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TYPICAL TEST PROCEDURES

3.20.07 Testing Repeater Receiver Desensitization

Repeaters operate commonly in 2 bands usually at UHF 450 – 470 MHz and 800 MHz.

They are occasionally found in the 150-160 MHz VHF bands as well.

The COM3010, with its high stability accurate signal source using a calibrated isolator T

connector allows you to accurately and quickly verify correct duplexer operation. It is also very

easy to check Receiver Desensitization or what’s often referred to as Receiver Desens. That

occurs when the transmitter in a full duplex system (such as a repeater) interferes with the

receiver, causing degraded sensitivity. A poorly tuned duplexer, or bad interconnect cables are

the primary causes of Receiver Desens.

This tuning procedure applies to any type of duplexer such as Band Pass, Band Pass-Band

Reject or Band Reject square or round cavity design.

Be sure to check the manufacturer’s specifications to verify insertion loss.

The use of the calibrated isolator T assures that the COM 3010 is isolated accurately from the

antenna line. This will prevent the 3010 from switching to the transmitter test mode thus

turning off the internal signal generator.

IMPORTANT NOTES:

Be sure the cables used for duplexer testing are of high quality double shielded type with

the proper connectors. BNC-N and BNC-BNC, RG 142 cables from Pasternack.com or other

communications distributors are a good solution.

You will need an adjustable isolator T such as the RF industries Unidapt T and a good

quality 50 Ohm load.

The Generator output should read -dbm.

The Receiver input should read RSSI –dbm.

Make sure the 3010 has been calibrated.

Set up the COM 3010 to generate and monitor the same frequency. The COM 3010 can be

linked for either the transmitter or receiver frequency.

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Ramsey Electronics SG560 Guía de usuario Pagina 50