An "easy" home built frequency synthesizer

Download the ExpressPCB schematic file

A good 10 Mhz reference is a requirement if a clean LO is desired. This is very important. Cheap TTL square wave oscillators as used in clock applications might be useful for marker generation, but will not allow the performance potential of the chip to be realized.

This does not appear too remarkable at first glance, however this chip has, onboard, the VCO,  loop filter  and dividers. This means that it will work without a great deal of fuss and very little test equipment. It can be programmed with a PIC that costs less than $2.00.

The SI4112 is generally useful as the LO for transverters that require a crystal in the range of 90 to 120 MHz or 180 to 240 MHz.  The synthesizer VCO covers  about 526 MHz to 1000 MHz, and the synthesizer output can be divided by 1, 2, 4 or 8. This results in frequencies between 65 and 119 MHz, 130 - 238 MHz, 260- 476 MHz and 526 to 1000 MHz. This project was deliberately limited in scope, to be small and hold down cost.   I am using this in transverters for 220, 903, 2304, 3456, 5760, 10368 and 24192 MHz.

For most of what I have done, it has been easiest to remove the original LO board and drive the transverter directly. This is also useful to generate marker frequencies. through 1296.1 MHz.

Here is some guidance on writing the registers in the PIC that load the frequencies into the synthesizer.

March 27 2010  I just ordered another round of boards and parts, and the total, per board, including shipping, is about $45.00 USD.

Click here for source code Note that all of these files are FREE, not guaranteed, but have been built and tested. 

ordering boards from ExpressPCB  

Download the ExpressPCB board file

Schematic file here   

Data sheet for SI4133 family  (you have to read between the lines, as this data sheet covers all synthesizers in this family of parts.)

What is needed to build a system