# Design

#### Spread Spectrum Clock (SSC) on Commercially Available Off-The-Shelf (COTS) Products & MIL-STD-461F Testing

Posted on February 22nd 2012 by Desmond FraserA client recently inquired as to whether it would be possible to see a reduction in radiated spurious emission levels on Spread Spectrum Clock (SSC) fundamental frequency and harmonics using Peak Detectors during MIL-STD-461F testing of a COTS product, when previous FCC Part 15 testing of the COTS product proved compliance using Quasi-Peak Detectors. We are pleased to share our response: If COTS with SSC products with Part 15 compliant fundamental frequencies and harmonics are tested to MIL-STD-461F using required Peak Detectors, the spectral peaks of their fundamental frequencies and harmonics should comply with MIL-STD-461F, provided the SSC timing parameters are properly configured. A properly configured SSC would produce lower spectral peaks of the fundamental frequency and harmonics in the SSC mode than the spectral peaks of the fundamental frequency and harmonics in the non-SSC mode by levels that are dependent on the manufacturer of the SSC, modulating waveform profile, modulation rate used to modulate the fundamental frequency clock frequency in the SSC mode, spreading rate style used (down, center or up) as depicted using (Δ) in Figure 1 below:

#### Use of Peak Detectors in MIL-STD-461F Product Testing

Posted on February 9th 2012 by 斗地主达人Desmond FraserRhein Tech Laboratories, Inc. is pleased to share a response we provided to a client’s recent request for an explanation of the measurement detector requirements in MIL-STD-461F product testing. MIL-STD-461F requires peak detectors for all product testing. MIL-STD-461F, paragraph A.5.1.1 (5.1.1) Units of frequency domain measurements states: “All frequency domain limits are expressed in terms of equivalent Root Mean Square (RMS) value of a sine wave as would be indicated by the output of a measurement receiver using peak envelope detection.”

#### Electromagnetic Interference Test Procedure (EMITP) in MIL-STD-461F Product Testing

Posted on February 6th 2012 by Desmond FraserRecently, a client contacted Rhein Tech Laboratories, Inc. about requirements for Electromagnetic Interference Test Procedure (EMITP) in MIL-STD-461F product testing. We are pleased to share our response below. The MIL-STD 461F standard requires that a product be tested and evaluated, taking into consideration its unique functional characteristics and operational environment

How does one calculate a radar’s maximum range (*R _{max}*), if it is a C band with 2.5MW peak transmit power (

*P*), operating at 5.8GHz with an antenna gain (

_{t}*G*) = 40dBi and an effective temperature (

*T*) = 290K, and its pulse width (

_{e}*?*) = 0.25 ?sec? The radar’s minimum threshold is (

*SNR*)= 25dB, and we assume its Radar Cross Section (RCS) (

_{min}*?*) = 0.15m

^{2}and its Noise Figure (

*F*) = 3 dB. To determine the radar’s maximum range (

*R*we must first calculate its bandwidth (

_{max})*B*) and wavelength (

*?*) using equation 1 and equation 2 below.

#### Radiated Power From A Cell Phone In Free Space Or Submersed In Water

Posted on January 11th 2012 by Desmond FraserSubmersible cell phones are advertised on the Internet, but what is the radiated power of a cell phone submersed in water compared to when it radiates in free space? What should its current be with the antenna submersed in water in order to maintain the same radiated power as in free space? The cellular phone in this example has the following parameters, ?_{r} = 81, ? = 0, ? = ?_{0}, and uses a 0.008 m (8 mm) long shot dipole antenna that carries 2.5 A current and radiates at 1850 MHz. In order to prove that any change in radiated power is as a result of a change in the medium’s permittivity in which the dipole antenna radiates, and that the permittivity affects its intrinsic impedance, we must first show that the dipole antenna is a Hertzian dipole. To do so, we must calculate the dipole antenna’s wavelength in air and compare it to its physical length, in order to determine if it is electrically shorter than the wavelength of the cell phone’s operating frequency. We will use Equation 1 below.

