20m RIG Test 5 Setup


The DDS frequency is measured with the PIC instead of calculating
A 12.800 Mhz TCXO (Temperature Compensated Xtal Ocillator) is used to clock the PIC and also the timebase counter inside the PIC
This TCXO is ripped from an old NOKIA NMT, where you can also find two SBL-1 Mixers.

After experimenting with this solution I have found out that it works OK, but the time it takes to measure the frequency is too much.
So I have now dropped the counter solution, and made a calculation instead, this is much faster only 1.2mS for the whole Frequency to DDS word calculation
But now the DDS clock (128Mhz) needs to be more accurate and not have a big temperature drift,
This can be done using The 12.8Mhz Temperature Compensated Osillator, that I have from an old NMT.
It can be done with a X2 and a X5, but this will also multiply any small drift by 10,
so the best way is to make a VCO that runs at 128Mhz and lock it to the 12.8Mhz TCXO reference
with a PLL, this is the best way to make a good and stable 128Mhz for the DDS.

But more about this later.. See test 6 it's done now, only a week later !

BACK