[ARC5] TCS Transmitter Tip

[Bob Moody]

Wayne:

40 years ago I was part of a high altitude balloon flying outfit in Palestine, Texas.  (Along with WA5JCI who is in the woodwork here - Good morning Pete.)  These unmanned balloons went above 130,000 feet and carried payloads of thousands of pounds.  We tracked them coast to coast and border to border using Cessna 310 twin engine airplanes.  Radio commands were sent from the airplane to the payload for a variety of functions, one of which was to cut the cable between the balloon and the payload to finish the flight.  The payload would then descend on a parachute for recovery.  In about 1974 we began using a new digital command encoder which had a thumbwheel command selector of ~ 77 discrete commands, and two push buttons, ARM and FIRE.

One "Dark and Stormy night" we were about to terminate a flight.  I selected the TERMINATE command in the thumbwheel window about 1 minute prior to cut-down.  Next I reached over and switched on both engine fuel boost pumps and POW!!!  Here she comes!  The balloon flight terminated spontaneously!  

Well, not spontaneously it turns out.  The inductive kick from the boost pumps tickled the digital encoder which interpreted the spike as a valid FIRE command.  The digital encoder did what it was programmed to do and sent the FIRE command.    Couple of days later at the shop we were able to duplicate the failure.  Diodes across the boost pumps gave us some sense of security.  (I also went to our aircraft overhaul facility and dioded all the spare pumps on the shelf.)  

That incident gave me a heightened awareness of "inductive kick", and a continuing distrust of digital systems.    

Bob    K7IRK
Tillamook, Oregon       



  ----- Original Message ----- 
  From: Robert Eleazer 
  To: arc5 at mailman.qth.net 
  Sent: Friday, November 25, 2016 7:24 AM
  Subject: [ARC5] TCS Transmitter Tip


  Isn't it modern practice to put a solid state diode across relay DC energizing coils?  Given electron tubes' higher voltages and thus their resistance to spikes do we not need to worry about that?

  Wayne
  WB5WSV   


------------------------------------------------------------------------------


  ----- Original Message ----- 
  From: Robert Eleazer 
  To: arc5 at mailman.qth.net 
  Sent: Friday, November 25, 2016 7:24 AM
  Subject: [ARC5] TCS Transmitter Tip


  Isn't it modern practice to put a solid state diode across relay DC energizing coils?  Given electron tubes' higher voltages and thus their resistance to spikes do we not need to worry about that?

  Wayne
  WB5WSV   


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