[Premium-Rx] Any expert on RFT EKD-500 out there?

[Werner]

Hi Karl-Arne,

I took measurements in PLL number 2. That is the one that generates the 10Hz, 
100 Hz, 1 kHz and 10 kHz steps. The VCO control voltage from the "frequency 
divider No. 2 unit" going into the oscillator varies between about 2.5 Volts 
for 99.99 kHz (indicated) and then drops sharply to about 1.9 Volts for 00.00 
kHz. The steep gradient obviously is answered by the oscillator by some 
frequency fluctuations causing the tuning noise. Since I have only a digital  
voltmeter I can not see any significant voltage fluctuations.  Maybe some 
capacitors in the oscillators are really aged an do not what they are 
supposed to do.

Regards

Werner

 Am Sonntag, 6. Mai 2007 11:10 schrieb Karl-Arne Markström:
> I am quite sure that this is the result of component ageing in one or more 
PLL loop filters.
> 
> The EKD500 family uses a multi-loop synthesizer, and it is very likely that 
a loop instability or unlock condition is more prone at some frequency 
increments due to the frequency control scheme.
> 
> Such behaviour can however be very difficult to track down as multi-loop 
synthesizers usually influence each other.
> 
> One suggestion is to monitor the VCO control voltage for each loop when 
changing frequency
> and check if there are oscillations or transients on any of the loop 
voltages. Then look for component ageing in the
> loop that shows the largest transients or takes the longest time to relock.
> 
> There may also be a frequency range where this can be more marked due to the 
variation of PLL loop stability margin with tuning voltage and oscillator 
presetting.
> 
> 73/
> 
> Karl-Arne
> SM0AOM
> 
> 
>