On 2006-08-04, W3JDR wrote:
unmarked coupling cap feeding into U4A is probably just a large value "DC
block", since the U4A stage design will have a fairly high input impedance
and so will not substantially load the tuned impedance step-up network.

That was my assumption, however when I replicated that part of the
circuit, I found that when U4 was at 8V, the signal picked up a LOT
of phase noise. I'm assuming that the 10k feedback resistor that
biases the inverter for linear operation was back-driving the tank.
Or perhaps it's the fact that in the inverting amplifier configuration
the XC of C20 is required to set the gain at a reasonable ~3x instead
of essentially infinite. In that case I should have been able to
use a .1u + 3k R for the same effect.

Anyway, I've found this tiny bit of circuitry to be very informative!

--
Ben Jackson AD7GD

http://www.ben.com/