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

[Karl-Arne Markström]

Dear Werner,

Nice to hear that everything works OK now.

Your experience serves as a reminder that in PLL circuits.
everything affects each other.

When the VCO frequency presetting does not work, the loop remains
in an unlocked condition until the switching transient has died out and the
VCO frequency, often "by chance", has come close enough to the capture range 
('Fangbereich') of the phase detector.

By using 'loop presetting', the designer can make the PLL better in two ways;
first that the sideband suppression becomes better due to the lower frequency deviation
for a given error or noise voltage on the VCO control voltage, and second that the loop
dynamics can be optimized for a given reference frequency and frequency step.

Chapter 7 "Frequency Control and Local Oscillators" of Ulrich Rohde's et al book "Communications Receivers"
can provide more insight in these questions.

73/

Karl-Arne
SM0AOM




----- Original Message ----- 
From: "Werner" <w.r.l at gmx.net>
To: <premium-rx at mailman.qth.net>
Sent: Tuesday, May 22, 2007 7:44 PM
Subject: Re: [Premium-Rx] Any expert on RFT EKD-500 out there?


> Here comes an update on my EKD-500-PLL problem: A least I could isolate the 
> defective portion in the oscillator-PLL assembly. It is a circuit which is 
> called "Fanghilfe" (catching aid?) by RFT. It is responsible to "precharge" 
> the oscillator with a voltage that is dependant on the chosen frequency. This 
> enables the phase discriminator to adjust more quickly to the reference 
> frequency. Without it it needs some time (the "noise") during the "frequnecy 
> rollover" (it is actually a 40 to 30 MHz change and vice versa). Since it is 
> not simple for me (no oscilloscope) to detect "the one" faulty part 
> (suspects: 3 transistors, 3 digital ICs, 1 ops-amplifier IC) I bought the 
> whole oscillator board (new old stock) for reasonable money from somebody who 
> has still some spares. Just installed it and everything is fine.
> Again, thank you all for your help and suggestions. 
> 
> Werner
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