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Test Necessities & Accessories


Precision Mismatches

INTRODUCTION: Mismatches for 50 Ohm lines are terminations which have been designed for terminating lines with a characteristic impedance other than 50 Ohms. For example a termination, designed for reflectionless termination of a 25 Ohms line, will cause a mismatch of 2:1 when used on a 50 Ohm line (50:25 = 2:1).

Applications: Mismatches are used as standards of reflections in calibrating reflectometer setups and/or other impedance measurement devices. Mismatches are also used to simulate known impedances other than 50 Ohms, to introduce test conditions in a system and to measure the results that would be encountered, once the actual component is installed in the system.

Mismatch Values: Standard Mismatch Values for a 50 Ohm transmission line are known as 1.25:1, 1.5:1, 2:1, 4:1, etc. For specific applications any mismatch value can be designed.

Frequency Range: The frequency range of the Mismatches depends on the design. Theoretically Mismatches can be designed for almost any frequency range.
Power: Precision Mismatches are usually designed and needed for test and calibration purposes, operating at low power. For other applications units can be supplied as special, engineered exactly to the customers' needs.

VSWR: VSWR is the ratio of the reflected signal and the incident signal. Mismatches are designed to provide reflectionless termination of a line other than 50 Ohms. For the 50 Ohm line however they show a known VSWR over the frequency range specified. The better the design and the lower the manufacturing tolerances, the more constant the VSWR will be over the frequency range.

Connector Configuration: Most of the Mismatches manufactured by Spectrum Elektrotechnik GmbH are available with different connector configurations, providing that the frequency range of the connectors do not limit the frequency range of the application. BNC connectors operate to 4.0 GHz, HN and SBX connectors to 8.0 GHz, C, SC and 1.8/5.6 to 10.0 GHz, TNC (per MIL-C-39012) operate min. to 11.0 GHz (as per MIL-Specification, but this can be extended to 14 or even 16 GHz). SBY work to 12.0 GHz, 2/5.5 connectors operate to 14.0 GHz, SMA, SPM, N, TNC (per MIL-C-87104/2),TNX, BMA and 7mm connectors can be used to 18.0 GHz, 1.4/4.4 to 20.0 GHz, 3.5mm connectors to 26.5 GHz, or respectively to 35.0 GHz. K* and SMP connectors are designed to operate to 40.0 GHz and 2.4mm connectors to 50.0 GHz.

Standard Products: Although a number of products have been supplied to customer orders, a standard product line on Mismatches has not been established yet. But there is a possibility that the product required has been designed already or that a design, very close to the requirement exists. Therefore please check your requirements with our sales force, or our engineering staff.

Custom Designs: Spectrum Elektrotechnik GmbH has been designing and supplying special Mismatches to suit particular requirements, such as wide bandwidths, unique mechanical outline, unusual mounting or special connector requirements, etc., etc. Operating Temperature Range: It usually ranges from -54C to +125C, or it is even wider. The temperature range will affect the power handling of the devices.
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