The Devices mainly consists of a Power Supply, the DDS board and an Attenuator as well as an Microprocessor board.
The device may be powered by Mains via a Traco Power Supply (TXL015-15S) or by a + 15 V Source supplied by a LEMO connector.
The Power Supply Board consists of a DC/DC converter to generate the + 5 V. A relais switches the + 15 V and the + 5 V.
The 'OCXO' output is always powered on.
The DDS board consists of a VCO running at 400 MHz. It is phase locked to 10 MHz via a PLL. The output of the DDS
is low-pass-filtered via two SCLF-135 from MiniCircuits. An amplifier provides some gain to achieve the + 13 dBm.
The Attenuator board was designed using Relais (for educational reasons). It is possible to switch
attenuators of 0.5 dB, 1 dB, 2 dB, 4 dB, 8 dB and 16 dB. A total attenuation of 31.5 dB is possible.
This solution works fine up to 200 MHz.
In order to make this thing work, you need to calibrate it. A
Logarithimc detector is connected to the output.
A Voltage divider is used therefore, that the TL7702 switches at exactly + 13 dBm. (On the Microprocessor Board)
The ATMega128 does increase the amplitude as long as the input voltage is 'low'. If 'high', the value will be stored
in the internal eeprom and the frequency is
increased by 1 MHz. The Calibration process is started by pressing the button on the Microprocessor Board.
Note : You must calibrate this device. You will see nothing at the output unless you connect a very sensitive spectrum analyser ;-(
10 MHz Reference
The Software checks periodically, if the 400 MHz VCO / PLL is locked. The Display shows the lock-status.
Here the vco is free running, as no 10 MHz reference is connected.
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