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 Newsletter
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September 2002 edition of the Amphenol RF Connection v 1.5
In this issue:
Amphenol's reverse polarity connectors allow antenna products to comply with FCC
"Connectorizing" the wireless LAN antenna with Amphenol solutions
Dave’s Q & A: What causes PIM in connectors and how does Amphenol design low PIM connectors?
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Amphenol's reverse polarity connectors allow antenna products to comply with FCC
FCC regulations dictate that a non-standard connector must be used on antennas to prevent improper signals from being transmitted. Instead of developing a completely new connector series, Amphenol has developed reverse polarity versions of many standard connectors in the antenna market. Reverse polarity connectors are similar to standard connectors except the center contact and sometimes dielectric are reversed. For example, a Plug (Male) connector in a reverse polarity configuration would have the contact from the Jack (Female) in the same series.
The main benefit in the reverse polarity approach to non-standard connectors is economy of scale. Because the connectors still use the body components from standard connectors, they share production volumes thereby keeping overall cost down. Amphenol currently has reverse polarity connectors available in the standard interfaces typically used in antenna applications. This includes the series SMA, TNC, BNC, N, and MMCX.
Several years ago, the FCC attempted to increase the restrictions on non-standard connectors for antenna applications. Claims were made that reverse polarity connectors were becoming so prevalent that they could not longer be deemed "non-standard". After receiving much resistance form the industry because of the potential cost impact, the FCC backed down. Today reverse polarity connectors continue to be the most cost effective way to comply with the FCC regulations.
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"Connectorizing" the wireless LAN antenna with Amphenol solutions
Short range wireless systems are becoming the fastest growing market within telecommunications. Bluetooth and WLAN applications are setting the industry afire with product development to support both these applications. These technologies provide both "last mile" and "first mile" solutions for communications into and within the home between desktop personal computers, mobile laptops, cell phones, personal digital assistants (PDA's) and consumer appliances. Imagine the ability to eliminate the tangled mess of wiring previously associated with interconnecting these devices.
Devices designed to function within these applications operate typically in one of two WLAN spectrums, 83.5 MHz between 2.4/2.4835GHz and 455MHz between 5.15/5.35GHz and 5.470/5.725GHz. Both of these bands are internationally available and unlicensed (free).
FCC Rules, part 15 provides design guidance relative to "Unlicensed Spread Spectrum radio systems" which operate within these bands. Section 15.203 discusses the requirement for antennas utilized within these products. The design must ensure that no antenna other than that furnished by the responsible party shall be used with the device. The intent here is to avoid "Joe Handyman" from either making repairs or improving reception area of his device with the installation of gain antennas taking the device beyond its intended range. Except for devices that require professional installation, the antenna must be permanent or have a unique connector. The manufacturer may design the device so that a broken antenna can be replaced by the user but the use of a standard antenna jack or electrical connector is prohibited.
In May, 2000 the FCC issued Public Notice CA 00-1087 clarifying these requirements. It was stated in this public notice that MMCX, MCX, reverse polarity SMA, BNC and TNC connectors were no longer accepted due to their readily availability through local electronic outlets. They were considered no longer unique and a 30-day window was issued in order to give manufacturers time to comply. However, that effective date was extended indefinitely until a petition for reconsideration of the action is addressed. It remains on hold.
When determining whether an RF antenna connector is a common, readily available antenna connector, the FCC looks in RF connector catalogs to see what companies such as Amphenol have available. If the RF connector is advertised as standard and readily available it is not considered unique and therefore not acceptable.
Amphenol RF has many solutions to these applications both large and small. Custom, low cost interfaces are available to satisfy both of the spread spectrum bands. Right angle and straight cable plugs, mating printed circuit board (pcb) connectors are available with high electrical performance up to 6GHz. For those applications which ask for standard interfaces within the unit bulkhead adapters are available with a variety of standard interfaces on the inside or direct cable termination for jumpers to the pcb.
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Q: What causes PIM in connectors and how does Amphenol design low PIM connectors?
A: In our May 2002 issue of The Amphenol RF Connection Newsletter, I introduced you to Passive Intermodulation Distortion (PIM). In this issue I will discuss its causes in connectors and cable assemblies and how to prevent it from becoming a problem in your system. As discussed earlier, PIM is caused by non-linearities in a passive circuit. The main cause of non-linear action in a connector or cable assembly is poor contact junctions, which can be caused by any one of the following:
Insufficient contact pressure
Irregular contact surfaces
Oxidation-causes metal/oxide junction
Contact impurities
Corrosion
In addition, ferromagnetic materials such as nickel and steel, as well as contamination all contribute to the problem.
At Amphenol RF, our best performing connectors are designed with soldered center and outer contact connections using one-piece construction wherever possible. In addition, we have a line of N and 7-16 connectors that are over-molded to eliminate the effects of wind, vibration and thermal stresses. Contact forces and other aspects of the designs are such that sufficient pressure is assured in order to prevent PIM. Center contacts are plated silver or gold and connector bodies can be plated silver or white bronze. Connectors and cable assemblies are manufactured in clean environments and assembled by highly trained personnel who are aware of the causes and effects of PIM.
All assemblies are then tested to ensure that they meet all published specifications.
In a future issue I will talk about how PIM is measured.
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