A 1-60 MHz coverage VFO with built-in amplifier and variable output level from 1 to 4V p-p.
Midnight Design has been on family
vacation for a few weeks.
Tech Topic: DDS-60 Spectral Purity Study
Tech Topic: DDS-60 Temperature Analysis
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
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 reduced 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. The amplifier offers unconditionally stability (k>1) and yields spectrally-clean signals with harmonics down about 40 dB from the fundamental. It is an ideal signal source for serving as a VFO in the HC908VFO, as a measurement source in the Poor Ham's Scalar Network Analyzer (PHSNA), or 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.
(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 OrderSaving builders the hassle and uncertainty of soldering small surface mount components & IC's.
Assembled & Tested DDS-60 cards ... in stock!
Kits ... in stock!
Page last updated: March 21, 2018