In this episode Shahriar discusses some of the concerns surrounding the 5G Cellular Wireless Technology. It is important to understand the technology and the history of why 5G is unique in some ways compared with 4G LTE.
The evolution of cellular wireless technology is briefly discussed alongside with dangers of electromagnetic radiation across the entire spectrum. 5G mm-wave beam-forming technology is explored and the actual RF power levels at ground level is computed. Finally some questions about science and technology are discussed.
Perhaps this is the quote which captures my feelings toward this whole situation:
“I worry that, especially as the Millennium edges nearer, pseudoscience and superstition will seem year by year more tempting, the siren song of unreason more sonorous and attractive. Where have we heard it before? Whenever our ethnic or national prejudices are aroused, in times of scarcity, during challenges to national self-esteem or nerve, when we agonize about our diminished cosmic place and purpose, or when fanaticism is bubbling up around us – then, habits of thought familiar from ages past reach for the controls. The candle flame gutters. Its little pool of light trembles. Darkness gathers. The demons begin to stir.”
– Carl Sagan, The Demon-Haunted World: Science as a Candle in the Dark
In this episode Shahriar retrofits a vintage HP 8445B Auto Preselector for testing and characterization of high-performance data converters and oscilloscopes. The Preselector is in essence an electronically tunable band-pass filter with exceptional tuning range and quality factor.
After examining the schematic and block diagram of the instrument the unit is equipped with additional potentiometer, low-band, high-band switch and a voltmeter LCD screen which displays the center frequency. The modifications are applied to the front panel as well as internal circuitry to enable manual control of the preselector without the need for any external devices.
The modified instrument is used to measure the harmonic improvement of a 20GHz synthesizer. Several oscilloscopes are then characterized using the new preselector to determine the absolute performance of their internal data converter.
Finally, it is also time for a new giveaway! A brand new Keysight DSOX1102G scope! Patreon supporters are automatically enrolled.
The instrument does provide an RF output signal. However, there is also a large DC offset voltage present at the output RF port which changes depending the frequency band. The DC voltage is present even when the output RF signal is disabled. Furthermore, the OCXO of the instrument is defective and does not produce a 10MHz output signal.
The block diagram of the PSG is examined in details with emphasis on the final attenuator, coupler and doubler RF decks. Interestingly enough the output offset is traced all the way back to the Modulator Filter block. The teardown of the module reveals a series of PIN diode switches and after some investigation the fault is traced to a damaged PIN diode on the sub-3.2GHz path. Since the diode can’t be easily replaced, the control voltage to the diode is disabled instead which removed the DC offset problem.
The OCXO teardown reveals that during a prior repair, the oscillator module has been damages and torn off the PCB. New pins are added to the oscillator module which returns the crystal back to working condition. The performance of the PSG is verified using a spectrum analyzer and frequency counter.
In this episode Shahriar takes a look at a R&S SMBV100A Vector Signal Generator which does not produce the correct output level. Despite passing all self-tests and ALC checks, the output power level is far below expectation. The output also shows a high-pass frequency response.
The (heavily simplified) block diagram of the instrument is examined and discussed. The teardown of the unit reveals the output RF board which is presented in details. Since the instrument cannot detect the failure internally, it is very likely that the fault is part of the RPP output RF relay. The circuitry as well as the datasheet of the components are examined. Measurements show that the output RF relay is never activated due to a faulty PMOS transistor. After transistor is replaced, the unit shows the correct output level. The baseband generator functionality is also verified.
In this episode Shahriar takes a look at a malfunctioning Agilent N9020A MXA. This instrument was provided by AllTest who hold the largest inventory of used and refurbished instruments. They have trusted The Signal Path to attempt a repair on the instrument and to support the educational content of this channel. Thank you AllTest! Please visit their website for all your measurement, calibration and service needs:
The instrument fails RF Alignment despite the fact that all calibration signals are present and can be viewed on the unit. The front-end attenuators also appear to be fully functioning. A full sweep of the input shows that the instrument fails to make measurements between 8.4GH – 14GHz as well as above 17GHz. The block diagram is analyzed and the likely fault is traced to a doubler circuit on the A13 RF Assembly. The teardown of the assembly along with step-by-step reverse engineering is presented. An X-Ray of the module also reveals the hidden band-pass filter structure on the PCB. Various dies are also examined under the microscope. The A13 module is replaced with which corrects all the instrument faults and returns the unit to normal operation.
The Signal Path (TSP) is an electrical engineering video blog for industry professionals, students and hobbyists. TSP is a non-for-profit website dedicated to provide free education spanning a wide range of electrical engineering topics. Equipment reviews, tutorials and repair videos are posted regularly.