DDS-60 Kit from the AmQRP

DDS-60 Kit

A 0-60 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

NOTE: R19 Upgrade Available

NOTE: The new pc boards for this round of the kitting have been received from the vendor and we can now resume shipping!
All outstanding orders are being shipped today and tomorrow (April 18/19) via Priority Mail (or by Air Mail if to Canada or overseas)
and they should be delivered starting April 22. We are sorry for the delivery delay this time - we otherwise routinely ship within 5 days
after receiving the order. Thank you all for your patience and support, and please let me know if you have any problems or questions
with your DDS-60 Kit. (My address is at the bottom of this page.)
Regards, George N2APB

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

Schematic

(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, 6361 Berrybush Ct., Gilroy, CA 95020. Within a week or so Mike will be able to solder on your DDS chip and return it by mail. You can contact Mike by email at wa6ouw@aol.com if you have further questions.

To Order

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 n2apb@midnightdesignsolutions.com or use the links below.

(NOTE: When an order is placed through PayPal, a confirmation email is immediately sent by PayPal.
We also receive this same email, so please rest assured that we have logged your order into our
books. Other order confirmation notices may not be issued. Your kit will be shipped in 1-2 weeks
after our receiving the order, unless otherwise stated. Thanks for your support.)


            US & Canadian orders: $29.50    ( 8.25% tax is automatically added for CA residents.)

            DX orders: $34

            View your PayPal cart:

    Ordering by Mail:

            US & Canadian orders: $29.50    (CA residents: Please add 8.25% sales tax, or $31.93 total.)

            DX orders: $34

                Write check or M.O. payable to "Midnight Design Solutions, LLC" and send to:

Availability
In stock.

NOTE: R19 Upgrade Available (as of April 15, 2007)

Back in April of this year we noticed that the on-board trimpot will only adjust the DDS card ouput level up to about 2 Vpp, whereas the design is capable of generating clean signals up to 4 Vpp. By lowering the value for protection resistor R19, the 4 Vpp maximum can be achieved. A 24-ohm resistor is now supplied for R19 in DDS-60 kits going out the door as of April 15, 2007.

If you already have a DDS-60 card and would like a 24-ohm SMT resistor to use for R19, we'd be happy to get one to you. Just Add to Cart to order it via PayPal, or you may send an SASE or $1 via postal mail to the AmQRP postal address above and we'll promptly send you this little chip resistor.

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Page last updated: May 12, 2008