Surplus Parts Box: Bruker 2H Lockswitch Module

Being in want of some more surplus-sourced RF components, I picked up a Buker 2H Lockswitch module. It appears to be part of an NMR multi-band interface solution: AVANCE II with DRU TwoBay. Specifically, I have the 750-900 MHz version. And thanks to the university for retaining and publishing these esoteric pieces of documentation.

Front overview of the 1U chassis with SMA, N, and isolated SMA interfaces, plus power indicator LED

On the outside, there's not really much to it. Refer to the manual, Figure 1.1, for a block diagram, then further in Chapter 1 for specifications, suggested system diagram, and front panel connection diagram. Around back is just the fused IEC power inlet.

Internal overview of the contents of the 1U chassis, from left to right: high speed switch, routing coaxial SPDT relay, control board, hybrid coupler, and linear power supply

The inside turns out to be not particularly fascinating, but still full of repurposable components. There are two SMA/N internal cables, three SMA to SMA bulkhead external cables, and one N to SMA bulkhead external cable. The remaining SMA jacks are on the control board. Let's work through what these components have going for them.

To skate on past them, the control board is some logic, input optocouplers for the isolated inputs, and a relay driver. It's powered by a 7805 and the EP330PC-12 PAL configuration is given in Figure 5.3. The power supply is a low-profile transformer into a tiny diode bridge, big electrolytic cap, and 7815 for the system +15V.

Bruker BLKM 32-160 MHz high speed blanking switcher, as installed

High speed blanking switcher, top components under cover

High speed blanking switcher, top components shielded by the chassis it is installed onto

First up is the "Blanking Switch BLMK 32-160 MHz" detailed in Chapter 6 of the manual. This is an AC-coupled RF switch built around a pair of DH80050 dual PIN diodes, "DIODE PIN SW 10W". These would appear to be the top-side cans in this design. The top results for this part number appear to be surface mount single PIN diodes, so it's hard to tell if this is a special package or naming collision. The RF input port offers a terminated shunt to the TT40 flange load that has a heat sink block in the case. The output port has a 0.25 W 1206 termination. All coupling is done with high quality porcelain RF 1 nF capacitors plus a couple tuning capacitors of the same package. The channel selection is driven by the socketed TSC428CPA 18 V dual MOSFET driver with inverting/non-inverting channel configuration. Based on the series resistors, the open-terminated path uses a bias current of about 10 mA per diode and the through path is about 8 mA per diode. Overall, when powered, the switch is normally open/terminated. A TTL high input on BLK IN closes the switch.

For potential evaluation: port return losses in open versus through states, open/terminated isolation, through loss, and through bandwidth. A reason to actually calibrate my nanoVNA! Switching speeds and transient return loss would be much more sophisticated measurements to take.

Bruker 3dB HP Coupler 100-160 MHz packaged with N connectors on all three ports

Inside reveals the flange mount Anaren 1Z0280-3 hybrid coupler and isolated port termination resistor

Next is the coupler module "HP Coupler 3dB 100-160MHZ" detailed in Chapter 7 of the manual. The primary component is the 1Z0280-3 hybrid coupler rated 100-160 MHz, 23 dB isolation, 0.25 dB IL, 700 W CW. With the isolated port supported by a 150 W termination and limited heat sinking of the module to the chassis, that's where the overall rating will be limited. It looks great for amateur 2m operation, but I don't know how much this is necessary these days.

Freed electromechanical relay: Radiall R570312000

Popping off the relay required getting out the SMA coaxial wrench to get in there. This reveals a 0-3 GHz Radiall R570312000 SPDT, SMA connectorized, 12 V coil RF relay. The model is still in production and in distribution! A classic, really. Requiring a quarter amp of coil drive is where a lot of the system power consumption comes from, too. This will be particularly useful as an output TX/RX relay if I have a build for it.

Finally, I've got a 1U chassis with SMA and N holes in it already for reuse. It won't be really convenient for portable operations, but having something to build in is nice. No airflow might be a weakness if I have any power application. Into the Stuff Collection, for now!