Homebrew VHF Synthesiser with AD9859

VHF_Synthesiser_withAD9859.php 14159 Bytes 23-04-2024 14:10:31

VHF Synthesiser with AD9859 :: "RF-2859"

Yet another nifty tool for your lab !

Retired. Please consider the Ningmod as a superior replacement.

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 ;-)

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.

    Schematics 'Power-Supply'
    Placement 'Power-Supply'
    Target 3001 File 'Power-Supply'
    Datasheet TSR 1-2450 (DC/DC Converter)
    Datasheet TXL015-15S (AC/DC Converter)

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.

    Schematics 'DDS' (PLL)
    Schematics 'DDS'
    Placement 'DDS'
    Target 3001 File 'DDS'
    Datasheet VCO 'ROS-425-319+' from Mini Circuits
    Datasheet Lowpass 'SCLF-135' from Mini Circuits

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.

    Schematics 'Attenuator' (page 1)
    Schematics 'Attenuator' (page 2)
    Placement 'Attenuator' (top)
    Placement 'Attenuator' (bottom)
    Target 3001 File 'Attenuator'

Attenuator Performance

Microprocessor Board

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

    Schematics 'Microprocessor' (page 1)
    Schematics 'Microprocessor' (page 2)
    Placement 'Microprocessor'
    Target 3001 File 'Microprocessor'

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.

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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