CategoryElectronics

RF-multiplexer, 3rd prototype

This is the third prototype for the 1:8 RF-multiplexer (https://www.ohwr.org/projects/rf-mux-8ch). The board is now simplified with only one 10-pin ribbon-cable attaching it to the Arduino MKR Zero + Ethernet shield. Traco PSU for 5V supply.

10MHz-to-PPS board, rev2

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.

1PPS output is phase-coherent with the 10 MHz input.
10 ms long 1PPS output, ca 2.7V into 50R load.
PPS-board, rev2. sine-to-square at the top. Sync-input and dip-switch in the middle. PPS-outputs at the bottom.
PPS into 1 Megaohm - with ringing and 3.3V amplutide..

Arduino MKR Zero + Ethernet Shield

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.

Arduino stack: Ethernet shield, MKR Zero, and MKR proto shield

PPS-board prototype

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..

PPS-board 2018 August prototype. Note bypassed sine-to-square circuit on the left.

Multiplexer, 2nd boxed version

The second multiplexer prototyped, with a slightly larger enclosure placing the Arduino Due + Ethernet Shield directly in the front panel. This requires desoldering the DC-connector on the Arduino Due.

Bandwidth, insertion loss, and pulse-shape distortion measurements should be done next.

Mux-in-a-box

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).

RF Multiplexer - version 2

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.

500 MHz SFP-board (v4)

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.

RF Multiplexer - first try

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!)

Aivon LTD makes FDA/PDA ohwr-design

My open-hardware design for a 1:8 pulse and frequency distribution amplifier is now available from Aivon LTD.

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