N3ZI DDS 2

Display showing 1Hz resolution
(0 on the left is memory number)

My first DDS has been very popular, but there have been a few requests for improved performance. The chip I chose for that design was the lowest cost chip available for the HF frequency range. The initial request for expansion was the frequency range, the first version was limited to 20MHz output, but I was able to overclock that inexpensive get to get 30MHz out.

So I have redesigned my DDS, now called DDS2, using a different DDS chip, AD9834. This has many improvements and is only slightly more expensive.
Download Manual

DDS Kit $79 via Paypal

Optional LCD Cable kit $5.95 The LCD cable kit consists of two 10 pin headers, one for the DDS PCB, one for the LCD module, plus a 6 inch flat 10 conductor cable with female connectors on each end. You don't really need this cable, you can just solder wires for the 10 connections, but it makes for a neater and more reliable connection.

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Significant Improvements:

1) 1Hz step size. This was the most requested improvement, and this chip has it. Furthermore the LCD will display the frequency with 1 Hz resolution. I'm going to set the step size to something higher than that, but those of you who demand precision will be able to change the default step size. The LCD display will show 9 digits of frequency (a sign, 2 megahertz digits, 3 kilohertz digits, and 3 Hz digits.

2) No (or very little) overclocking. All these kits will be shipped with 80MHz clock modules. This along with an improved output filter will allow operation up to 34MHz.

3) Fast RIT and FSK. This chip has two frequency registers, and there is a direct connection to select between the two. Switching is instantaneous and phase continuous, you can use it with CW QSK and even FSK (RTTY) is you want. The push switch on the rotary encoder allows you to set the RIT offset, tuning speed, and calibration.

4) Vastly improved Encoder tuning. The dial now operates much like an analog VFO dial. I have an acceleration algorithm that works very nicely, so the push switch for speedup is no longer required. New debounce and other changes make the action smooth like an optical encoder using an inexpensive mechanical encoder. There is no lag for the LCD, and no queuing, no glitches, and catch-up.

5) Phase continuos frequency changes. The old chip had to be turned off then back on for a frequency change. So there was a brief but noticeable glitch. The new chip has phase continuous frequency changes meaning than the instant a new frequency is selected, the output waveform continues smoothly by sloping and the proper rate for the new frequency

Features and Specifications:

1Hz user tuning steps

User settable rate via tuning knob
0.3Hz internal step size.

Glitch free, phase continuous tuning.

Virtually indistinguishable from an analog VFO

Very fast tuning updates

100x faster than my previous DDS

User friendly auto acceleration, with user adjustable parameters.

Advanced debounce and tuning algorithms make the supplied mechanical encoder feel like optical encoder.

User tweekable parameters to accomdate other encoders

Very fast RIT frequency shift

Better than 1ms frequency shift time
Can be used for QSK or FSK/RTTY
Shift amount settable via tuning dial.

Complete DDS kit

Just plug it in, turn the dial, and outcomes your VFO signal.

No computer needed. No Frequency counter required.

A digital display is part of the DDS board, and gives you full frequency readout

Full precision LCD frequency readout to 1Hz resolution

Serial LCD included in the kit
Works with 3rd party LCDs including backlit LCDs More info

80MHz reference included

Fast easy to use, user calibration, push then knob then zero beat to a reference

Digital calibration in extremely fine 1ppb steps. (ppb=parts per billion)

Maximum output frequency of 34MHz

Microprocessor does not limit upper frequency

Frequencies up to 39MHz will work, but with incresed mirror spur

DDS SPECIFICATIONS

Total Harmonic Distortion: -66db dBcf

Mirror Spur supression -60 db to 30MHz, -45 db to 34MHz.
Spurious-Free Dynamic Range (SFDR)

Wide Band (0 to Nyquist) -60 dBc
Narrow Band (±200 kHz) -74 dBc
Performance details

Main output is a filtered sine wave

250mV p-p, when driving 1K load.

Secondary unfiltered analog output

5v Digital square wave output also available

Supports IF+VFO, IF-VFO, and VFO-IF radios.

Expands the frequency coverage of many radios.

Only 1 surface mount part, 20 Pin TSSOP (AD9834)

Solder it yourself, it's easier than you think.
Kitbuilders will do it for $10

Requires 9 to 15 volt DC supply, approx. 50mA, more if a backlit display is used.
10 Memories plus A/B VFO all with their own IF offset setting.

Separate A/B VFO input signal line.

Separate RIT memory & control

IF offsets settable via RS-232 or LCD/Button/Dial

Easy to set RIT from tuing knob

Normal range +/-9.999KHz (1Hz steps)

But can be set up +/-9.999MHz for special applications

Non volatile memory storage of last operating frequency and all memories/IF's
Front Panel components can be remoted (LCD, Rotary Encoder, Buttons)
Top quaility commercial PCB with Separate Analog and Digital ground planes for best output purity.
12v RS-232 port available for setup and debug Interface Manual

Not required for operation

USB possible using inexpensive 3rd party adaptor.
(I have tested several adaptors off of ebay, with both windows and Linux, and they all work fine)

Feature	DDS	DDS2
Maximum Output Frequency	20 or 30 MHz	35MHz
Step Size	10Hz	1Hz
LCD Display Resolution	100Hz	1Hz
Tuning Speed	500ms per step	Instantaneous
RIT	None	+/- 1Hz to +/- 10MHz
QSK support	No	Yes
LCD update lag	500ms	not perceivable.
Cost	$50 to $70	$79 (Complete kit, including PCB, programmed Micro, DDS chip, LCD and Encoder)
Tuning	Discontinuous (glitch)	Phase continuous (no glitch)
Number of Surface mount parts	1 16Pin TSSOP	1 20Pin TSSOP
Memories	10	10
A/B VFO	Yes	Yes
FSK and PSK support	None	Yes
LCD Included	Yes	Yes
Works with 3rd party LCDs	Yes	Yes
Encoder Included	Yes	Yes
Chip Used	AD5932	AD9834
Optical Encoder	Helpful	Not necessary

I still have stock of the original DDS, and will continue to offer those until the PCBs are gone. The new DDS is so much better, I do not plan to continue offering the old one. Some may have noticed that I am now offering the old DDS with a 'no chip' option. I will not be doing this with the new design. Although it is true that hams can usually get a free sample of DDS chips from Analog Devices, I don't want to exploit their generosity too much. The more chips I buy the lower the prices. Analog devices has tightened up the rules on this for factory direct purchases, and I will be buying the new DDS ship factory direct in decent lots to keep the prices low. With the old design, it turns out that I have more PCBs left than I do chips. I had planned to continue to offer both kits. But the new one, especially the tuning, is so much nicer, I felt I needed to close out the old one, so I could get the volumes up on the new one, and thereby get the price down as quickly as possible. Closeout prices on the old DDS kits.