Page 452 - Complete Wireless Design

Wireless Issues

Wireless Issues 451

Mobile radios, licensed or unlicensed, as well as virtually all high-volume
unlicensed transmitters of any kind, must obtain an FCC Certification. This
covers the great majority of wireless devices, such as cordless and cellular
phones, wireless local-area networks (WLANs), 802.11 devices, handi-talkies,
and citizen band radios. Certification is quite intensive and expensive. It
involves testing, substantial paperwork, and a large filing fee. Even then the
device cannot be sold until the FCC approves the application, which can take
3 months or longer (private testing facilities may soon be approved to issue
such Certifications, and in much shorter time periods).
After any engineering changes to an already authorized (either by
Verification, DoC, or Certification) device that may have altered its RF com-
pliance—such as a change in power, frequency, shielding, or isolation—a retest
should be conducted to confirm that these changes have not dropped the prod-
uct from the compliance standards. If the compliance tests on the modified
device fail, all sales must be halted, and any problems fixed. However, if the
engineering changes either have not affected the device, or have actually
improved its compliance, then nothing need be done in the Verification or DoC
cases (except maintaining all new test and design paperwork). In the case of
Certification, things become more complicated. Almost any changes to the
radio’s (or other authorized device) frequency-generating stages, or any
increase in output power, must typically obtain a completely new Certification.
Still, if the modifications were to other circuits that are not involved in the
normal compliance tests, and no degradation in test results occurred, then the
device may be allowed to continue to operate as before, with no new FCC fil-
ing necessary. Even if the device now has test results that are slightly inferi-
or to the original device, then the manufacturer may still file a “Class 2”
application, along with the current test data, and hope for FCC approval.
If the original or modified product is denied authorization by the FCC
because of a specific, and correctly interpreted, rule or regulation, then it may
be possible to obtain an FCC waiver that will permit your product to be sold.
Or you may actually attempt to change the rules that are impeding your FCC
authorization. This, however, is a highly complex, time-consuming, and expen-
sive alternative—with no guarantee of success.

10.12 Support Circuits
10.12.1 Introduction
The following introduces assorted support circuits that are used frequently in
wireless design. This book does not go into any design detail because many of
them are usually placed in ICs (and may be but a small part of an overall
RFIC) and rarely need to be designed by the wireless engineer today.

10.12.2 Circuits
Speech processing. Speech processing is a general term for a circuit that
adjusts an input audio signal in amplitude, frequency, or both, before it is

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