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Functions in SDR


DBell
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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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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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