AD9851 EME167 DDS KITS
Thursday 5th January 2011

EME167 KIT1 DESCRIPTION

The EME167 KIT1 is ideal as a simple VFO for many Radio projects, & produces a +10dBm sinewave output from DC to 70MHz. The description below is for those that are wanting to know if this Kit is suitable for their own application.

The Kit comes complete with detailed circuit & construction information including schematic & board overlay diagrams. The Basic EME167 KIT1 can be used for various applications using your own Microcontroller & software, or it can be used with the Mini-Kits EME170 DDS controller Kit to construct a simple DDS VFO, or SWEEP Generator. More information on Mini-Kits DDS controller & software is available on the DDS VFO webpage.

The EME167 PC Board was designed to use the AD9851 10 bit 180MHz chip but can also be used with the AD9850. The Kit is for constructors that have some experience in soldering SMD components, with many of the conventional sized SMD components being easily fitted. This Kit may be a challenge for some with soldering the AD9851 chip to the board, so Mini-Kits does offer a service at extra cost to fit just the chip, & also can provide fully built Kits.

EME167 KIT2 DESCRIPTION

The EME167 KIT2 is ideal as a simple VFO for many SDR Radio projects using switching Mixers, & produces two 90 degree phase shifted I/Q square wave outputs up to 35MHz.

The Kit comes complete with detailed circuit & construction information including schematic & board overlay diagrams. The Basic EME167 KIT2 can be used for various applications using your own Microcontroller & software, or it can be used with the Mini-Kits EME170 DDS controller Kit to construct a simple I/Q DDS. More information on Mini-Kits DDS controller & software is available on the DDS VFO webpage.

The EME167 PC Board was designed to use the AD9851 10 bit 180MHz chip but can also be used with the AD9850. The Kit is for constructors that have some experience in soldering SMD components, with many of the conventional sized SMD components being easily fitted. This Kit may be a challenge for some with soldering the AD9851 chip to the board, so Mini-Kits does offer a service at extra cost to fit just the chip, & also can provide fully built Kits.

FURTHER INFORMATION

The AD9851 is a +5v device & has been interfaced to a 16 Pin IDC I/O header plug C1 to make it easier to connect to a Microcontroller board. When the Kit was developed, it was decided to just use the common connections that are normally used in AD9851 DDS projects. So the IDC header only supports serial load, & does not support parallel load of data to the AD9851. The 16 Pin IDC I/O connector C1 has the following pin connections available.

A number of resistors, R1, R2 are used on the board as links that may not be required for your application, but are required when using the EME170 PIC Controller & dd_synth ver2.x software. See the Kit schematic diagram for where the resistors are located.

The PC Board is a professionaly made board & has single analogue & digital power supplies & ground. No attempt was made to use separate supplies & grounds as the improvement to reduce noise would have been minimal.

The standard clock module that can be ordered for the Kit is a 30MHz 5v HY-Q QXO-14BAA 100ppm CMOS 9x14mm module. This requires the use of the internal x6 multiplier to get a 180MHz clock.

EME167 KIT1

The DDS output uses a 70MHz 5th order elliptic Low Pass Filter, which is used to reduce the aliases & quantization noise from the DAC outputs. This allows us to use the maximum recommended output frequency of 70MHz from the DDS for a 180MHz clock. To keep the Kit simplified, no transformer has been used on the DDS DAC output. A Gali amplifier with a gain of +25dB & a IP3 of +38dBm was chosen as it was much lower cost compared to more complex amplifier designs. The DAC current RSET has been adjusted to provide a good Spurious Free Dynamic Range, & drives the high gain Gali device to around 1/2 its capable output power to produce a clean +10dBm output. With reference to the fundamental output @ 0dBm, the 30MHz clock is -55dB, 2nd Harmonic -32dBc, 3rd -55dBc, all other spurs are
> -50dBc

EME167 KIT2

The circuit uses both DAC outputs from the AD9851 DDS & feeds one through the high speed comparator & a 70MHz low pass filter to a divide by two circuit. This produces two 90 degree phase shifted squarewave outputs at 1/2 the DDS output frequency. The maximum I/Q squarewave output frequency is 35MHz which is half the DDS output frequency, & this allows a simple SDR project up to 35MHz to be constructed.

EME167 KIT CONSTRUCTORS ALERT

There are no alerts at this time. For any problems with your kit, please refer to the kit faults & modification section below.

KIT FAULTS & MODIFICATIONS

1/ Low RF output from the DDS Board. There are a number of things that can cause this. The most common is one of the chip capacitors in the RF path is cracked. Other things that can cause this is, the 10uH choke not being soldered to the board, or one of the Gali-84 leads being shorted to ground, which turned out to be a solder bridge under the Gal-84 pins.

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