[TenTec] DDS PTO replacement for old Ten Tec rigs

Curt Benjamin k8aicurt at yahoo.com
Sat Oct 28 14:48:20 EDT 2017

Well, I started working on the circuit using a 9.6 MHz crystal (I have a bag of them) for the VXO, hoping that that will be a good frequency to mix in order to get 5 to 5.5 MHz. Using a 10uH inductor and a ~30pF varactor, I've got it tuning +/- 2.5 KHz from 0 to 12V (I can tweak this later). The next step, I'll get the DDS to output 4.0875 to 4.5975, amplify and pad it to +7dBm and run both sigs into a DBM (I have a number of SBL-1's I can use).

I'm not really sure how to properly terminate the DBM except maybe terminate it around 200 Ohms (I've seen that elsewhere) with a pad, filter it through a 5.25 MHz fc BPF, amplify and pad it to the level required by the radio.

Regarding the Arduino and using one of the analog inputs for RIT, I don't know how to write it into the code in order to experiment but I was told it would be something like this:

void loop()
  int RIT = map(analogRead(A0), 0, 1023, -1000, 1000);

Supposedly, you use the "map" function to take 0-5V on the analog input (A0 in this case) and "map" it to a value from 0 to 1023 and that value can be used to shift the frequency control word going to the DDS module. I haven't the foggiest as to how to write that in, thus the other (possibly cobbled up) way I'm working on doing it.

Curt, K8AI

>The Arduino analogue inputs provide 1024 level discrimination. 
>Translated to +/- 1000Hz that equates to 2Hz steps. I don't know why 
>that would be considered not smooth enough?
>I sent you the source code by private email yesterday.
>Steve G3TXQ

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