In this short episode Shahriar takes a close look at a pair of Hewlett Packard microwave electro-mechanical step attenuators operating up to 26.5GHz. Mechanical attenuators offer excellent repeatability, low insertion loss and nearly limitless linearity. The teardown reveals that the construction of both modules is very similar on the microwave path. In fact, the lower-frequency model still uses the same attenuator components. The newer model employs electronic control circuity while the older generation attenuator uses purely mechanically controlled DC path. Both models use a solenoid style actuators for step attenuation control.
Tag Archive for RF
In this episode Shahriar attempts a difficult repair of a Tektronix RSA real-time spectrum analyzer. This well-equipped instrument reports several error messages during startup POST including LO Unlock as well as Signal Path failures. The service manual of the instrument does not provide any detailed block diagram and no schematics. Most failures require the instrument to be serviced by the Tektronix factory. The equipment has various advanced options including 110MHz analysis bandwidth, digital modulation analysis, wide-band IF output and deep memory.
The teardown of the instrument reveals a multi-board, multi-module design. The top of the instrument contains all digital blocks and boards while the bottom of the instrument houses the RF deck assembly. The RF deck is broken into various stages such as attenuator, RF switches, first converter, second converter, IF block, reference synthesizer and LO generator. For the purposes of addressing the YIG problems the LO board is examined. The problem is traced to two components, both dividers in the complex PLL system of the LO subsystem. The LO board is fully analyzed and described and the defective components re replaced.
The repaired instrument is tested for various functionality including DPX, de-modulation and measurement of beyond 8GHz CW tones. The instrument passes all self-tests, alignments and detailed diagnostics.
In this episode Shahriar performs a full review on the Tektronix MDO4000C series mixed domain oscilloscope, particularly model MDO4104C-6. The MDO4000C combines up to six instruments including a function generator and a built-in spectrum analyzer. Unlike any other instrument, it can synchronize RF, analog and digital channels. These correlated measurements provide insight into difficult to find problems particularly intermittent events.
This review begins with a comparison between the MDO4000B and MDO4000C instruments. The full review of the MDO4000B can be viewed here. All experiments demonstrated in the MDO4000B review are also relevant to the MDO4000C instrument.
The teardown of the instrument reveals a multi-board construction where the ADCs, FPGAs, application processor and memory are on the main system board. A complete analysis of the entire system is presented including the operation of the RF module.
In order to demonstrate the instrument’s capabilities, an encrypted frequency hopping transmitter system is analyzed. The system exhibits various problems such as high BER, low SFDR, poor phase-noise and EVM. The MDO4000C is used to perform advanced measurements across analog, digital and RF domain to track and resolve these problem. The complete block diagram of the experiment can be found here.
In this episode Shahriar presents the inner workings of an Agilent 86109B optical/electrical DCA-X oscilloscope module. This particular model offers up to 50GHz of electrical bandwidth and an optical input capable of receiving up to 40Gb/s data rates. The differences between a real-time and sub-sampling oscilloscopes are presented with focus on ADC resolution, signal periodicity requirements and input bandwidth. The block diagram of the module as well as a sub-sampling oscilloscope is also presented.
The teardown of the module shows various components such as samplers, O/E conversion block, impulse generator as well as a step-recovery diode driver. I/O interfaces as well as various analog blocks are also shown. Several modules are further disassembled to observe the inner semiconductor designs under the microscope.
In this episode Shahriar demonstrates the architecture and design considerations for high-power microwave amplifiers. Two architectures are presented, the balanced and Doherty microwave amplifiers. The block diagram, circuit properties and the pros/cons of each architecture are presented. Two available high-power amplifiers modules for cellular applications are also examined. The PCBs show an implementation instance of each amplifier type capable of delivering 100W of RF power. The datasheet of various components as well as an overall system structure are also presented.