For those using a Quadrature FM detector the following may be useful and interesting: (1) The center frequency of a quadrature detector is dependent to a first order on the LC of the quad coil. So to move the characteristic of the detector in frequency fix L and change C. The easiest to do. (2) To set the differential output swing change the resistor. The output swing is directly proportional to the value of the resistor.

# X parameters: What are they?

High frequency designers have used S – parameters for a long time when the circuit or device is being characterized in the linear domain. However, once the device or circuit goes beyond the strictly linear domain and enters large signal or nonlinear operating modes a new set of parameters need to be used. A new paradigm is being used now called X parameter analysis, synthesis, measurement and modeling. The Wikipedia description of X parameters is :

“X-parameters represent a new category of nonlinear network parameters for high-frequency design and were developed and introduced by Agilent Technologies as functionality included in N5242A Nonlinear Vector Network Analyzer  and the W2200 Advanced Design System  in 2008. (Nonlinear vector network analyzers are sometimes called large signal network analyzers.)

X-parameters are applicable to both large signal and small signal  conditions, for linear and nonlinear components. They are a mathematical superset of s – parameters meaning that, in the limit of a small signal, Agilent’s X-parameters reduce to S-parameters.

They help overcome a key challenge in RF Engineering, namely that nonlinear impedance differences, harmonic mixing and nonlinear reflection effects occur when components are cascaded under large signal operating conditions. This means that there is a nonlinear and as such non-trivial relationship between the properties of the individual cascaded components and the composite properties of the resulting cascade. This situation is unlike that at DC, where one can simply add the values of resistors connected in series. X-parameters help solve this cascading problem: If the X-parameters of a set of components are measured individually, the X-parameters (and hence the non-linear transfer function) can be calculated of any cascade made from them. Calculations based on X-parameters are usually performed within a harmonic balance* simulator environment.”

X parameters are a useful tool to not only analyze but also to characterize circuits, devices, IC packages or other multiport networks. It is a good tool to learn and know when one works with RF circuits.

* See a tutorial paper on Harmonic Balance Simulation in this blog.

# Using a rework station for surface mount PCB hand assembly

Just a very brief post on a PCB SMD/surface mount assembly technique using a rework station from ATTEN ( a fairly low cost ~ \$75.00 piece of equipment). The smallest size for assembly was 0402. The board itself was 0.062 inch thick. The copper was 1 oz on both sides of a two sided FR-4 board.

It was found that if the board was heated slightly by a 30 watt reading lamp the temperature of the hot air blower on the rework station could be set to 384 degrees to get good results. The solder used straightforward solder paste dispensed from a syringe. The hot air blower speed was about 1/4 of maximum.

It took about 3 to 5 seconds for the solder to melt and get pulled by surface tension to the pins being soldered. The solder first spread out a bit and became grayish. Just before it melted very small pinpoints of the paste became shiny.

The distance of the hot air tube was about 0.5 inch to 1 inch from the component and the paste.

The assembly of these SMD components can be done by almost anyone. It just needs about an hours practice, a steady hand and a good eye. A  microscope is a definite plus ( in fact we highly recommend that it should be used. These 10X – 20X scopes can be bought used at reasonable prices ).