| https:///weradocs/Measure_Decoupling.shtml |
| 1. | You need an X-Y scope and a step attenuator (1&10dB steps). |
| 2. |
Connect the TX output to the scope's input by a BNC cable
(N-BNC adapter required), terminating the 'scope' end of the cable with a T-connector and 50 Ohms. Select 'test calibration' and '80 Hz offset' from WeraDesk and measure the peak-to-peak voltage. Convert voltage to dBm using the attached table. Now you have TXout in dBm which can be used as a reference. A typically value is TXout = +20 dBm . |
| 3. |
Disconnect the scope and plug the 'ex-scope' end of the cable
to the step attenuator. Set the step attenuator to ~80 dB. Connect the other side of the step attenuator to the receiver input of the antenna nearest to the transmitter (a second N-BNC adapter required). Set the scope to X-Y mode and connect it to the receiver I and Q channels using the Lemo-to-two-BNC test cable. Adjust the step attenuator until you see a circle at +/-8 volts on the scope. You now know the receiver's input power at 80 Hz offset for full scale output: RXin [dBm] = TXout [dBm] - attenuator [dB]. A typically value is RXin = -42 dBm . |
| 4. |
Connect the receiver input back to the antenna cable running outside. Connect the transmitter coax cable through the step attenuator to the TX output. Adjust the step attenuator to read +/-8 volts at the scope again. Be careful not to drive the power amplifier to more than 30 watts, ie. do not switch to values below the value found during WERA set-up section 6.3. With a power amplifier gain of 41 dB, you get TXtoRX [dB] = TXout [dBm] - attenuator [dB] + 41 [dB] - RXin [dBm] , eg. TXtoRX [dB] = +20 -20 +41 -(-42) dB = 81 db . Note that TXtoRX includes all cable losses, but this is correct in this context, as the actual direct path power at the receiver input is the critical value. |
| 5. |
As a quick-check:
Set the offset to 80 Hz, select 'test calibration' from WeraDesk, and connect an X-Y scope to the receivers (one after the other, all along the array). Does the direct path signal give more than +/- 8 volts? If yes, how much additional attenuation is required to get +/- 8 volts? Note, this additional attenuation should be less than 10 db to prevent overloading the receiver. |