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DDS-60 Kit
A 1-60 MHz coverage VFO with built-in amplifier and variable output level from 0 to 4V p-p.
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DDS-60 Kit
A 1-60 MHz coverage VFO with built-in amplifier and variable output level from 0 to 4V p-p. |
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View (click for larger image)
Bottom View (click for larger image)
Note: U5 is shown in this photo, but the function
didn't work out well
.
and U5 was removed from the design and from the kit.
.
| Overview | Schematic | Ordering | Availability | Ways to Use |
| Assembly & User Manual | Quick Assy Guide | Builder's Notes |
Article: "Working with Surface Mount Technology (SMT) Parts"
Tech Topic: DDS-60 Spectral Purity Study
Overview
Some three years ago we introduced the original DDS
Daughtercard (www.njqrp.org/dds) 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 (available as a free sample from the good people
at Analog Devices) 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 kit 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 of –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 quite usable in a variety of applications. This amplifier chip replaces the single-chip MMIC amps used in earlier versions of the DDS Daughtercard. Our new amp is much improved compared to the previous design by offering unconditionally stability (k>1) and yielding spectrally-clean signals with harmonics down more than 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.
Specifications
Ø
Power
requirements: 8-12V DC at 130 ma (typical).
Ø
RF
Output – fully adjustable to +16 dBm, or about 4V p-p into a 50-ohm load.
Ø
Output
signal not affected by varying +V supply voltage – great for battery
operation.
Ø
Near-constant
output level from 1-60 MHz. (1.8 dB droop due to sinx/x sampling theorem)
Ø
Good
signal purity – harmonics down approximately 40 dB from the fundamental.
Ø
Pin-compatible
with the original DDS Daughtercard module
Ø
Only
few changes needed in existing 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. Essentially, all you need to do is combine it with your favorite microcontroller project to form a high-quality VFO. Click here to see lots of ideas!
Getting a free sample of the AD9851 DDS chip
The AD9851BRS DDS chip is not provided in the kit because homebrewers can obtain a free sample from the Analog Devices website at: http://www.analog.com/en/prod/0%2C2877%2CAD9851%2C00.html). Just go to this Internet location, register with Analog Devices (i.e., give them your mailing address), and within a week or so you will receive a free sample of the DDS chip by mail.
Need help attaching the DDS surface mount chip?
If
desired, the NJQRP has lined up a great resource to assist in soldering the SMT
integrated circuits onto the printed circuit board. Once you’ve acquired your
free AD9851BRS DDS chip from Analog Device, send the DDS chip, the op amp chip
and the digi-pot along with your DDS-60 circuit board to Mike WA6OUW, at “KitBuilders”.
For $10 he will attach all three surface mount chips to the pc board and
return it promptly by mail. It’s not tested because at that point it’s only
the DDS chip on a bare pc board, but Mike does excellent work. (The NJQRP uses
KitBuilders for assembly of the HC908 Daughtercard product, so we know the
quality is there!) Just place your DDS chip, pc board and a $10 check or M.O.
payable to “KitBuilders” into a padded envelope and send to: KitBuilders,
The DDS-60 Kit costs $29.50 (US & CAN) and $34 (DX) and we'll have lots of them ready to ship. You can order the DDS-60 Kit electronically by PayPal, or by conventional postal mail.
Ordering electronically by PayPal to
or use the links below.
Ordering by Mail:
US & Canadian orders: $29.50 (MD residents: Please add sales tax.)
DX orders: $34
Write check or M.O. payable to "Midnight Design Solutions, LLC" and send to:
Availability
In stock.
Page last updated: October 19, 2008
