Tuesday, January 31, 2012

Learn to sail then travel to amazing places

I do not post about my vacations but this one was absolutely amazing because it shows the value of learning how to do something old school, in this case sailing, then using it to facilitate an incredible life experience.

My friend Brian has more details on where we went this past January with a google map itinerary and additional photos here: http://pletchtrip.blogspot.com/2012/01/british-virgin-islands-sailing-trip.html

In summary; learn to sail, have fun, and travel to amazing places.

Tuesday, January 24, 2012

DIY Phased Array Radar Demo for MIT IAP 2012

A demo using the DIY Phased Array Radar system made from pegboard and wi-fi antennas.

The purpose of this system is to show students how phased array systems work by actually building one.

Monday, January 23, 2012

DIY Phased Array Radar using pegboard and wi-fi antennas

I am very excited to report that I am one of the lecturers for this very unique MIT IAP short course in radar, where teams of 3 build a digital phased array radar system using $950 in parts using pegboard, wi-fi antennas, and a  handful of other parts.

The abstract for this course can be found here (scroll half-way down).

The creators of this class include:
Dr. Bradley Perry, Dr. Jonathan Paul Kitchens, Dr. Patrick Bell, Dr. Jeffrey Herd, Dr. Gregory L. Charvat.  Brad Perry is the lead and has done an amazing job putting everything together!

This phased array radar system is a switched antenna array based on my previous work on thru-wall imaging here.

The radar back end is in fact one of the coffee can radar systems, where you can build your own here.

Complete documentation and lectures from this phased array radar course will be posted on the MIT OCW site soon so that you too can build your own phased array radar using pegboard and wi-fi antennas.

If that is not enough, anyone can sign up for this course offered by the MIT professional education program: http://web.mit.edu/professional/short-programs/courses/phased_array_radar_sensor.html

Sunday, January 22, 2012

News Flash: MIT Students measure the doppler signature of a shopping cart, with someone in it

Vinay Ramasesh, Kevin Fischer, and Emily Davis measure the doppler signature of a shopping cart traveling down a concrete slope.  To be discussed tomorrow at the MIT IAP '12 radar course.

Friday, January 13, 2012

re-winding an RF coil in a Colin B. Kennedy model 20B

Even after re-stuffing the decoupling caps my CBK 20B was still not working properly.

It turns out that one of the primary windings was broken in one of the 3 high-Q RF resonator transformers.  

Removing the transformer was difficult (see photos above).  I had to remove a bottom panel then bend-out small metal tabs, and break-free the glue that glued the top of the transformer to its shield (very unusual construction techniques are used in this radio compared to most old radios that i've worked on).

I un-wound this coil and found the break about half-way in, probably due to the bad decoupling capacitors.

After re-winding it the radio still did not work well.  It turns out that the wiring in the schematic did not match the factory wiring in my radio.  No surprise, as my AF output tube is different (class A as opposed to push-pull) and a few other things.

I touched the grid cap on the first RF amplifier and the radio came to life.  I then traced the circuit from the primary of the first RF transformer to a potentiometer on the front panel.  It turns out that the RF input of this radio goes directly through a potentiometer which is ganged with the control grid potentiometer which controls the volume.  This was not a bad repair job, it was factory wiring cable laced in, etc etc.

I removed this wiring and tied the primary to the antenna input and radio came to life.  Very sensitive as expected, but a new problem was noticed.

The control grid rheostat is not working well.  I think there are open windings or the bushing is not making electrical contact with the wiper.

Stay tuned for more....

Friday, January 6, 2012

Colin B. Kennedy Model 20B radio repairs

Recently had some new problems occur with my CBK 20B:

The RF decoupling capacitors on each stage of the TRF circuit were going bad.  At least one or more were shorting out.  I neglected to replace these initially because they were in nice metal enclosures, but after watching some of bandersontv's videos on re-stuffing caps i decided to re-stuff these.

The caps look great, but the radio still did not work properly.  Stay tuned for more...