julius wrote:
> On Jun 26, 9:41 pm, Steve Underwood <ste...@dis.org> wrote:
>
>> In most practical cases, the result of the Gardner calculation should be
>> thought of as little more than a "go left" or "go right" indication.
>> Trying to use the actual magnitude of the result, rather than just its
>> sign, works fine in a sterile noiseless model. In the real noisy world
>> the impairments mean trying to scale the adjustment with the magnitude
>> of the result can be less than spectacularly successful.
>>
>> Steve
>
> This may work in some cases, but the safest approach is to derive the
> "gain"
> factor of the TED. This is especially important if the output is fed
> into a
> feedback tracking loop, since it can/will determine the performance/
> stability
> of the loop itself :-P.
>
> Julius
>
As someone else pointed out, if you use Gardner for QAM, you can do
nothing more than use it as a nudge left/nudge right indicator. As you
say, a stability analysis is important. With limited excess bandwidth
the darned thing can get stuck in the wrong place, unless you take care.

Steve