Wide band power detector to control microwave station


Posted on Feb 4, 2014

The particular interest of the ADL5519 is focused on bandwidth which is specified up to 8GHz (but still usable in 10GHz with reduced dynamic). With two channels, it is possible to measure the power transmitted to the antenna and the reflected wave, to calculate the return loss and block the PTT when problems arise. As I originally destined it to my EME 13cm station the module is controlled remotely by serial interface (RS232 and RS485) to be installed in the antenna 30m away the shack. A simple RS232 VT100 terminal allows the full control of the assembly as the whole software is embedded. The set also includes some additional features such as measuring the temperature of the PA with KTY probes and power supply voltages.


Wide band power detector to control microwave station
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Wide band power detector to control microwave station - image 1
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Wide band power detector to control microwave station - image 2
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The calibration process is the action of putting a well known level at the RF input and entry this level to the microcontroller to correct the measurement error. Of course few points are necessary to obtain good correction and those are frequency dependant. The calibration algorithm finds then the best linear regression minimizing the error over the full dynamic. This process is done by an external test bench based on RF synthesizer and commercial power meter, taking about 50 points Vdetected = f (Pin), and calculating the gain and offset for each frequency. These values are then stored in ROM. The calibration takes into account the linearity error of the detector and the imperfection of input attenuator. The measurement is then displayed directly in dBm. Basically for the kit proposed below two calibration are possible: . Default standard cal (kit#1 and kit#2) accuracy around typ. +/-0.5dB up to 1.2G and typ +/- 1dB for higher freq. . Calibration dedicated to the DetLog board mounted and tested only possible on kit#3. Then the accuracy is around +/- 0.2dB Remark: The calibration algorithm does not work on the frequency axis. It means that between two calibrated frequencies no correction is done. Example: If you want to measure at 3400 MHz you have to use the closer cal, let say 2320 MHz and then correction is not optimal. You could run the built in calibration process at 3400 MHz to calculate the...




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