864 MHz exciter module

 


There are several builds of this module. All use the same multiplier pcb, which is driven at 27 MHz. The differing build is determined
by the actual crystal frequency in use, as below: 

a) 6.75 MHz - requires a x2 x2 multiplier to get to 27 MHz
b) 4.50 MHz - requires a x3 x2 multiplier to get to 27 MHz (in practice, the same pcb as above)
c) 27.0 MHz - no multiplier required.

Details shown apply to the 6.75 MHz oscillator.              
 exciter

Pcb details
One varicap is fed from the on board thermister derived temperature compensation, the other is for PLL control
and has the response below:
PLL volts		 oscillator   

The 6.75 MHz oscillator  pcb feeds the multiplier circuit shown on the right, resulting in the spectrum below.
multiplier O/P spectrum
 buffer


 

multiplier

multiplier top side           multiplier bottom side          864 MHz spectrum

The final two multipliers are not that good at suppressing the drive frequency, but the level is low enough considering the selectivity that follows this module