Faezahn Clock feedthrough refers to the magnitude of the MCLK signal relative to the fundamental frequency in the output spectrum of the AD In this technique, the component side of the board is dedicated to ground planes and signals are placed on the other side. Refer to the AN Application Note for more information. To achieve the best performance from the decoupling capacitors, they should be placed as close as possible to the device, ideally right up against the device. This is to ensure that the output impedance aad the internal switch does not change, affecting the spectral performance of the part. However, these are nonlinear and not easy to generate except through piecewise construction.

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I still do not know what the abbreviations PS and PSY stand for, although I was able to deduce what to do with one of them. Glen Wilson very kindly sent the following corrected figures, and explained the abbreviations that had puzzled me. According to Mr. Low selects one of the pre-programmed frequencies as stored by the Arduino program; a high will send the other. Pselect is similar [but] selects different phases for PSK modulation.

Many hours went down the tubes in a variety of failed attempts to communicate with the AD before I came across a tremendously useful test sketch authored by Alexander C. Frank, and originally written for the AD The sketch may be found near the bottom of this page.

The PCB master clock frequency is stamped on the crystal photo left. To adjust Mr. That is in fact the only thing I changed in the sketch. One other very minor clarification When entering a test frequency and waveform type via the serial device use ASCII 10 newline as the command terminating character.

Generated sine and triangular waves are output via the Sine1 jack, while square waves are output via the top-mounted jack. The oscilloscope probe was capacitively coupled for the test sine wave shown above 7. In other words, while the Square wave output is centered on 0 volts, the triangle via Sine1 is centered on half its P-P voltage, and the sine output would be also if the probe were not capacitively coupled. The drop-off in output with increasing frequency is greater than I recall seeing from the AD Above 30 MHz the signal is messy, and hardly measurable.

Of course, these readings reflect breadboard wiring, with a ohm load resistor. A better result might be expected from an improved test setup. It occurred to me that the two programs sketches could be combined and that one Nano would suffice for both FSK and controlling the DDS.

Blending the two programs turned out to be easier than expected. It was unclear at first how to turn transmit OFF, but specifying 0 Hz for the frequency worked!

For the audio FSK demonstration in the first part of the preceding video, output from the DDS was fed to the computer sound card line-in jack. In the second part of the video, the AD was configured to generate RF at 7. According to my calculation, output power was less than 1 milliwatt. However for this demo, transmit and receive antennas were only about 50 feet apart. For this exercise, the receive antenna was a length of wire hanging over the stairwell, no more than 10 feet from the transmit antenna!

On the right SDR receives the 7. Observe that decoding lags a couple of characters behind the sender. All this started as a small-scale exploration of the AD At some point I wondered whether DDS output could be boosted sufficiently to drive the Pacific Antenna watt linear amplifier. That would mean increasing the output to a few hundred milliwatts at least. Unfortunately I know almost nothing about RF amplifiers. An obvious next step was to examine a few example low-power RF circuits, such as the Pixie or the One-Watter both described near the top of this page.

I also found a couple of circuits on the Internet covering the power range of crystal oscillator to fractional-watt output. Although differing in detail, these reference circuits exhibit common features, which I attempted to understand and duplicate. A little bit of experimentation with different components or values and two stages of amplification eventually led to a potentially exploitable result.

So far so good, although the second stage transistor got very hot. To address the heat problem, I fabricated a heat sink from aluminum bar stock and a ring terminal. The idea of using a ring terminal for bonding the heatsink to the TO came from the Pacific Antenna QRP amplifier project, where a ring terminal is used to draw heat from a diode.

Loose wires are the bane of breadboard construction—the greater the component count the more likely it is that something will work loose. So it was with the amplifier. Sometimes it worked and sometimes not, so I reconstructed the circuit on a generic PCB, more or less the same as it was, adding a PTT relay and some test points. Sometime later a transistor lead broke due to the heatsink bending whenever the board was turned over, or from accidentally setting my coffee cup on it.

When this happened, I unsoldered the transistors and installed 3-hole headers so that the transistors could be easily replaced or exchanged for different values, etc. But that was later. First I hooked the PCB preamplifier to the watt linear. In fact, transmit keying was not consistent. When fortune smiled, the tuner meter moved. Yes I know it is ugly, but h owever that may be, in my world when the meter moves the experiment must count as a success!

Of course, something is not right. How could a resistive load reflect a third of the power? To investigate further I have ordered a few bigger transistors, with a view to adding a third stage to the preamplifier. To be continued, maybe This does not happen often and was therefore especially gratifying, although an acrid smell lingered for several hours afterward.


AD9833: Difference between AD9833 and AD9834

The model number is a specific version of a generic that can be purchased or sampled. Status Status indicates the current lifecycle of the product. This can be one of 4 stages: Pre-Release: The model has not been released to general production, but samples may be available. Production: The model is currently being produced, and generally available for purchase and sampling. Last Time Buy: The model has been scheduled for obsolescence, but may still be purchased for a limited time.



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