AD frequency range: MHz. Square wave: MHz. AD adopts MHz Active Crystal. The module can output two sine waves and two square. IC AD is an ADI DDS chip which be common used in many DDS projects. This AD DDS module is basic on this ADI AD chip. This module provide. IC AD is an ADI DDS chip which be common used in many DDS projects. This AD DDS module is basic on this ADI AD chip.
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The description below may help people who need to adjust an AD module for use in an Ultimate3 kit. A great relief, actually A9850 the Ultimate3 AD module is now manufactured to order in a factory.
This is more expensive but the modules are evidently of a higher quality. Some failed to produce any output at all. There is therefore no squarewave output from the AD on-chip comparator.
Nooelec – AD 40MHz DDS Function Generator Module
Since it may not be easy for many kit constructors to carry out this adjustment, and there are already enough variables, it seems only polite for QRP Labs to supply the module ready-adjusted. Effectively therefore, the kit is simply transmitting a continuous carrier at 10, The second dit speed ensures that nothing could possibly change state that could interfere with any measurement.
The signal at the DDS squarewave output pin 7which is also the same as microprocessor input pin 11, is monitored on a MHz oscilloscope via a x10 probe.
Note that for these tests, the U3 PA is actually disconnected.
The adjustment is quite sensitive, the tiniest movement of the potentiometer affects the output waveform, and for the majority of the potentiometer’s travel, there is no waveform output at all. Note that it is Ok to ignore ringing on dss edges, this is not related to the potentiometer setting. This is how the ‘scope trace looks when the potentiometer is turned all the way anti-clockwise to its limiting position.
AD9850 40MHz DDS Function Generator Module
The adjustment is almost correct here, but still slightly too anti-clockwise. In this condition the Ultimate3 will produce power output, but much less than it optimally should. The adjustment is almost correct here, but still slightly too clockwise. This is how the ‘scope trace looks when the potentiometer is turned all the way clockwise to its limiting position. To test the frequency stability, a simple 30m band direct conversion receiver is used, powered from a well-regulated linear power supply.
The audio output of the receiver is fed into a laptop PC via a Logitech USB headset whose headset has been cut off and replaced by sockets, so that the USB audio ADC can be used to feed good quality audio into the laptop. The result should be a sharp, straight line without any instabilities or wiggles. Upon switch on of a new AD module of course, there is some warm-up drift of the MHz crystal reference oscillator, which shows as drift of the ARGO line.
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This is fine, not a problem. What we are looking for is the absence of short-term instabilities that would show up as easily visible wiggles in this line. The image to the right shows 90 seconds of testing. In practice, seconds is sufficient to show any instabilities. Note that the adjustment of the ddss threshold described above is carried out at 10, in the 30m band.
Some kit builders have noted poor output on 10m, which has been resolved by very very slight adjustment of the comparator potentiometer. Apparently the comparator performance is less good as the frequency rises, so the adjustment mdule a lot more critical.
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AD9850 0-40MHz DDS Module
The following examples are NOT correct oscilloscope waveforms: All the way anti-clockwise: Vds the potentiometer clockwise “right” carefully, until a pulse waveform is seen. Turn the potentiometer clockwise “right” carefully, just a little at a time! Turn the potentiometer anti-clockwise “left” carefully, just a little at a time!
All the way clockwise: Turn the potentiometer anti-clockwise “left” carefully, until a pulse waveform is seen.
Frequency stability test To test the frequency stability, a simple 30m band direct conversion receiver is used, powered from a well-regulated linear power supply.