#### Radiated Power Calculation Using an Electrically Short Dipole Antenna

Posted on January 2nd 2012 by Desmond FraserImagine a Hertzian dipole antenna is used by a radio amateur at this home and the FCC specified field intensity limit is less than *21?(2) ^{?V}/_{m}* and the limit distance is (

*). What is the maximum average radiated power that can be achieved using the dipole antenna? The maximum intensity of the field intensity is (*

^{?}/_{2}_{?}*E*), the time average power density

_{max}*S*

_{av }they are related as in equation 1 below.?

#### Finding The Radius From Flux Through An Enclosed Surface

Posted on October 3rd 2011 by Desmond FraserCylindrical resonators operating with the (*TE _{011}*) mode are used to measure the complex permittivity of different dielectric materials such as dielectric sheets, foams etc. To design such a resonator, the empty cavity must have a relatively high Q-factor; say 20,000 for the Ku-band. For the (

*TE*) mode to be resonant at 15 GHz, the corresponding resonant free-space wavelength can be found using equation 1 below, where the relative permeability

_{011}*(*

*?*

_{r}*)*and the relative permittivity

*(*

*?*

_{r}*)*of air = 1, the cavity height is

*(d)*, the cavity radius is

*(a)*,

*(d) = (2a)*and the propagation constant is

*(S*= 3.832.

_{01})#### Determining Current Density & Displacement Current on a Plate Capacitor

Posted on September 16th 2011 by Desmond FraserMaxwell corrected Ampere’s duality law that a time vary electric field produces a magnetic field by proposing the *displacement current J _{d}* in which the curl of the

*magnetic intensity (H)*is directly proportional to the

*current density (J*斗地主达人as in equation 1 below. If divergence is applied to equation 2 Ampere’s law, the current density must have zero divergence because the divergence of the curl of a vector is always zero.

_{c}) + the displacement current (J_{d})#### Simultaneous Battery Current Drain, Battery Life, & FCC Frequency Stability Testing under Normal & Extreme Temperatures

Posted on September 7th 2011 by Desmond FraserComparing Simultaneous Battery Current Drain, Battery Life, and FCC Frequency Stability Testing under Normal & Extreme Temperatures We are often asked by our clients whether they would lower their testing costs by simultaneously performing battery current drain, battery life (length of time the battery is capable of sustaining its rated current capacity after repeated charge and discharge cycles over an extended time period, i.e. 1 year), and FCC licensed frequency stability testing under normal and extreme temperatures. This article explains the different measurements and concludes by suggesting a configuration that could help achieve some cost savings. The purpose of a battery current drain test is to measure and record the device total current drain (*I _{TCD}*) under normal and extreme temperatures (i.e. -30° C to +50° C), with the device functioning in its worst-case current-consuming operating mode for 24 hours, less the time it takes to charge its battery to its maximum current rated capacity. For example, if it takes 2 hours to charge the battery to its maximum rated current, the device current drain (

*I*) shall be measured over a 22-hour period as often as possible, say every 15 minutes, to improve measurement accuracy. The total current drain (

_{CD}*I*) is calculated by adding all (

_{TCD}*n*) individual current drain (

^{th}*I*) measurements, where n = 88 = total number of sample measurements taken in a 22-hour period, such that the total current drain (

_{CD}*I*) can be calculated using Eq. 1 below.

_{TCD}It is often necessary to determine an unknown load impedance (Z_{L}) of a transmission line when mitigating radiated emission noise from harmonics of the carrier frequency in wireless devices in order to meet MIL-STD-461F RE102, FCC, IC, R&TTE standards, rules and regulations emission limits. To do so, one only needs to make Voltage Standing Wave Ratio measurement (VSWR, or S) and determine the electrical distance of the first minimum of the voltage standing wave pattern (z_{min}) of the transmission line. The phase (?) is related to the reflection coefficient (?) at the location of the first minimum and the VSWR determines its magnitude. The Phase (?) can be calculated from the wave number (?= 2•?/?) using Eq. 1: In practice, measuring the location of any of the transmission line minima (?/2), can be used to determine the first minimum, in which successive minimas are separated by ?/2.