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

[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


----- Original Message ----- 
From: "Werner" <w.r.l at gmx.net>
To: <premium-rx at mailman.qth.net>
Sent: Saturday, May 05, 2007 6:40 PM
Subject: [Premium-Rx] Any expert on RFT EKD-500 out there?


> Hi,
> I have a RFT EKD-515 for a while. It is a kind of new old stock. Was produced 
> in late 1990 and stored for almost 16 years. I had to fix some relais in the 
> preselector board. It works great so far.
> One strange behavior developed some weeks ago. Not a big problem but annoying: 
> When tuning the VCO (or entering the keyboard or controlling the rx from a 
> PC) and a "full" 100kHz mark is passed, the PLL needs some time to adjust. A 
> "noise" resulting from fluctuating frequency is heard. After that everything 
> is stable. I doesn't matter whether the tuning increment is 10 Hz (smallest 
> step) or 100 Hz, 1kHz, 10 khz or anything in between. It is only important 
> that a 100 khz value is a result by a tuning increment smaller than 100 kHz. 
> Full 100 kHz tuning steps do not show this behavior. Examples:   5999.99 to 
> 6000.00 (10 Hz increment) -> noise. 5900.00 to 6000.00 (100 Khz increment) -> 
> no noise.
> Again, this only happens when going over the 100 kHz mark. All other frequency 
> are "normal".
> Any EKD experts out there with suggestions?
> B.T.W: I have all the schematics an  the repair manual.
> 
> Regards, Werner
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