Category Archives: Amateur Radio

Tony’s Diamond Chop Saw (Part 4)

Finally, I bring you the conclusion of my Diamond Chop Saw series!

In this part I’ll cover a few remaining issues, but mostly I’ll report on my use of the machine in the construction of my 47 GHz radio, for which this project was intended.  If you’re not already familiar with this project, you might want to go back and start by reading Part 1.

Attaching/Aligning the Blade

Attachment of the blade to the hard disk platters (see part 2) sets the basic accuracy of the tool.  If the blade is out of plane the cut will be wider than the blade.  If the blade is off center, portions of the blade will wear faster.  Achieving perfection is virtually impossible, but I managed to get a ‘good enough’ result.

My method was to lay the ring blade down onto the larger platter and use tape to temporarily hold the blade in place while I manually spun it around to check for centering.

Method for centering the blade
Method for centering the blade

A little fiddling and re-alignment will get things pretty close.  After the centering is good, the next step is to glue the blade into place.  I used tiny drops of Zap-a-Gap around the inner edge of the ring and held the two together firmly as the glue set.

After gluding the blade, spots of glue are visible on the top surface
After gluding the blade, spots of glue are visible on the top surface

The result is not perfect, but cuts I have done seem to be sufficiently narrow.

The Cutting Setup

The picture below shows the setup for making cuts.  The large silver box in the background is the vacuum pump, the green vise in front is holding a digital indicator (for making precisely measured cuts) and the blue airbrush is ready for spraying water onto the cutting surface.

Dicing saw setup
Dicing saw setup

The parts to be cut are mounted on glass slides using Crystalbond adhesive, a thermoplastic mounting polymer.

Test substarets about to be cut
Test substrates about to be cut

Using the Chop Saw

Below are some pictures of cuts made with the saw.

A partial cut through one of the substrates
A partial cut through one of the substrates
Several diced pieces.
Several diced pieces.
Microscope view of a part diced into three pieces
Microscope view of a part diced into three pieces

From the photos above it is clear that the saw is working reasonably well.  The cuts are straight, the pieces have no obvious large chunks missing, and the gold metallization shows minimal signs of peeling.  I have made many cuts using this saw including angled cuts.  I have also used the saw to carefully strip off the backside metallization.  This will come in handy when I am making diveboard-style waveguide transitions.  I have also used the X/Y table to feed the piece along the blade, allowing me to make much longer cuts than in “chop” mode.  These came out very nicely as well.

The accuracy of the saw is reasonably good.  Using a dial or digital indicator, cuts can easily be made with 0.001 inch accuracy, which is sufficient for circuits working through 50 GHz at least.

One issue that was of concern initially was whether a hard drive motor actually had enough power to do the job.  It turns out the motor works fine as long as the cuts are made slowly.  Fast cuts are not advisable anyway, as the part is more likely to fly off into oblivion.  Some of the substrates I cut had fairly thick metal backing and required slower cuts.

Future Improvements

Every project ends up with room for improvement.  With this project a few things come to mind including a precision machined spindle with a better mounting mechanism.  This would require a much larger lathe than what I own, and some careful though into balancing.  Another improvement would be a self-contained coolant sprayer and vacuum pump for the chuck.  Setting up the dicing saw currently requires a vacuum pump, an air compressor, and so on.  Another nice feature would be a microscopic camera to observe the cutting in action.  And finally a CNC retrofit would be nice.  All of these upgrades would be handy, but as it is, the saw is immensely flexible and precise.  I’m still on the first blade which is showing no signs of wear.

Conclusion

It has been a lot of fun putting together this series of articles and even more fun putting together and using this saw.  So if you are planning on putting together a saw like this, happy cutting!  If you are just planning on building something with a hard drive motor, they are really handy for certain applications where high precision, high RPMs, and cheapness are required.

Upcoming San Francisco Ham Radio Exams

If you live in the San Francisco Bay Area and are interested in getting your amateur radio license, there are a couple testing sessions coming up in 2010 that may be of interest:

BAERS

The Bay Area Educational Amateur Radio Society (BAERS) is hosting a Ham Cram on Saturday, January 9th from 8AM-5PM at St. Mary’s Cathedral in San Francisco.  The cost is $30 including the VEC fee.

A “Ham Cram” is a one day workshop where you can get your ham radio license (usually the Technician level) without studying in advance.  I’m not sure I completely agree with their methods of blind memorization over actually understanding the rules, but apparently this method works and most people pass on their first attempt.  If you’re short on time and want to get your license in a hurry, this is one option.

Thanks to Robert for the heads-up on the January session.

AERO

AERO is another SF-based group that regularly posts flyers advertising their own ham cram sessions.  Their most recent poster is outdated, but the site mentions there will likely be an upcoming session in February 2010.  I just took the General license exam at their November session and was really impressed by how many people were there and how professionally run the event was.

