Transceiver Architecture 2.18
The Final Filter
I am so glad that my brain works while I sleep as that often keeps me out of trouble or at least may minimize some downstream trouble.
When I awoke the other morning I got a message from my brain about the effect of stray capacitance and the design of my compact board. The pads as cut are 0.5 inches by 0.5 inches and there is a pad to pad capacitance as well as a pad to ground plane capacitance. So I took my handy AADE LC meter and measured away. Boom the pad to pad capacitance is in the range of 3 PF and fairly consistent from pad to pad and the pad to ground is higher in the range of 4 PF. So those values are in parallel with what I am soldering to the board. Thus I need to re-look at the values I have chosen for the caps and this may negate the need to have trimmers installed.
It may take a day or two but this is a precision crystal filter and thus will need to rethink the install. There has also been traffic on the illuminati reflectors about capacitor Q and how this impacts the use of caps in various tuned circuits. I purchased precision MLCC 1% caps so I am not starting in a deep hole for those who will be quick to email me about the Q of capacitors. I have been advised accordingly so am aware of this concern. Thanks Greg.