A second try at the PPS board, this time with the correct footprint for the transistors on the sine-to-square input stage.
Still some bugs left as I had to add a diode on the MCLR pin for the PIC-programmer to work correctly.
Here's a new revision of the RF-mux board, with a 10-pin ribbon cable for +5V, +3.3V, and SPI-signals from an Arduino MKR Zero.
An evolution of my PICDIV-board from 2016. Takes 10MHz input and produces 1PPS (one pulse per second). This one has a TADD-2-mini inspired sine-to-square converter on the input (far left), a PIC12F675 with Tom van Baak's PICDIV-code (right), an ICSP-header for programming, and output-buffers inspired by the pulse distribution amplifier. A 3-position DIP-switch (middle left) allows config-changes, and a blinking LED indicates 1PPS (middle right).
Fixed a few bugs in the first PCB-revision and will order boards for version two soon. Eventually to be published on github/ohwr - stay tuned..
Update: Insertion-loss measurement with a spectrum analyzer:
RF-multiplexer v2 board in enclosure, controlled by Arduino Due with Ethernet Shield. SATA-cable for 4 SPI-lines (SI, SO, SCLK, CS).
When issuing commands to change state as fast as possible this combination seems to do a state-change in about 45 milliseconds - this is not verified on the RF-side (didn't measure that there is actual RF contact made/broken in those 45 ms).
Version two of the RF Multiplexer adds more relays to the 8 pcs HF3 I was using in the first attempt. The added relays keep the RF-path from the selected input to the COM-output as clean as possible with no unterminated branches or stubs. The cost is anothe 7 relays with associated darlington-drivers and control-logic.
Next test is to see if there is any measurable change to the rise-time of a fast pulse-edge, e.g. from a distribution amplifier.
This is the fourth version of an interface board to Small Form Factor Pluggable optical transcievers (SFPs) with a bandwidth of >500 MHz. These are useful for various time/frequency experiments, with a measured frequency stability of <1e-13 @ 1s (in 0.5 or 5 Hz bandwidth) - perhaps slightly depending on what SFP is used. The SFP allows sending the signal along a single-mode fiber for 1-100 km easily.
ADT2-1T converts to and from differential signals while LMH6702 op-amps provide 3 dB gain. There are parallel outputs on the RX pins. The current-draw on +3V3 by the SFP is quite high - usually requiring heat-sinking on the voltage-regulator
KiCad files available on request.
And now an entry in the "Plan to throw one away" section.
RF Multiplexer, 8 inputs, 1 output, BNC-connectors, TE HF3 relays specified to 3 GHz, an ULN2803A to pull the relay-coil, and an SPI I/O expander to drive the ULN - should be easy - right?
Well no, PCB trace-geometry does strange things beyond VHF. I clearly don't grok UHF very well.
Onward towards version 2! (any thoughts and advice on simulation or trace-geometry optimizers appreciated!)
For isolated 1PPS distribution I made this distribution board.
The input is a TLP117 (or similar) optoisolator driving a LT1711 comparator with a 1.0 V trigger level. An output LED-blink is provided by LTC6993. Outputs are driven by IDT5PB1108 buffers.
In jitter measurements with a HPAK 53230A counter the jitter between two 1PPS pulses (from masers) seems to degrade slightly through this amplifier: from RMS 16-19 ps directly on the maser-outputs to between 21 and 26 ps RMS from the outputs of the ISOPDA. Maybe a faster optoisolator would be better?
KiCad sources available on request.