards don’t go all the way through the substrate.  Notice, in both designs, that there is a small lip around the perimeter of each well.  This is there to hold the boards and to electrically connect to the ground vias on the perimeter.  This design also uses right-angle connectors and hard pipe.

With these designs in mind, I sought out the things I would need.  First, of course, was the aluminum itself.  I had looked into McMaster-Carr (hopefully this link works), and a 1/2″ thick 12″ square costs about $40.  Then, my brother suggested looking on eBay.  I was able to find an equivalent sheet for about $30 after shipping.

Frame block layout

Once I had a cool hunk of 6061 alloy in my hands, I started designing the layout of the frame.  I started with OmniGraffle (it’s like Visio) because I could lay it out to scale, and the connections move in a natural way.

Once the layout was complete, I transcribed the design, complete with all the details into AutoCAD.  By this time, about a month passed, and I was able to find someone willing to machine it for me as a favor.  I also got a quote from another friend, which was about $250.  This is a reasonable cost for something like this, in case you’re looking to duplicate my results.

Close up of one of the wells

It took several weeks to get the parts back from the machinist, but the results are totally worth it!  The larger hole was cut with a 1/8″ end mill, and the inner pocket was cut with a 1/4″ mill.  With the majority of the modules, the inner radius is fine.  There were a few exceptions, however.

Small relief for DDS capacitors

This photo shows some of the rework I had to do to accommodate a few capacitors right at the edge of the DDS module.  It’s very difficult to take a picture of a small notch in a shiny material, but hopefully you can see the cut into the side of this pocket.  I made that mostly by making small, successive cuts using an exact-o knife.  The PLO reliefs were a bit more aggressive (there is a power header right in the corner), so I had to use a Dremel cutter bit in my drill press.

Relief for the PLO module

Once important lesson learned in this process is that 1.2″ or 2.4″ set into a PCB specification is more of a suggestion rather than something that you can count on all that much.  I had to sand almost every module to get it to fit.  Once that was done, however, everything fit like a glove.

Making custom coax jumpers

The final piece in the puzzle is the coax.  The perfect jumpers that both the other designs featured were definitely something that I wanted.  It’s possible to get these right-angle SMA connectors from China for about a dollar a piece, much less than the ~$5 that you’ll spend at Digi-Key.

Connector end, ready for solder.

To make them, all you really need to do is measure the coax sections, strip the ends, and solder…

Soldered center conductor

Soldering around the shield of the coax is the hardest part, and it’s not even that bad.

Final product!!

That’s all there is to it!  I’m really happy with how well things turned out.  Certainly something to be proud of.  Over the next few days, I’m going to try to keep posting about the other advancements.  I have a bit of a backlog, so I should be able to keep them coming…



USB to RF Transceiver prototype complete!

December 18th, 2011 No comments

Collection of transceivers

This is just a post to point you over to my new Transceiver page.  I took the work that I did on the MRF49XA transceiver, and added an Atmel AVR USB micro controller.  I prototyped is using the AT90USBKey development kit, and designed a custom PCB that includes the transceiver and an AT90USB162.

I wanted to design the board such that all the “guts” were on the “back” side of the PCB.  The photo above shows the transceiver circuit (surrounded by a strip of track that you can use to solder a “fence” or “can” to manage RF interference), and the AT90USB162 micro controller.  This can be replaced by and 2 series USB micro controller, like the ATMega32U2 or the AT90USB82.  I recommend using the ATMeta32U2, though the first run of boards have the AT90USB162.  I’ve also included a dedicated 3.3v voltage regulator, because the built-in regulator inside the AVR doesn’t have a clearly marked current capacity, and I didn’t want to risk it.  I’ve also included every spare pin from the AVR that was practical.

The other side of the board contains all the user facing parts.  This includes the status LEDs, the SMA connector, USB port, and the boot loader and reset buttons.  My grand idea here was that I could mount a piece of plastic to the component side to protect them, while having access to all the bits I need to use.  In hindsight, this means that it’s a “double-sided load” which is harder to manufacture.  I ended up having to learn a new technique to solder the USB port.  Notice that the can of the USB port covers the pads?  It’s very difficult to solder those on.  It helps to “tin” the pads first, then set the USB port on top of them.  Luckily, the USB port has little plastic pins that keep it aligned.  When you’re pressing down on it, just hit it edges of the pads with the soldering iron, and it should solder just fine.  When that’s finished, solder the mounting tabs on the sides.

Also, the buttons I bought aren’t “process compatible” which means that you can’t wash the board with them installed.  To deal with this, I reflow solder the entire board, then put them in my new ultrasonic jewelry cleaner with time isopropyl alcohol and brush them with a toothbrush, finally rinse off the alcohol and dry with compressed air.  Once the board is cleaned, then I solder on the buttons.

Lessons (mostly) learned?  Think about how you would assemble something when you’re designing it!!  Building the board this way adds 15-20 minutes of assemble time.  Bummer.

PDFs of the transceiver PCB artwork.  Sorry it’s so ugly, the “high quality” rendering in Gerbv doesn’t work in mac os anymore. transceiver-top transceiver-bottom

Component side artwork

User side artwork

Also, here is are the gerber and eagle design files: Design files.

Work on the software is ongoing.  Click on the transceiver’s main page (link at the top) for updates.  Enjoy!



Helical Quad Antenna for Weather Satellites

October 23rd, 2011 12 comments

Finished and installed antenna!

It didn’t take long after my first successful attempt at receiving weather satellite broadcasts for me to realize that I would need a much better antenna.  I had been using a 1/4 wave whip with a 4-wire ground plane.  There performance out of this antenna was poor.  I read up on QFH (Quadrifiliar Helix antennas) from many of the high quality posts from around the world.  I took what I could from these implementations, and did my best with the supplies I had available.

Read more…

Homebrew bubble counter

October 19th, 2011 14 comments

Counting bubbles during secondary fermentation

For a while now, my friends and I have been brewing beer at my house.  I was inspired by an old Sparkfun tutorial about a bubble logger for Nate’s terrible wine.  I figured that while logging bubbles is interesting and all, wouldn’t it be more useful to have real-time information on the fermentation process?  I basically copied the optical gate method of counting bubbles, added a sensitive pressure sensor, and an AVR development board (Yes, Arwen, that’s your old TekBots board! :) ).  Read more…

SKY65116 Amplifier

September 15th, 2011 1 comment

Amplifier breakout board

I’ve finally gotten around to assembling a breakout board for the Skyworks SKY65116 UHF amplifier.  It’s really amazing how the state of the art in RF ICs has advanced.  They can still be on the expensive side ($6 at digikey), but still relatively cheap when you consider the cost of all the support parts that it takes to build an amplifier from a RF transistor.  This particular amplifier has a 50 ohm input and output, and 35dB of gain.  It works from 390Mhz to 500Mhz, which means its perfect for the 70cm ham band.  The breakout board is stupid simple, copied directly from the evaluation board schematic in the datasheet,  but I’ll include schematic and design files anyway. Read more…