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MAIN  |  MODEMS  |  TELEPHONE LINE INTERFACE  |  WIRELESS DEVICES      
FREQUENTLY ASKED QUESTIONS
 
If our available technical information doesn't fill your need, contact our Applications Engineering staff. You may also go to the Contact Cermetek page for complete telephone, fax, and address information.
 
Modem Questions:
 
How does the transferable FCC Registration work?

Any equipment plugged in to the telephone network in the United States must be registered under FCC Part 68 Rules. All Cermetek modem modules are FCC Part 68 registered. Cermetek customers can utilize this registration on their systems by following a few simple design rules and properly labeling their products. By utilizing the existing registration, Cermetek customers eliminate the need for additional FCC Part 68 testing.

 
Are Cermetek products UL Listed?

Many Cermetek products are UL Recognized. UL recognition verifies that the products are safe to use if properly integrated into a design. However, because Cermetek products are components they are not eligible for UL listing.

 
What is EMI?

EMI is the abbreviation for Electromagnetic Interference. EMI results from high frequency signals escaping system enclosures. FCC Part 15 Rules regulate the amount of EMI that and device is permitted to produce in the US. All equipment which uses an oscillator of 9 KHz or greater is subject to FCC Part 15 regulations. See the available application note for system design tips for reduced EMI.

 
Are the high voltage capacitors and ferrite beads shown on the typical connection diagram necessary?
These components are recommended for EMI filtering but are not required. If your design does not include some form of EMI filtering, a redesign will be required if excessive EMI levels are produced. The components used in the EMI filter affect only very high frequency signals and have no affect on normal communications or FCC Part 68 compliance.
 
Is it necessary to add lightning protection?
Unless otherwise stated, Cermetek includes lightning protection in all of its FCC Part 68 Registered products. The integrated lightning protection allows Cermetek modems to survive the lightning simulations tests found in FCC Part 68.
 
What is TBR21?
TBR21 was a technical requirement produced by the European Union to define the requirements of equipment to be connected to the telephone network throughout Europe. It was superseded in April of 2000 by the R&TTE directive. However, because the R&TTE directive did not create a new technical standard many manufacturers and customers continue to rely on compliance with CTR21 to insure functionality throughout Europe.
 
OK What is the R&TTE directive?
I knew this question was coming. The R&TTE directive replaces pre certification of equipment to technical standard like TBR21 and replaces that with "market surveillance. Meeting a standard is replaced by functionality in the real-world.
 
At what data rate will my modem accept commands?
Cermetek modems automatically detect the data rate that commands are issued to them. The data rate of the incoming characters is determined by measuring the bit-width of the incoming "AT" prefix. The maximum data rate from incoming commands varies by modem type.
 
What is flow control?
Flow control allows the modem and host processor to regulate the flow of data to prevent any information from being lost. There are two primary types of flow control used on a serial port; hardware and in-band. Hardware flow control uses the RTS and CTS signals to regulate data flow. The modem deactivates CTS when its incoming buffer is full to signal the host to stop the flow of data; the host will drop RTS to notify the modem that its input buffer is full. For in band flow control XON and XOFF signals in the data stream control data flow. An XOFF character is inserted when the input buffer is full and an XON character is issued when the buffer has been emptied
 
Are Cermetek modems AT compatible?
Yes, Cermetek modems utilize AT commands for control and configuration, but be cautious about the term "AT compatible." There is no standard implementation of the AT command set. Virtually every vender offers variations on the basic commands.
 
Can Cermetek modems be connected directly to an RS232 serial port?
An RS232 port has voltage levels up to plus and minus twelve volts. Cermetek modem products have a zero to five volt or zero to 3.3 volt serial interface. To connect a Cermetek modem module to an RS232 port line drivers and line receivers need to be employed.
 
Are sockets available for Cermetek modem modules?
Cermetek modem modules can be mounted in sockets; however, only our Hybrid PLCC (HyPLCC) products, such as the XE2420, XE2400G, XE5690G and XE5617G modems, fit in an industry standard socket. The HyPLCC products fit in a standard 68 pin PLCC socket. For other Cermetek products there is no standard socket; however, strip sockets can be used on through-hole modules.
 
