Having now made up two DDS boards that worked first time, the kit is ready to
go...
Andy G4JNT.
AD9852 Direct Digital Synthesiser Module
This DDS unit is capable of being clocked at up to 300M Samples./ second, so
can be used to generate a signal from DC up to approximately 100MHz with a
resolution of micro-Hertz. The module, when completed, contains a clock
source, the DDS chip, power supply regulators and a PIC microcontroller to
allow a simple interface for programming over a serial link to a PC. Once
frequencies are programmed, the settings can be saved in non volatile memory
for automatic start up next time power is applied.
As well as generation of CW signals, the chip is capable of generating
automatic Frequency Shift Keying between two arbitrary frequencies, amplitude
control and automatic ramping and chirp generation. All these features can be
accessed over the serial link.
An external clock input can be used, and the on-chip PLL multiplier allows this
to be multiplied between 4 to 20 times, meaning that a 10 MHz reference signal
from a high stability oscillator can be used to directly give a clock of 200MHz
which in turn will allow any frequency up to approximately 70MHz to be
generated.
Power output is approximately 4dBm and pads on the PCB allow the components for
a 5th order elliptic low-pass filter to be installed.
The unit is built on a double sided PCB with plated through holes, board
dimensions are 93 x 58mm. A 3.3 Volt voltage regulator needs to be mounted on
a separate heatsink, but apart from that components are SMT types fitted on the
top side of the PCB. The module will run from a power supply voltage between
6.5 to 15 Volts. Current consumption depends on the clock frequency in use but
is typically about 500mA for a 240MHz, reducing to around 200mA for 30MHz
clock.
G4JNT Part Kit.
The part kit contains the PCB, AD9852ASQ chip and a programmed 16F84 PIC for
the controller. The rest of the components need to be supplied by the user,
and these consist of chip resistors and capacitors, two voltage regulators,
crystal oscillator module (or other frequency source) and a small ferrite
transformer for matching the output. This last item can be omitted and
replaced by two resistors if 6dB lower power output is acceptable.
Assembly and use instructions are supplied, but to gain full advantage of the
device's capabilities, these need to be read in conjunction with the data sheet
for the AD9852 available from www.analog.com. The only other item needed will
be a PC running Hypertrm serial driver software, or any other serial terminal
capable of plain ASCII text at 19200 baud.
Software Support
A virtually limitless set of control functions can be programmed into the PIC
controller, and at some point a rotary encoder / LCD display system will be
written to allow a complete single box DC to VHF synthesiser to be constructed.
The PIC is configured for on board programming, or alternatively can be
mounted in a socket.
Purchasers of the kit will have free software support if the PIC can be self
programmed, (this may be possible at some microwave and LF roundtables)
alternatively PIC upgrades will be available from myself at prices to be
announced.
Price and Availability
The part kit costs £60 (60 GBP) including post and packing to UK addresses
and is available directly from myself QTHR:
To avoid posting contact details on an open web site, contact via EMail first:
ACTALBOT(at)SOUTHSURF.COM
|
