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VHF_Synthesiser_withAD9859.php   12224 Bytes    16-07-2014 00:20:10


VHF Synthesiser with AD9859 :: "RF-2859"



Yet another nifty tool for your lab !



  FREQUENCY RANGE

  1 MHz ... 140 MHz (software limited)

  FREQUENCY RESOLUTION

  1 Hz

  OUTPUT POWER

  - 18 dBm ... + 13 dBm

  SYSTEM CLOCK

  Onboard 400 MHz Oscillator

  NEEDS

  External 10 MHz or internal OCXO ;-)




VHF Synthesiser with AD9859 VHF Synthesiser with AD9859

The Devices mainly consists of a Power Supply, the DDS board and an Attenuator as well as an Microprocessor board.




Power Supply



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.

VHF Synthesiser with AD9859




DDS Board



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.

VHF Synthesiser with AD9859




Attenuator



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.

VHF Synthesiser with AD9859




Attenuator Performance



VHF Synthesiser with AD9859 VHF Synthesiser with AD9859

VHF Synthesiser with AD9859 VHF Synthesiser with AD9859



Microprocessor Board



The Microprocessor Board mainly consists of an ATmega 128. It mayst be equipped with an Lantronix ETHernet interface. (Software not available).





Commissioning • Kissing awake that thing ;-)



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.

VHF Synthesiser with AD9859

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.

VHF Synthesiser with AD9859





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t1 = 3943 d

t2 = 310 ms

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