[time-nuts] Hetrodyning concept
Bob kb8tq
kb8tq at n1k.org
Mon Apr 27 12:22:00 UTC 2020
Hi
If you feed two identical signals into a double balanced mixer,
you get 2X the input frequency and a DC component as the “ideal”
outputs. You also have the input feed through and N x the input
bouncing around as “non-ideal” signals. ( = the full expansion has
a *lot* of terms in it).
A normal ( = saturated inputs) diode ring double balanced mixer has
a non-linear transfer function for the DC output. As you shift phase, an ideal
mixer would have a sine wave voltage vs phase plot. A saturated mixer
has something that looks more like a clipped triangle wave as it’s plot.
So, simple answer is that single double balanced mixer does not do
a very good job as a wide range phase detector. It’s great for phase
noise (when properly set up), but not ideal for an unlocked system.
Bob
> On Apr 27, 2020, at 4:08 AM, Taka Kamiya via time-nuts <time-nuts at lists.febo.com> wrote:
>
> I have a question on heterodyining concept.
> Say you have f1 and f2. Say you have f1 <> f2. Then the product is |f1+f2| and |f1-f2|. (fundamental is not considered here)
> What would happen f1 = f2? If phase is the same, it will be 2sin(omega t). (amplitude doubles) If phase is an odd multiple of pi radian different, result is zero. (cancels out each other)
> What I am trying to do is to first, understand this in case where f1 = f2, and second, mix f1 and f2 and get f3, which is a sum of f1 and f2. Doubling won't do.
> Can someone help me understand this? I haven't seen discussion of cases where source frequencies are equal anywhere.
>
>
>
> ---------------------------------------
> (Mr.) Taka Kamiya
> KB4EMF / ex JF2DKG
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