Mixer Testing

Mixers or frequency converters, by definition, exhibit the characteristic of having different input and output frequencies. Mixer tests can be performed using the frequency offset operation of the analyzer (with an external LO source) or using the tuned receiver operation of the analyzer (with an external RF and LO source). The most common and convenient method used is frequency offset.

Frequency Offset

For a single-sideband mixer measurement, the RF source can be offset in frequency from the input receiver frequency, allowing for a swept RF stimulus over one frequency range and measurement of the IF response over another (in this case the output IF).

To use the frequency offset guided setup for coniigurmg a mixer measurement:

1.Enter the IF and LO frequencies.

2.Set the LO source to the entered LO frequencies.

3.Specify up conversion or down conversion.

4.Select an RF that is higher or lower in frequency than the LO. (The RF frequencies needed are calculated by the analyzer.)

Tuned Receiver

The analyzer’s tuned receiver mode allows you to tune its receiver to an arbitrary frequency and measure signal power. This is only possible if the signal you want to analyze is at an exact known frequency. Therefore, the RF and LO sources must be synthesized and synchronized with the analyzer time base. Since the analyzer is not phaselocking in this configuration,

you can use it to measure conversion loss of a microwave mixer with an RF frequency range output.

Note

You must take care to filter the output of the mixer because some of the

 

intermodulation and leakage products may be very close in frequency to the

 

desired IF. If these components are not filtered off, the analyzer may have

 

difficulty selecting the correct signal to measure.

 

 

Tuned receiver mode also increases dynamic range. Broadband techniques like diode detection have a high noise floor, while narrowband techniques like tuned receivers are much less susceptible to noise.

Application and Operation Concepts 6-157

Page 438
Image 438
HP 8753E manual Mixer Testing, Frequency Offset, Tuned Receiver, Difficulty selecting the correct signal to measure