I am very impressed by your knowledge Yves!
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My spectrum analyzer is fixed now - at least sort of fixed.
My fix was to replace C75, change from 3.3 pF to 2.2 pF.
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Conditions after the fix:
300 MHz VCXO is 299.922 MHz with 10 MHz Ref disconnected. When 10 MHz Ref is connected it is 300.000 MHz.
Maxed VTO_Tune (-13.27 Volt) gives VCXO of 300.026 MHz.
VTO_TUNE with connected 10 MHz Ref is -8.61 Volt (still some area left to -13.27 Volt).
CAL FREQ, CAL AMPTD and CONF TEST goes through without any problem.
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My Q12 bias voltage is 5.168 Volt so that was ok from start.
CR81 capacitor was not fitted in my unit.
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It was very fun to dig into this problem with your help!
This is the first time I use the HP spectrum analyzer - I have only used a TinySA Ultra before.
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Anders
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