[time-nuts] LTE-Lite Plans
SAIDJACK at aol.com
SAIDJACK at aol.com
Tue Nov 25 20:28:03 EST 2014
Guys,
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
chip.
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,
Said
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