Ramsey Electronics COM3010 User Manual page 51

STEP-1 CALIBRATING AN ISOLATION TEE (ISO-T)
1. You must calibrate the Iso-T to 40dB first in order to insure sufficient isolation and to
accurately measure the receiver sensitivity.
2. The COM3010 is set up to generate at the repeater receiver frequency.
3. Attach cables, 50 ohm load and Iso-T as shown in Figure-1 below.
4. Set the generator to -60 dBm
5. Loosen the locking nut on the Iso-T and slide the adjustable stub until the receiver
display is exactly at -100 dBm
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SET COM3010 TO REPEATER RX FREQ
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STEP-2 RECEIVER DESENSITIZATION TEST
1. Disable the repeater function.
2. Attach a local microphone (or have a local PTT switch you can use)
3. Monitor the received signal through the local speaker only.
4. Set up the 3010 for SINAD test, attach to audio point as needed.
5. Set up the COM 3010 to generate the repeater receiver frequency.
6. Attach the already calibrated Isolator T into the transmission line as shown in Figure-2.
7. Start by injecting a signal, set generator to achieve 12dB SINAD.
8. This will be approximately -115dBm. Remember to calculate the actual value you are
setting the COM3010 to an output level that is 40 dB greater due to the insertion loss of
the T. Since you have already calibrated the isolator T for 40 dB of insertion loss you
simply add the loss to the generator output to arrive at the repeater's true sensitivity.
9. For example if the generator is set to -75 dBm, simply add 40dB to arrive at -115 dBm
actual output.
10. Record the transmitter turned off 12 db SINAD value
11. Key the transmitter with the local microphone or local PTT switch.
TYPICAL TEST PROCEDURES
FIGURE-1
ISO-T CALIBRATION
40 DB CALIBRATED ISOLATOR
T ADAPTER (ISO-T)
50 OHM LOAD
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