[time-nuts] LTE-Lite Plans

SAIDJACK at aol.com SAIDJACK at aol.com
Tue Nov 25 20:28:03 EST 2014

I never expected such an intense discussion about using and buffering  the 
outputs from the LTE-Lite board since the actual circuit to use can  be 
quite simple.
To address these questions, I drew up a simple schematic that uses a DIP-14 
 74AC04 gate, six resistors, and two caps. Everyone who can solder should 
be able  to build this simple circuit as a dead-bug type build on a 
copper-clad  board.
This circuit will buffer all three outputs (1PPS, TCXO RF, and Synthesixed  
RF) of the LTE-Lite eval board with CMOS 3.0V levels that can drive 50 Ohms 
 terminations. For simplicity I grab the 3.0V power from the DIP-14 TCXO on 
pin  14 of that part on the eval board, even though I would strongly 
suggest to use a  separate low noise 3.3V or 5V power supply to power the 74AC04 
You can add 100nF caps in series to the two RF signals before they feed  
into the coax output connectors for less power consumption and removing DC for 
 instruments that don't like DC inputs.
Using a single IC for the three signals will result in crosstalk between  
the signals, but it should be clear from the schematics how one could break  
up the signals by using three independent ICs to minimize crosstalk. 
We use this circuit in a small box here using SMT components, and it works  
really well.
Excuse my horrible writing, using keyboards has made my fingers  numb..
Hope that helps,
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