Will Cermetek products work on a leased line?

Leased lines provide a continuous connection between two points. Because the connection is always present, there is no need for loop current on the phone line. Loop current is used by the phone company as an indication that a dial-up line is in use. Operating on a telephone line which does not provide loop current requires specialized DAA circuitry. Cermetek provides leased line versions of many of its products.

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Telephone Line Interface Questions [DAA's]:
 
How does the transferable FCC Registration work?
Some Cermetek DAA modules including CH1840 and XE0068DT are FCC Part 68 registered. Cermetek customers can utilize this registration on their systems. By following a few simple design rules and properly labeling their products. By utilizing Cermetek existing registration Cermetek customers eliminate the need for additional FCC part 68 testing.
 
What does DAA stand for?
DAA is the abbreviation for an archaic telecom term, Data Access Arrangement. It is a throw back to the days when Ma Bell was in control. 
 
What is a DAA?
A DAA provides the interface circuit to the telephone network for any equipment to be connected to a telephone line.
 
What is EMI?
EMI is the abbreviation for Electromagnetic Interference. EMI is the result of high frequency signals escaping from system enclosures. FCC Part 15 Rules regulate the amount of EMI that and device is permitted to produce. All equipment which uses an oscillator of 9 KHz or greater is subject to FCC Part 15 regulations. See the available application note for hints on system design fro reduced EMI.
 
Are the high voltage capacitors and ferrite beads shown on the typical connection diagram necessary?
These components are recommended for EMI filtering but are not required. If your design does not include some form of EMI filtering, a redesign will be required if excessive EMI levels are produced. The components used in the EMI filter affect only very high frequency signals and have no affect on normal communications or FCC Part 68 compliance.
 
Is it necessary to add lightning protection?
Cermetek includes lightning protection in all of its FCC Part 68 Registered products. Lightning protection does need to be added when a non registered DAA is being used.
 
Are Cermetek modules socketable?
Cermetek telephone line interface modules can be mounted in sockets; however, there are no standard sockets available for these products.  Strip sockets can be used to install Cermetek telephone line interface modules.
 
Will Cermetek telephone line interface modules work on a leased line?

Leased lines provide a continuous connection between two points. Because the connection is always present, there is no need for loop current on the phone line. Loop current is used by the phone company as an indication that a dial-up line is in use. Operating on a telephone line which does not provide loop current requires specialized DAA circuitry. Many Cermetek telephone interface products will operate on a leased line

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Wireless Device Questions:
 
How does the transferable FCC Registration work?
The FCC allows wireless modules operating in the ISM (Industry, Science and Medical) bands to achieve a Modular certification to FCC Part 25 Rules.  A certified module may be used without additional FCC certification testing. By utilizing the Cermetek modular certification, Cermetek customers eliminate the need for additional FCC Part 15 testing
 
How is the Range of a wireless device calculated?
You can calculate the theoretical range of a device from the transmit level and receive sensitivity.  However, this provides only a theoretical value.  Real world range is affected by the conditions including radio interference, physical obstacles and atmospheric conditions.  The wireless protocol also affects range through its error correction and link recovery abilities.   Cermetek only promotes the range of its products as tested in real world conditions.
 
What is Spread Spectrum Transmission?

To prevent interference between wireless spectrums, rules prevent an RF an RF device from transmitting too great a signal over any one frequency.   A spread spectrum transmitter spreads that signal throughout the frequency band permitting higher signal power. Two methods of spread spectrum transmission are used, Frequency Hopping (FHSS) and Direct Sequence (DSSS). A frequency hopping transmitter transmits briefly at one frequency before jumping to another frequency and resuming transmission.  25 or more unique channels are typically used to spread the signal power.  A direct sequence transmitter replaces the data with a pseudo random data string which spreads the signal across the available frequency band. 

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