Heterodyne Mixer for FFT Spectrum Analyzer
 

I have a PC-based oscilloscope/spectrum analyzer that covers up to 16
MFz. I can see the second harmonic of a 40 meter signal, but that's
about the maximum extent of its utility. I recently came across an
idea where a set of local oscillators and a mixer could be used to
extend the range, with the 0 to 16 MHz input of the FFT SA being the
IF, essentially. I can't recall where I saw that, unfortunately.

I figure I could use 4 or 5 LOs in a shielded compartment, outputs
matched for gains, and switch them into the mixer to produce frequency
ranges in 16 MHz increments. I have some wideband MAR-8 MMICs that I
could use (attenuated) for the RF to make up for the Mixer loss; i.e.,
deliver the same signal level I currently get at 50 ohms with 0 to 16
MHz signals.

Anyone have any suggestions on this idea? The unit I have is pretty
neat, being able to store the o-scope and SA plots digitally, with
positionable cursors for readouts of points on the waveforms.

73,
Ted KX4OM

Heterodyne Mixer for FFT Spectrum Analyzer
 

Simplest way is to use a double balanced mixer, like a mini circuits
module, and a signal generator for the LO. Works great.

73
Gary K4FMX

On Tue, 28 Mar 2006 17:24:20 -0500, Ted
wrote:

I have a PC-based oscilloscope/spectrum analyzer that covers up to 16
MFz. I can see the second harmonic of a 40 meter signal, but that's
about the maximum extent of its utility. I recently came across an
idea where a set of local oscillators and a mixer could be used to
extend the range, with the 0 to 16 MHz input of the FFT SA being the
IF, essentially. I can't recall where I saw that, unfortunately.

I figure I could use 4 or 5 LOs in a shielded compartment, outputs
matched for gains, and switch them into the mixer to produce frequency
ranges in 16 MHz increments. I have some wideband MAR-8 MMICs that I
could use (attenuated) for the RF to make up for the Mixer loss; i.e.,
deliver the same signal level I currently get at 50 ohms with 0 to 16
MHz signals.

Anyone have any suggestions on this idea? The unit I have is pretty
neat, being able to store the o-scope and SA plots digitally, with
positionable cursors for readouts of points on the waveforms.

73,
Ted KX4OM

Heterodyne Mixer for FFT Spectrum Analyzer
 

Gary,
OK, that rings a bell. I believe a sig gen was mentioned wherevever
it was I saw the idea. The old Heathkit IG-102 is pretty darn stable,
but the resolution leaves a bit to be desired. I wouldn't be sweeping
it though, just using it as the adjustable LO. It's certainly easy
enough to try; I have a few SBL-1's and a return loss bridge.

Tnx,
Ted KX4OM

On Wed, 29 Mar 2006 11:25:33 -0500, Gary Schafer
wrote:


Simplest way is to use a double balanced mixer, like a mini circuits
module, and a signal generator for the LO. Works great.

73
Gary K4FMX

On Tue, 28 Mar 2006 17:24:20 -0500, Ted
wrote:

I have a PC-based oscilloscope/spectrum analyzer that covers up to 16
MFz. I can see the second harmonic of a 40 meter signal, but that's
about the maximum extent of its utility. I recently came across an
idea where a set of local oscillators and a mixer could be used to
extend the range, with the 0 to 16 MHz input of the FFT SA being the
IF, essentially. I can't recall where I saw that, unfortunately.

I figure I could use 4 or 5 LOs in a shielded compartment, outputs
matched for gains, and switch them into the mixer to produce frequency
ranges in 16 MHz increments. I have some wideband MAR-8 MMICs that I
could use (attenuated) for the RF to make up for the Mixer loss; i.e.,
deliver the same signal level I currently get at 50 ohms with 0 to 16
MHz signals.

Anyone have any suggestions on this idea? The unit I have is pretty
neat, being able to store the o-scope and SA plots digitally, with
positionable cursors for readouts of points on the waveforms.

73,
Ted KX4OM