Sunday, 10 November 2013

40 MHz DDS Generator

Last Friday the DDS AD9850 module arrived from China.

                                      The $ 5 AD9850 DDS module has arrived..

Time to unite the module with the rest of the circuit which I had prepared already according to the design of VK5TM:
See also my blog posting of October 25 showing how the control circuitry with 16F628A PIC and display has been designed.

Test set-up. The generator provides a 7380 KHz signal which is monitored by the frequency counter in the back. It was verfied that the generator upper frequency is 40 MHz.

I added a small seperate power supply circuit with a LM317T to provide a 3.3 Vdc voltage for the DDS module. The module is located on the right upper side of the housing.

The sine output of the DDS module is fed to a filter circuit with a cutoff frequency of appr. 60 MHz. 

A 1 transistor output stage with 2N3904 provides some gain.
                                                      1 stage transistor amplifier

Below you see the output of the DDS Generator on my scope. This looks like a real sine form don't you think so?  In this case a 17.460 MHz signal was applied. 6 divisions times 0.4 Volts makes a signal amplitude of 2.4 Volts peak-peak. At the end of the range (40 MHz) the amplitude drops to about 1.6 Volts peak-peak

Anyway, I think we are spoilt these days with nice electronics like this 40 MHz DDS module for sale for under $ 5...


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