Why are the 169Mhz circuits biased as class C, while all other frequencies are biased as class AB? What is it about the lower band that predicates class C?
As far as I know this is not a requirement, that design was created this way at the time. The creator of that design is on vacation this week, but he will provide a more accurate answer on this question as soon as he is back.
When the PA operates at lower frequency such as 169MHz, there are some high spurs on other frequency in the PA output. When i add the parallel resistor with the matching capacitor, the spurs were vanished, and the fundamental power is better than before, thus it tuned the match into C-type.