![\"IMG_20141010_202053361_web\"](\"http:\/\/www.kv6o.com\/wordpress\/wp-content\/uploads\/2014\/10\/IMG_20141010_202053361_web.jpg\")
<\/a><\/p>\nThe module is being controlled with an Arduino UNO – it sends the desired frequency serially to the DDS chip. \u00a0The Arduino is also attached to a rotary encoder for frequency input, as well as an LCD display. \u00a0In this prototype, the LCD display is showing the DDS frequency, not the VFO frequency. \u00a0I don’t really need a display on the VFO since the DG5 emulator already displays the dial frequency. \u00a0An additional advantage to this is I don’t have to worry about the radio Carrier\/BFO and Heterodyne oscillators warm-up drift as the dial frequency is being calculated using these actual frequencies by the DG5 emulator.<\/p>\n
I put a 0.01uF cap between the output of the DDS and the VFO signal input on the TS-520 to block any DC component present on the output from the module. \u00a0 The stock output was a little low, but worked – signals were a bit low- 3-4 S units as compared to my K3. \u00a0Looking at the datasheet<\/a> for the DDS module, there is a 3.9k ohm resistor called “Rset”, which sets the DAC’s full scale output current. \u00a0I put a 2.2k resistor in parallel with it (just soldered it on top of the existing 3.9k SMD part, you can see it in the pic above) to lower the Rset value and increase the DAC output – bingo! \u00a0Signals are on par with the K3, and signal reports are good. \u00a0I’ll need to make sure I am not saturating the output or causing any distortion – I might need a buffer amplifier if there are any problems. Looked OK on the scope.<\/p>\n <\/p>\n