DDS-60 Daughtercard

A 1-60 MHz coverage VFO with built-in amplifier and variable output level from 0 to 4V p-p.


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Assembly & User Manual Quick Assy Guide  |  Builder's Notes  |

Article:  "Working with Surface Mount Technology (SMT) Parts"

Tech Topic:  DDS-60 Spectral Purity Study

Tech Topic:  DDS-60 Temperature Analysis

Sold Out! ... A new batch of Kits is being prepared 

    A number of years ago we introduced the original DDS Daughtercard ( to the QRP community, providing a low cost and modular way to add a precisely-adjustable 0-30 MHz signal generator to one's project. All you had to do was add an AD9850 DDS chip and +12V, and then any number of popular microcontrollers could control the DDS Daughtercard to have it serve as a rock-solid VFO.  Over 1,000 of these little cards were sold!

    Well, there is still a demand for this inexpensive card and an ever-growing list of uses for it so we updated the basic design and are now ready to provide the new_and_improved  DDS-60 Daughtercard. This self-contained functional module generates a good-quality RF signal from 1-60 MHz by using a small pc board to contain just the bare DDS essentials – an Analog Devices AD9851 DDS chip, a clock oscillator, a 5th-order elliptic filter and an adjustable-level RF amplifier.  Additionally, an onboard 5V regulator is provided so you only need provide a battery or power supply ranging anywhere from 8-12V DC. The three digital control lines, the power supply, and the output signal are all available on a pin header at the board edge, and the DDS-60 is pin-compatible with the original DDS Daughtercard.  The schematic is shown below on this page.

      The 8-position pin header at the board edge serves to allow DDS-60 to be plugged into and used in any project you might have on your bench, regardless of which microcontroller is employed. Just provide a single strip socket (e.g., a 16-pin IC socket split lengthwise) on the project board and plug in the DDS Daughtercard. Heck, you don’t even need a dedicated microcontroller – use a cable connected to the parallel printer port of your PC and use public domain PC software to control the DDS board!  See the Ways to Use section for a number of custom solutions for you to easily control your DDS-60 daughtercard.

      Once your controller-of-choice serially loads the 40-bit control word into the DDS, the raw waveform is presented to an elliptic filter that removes unwanted high-end frequency components, resulting in a signal of sufficient quality to serve as a local oscillator for a transceiver. We regularly see great signal quality, with harmonic content down to about –40 dB.

        The signal generated by the DDS chip itself is quite small so we use an AD8008 low power amplifier to provide about 18 dB of gain to boost the signal to almost 4V p-p, which is 40 mW or about +16 dBm into a 50-ohm load ... quite usable in a variety of applications. This amplifier chip replaces the single-chip MMIC amps used in earlier versions of the DDS Daughtercard. The amplifier offers unconditionally stability (k>1) and yields spectrally-clean signals with harmonics down about 40 dB. It is an ideal signal source for making impedance measurements in the Micro908 Antenna Analyst and other demanding designs. A trimpot allows precise setting of desired output levels.

The amplified signal is then presented to P1 pin 6 on the pin header where it can be used as a 50-ohm source input signal. If not used as an input to any other component or module, the output should be terminated with a 50-ohm resistor in order for the stated specifications to be realized.

      Power requirements: 8-12V DC at 130 ma (typical).  
RF Output – fully adjustable to +16 dBm, or about 4V p-p into a 50-ohm load.  
Output signal not affected by varying +V supply voltage – great for battery operation. |
Near-constant output level from 1-60 MHz. (1.8 dB droop due to sinx/x sampling theorem)
Good signal purity – harmonics down approximately 40 dB from the fundamental.
      Pin-compatible with the original DDS-30 Daughtercard module (Easy changes to the AD9850 software drivers.)


(Download full-resolution PDF version of the schematic)

So, what can you do with the "DDS-60 Daughtercard"?
There are many ways for you to use the DDS-60.   For example, all you need to do is combine it with your favorite microcontroller project to form a high-quality VFO.  Click here to see many ideas!

To Order

The "assembled & tested" version of the DDS-60 card is out of stock.  A new batch of DDS-60 KITS is being prepared and should be ready by mid-February.

Not currently in stock.  Kit availability expected in February.

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Page last updated:  January 2014