EME167 AD9851 DDS Kits

AD9851 DDS EME167 Kit1

Basic EME167 AD9851 DDS Kit

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There are two versions of the EME167 DDS for different applications. The EME167 KIT1 is ideal as a simple VFO for many Radio projects, and produces a +10dBm sign wave output up to 70MHz. The EME167 KIT2 is ideal as a simple VFO for many SDR I/Q Radio projects using switching Mixers, and produces two 90 degree phase shifted square wave outputs up to 35MHz.

 

EME167 DDS-VFO KIT1 Description:

The EME167 KIT1 is ideal as a simple VFO for many Radio projects, and produces a +10dBm sine wave 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 and construction information including schematic and board overlay diagrams. The Basic EME167 KIT1 can be used for various applications using your own Micro controller and software, or it can be used with either the Mini-Kits EME170 DDS controller to construct a simple DDS VFO, or with the M1-DDS Controller Kit for more complex Receiver or Transceiver project.

More information on Mini-Kits DDS controller and software is available on the DDS VFO and M1-DDS webpages.

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 DDS chip, and also can provide fully built Kits.

The Basic EME167 DDS uses a 70MHz 5th order elliptic Low Pass Filter, but is also available with a 40MHz filter option for use with the M1 Transceiver. The filter helps to reduce the aliases and quantization noise from the DAC outputs, and the 70MHz filter 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 Gali84 amplifier with a gain of +25dB and a IP3 of +38dBm was chosen as it produces a very clean RF output when underdriven from the DDS. The DAC current RSET has been adjusted to provide a good Spurious Free Dynamic Range, and 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 greater than -50dBc

 

 

EME167 KIT1 Top ViewEME167 KIT1 Bottom View

EME167 I/Q-DDS KIT2 Description:

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

The Kit comes complete with detailed circuit and construction information including schematic and board overlay diagrams. The Basic EME167 KIT2 can be used for various applications using your own Micro controller and software, or it can be used with either the Mini-Kits EME170 DDS controller to construct a simple DDS VFO, or with the M1-DDS Controller Kit for a more complex Receiver or Transceiver project.

More information on Mini-Kits DDS controller and software is available on the DDS VFO and M1-DDS webpages.

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 DDS chip, and also can provide fully built Kits.

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

 

 

EME167 KIT2 Top ViewEME167 KIT2 Bottom View

BOARD INTERFACE INFORMATION

The AD9851 is a +5v device and has been interfaced to a 16 Pin IDC I/O header plug C1 to make it easier to connect to a Micro controller 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, and does not support parallel load of data to the AD9851. The 16 Pin IDC I/O connector C1 has the following pin connections available.

 

IDC I/O connector ( C1 )

2 RESET 4 FQ_UPDATE 6 NC 8 SCLK 10 SERIAL LOAD 12 SERIAL LOAD 14 NC 16 NC
1 +5V 3 GND 5 +12V 7 GND 9 NC 11 GND 13 NC 15 NC

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 Mini-Kits DDS controllers and software. See the Kit schematic on board layout diagrams for where the resistors are located.

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

Kit Constructors Alert:

1/ Please be aware when fitting the GALI-84 on the DDS-VFO Kit1 as there is no solder mask on the PCB under where the device is fitted. This can cause the leads of the GALI-84 to be shorted to ground.

Kit Changes and Modifications

EME167- KIT1

1/ Low RF output from the DDS Board. There are a number of things that can cause this. The most common 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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