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Azur Electronics

The HP 33312B Coaxial Switch is a 4 port transfer switch that can be used to insert or remove a component to/from a signal path, or switch between inputs and outputs.  The 33312B cost $630 in 1988 and has been superceded by the 8763A.


Bandwidth: 10MHz to 18GHz
SWR: 1.25:1 to 12.4GHz, 1.4:1 to 18GHz
Insertion Loss: <0.5dB @ 18GHz
Isolation: >90dB to 18GHz
Switching Speed: <30mS

September 2007

Bought on eBay. This Coaxial Switch requires a momentary or fixed 5V to switch contacts. HP recommends a 7404 Inverter, DS75351N Driver, 7406 Driver to build a circuit for this.

February 2008

Bought 4 off SMA(m) to BNC Cables to make a test setup, limited to 2GHz approx.

January 2017

More investigation into a control circuit. The RF switches are 'break before make'. The DS75351N Driver is obsolete, a logic control circuit is only required if remote control from a TTL pulse or HP-IB is required. A simple 5V is adequate with either solenoid pins 1 or 2 grounded. After the switch is fully latched (30ms), the drive current is automatically disconnected.

Azur SCU119 Switch Control Unit
A Switch Control Unit was built in a plastic box and for portability a 9V Battery was used as the power source.  This 33312B has Option 011 which is 5V drive rather than the standard 24V.  A 5V Regulator circuit drives the 33312B and a SPDT switch selects which solenoid pin is earthed.  The SMA to BNC cables limits the bandwidth to 2GHz approx.  See also HP 8761A SPDT RF Switch for operation to 18GHz.

Front and rear views of Azur SCU119 Switch Control Unit
This is a useful accessory.  It can be used to: switch one input to either of two outputs; or switch one of two inputs to one output; or switch a device (attenuator, cable, filter, mixer, test item, etc.) in and out of circuit.  This all saves time when making repeated measurements.