Thursday, April 8, 2010

The KD8JHJ Bug Tamer

                                                                                        
After a product development and testing phase that has lasted 6 months I believe I have finally perfected the KD8JHJ Bug Tamer.  The picture above shows the Vibroplex Original semi-automatic key with the standard moveable weight installed on the pendulum arm.  The pendulum is connected to the lever of the key by a piece of flat spring steel.  When the lever is actuated the pendulum begins a back and forth oscillation.  This movement quickly closes and opens the "dot" contact creating a stream of  Morse Code "dots" which continue until the lever is released.  
One of the myriad of adjustments available to the bug operator is the sliding weight.  Moving the mass further away from the spring slows the oscillation of the pendulum arm while positioning the weight closer to the pivot point speeds up the motion.  By nature of it's design the Vibroplex is a speed key.  It works at code speeds starting around 25 or 30 Words Per Minute and depending on the skill of the operator speeds of 40 and even 50 wpm are possible.  By contrast the traditional straight key familiar to most as seen in movies and tv produces speeds ranging from 5 wpm to 20 wpm or a little faster if the operator is highly skilled.  In years past the Vibroplex shipped with a weight half the size of the standard weight shown above.  In the early days a Vibroplex typically cost a telegrapher a couple weeks worth of wages so by the time an operator could afford to upgrade he was already proficient at copying high speed code.  In my case even after one year of using Morse Code my copy speed was not up to even the slowest speeds of the Vibroplex.  Because of my desire to use this key on the air for amateur radio at my comfort level of 18 to 20 wpm I would have to either buy or build a means of slowing the pendulum action of my key.
There are commercially made devices available to slow down the dot stream but I thought this would be a great opportunity to exercise the old ham tradition of  "build it yourself" or homebrewing as it is known.  I studied all the pictures I could find on the internet of different designs both commercial and homebrew.  I settled on a design based on the parts I could find at the local hardware store.  The final revision of the KD8JHJ Bug Tamer is shown below positioned to yield sending of about 20 wpm.

The silver weights are steel shaft collars with a set screw that locks down the collar in place.  I found a piece of brass tubing that fit over the round steel pendulum arm.  The locking collars in turn slide onto the diameter of the brass tube and are held in place by their set screws.  Hidden from view is a short piece of solid brass rod about 5/8" long that fills the empty end of the tube that extends out past the end of the steel pendulum arm.  (The brass rod is positioned under the three weights.)
During the testing phase I experimented with different tube lengths and number of locking collars to add more weight and to get an idea of how the placement of mass affected the performance of the key.  My initial version was set up with all the weights at the end of the tube farthest away from the pivot.  During the course of a QSO the whole assembly would slowly creep outwards letting the mass move furthur and further from the spring, slowing down the characters.  To fix this problem I positioned one of the locking collars at the inside end of the brass tube.  Snugging the set screw prevented the slow creep during use yet remaining loose enough to allow the bug tamer to be moved in and out to adjust the dot speed.
Not only does the position of the mass affect the action of the pendulum but the amount of weight also contributes to the smoothness or lack thereof in the keys operation.  Through my experimentation I was able to get an idea of the parameters of weight and placement of the mass to come up with a design that slowed the action of the key while still providing crisp closing of the electrical contact.  If the mass is too far out past the damper assembly it causes the key to feel "clunky" and makes it more difficult to make accurate transitions between the dashes and dots of the code characters.  In some of my earlier pictures only two weights were positioned at the end of the brass tube and the whole bug tamer would be extended out further.  This did provide crisp feel but the dots seemed softer or "mushy".  Adding another weight and running the bug tamer closer in to the pivot point let the contact close with more authority and seems to produce the nicest sounding dots. 
The Vibroplex is a wonderful mechanism and makes a great test bed for tinkering if one is so inclined.  I believe that this exercise has helped me to better understand the intricate workings of the semi-automatic key.  After 6 months using the key on the air I have become confident in my sending with the bug and have received several compliments on my good bug fist.  I truly believe that in order to be a good bug op one has to have a solid understanding of the mechanics of the bug key.  The only way to gain this understanding is to spend time playing with the various adjustments and observing how these changes interact with the operation of the key.  From time to time I do put the original weight back on and do some practice sending but still find it a bit too fast for accurate sending.  As a rule a ham should send out a call at a speed he or she can easily copy as the op who answers the call will usually do so at the same speed.   


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