Update: Their next session is on February 7th, 2010 at 8:45AM.  Details here.

Studying the old fashioned way:

If you don’t like the “cram” method, you can always pick up a study guide (Technician, General, Extra Class) and spend a few weeks studying for the test like I did for both my Technician and General license exams.  There are even a couple online practice tests to help you study.  When you feel comfortable with the material, you can take the exam at the sessions above for a $14 VEC fee without doing the cram.  I know AERO allows this, but it would probably be a good idea to check and make sure BAERS permits this as well.  In either case, I recommend that you RSVP to ensure you get a seat and get notification about changes to the venue, etc.  Contact info for each group is on their respective websites.

Good luck and 73 from KF6PBP!

Ham Radio – Studying for the General Class Exam

When my renewal notice came in the mail, I was surprised to learn that I’ve had my ham radio license for just over ten years.

I received my Technician class license in college shortly after my classmate Tony introduced me to the world of amateur radio.  I started out playing with TNC‘s and packet radio.   Later, with Tony’s help, I built various microwave radios so I could participate in the very active San Diego Microwave Group.  Some of my projects included a 10GHz transverter and a simple 24GHz wideband radio that used a surplus gunnplexer as an RF source, the same kind as found in police radar guns and many automatic door openers.  (Please excuse my ancient webpages, they were cool ten years ago, ok?)

Here I am with my 10GHz transverter in the summer of 2000 during the ARRL 10GHz and Up Contest.

10GHz Transverter
Sun, sand, and microwaves in Santa Barbara.

I also used to be somewhat active on 2m/440 and still have the Kenwood TH-79A radio my Dad bought me after I got my license.  I still use it today, but not for voice communications.  It has a new life now as part of my APRS Tracker project.

After seeing how many hams there were at NOTACON earlier this year, I finally decided it was time to upgrade my license to General class.  This will give me more operating privileges on the HF bands, the traditional low frequency / long distance communication bands that are most commonly associated with amateur radio.  My goal is to set up an HF station at home and maybe start playing with a Software Defined Radio system such as GNU Radio with custom homebrew hardware.

Before my trip to HAR I picked up a copy of the ARRL General Class License Manual and printed out a list of VE sessions in the Bay Area over the next couple of months.  Now that I’m back, it’s time to start studying!

APRS Tracker

APRS Tracker

This week, my brother is relocating from the San Francico Bay Area to Texarkana, Texas.  I’m helping him move, so for the next two weeks we’ll be on a road trip through California, Arizona, New Mexico, Texas, and maybe a little bit of Oklahoma.  We’re planning to see the Very Large Array, visit Truth or Consequences, and check out The Black Hole in Los Alamos.  That is, if the trailer stays connected and we don’t break down too many times on the way.

I though this would be a good opportunity to dust off my APRS tracker so friends and family can watch our progress.

What is APRS?

APRS, short for Automatic Packet Reporting System, is a radio network that uses amateur radio frequencies to relay short messages.  Think of it as a precursor to twitter, developed 20+ years ago by Bob Bruinga, WB4APR.  The messages usually contain GPS coordinates, and they are relayed via radio to internet connected stations that send the data to the APRS-IS network.  Database servers, such as findU, cache the packets so that client software can access them without needing a radio or realtime access to the network.

The coolest client I have seen so far is aprs.fi, a clever mashup of APRS and Google Maps:

APRS map of San Francisco
APRS map of San Francisco

The hardware:

I made this APRS tracking box a couple years ago, so I’m a little fuzzy on the construction details, but it consists of the following parts:

  • A Trimble ACE III GPS module, originally used in a police car, $5 on eBay.
  • An external mag-mount powered antenna for the GPS that I found at HSC, also $5.
  • A Tinytrak3+ microcontroller-based APRS encoder and modem, $30
  • My old Kenwood TH-79A handheld 2 meter/144-148 MHz ham radio
  • A mag mount whip antenna for the HT, found at the electronics flea market.
  • An aluminum box, probably the most expensive part.
  • Some cables to glue all the pieces together, mostly salvaged from my junk box.

The APRS tracker acquires a GPS fix and the current GPS time.  Every so often (fully configurable), it transmits my position over the radio, where it is received by other APRS relay stations in the area.  Speed, direction, and altitude are also included with the position packet.  I connected a piezo buzzer to the TX signal so I hear a beep when the position is transmitted.  Within a few minutes, a point corresponding to the position shows up on the map at aprs.fi or in the findu database.

It’s really neat to play with, especially on long trips.  On a trip to Moab two years ago, my position was received by the APRS network even in areas with no cell coverage, which included most of Utah!

Note that to use the APRS system, you need to have an amateur radio license.  If you’ve ever been interested in amateur radio, this is a really good reason to get your license and start experimenting!