15nov10

Sections:
rack 12.14: generate delays for T/R switch
rack 12.16: control of transmitter.
Example setups:

• Example 1: 430rf=45,430Beam=45,50rf=20, ipp=1000.
• Example 2: 430rf=45,430Beam=45,50rf=45, ipp=2000
  

Notes:
See also: 430 Mhz Tx timing

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Control room chassis: (top)

    The 46.8 MHz transmitter (I also refer to it as the 50 Mhz xmter)  has two chassis located in rack 12 in the receiver room:

Rack 12.14. Generate delays for t/r switch

    This chassis is labeled 46.8 MHz xmiter and  is located at rack 12.14. Its function is:

• What the box does:
• input from extTtlIn.
  
• chop 10 usecs from the start of this pulse and output it to RFON.  The rf is delayed 10usec from the t/r switch going to xmit. This protects the rcvr when going from rcv to xmit.
• add 2,0, or 14 usecs to extTtlIn (depending on 2,0,14 switch) and output this as the T/R output. This is to protect receiver when going from xmit to rcv.
  
• Inputs
  
• ext ttlIn. This can generate the beam,rf for the 46.8 Mhz xmiter.
  
• It can come from the sps rf pulse, sps beam, spsUse50Mhz.. (depends on the duty cycle).
  
• ext/int switch should be on ext to read ext ttlIn
• T/R falling edge extension: 2usec, 0 usec, or 14 usec. Usually set at 2 usec.
•  This is the delay added to the end of ext ttlIn before going to  T/R output.
  
• Outputs:
  
• T/R  
  
• rises with ext TtlIn
• falls 2,0, or 14 usecs after ext ttlIn falls (depends on 2,0,14 usec switch)
• RFON
• Rises 10 usecs after ext ttlIn rises. This lets the "beam" get switched on.
• This delay is generated by this chassis.
  
• Falls with ext ttlIn.

The picture below shows the rack chassis and the relative timing of the signals

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Rack 12.16: input signals for 46.8 MHz xmiter. (top)

• key to turn on xmiter. There is a N minute warm up delay.
• T/R  SWITCH.
  
• switches between transmit and receive.
  
• It normally comes from rack 12.14.
• It is limited to a 5% duty cycle.
• If > 5% duty cycle then alarm goes off and no rf output.
  
• It should come on 10 usecs before rfon goes high.
• It should stay high for about 2 usecs before rfon goes low (to protect the receiver).
  
• RF ON
  
• This turns on the rf.
• It must have no more that a 2% duty cycle.
•  If > 2% then alarm will sound and no rf is xmited.
• It can come from
•  rack 12.14.
• sps rf, spsbeam, or spsuse50Mhz.
• In this case user must verify
•  10 usec delay T/R rise to RFON
• 2 usec delay RFON fall to T/R fall.

Example setups:  (top)

Example 1: 430RF=45,430beam=45,50RF=20,IPP=1000 usecs

• this is used by john matthews for meteor studies.
  
• sps setup:
• spsipp               : 1000 usecs
  
• spsBeam          : 45 usecs
  
• spsRf                : 45 usecs
• spsUse50Mhz : 20 usecs
• Connections:
• spsRf -> 12.14 ext ttlIn
• 12.14 T/R -> 12.16 T/R
• 12.14 RFON not used
  
• spsUse50Mhz -> 12.16 RFON
• 12.14 delay switch: 2 usecs (but 14 usecs is also ok)
  
• Duty cycles:
• Beam 430: (45+10)/1000 = 5.5%
• T/R 50     : (45+2)/1000   = 4.7%
• RF 50      :  (20)/1000      = 2.0 %
  

• Timing:
• 
  

Example 2: 430rf=40,430Beam=40,50rf=40, ipp=2000

• This was used for the chirped meteor studies.
  
• sps setup:
• spsipp              : 2000 usecs
  
• spsBeam         : 40 usecs
  
• Note: the sps software adds 10usecs to the user requested 40 usecs.
  
• spsRf               : 40 usecs
• Connections:
• spsBeam -> 12.14 ext ttlIn
• 12.14 T/R -> 12.16 T/R
• 12.14 RFON -> 12.16 RFON
• 12.14 delay switch: 2 usecs (but 14 usecs is also ok)
  
• Duty cycles:
• Beam 430: (40+10)/2000       = 2.5%
• T/R 50     : (40+10+2)/2000   = 2.6%
• RF 50      :  (50-10)/2000       = 2.0 %
• Timing:
• 
  

Notes:  (top)

• The 50 Mhz has a 2% rf duty cycle and a 5% t/r switch duty cycle.
• The 430 Mhz has a 6% duty cycle max.
  
• The keyword use50Mhz is a numeric value that specifies the duration of the use50Mhz output bnc.
  
• This pulse is right justified in the 430 Mhz rf pulse (if it is less).

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