[NLRS] More on sequencers

[W0ZQ at aol.com]

In a message dated 3/27/2006 4:52:17 P.M. Central Standard Time,  
chrise at pobox.com writes:

These  sequencers are all cool and everything but there is still one
fundamental  problem I don't see getting solved--  namely, how do you
keep the RF  from coming out of the IF rig until all of the other stuff
has been  sequenced?




I have wondered this from time to time myself.   I suspect that  the answer 
is that it usually doesn't matter.  
 
The current modification to the DEM TIS circuit that I am looking at may  
make this worse .... I am looking to use the IF rigs (FT-817) PTT output line to  
key the SMA relay right away, but the circuit will hold off on keying the  
transverter & external 8 watt amp for say 100 ms thus allowing the SMA  relay 
time to switch.   This would prevent hot switching of the SMA  relay.  As you 
point out, the FT-817, since its driving the bus here, has  started to send 144 
MHz RF out its IF line not too far behind when its PTT went  active (low), yet 
the transverter is being held out of transmit mode for 100 ms  by my control 
circuit.   In this case I think the receiver mixer may  see whatever the drive 
level is that is typically being used at the transmit  mixer (for those 100 
msec or a bit less).   Question is, can the  receiver mixer take this power ?   
If so, than it doesn't matter and  this approach should work.   If they 
can't, I blow the receiver  mixer.   
 
So that's the question ; can the receiver mixer withstand the same 144 RF  
power level that is typically directed to the transmit mixer ?    According to 
the DEM parts list, the transmit mixer and the receive mixer are  the same type 
of device, a MA4E2054B.   I suspect the answer is yes IF  you have a well 
controlled (ie; no spikes) IF source.   Any RF  power spikes coming from your IF 
rig would most likely blow the receiver  mixer.
 
Comments ?
 
73, Jon
W0ZQ
 
 
Come and join  us here in Bloomington, Minnesota, home of the Mall of 
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