Re: PLL stabilized Q-multiplier
- From: "garyr" <garyr@xxxxxxxxxxx>
- Date: 23 Apr 2005 07:43:48 -0700
Joerg wrote:
> Hello Gary,
>
> Tim already explained it pretty well. I don't have a schematic at
hand
> but there are some in older ARRL Handbooks. The last Q-multiplier I
> built was at least 20 years ago.
>
> Like Tim said, it is basically an oscillator where the feedback is
set
> so it just barely doesn't oscillate. How close you are to that point
> will determine the Q and thus the bandwidth of the connected LC
circuit.
> Mostly a Q-muliplier was realized by bringing the first IF stage
really
> close to the point of oscillating. In your case it would likely be
one
> of the 60kHz stages since you probably won't have an IF.
>
> PLL control is needed to keep a very high Q LC-circuit at the desired
> frequency. For that you have to bring the Q-multiplier stage into
actual
> oscillation once in a while, else the PLL divider would have no input
> signal. With a signal such as WWVB that's no big deal since you don't
> need to receive all the time.
>
What sort of Q would you expect to be able to obtain with this
technique?
> Nowadays I'd use crystals, or at least a lower frequency IF stage.
> Switched capacitor filters can make really nice filters at a few kHz
but
> the required chips cost more than a crystal. If you try the
Q-multiplier
> make sure nothing gets radiated out when it oscillates.
>
> Regards, Joerg
>
> http://www.analogconsultants.com
.
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