The E1938A has both an ALC loop (common in many oscillators) plus an AFC
loop, which is exclusive to the patented bridge stabilized circuit. I
am thinking that maybe the AFC circuit was causing the hump. That
theory could be verified by disabling the AFC and seeing if the hump
goes away. The AFC is not necessary just to make the oscillator play
for noise testing.
Rick N6RK
On 12/25/2021 9:38 PM, Bruce Griffiths wrote:
Was it related to the cause of the hump in the PN plot vs offset frequency that
the E1938A exhibits?
Bruce
On 26/12/2021 17:56 Richard (Rick) Karlquist <[email protected]> wrote:
I'm sure I said that ... a long time ago. I can't remember now what the
fix was, but I am fairly sure it would only apply to phase noise at
more than 1 kHz offset. If anyone can jog my memory about it I might
be able to remember the details.
Rick N6RK
On 12/25/2021 2:09 PM, Stewart Cobb wrote:
Rick Karlquist mentioned some time ago that the phase noise of the E1938A
could have been improved by a simple change, but the production managers
were unwilling to apply that change because there was no customer demand
for it.
What was that change, and is it feasible for a skilled hobbyist to make
that change on an individual existing unit or two?
Cheers!
--Stu
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