[time-nuts] Re: E1938A phase noise improvement

[Richard (Rick) Karlquist]

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 <richard at karlquist.com> 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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