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Frequency shifter without LO, is that possible?

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neazoi

neazoi

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Is that possible to achieve frequency shifting without using a mixer and local oscillator?
I am not talking about dividing or multiplying, I am talking about actual frequency shifting of an input RF signal to the supposed device.
 

I presume you are talking about a modulated carrier and you want to change the carrier frequency but preserve the modulation, right?
 

betwixt said:
It IS possible using Doppler shift -
Click to expand...

I presume you are not serious but this is a variant of the Local Oscillator principle.

Any sine wave can be decomposed into two oppositely moving circular waves. Each of them will combine with the carrier two produce two beat frequencies. (f0+/-f).

We use Doppler shift to find out the velocities of distant stars and galaxies. Modern standard of time is based on frequency but it is turning out to be a not so good these days.
 

yes, of course you can. there are a bunch of ways. One common way in the EW field is to use a "Serrodyne Frequency Translator" using a 4 bit phase shifter, where you send digital commands to step the phase at a fast rate from 0 to 359 degrees, and then repeat over and over. The added/subtracted phase makes the output sine wave period either look wider or narrower, hence a true frequency change.

there are, of course, sidebands generated.
 
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    neazoi

    neazoi

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betwixt said:
It IS possible using Doppler shift - but you have to keep on the move - and very fast!

Brian.
Click to expand...
How haven't I thought it?
Is there any way to accomplish it with electronics, or it is just a "mechanical" apploach?

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biff44 said:
yes, of course you can. there are a bunch of ways. One common way in the EW field is to use a "Serrodyne Frequency Translator" using a 4 bit phase shifter, where you send digital commands to step the phase at a fast rate from 0 to 359 degrees, and then repeat over and over. The added/subtracted phase makes the output sine wave period either look wider or narrower, hence a true frequency change.

there are, of course, sidebands generated.
Click to expand...

This is very new to me!
as fas as I search advanced stuff...
I was thinking in simple terms, some passive components for example, so obviously the topic is much more advanced.

You know, you could downconvert a n RF signal to audio, if you could split it ans shift the frequency of one of the signal parts by 1KHz or so, without the use of a local oscillator.
 

As far as I know, it is not possible to straightforwardly shift some carrier by some state of the art apparatus, than already done indirectly by VCO's. The frequency of a signal implies that there are changes of wave polarity in time, and unless you're able to change the time itself, as Brian humorously pointed above in post #3, this will be not possible.
 

The whole question sounds confused and the problem specification vague.

It's basically possible to up- or downshift a signal by single side band modulation techniques (local oscillators and quadrature mixers). It's unclear what's the sense of asking for other means than local oscillator and mixers. The consecutive phase shifting method sketched in post #5 achieves the same result with different means, but it also involves an oscillator (which generates the switching steps) and switches (which can be considered as the mixer in this setup).

In other words, all available methods can be related to similar signal processing operations. Frequency shift without some kind of LO isn't feasible.
 

All these electronic methods, including time expansion/compression still require some kind of extra oscillator or clock.
There is simply no passive circuitry that can do this.

I would say the answer to the original question is no.

Doppler shift is a very clever answer which deserves some recognition.
But its hardly a practical solution.
 

Warpspeed said:
All these electronic methods, including time expansion/compression still require some kind of extra oscillator or clock.
There is simply no passive circuitry that can do this.

I would say the answer to the original question is no.

Doppler shift is a very clever answer which deserves some recognition.
But its hardly a practical solution.
Click to expand...

Thanks, this answers the question.
 

I disagree. you could use passive means. A saw delay line with a parabolic phase curve will generate a chirp in frequency. Taking a piezoelectric crystal and shocking it with a mechanical force while microwave signal passes thru it would alter the frequency. You could rotate a microwave holographic image and the reflections would vary in frequency as the image was mechanically moved. You could bounce microwaves off a moving surface, such as an ultrasonic cleaner bath and get frequency shift. you could alter the DC magnetic field on a ferrite substrate transmission line as microwaves passed thru a line on it. you could pump a microwave signal into a nonlinear media or semiconductor set to resonate at a different frequency and get parametric frequency conversion. and on and on.....Stop thinking so "linearly" everybody.
 

biff44 said:
you could pump a microwave signal into a nonlinear media or semiconductor set to resonate at a different frequency and get parametric frequency conversion
Click to expand...

I'm not aware how works this aparatus, but it perhaps would not meet the original demand, that is a direct way to achieve this shift in frequency.
 

My answer to the original post would be also: NOT POSSIBLE...at least in our life time.
Other utopic options are not applicable in usual electronics applications.
 

Since frequency shifting is mathematically equivalent to multiplication in the time domain, frequency shifting inherently requires multiplication with an external function or signal. Regardless of how the multiplication is implemented, there would be an LO buried in there somewhere.

Dopplar shift did cross my mind, but I don't think of it as really shifting the frequency. You just measure a different frequency by observing the same signal in a different (moving or stationary) reference frame.
 

Doppler shift causes by the way a different signal manipulation, proportional to carrier frequency instead of constant frequency offset.

A similar effect can be achieved with a stationary system by stepwise increasing or decreasing a time delay and returning it periodically as classically done with rotating head drum tape recorders. The proportional frequency shift by a variable time delay is opposite to the frequency offset achieved by a variable phase, see post #5.
 

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