Archive for February 2, 2020

SAF Ka-Band Spectrum Compact 24 – 40GHz Portable Analyzer Review, Teardown & Experiments

In this episode Shahriar reviews another SAF Spectrum Contact. This model covers the Ka-Band (24GHz-40GHz), intended for 5G mm-Wave field measurements. The K-Band unit offers additional functionality such as 10MHz minimum span as well as RBW/VBW control down to 100kHz.

The teardown of the instrument reveals a similar architecture to the previously reviewed V-Band unit. Various system components are analyzed and explained. Some of the instrument’s GUI capabilities are also presented.

For experiments, a 900-element 38GHz planer array antenna is used at a distance of 2.5 meters. A slow-FM modulated RF signal centered at 38GHz is generated and measured which allows for the antenna gain characterization as well as exploration of the instrument’s capabilities.

Teardown & Repair of an Agilent N5182A MXG 100kHz – 3GHz Vector Signal Generator

In this episode Shahriar repairs a malfunctioning Agilent N5182A MXG Vector Signal Generator. While the instrument operates perfectly above 250MHz, below 250MHz the output is very low with a significant increase in the noise floor.

The block diagram of the synthesizer is presented showing various RF signal paths. It is shown that the sub-250MHz band is derived from a hetrodyne section which is where the problem located. Using a EM probe, various signal flows are discovered on the main board and compared with the block diagram. The main problem is traced to a doubler circuit which generates a 1-GHz LO signal for the hetrodyne section. The doubler comprises a transformer coupled to a dual diode surface mount IC. The IC is replaces which restores the doubler functionality and repairs the instrument.

Tutorial on Theory, Characterization & Measurement Techniques of Phase Noise

In this episode Shahriar demonstrates the fundamentals of Phase Noise. The theory behind phase noise is presented both from a time-domain and frequency domain points of view. Various mathematical equations which represent phase noise behavior is also presented.

Phase noise measurement challenges and techniques are covered. Capabilities and limitations of different instruments for phase noise characterization is explained. The experiments show AM/PM modulations both in time and frequency domain and their relationships to phase noise measurements. Using a spectrum analyzer the phase noise of several synthesizers are shown. However, it is clear that the phase noise of an ultra-clean 1-GHz reference signal cannot be measured using traditional methods.

The concept of cross-correlation is introduced as a means of measuring phase noise below the phase noise of the measurement instrument. The block diagram of the an Agilent Phase Noise Analyzer is presented followed by a short teardown. The measured phase nose of the ultra-clean 1-GHz source is shown using correlation techniques which matches the datasheet.

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