Tuning power of harmonic oscillator with multi-stage amplifier using schottky mixers.

[Terminator3]

Oscillator consist of few multiplication and amplification stages. Can tuning be done this way? :

1. put schottky mixer + single diode DSB modulator at each stage output (all microstrip air coupled)
2. output from stage comes to DSB diode and modulated using constant amplitude low frequency waveform
3. output from stage mixed with modulated output from stage, get IF
4. measure amplitude of IF for each stage, tune stage for maximum IF amplitude

In other words, we use each stage output as LO signal source, modulate it and mix back with itself. I think that with bigger LO we get bigger mixing IF. Because modulation waveform amplitude is constant, it does not affect measurement. Because all elements are microstrip air coupled, waveform DC will not affect amplitude measurement.

If we use geterodine with some LO, the bigger amplitude of LO, the better mixing we get, right?

I hope it can be done, if not tell me why..

 

[vfone]

Overall the the step-by-step explanation confuse me, an I do not have a general view what you inted to do.
To make a DSB modulator you need at least two diodes mixer (single-balanced), otherwise cannot suppress the carrier.
In the most of the mixer types, higher the LO level, higher the conversion gain is (or lower conversion loss for passive mixers). Also, sometimes higher LO improves mixer linearity (needs some tuning for this).

 

[jiripolivka]

Your definition is very confusing.

In a converter with a Schottky-diode mixer, two separate signals are mostly needed:

1. a fixed frequency local oscillator, with a power defined by a specific mixer type. If you need to tune LO frequency, things become quite complex.

2. RF signal carrying modulation to mixer RF port. Typical input level is from noise floor to a P-1dB (linearity limit). Mixer output is then an IF spectrum to be processed later.

3. In upconverters, IF input signal can carry the modulation and its power must be ~10 dB lower than LO input for good result. Then RF output is available but must be filtered to generate a clean spectrum.

Explain clearly what you need to do, then I can offer you some advice.

 

[Terminator3]

I make RF signal from LO using diode modulator: RF=LO+sine.
Then, air coupled, it goes through microstrip to mixer and mixes back with LO: RF-LO=sine
so i can get low frequency sine, and want to use it's amplitude and noise parameters to analyze current stage performance.
Each stage have separate modulator and mixer. LO for modulator and mixer borrowed throug directional couplers (microstrip).

Sine - it is just low frequency sinusoidal signal, provided by DAC or other schematic.
LO - taken from each stage using directional coupler
RF - made from LO using sine + two diodes with ring mixer or some kind of

 

[jiripolivka]

I make RF signal from LO using diode modulator: RF=LO+sine.
Then, air coupled, it goes through microstrip to mixer and mixes back with LO: RF-LO=sine
so i can get low frequency sine, and want to use it's amplitude and noise parameters to analyze current stage performance.
Each stage have separate modulator and mixer. LO for modulator and mixer borrowed throug directional couplers (microstrip).

Sine - it is just low frequency sinusoidal signal, provided by DAC or other schematic.
LO - taken from each stage using directional coupler
RF - made from LO using sine + two diodes with ring mixer or some kind of

BY feeding the mixer with LO and LO AM- modulated , the mixer generates the product of both, and harmonics.
If you filter out the harmonics by a low-pass filter, you get the DC component as the coherent product of both carriers, and the original AM modulation signal.
With an adequate LO input like +10 dBm (depends on diode type), mixer diodes operate as switches and will not introduce any signal distortion. Then the mixer can evaluate distortion of your AM modulator.
By attenuating the RF input to mixer you can evaluate its dynamic range, from the noise floor up to P-1dB point which occurs typically at LO input minus 7-10 dB.