modules with terminated rf relays for the r&s®osp switch

Example of signal distribution

T

T

T

T

Splitter SPDT relays,terminated

RF receivers

1

Modules with terminated RF relays for the R&S®OSP switch and control platformNew modules featuring terminated RF relays expand the application range of the R&S®OSP open switch and

control platform. The relays terminate open contacts with built-in 50 Ω resistors to reduce frequency-depen-

dent reflections in otherwise unterminated RF cables – a precondition for reliable measurement results.

Termination ensures defined RF operating conditionsOpen, unused paths in an interconnection of several RF devices, e.g. in test systems, can cause inputs of ampli-fiers or connectors of splitters, combiners or couplers to remain open. This produces undesirable effects. Open inputs of amplifiers without protective circuits can lead to oscillation or may cause undefined states at the output. Open inputs of splitters, combiners or directional couplers cause reflections – i.e. superposition of the useful signal and the reflected wave – which influences the parameters of other connectors.

Reflections are avoided by terminating RF circuits properly according to wave impedance. This is accomplished in the active path of an RF circuit through the use of 50 Ω cables and the 50 Ω impedance of the measuring instruments. Ter-minated RF changeover relays are used to prevent any paths from remaining open if the wiring of components in an RF system is changed. These relays are equipped with internal resistors that can terminate open paths into 50 Ω (FIG 1).

Basic architecture of terminated relaysWith terminated relays, the open contact is switched to ground via an internal 50 Ω resistor. FIG 2 shows the basic technical implementation of a terminated changeover relay as well as an alternate circuit containing unterminated change-over relays. The alternate circuit may be required if the power exceeds the magnitude that the relay’s built-in resistor can handle; in this case, suitable external resistors have to be used.

Terminated multiposition relays have a similar architecture (FIG 3).

FIG 1 Distribution of two antenna signals to four receivers via splitters.

When switching, terminated RF changeover relays use their built-in 50 Ω

resistors (blue) to terminate non-active RF paths.

The R&S®OSP open switch and control platform was first presented in News from Rohde&Schwarz (2008) No. 195, pp. 28–31. Another article appeared in NEWS (2008) No. 197, pp. 27–29, describing the new R&S®OSP130 base unit with integrated display (shown below) and the expanded range of modules.

GENERAL PURPOSE | Test systems

SPDT relay concept

SPDT relay, terminated Alternate circuit with unterminated changeover relay

Basic architecture of a terminated changeover relay

c

50 Ω

no

c

nc

Tno

ncc

no

nc

50 Ω

50 Ω

50 Ω

SP6T relay concept

SP6T relay, terminated Alternate circuit with unterminated relays

Basic architecture of a terminated multiposition relay

6 × 50 Ω 6 × 50 Ω

c

123456

1

2

3

4

5

6

c

1

2

3

4

5

6

T

c

FIG 2 Basic wiring of terminated

changeover relays (SPDT).

FIG 3 Basic wiring of terminated

multiposition relays (SP6T).

Overview of R&S®OSP modulesAmong the new modules with terminated coaxial relays for the R&S®OSP open switch and control platform are the two base modules: the R&S®OSP-B121, with three RF change-over relays (single pole double throw: SPDT), and the R&S®OSP-B122, with one multiposition RF switch (single pole six throw: SP6T).

The relays are monostable, i.e. they return to the start-ing position if there is no control voltage. In the case of SPDT relays, this is connection c and nc (normally closed); with SP6T relays, however, all six contacts are open and

terminated. This feature can be used, for example, to ensure defined states during a power failure or at system startup.

Due to the increased volume of terminated relays, the packing density of the modules is lower as compared with unterminated relays. As a result, a standard mod-ule contains only three terminated SPDT relays instead of six unterminated relays or only one terminated SP6T relay instead of two unterminated relays. To accommodate as many relays as possible in the R&S®OSP, mixed mod-ules with terminated SPDT and SP6T relays are offered.

NEWS 202/10 2


3

For example, the double-width R&S®OSP-B123 contains six SPDT relays plus one SP6T relay. The R&S®OSP-B124 module has two SP6T relays and in addition three SPDT relays. This makes it possible to reduce the number of module slots when combining relays. Analogously, the R&S®OSP-B125 triple-width module contains not only the three SP6T relays of the R&S®OSP-B126 but also six SPDT relays. FIG 4 shows a selec-tion of modules, and FIG 5 contains a list of all standard mod-ules currently available.

Connectors Module Symbol Features

¸OSP-B101 RF switch module(1505.5101.02)

6 × RF changeover relay (SPDT), 0 Hz to 18 GHz


2 × RF multiposition relay (SP6T), 0 Hz to 18 GHz


6 × RF changeover relay (SPDT), 0 Hz to 40 GHz


2 × RF multiposition relay (SP6T), 0 Hz to 40 GHz

FIG 5 Overview of modules for the R&S®OSP open switch and control platform.

FIG 4 Selection of available

modules for the R&S®OSP.

SummaryThe addition of terminated relays to the range of available switch modules for the R&S®OSP switch and control platform opens up new applications and simplifies the implementa-tion of switching matrices. A further expansion of the range of modules is in the pipeline.

Gert Heuer


Connectors Module Symbol Features

new ¸OSP-B121 RF switch module(1515.5504.02)

T

3 × RF changeover relay (SPDT), 0 Hz to 18 GHz, terminated


T

1 × RF multiposition relay (SP6T), 0 Hz to 18 GHz, terminated

new ¸OSP-B123 RF switch module(1515.5527.02) T

T 6 × RF changeover relay (SPDT), 1 × RF multiposition relay (SP6T), 0 Hz to 18 GHz, terminated






T

3 × RF multiposition relay (SP6T), 0 Hz to 18 GHz, terminated


6 × RF solid-state relay (SSR, SPDT), 0 Hz to 6 GHz


3 × SPDT

(N)

3 × SPDT

(BNC)

3 × SPDT (BNC), 0 Hz to 900 MHz, (20 W to 60 W), DC: 60 W, 2 A 3 × SPDT (N), 0 Hz to 12 GHz, (700 W to 200 W)

¸OSP-B103 digital I/O module(1505.5301.02)

16

16

16

16

16 × digital input (LV-CMOS, TTL); 16 × digital output (open drain)

¸OSP-B104 relay driver module(1505.5401.02)

Status

4 × 2

28 V DC

Control of four external power relays; additional digital inputs/outputs; interlock

¸OSP-B108 multiplexer module(1505.5718.02)

4

1 to

6

4 …

4

1 to 6, four-wire, (2 A, 30 V; 1 A, < 60 V)

NEWS 202/10 4


modules with terminated rf relays for the r&s®osp switch

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