HP 59307A VHF Switch – Frontansicht

HP 59307A VHF Switch
(click images to enlarge)

The HP 59307 VHF switch contains two 4-throw RF switches (built using three SPDT RF relays each), which can be controlled with front panel pushbuttons or via bus commands.

The manual specifies the relays having a load capacity of 0.5 A at 25 V (i.e. 12.5 W at 50 Ω). Usable frequency is given as DC to 500 MHz, with VSWR < 1.25 and isolation of > 40 dB at 100 MHz.

Small light bulbs (not yet LEDs) in the buttons indicate the switch positions.

The back panel carries 10 BNC connectors for input/output, the power and HPIB sockets, and the HPIB address switch.

The RF relays are mounted on a circuit board just behinde the BNC sockets on the rear panel. The main board contains only SSI TTL ICs, nothing more complicated than a 7485 (4 bit comparator) or 74138 (3-to-8 decoder).

Controlling the 59307 is easy - send a letter "A" or "B" to select one of the switches, followed by a digit from "1" to "4" to select the output for that switch.

HP 59307A, rear view

HP 59307A, rear view

HP 59307A, interior view

HP 59307A, interior view

However, owing to the simplistic decoding of characters received from the bus, the 59306 will also respond to characters other than "0"–"9" range as digits — unfortunately, this is also true for carriage return and line feed characters.

Therefore, if e.g. in an HP-85 program, the 59307 (assumed on interface 7, HPIB address 12) were controlled with

OUTPUT 712; "B1"

the computer will silently add CR LF to the end of the string, and the wrong output will be connected.

HP 59307A Detail: Key status light

HP 59307A Detail: Key status light

A close relative of the 59307 is the 59306A Relay Actuator.

There are several ways to sidestep this issue, one of them being to send the command "manually":


This code explicitly addresses the 59307 (Unlisten, My Talker Address, Listen Address 12) and sends exactly two data bytes to the unit.

A more elegant solution uses a feature of the OUTPUT USING statement that is a little hidden in HP's documentation – prefixing the format string with # suppresses the line feed:

OUTPUT 712 USING "#,A,D" ; "B", 1

This and many more details are described in a Programming Note for using the HP59501A with the HP-85.

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