Building transverters for 23, 13 and e.g. 9 cm in the nineties was a tedious job.
First hurdle was building a local oscillator (LO). Typically a crystal oscillator
between 90 – 100 MHz was multiplied towards the desired LO-frequency.
After some fiddling and tuning lots of sky trimmers several milliwatts (mW)
of LO signal was obtained to inject into mixers.
Nowadays building LO’s is a piece of cake due to enormous developments in PLL technology.
Analog Devices released a PLL chip with an internal oscillator some years ago: the ADF4351.
Despite very interesting specifications, these kind of PLLs reside in very small (SMD) packages.
Fortunately some ‘evaluation boards’ exist, making experimenting much more easier.
A few weeks ago I found such an evaluation board on Ebay for around U$ 25.
Despite the fact that these boards may contain a ‘fake’ ADF4351 (an ADF4350 with ’4351′ on it)
I gave it a try (Google on ‘ADF4351 evaluation board’).
Alain F1CJF made a signal generator with a similar evaluation board and an Arduino.
However, for my purpose his approach was too complicated for me. I don’t need displays, buttons etc.
Therefore I consulted the ADF4351 datasheet and started programming myself.
As gadget I wrote a simple beacon keyer in conjunction with the PLL initialization code.
This code may be optimized/simplified when inserted into an ATTiny13a or similar microcontroller.
ADF4351 control pins LE, CLK and DATA are ‘onboard grounded’ with 10k resistors. Interfacing
a 5V Arduino is simply done with 5k6 series resistors because the ADF4351 operates at 3.3V.
When the code is entered into an ATTiny13a (or similar small 8 pin DIL microcontrollers) and
powered with 3.3V, interfacing the PLL board is simply a matter of connecting wires and we’re done!
Below a picture of my test setup with an Arduino NANO is presented (click on image to enlarge in a new tab).
Here is a short movie how it sounds on 2320.829 MHz (when programmed for 2320.850 MHz).
What you see is a FT-480R (old skool 2m allmode rig) with an old skool DC8UG 13cm transverter
in receive mode. Keying of the ADF4351 is done with bit5 in R4.
The onboard 25 MHz (TCXO?) evaluation board reference results in a ‘reasonable’ frequency
stability (doesn’t sound bad eh ?) but is a bit off (i.e. -21 kHz) frequency.
Goal is to use a GPSDO reference for ultimate precision and stability.
Here is my Arduino ‘sketch’. No libraries, just plain code. Have fun! : -)