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Can i use an analogue IC switch being triggered at the same frequency I am receiving on to change a 10 m yagi's directivity by somehow combining received signals with different variable phase either from the same driven element or two or more driven elements?

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    $\begingroup$ Can you rather explain what problem you're actually trying to solve? You can't "combine" signals from a single driven element, and two driven elements means it's a custom antenna anyway, not an off-the-shelf yagi. And "Triggered at the same frequency" doesn't make sense. Antenna and matching systems are generally Linear, Time Invariant, receivers do mixing and stuff. $\endgroup$ – tomnexus Oct 16 at 9:31
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    $\begingroup$ horizontal directivity or vertical directivity? Do you want to rotate it, or is reversing front / back good enough? $\endgroup$ – user10489 Oct 16 at 11:21
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No, you can't; what you're building by switching something at its carrier frequency is a mixer to twice, four, six,… times the carrier frequency and to a broken 0 Hz baseband, so that's not useful.

The math is simple:

Just as your normal mixer multiplies with a cosine to mix the signal to the sum of the cosine and signal frequencies, and to their difference, the same happens when you multiply with a square wave instead of a cosine.

A square wave can be mathematically represented as sum of cosines of the fundamental frequency of the wave, and every odd harmonic.

Ergo, switching with some frequency $f$ just produces mixing products at your signal's frequency $\pm f$.

That's a standard mixer type, the switching or chopping mixer, but it's not a way of combining things with an adjustable phase.

Looking at that:

What you can do is use a switching mixers for each of two signals, where one square wave has a time (and hence: phase) offset; these mixers would produce a sum-frequency signal each, but with different phases. Then, add these and you get a phase-shifted sum.

You'll have a lot of unwanted harmonics to filter, and your phase adjustments of your square wave can be a bit hard to achieve, and you wouldn't want to use the carrier frequency of your signal, but a higher, adjustable frequency so that you end up on a useful IF.

But, technically, this is fun thing to consider, and whilst I'm pretty sure you didn't think it'd work like that, yes, you can use switching to phase adjust – but only in the context of using it as mixer.

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  • $\begingroup$ this is the x,y problem for me again :( the reason i ask this question is because i want to null out reception from a particular direction using variable phase and amplitude and two antennas and i thought using a fast switch could somehow accomplish this, the answer i need is in another question i posted answered by you and a few others. $\endgroup$ – Andrew Oct 18 at 22:35

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