# Functions in SDR

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I have what may be an odd question for the SDR gurus out there.

What would be the physical implementation (in software) of a broadband frequency divider?

For example, say I want to capture a signal at, 1 GHz, with a 10 MHz bandwidth, then divide it by a factor of 10,

I should get a down-sampled signal at 10 MHz with a 1 MHz bandwidth.

Yes, I know I would lose information, but assume this would be presented as a spectrum analysis, not full audio, video, etc.

Conceptually, could this be accomplished by sampling the RF at 2+times the highest frequency components, say at 2.5 GHz, then discarding 9 out of 10 samples - decimating the input stream?

Thanks,

Dave

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Edit:

Saw a dumb typo: I meant to write

"I should get a down-sampled signal at 100 MHz with a 1 MHz bandwidth."

Dave

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I have what may be an odd question for the SDR gurus out there.

kd6w - no such thing, just really silly answers.

What would be the physical implementation (in software) of a broadband frequency divider?

kd6w - a divider (which is a part of what a mixer does in hardware)

For example, say I want to capture a signal at, 1 GHz, with a 10 MHz bandwidth, then divide it by a factor of 10,

I should get a down-sampled signal at 10(0) MHz with a 1 MHz bandwidth.

kd6w - yes if the process is decimating and no if you are doing image conversion.

kd6w - Is the question - how to preserve the "image" of the 10MHz bandwidth centered up at 1GHz and move it down to 100MHz?

Yes, I know I would lose information, but assume this would be presented as a spectrum analysis, not full audio, video, etc.

Conceptually, could this be accomplished by sampling the RF at 2+times the highest frequency components, say at 2.5 GHz, then discarding 9 out of 10 samples - decimating the input stream?

kd6w - before you go there, a mixer is a 3 port device with 2 inputs and 1 output.

RF image + Oscillator = Intermediate Freq = RF image + oscillator freq AND RF image - oscillator.

Put a low pass filter on the IF output and bingo. RF 1 GHz with 10 MHz image + 900 MHz oscillator = 10 MHz image centered around 100 MHz on the IF output.

KD6W

Thanks,

Dave

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I have what may be an odd question for the SDR gurus out there.

kd6w - no such thing, just really silly answers.

What would be the physical implementation (in software) of a broadband frequency divider?

kd6w - a divider (which is a part of what a mixer does in hardware)

For example, say I want to capture a signal at, 1 GHz, with a 10 MHz bandwidth, then divide it by a factor of 10,

I should get a down-sampled signal at 10(0) MHz with a 1 MHz bandwidth.

kd6w - yes if the process is decimating and no if you are doing image conversion.

kd6w - Is the question - how to preserve the "image" of the 10MHz bandwidth centered up at 1GHz and move it down to 100MHz?

Yes, I know I would lose information, but assume this would be presented as a spectrum analysis, not full audio, video, etc.

Conceptually, could this be accomplished by sampling the RF at 2+times the highest frequency components, say at 2.5 GHz, then discarding 9 out of 10 samples - decimating the input stream?

kd6w - before you go there, a mixer is a 3 port device with 2 inputs and 1 output.

RF image + Oscillator = Intermediate Freq = RF image + oscillator freq AND RF image - oscillator.

Put a low pass filter on the IF output and bingo. RF 1 GHz with 10 MHz image + 900 MHz oscillator = 10 MHz image centered around 100 MHz on the IF output.

KD6W

Thanks,

Dave

Ah, there's the rub! I want to reduce the image bandwidth by the same divide factor, not heterodyne it down.

When I get the bandwidth reduced to where I want it, then I would mix it doown to IF (or baseband.)

Dave

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OK then. You want a true divide expression, fair nuff. The GRC has that exact function in the math operators. Since you are looking for even integers in your example, then you don't need the rational re-sampler.

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