RXM-900-HP-II Linx Technologies Inc, RXM-900-HP-II Datasheet - Page 11

• Manufacturer Part Number: RXM-900-HP-II
• Description: RECEIVER RF 900MHZ 8-CH PACK
• Manufacturer: Linx Technologies Inc

Specifications of RXM-900-HP-II

• Frequency: 902MHz ~ 928MHz
• Sensitivity: -95dBm
• Data Rate - Maximum: 50 kbps
• Modulation Or Protocol: FM, FSK
• Applications: Home / Industrial Automation, Remote Access, Security Alarms
• Current - Receiving: 18mA
• Data Interface: PCB, Through Hole
• Antenna Connector: Through Hole
• Voltage - Supply: 2.7 V ~ 16 V
• Operating Temperature: 0°C ~ 70°C
• Package / Case: 18-SIP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -
• Memory Size: -
• Other names: RXM-900-HP2; RXM-900-HP2

THE DATA OUTPUT
Once a reliable RF link has been established, the challenge becomes how to
effectively transfer data across it. While a properly designed RF link provides
reliable data transfer under most conditions, there are still distinct differences from
a wired link that must be addressed. Since the HP-II modules do not incorporate
internal coding/decoding, a user has tremendous flexibility in how data is handled.
The data output is generated by an on-board open-collector comparator and
swings from 0V (representing the reception of a logic “0”) to VIN (representing a
logic “1”). This output is capable of sinking 2 mA of current and presents a 4.7K
source resistance when sourcing current. If additional current sourcing or sinking
capacity is required, the user should use a buffer gate to service the additional
loads.
When a carrier is not present, the data output is continuously high. Although the
audio output of the receiver is pure noise, an internal squelch circuit is used to hold
the data output low. The data output will “break squelch” anytime the RF energy
present at the antenna input is strong enough to cause the RSSI voltage to rise
above the factory-set squelch level. Typically, a receiver will only break squelch
when a carrier is present on the desired frequency. However, strong signals at
interfering frequencies can also cause the data output to break squelch.
When a carrier is present with no modulation, the data output will remain
continuously high when the RF signal input level is above the DC Modulation
Sensitivity.
Note that the DC modulation sensitivity is higher than the data
sensitivity of the receiver. The ability to maintain a DC level on the data output
requires a higher SNR than is required to receive data. When the RF signal input
level is below the DC modulation sensitivity but above the data sensitivity, the
receiver’s output will contain valid data when the incoming carrier is modulated.
However, in this condition the receiver may not hold a continuous high level on the
data output when the carrier is not being modulated.
This feature is unique to the HP Series-II and is designed to support direct
operation with UARTs which require their input to be continuously marking (or
high). The HP Series-II transmitters and receivers can be directly connected
between two UARTs without the need for buffering or logical inversion.
Another area of consideration is that of data structure or protocol. If you are not
familiar with the considerations for sending serial data in a wireless environment
you will want to review Linx application note #00160 (Considerations for sending
data with the HP Series-II). These issues should be clearly understood prior to
commencing a significant design effort.
If you want to transfer simple control or status signals such as button presses or
switch closures, and your product does not have a microprocessor on board your
product or you wish to avoid protocol development, consider using an encoder and
decoder IC set. These chips are available from a wide range of manufacturers
including: Microchip (Keeloq), Holtek, and Motorola. These chips take care of all
encoding, error checking, and decoding functions and generally provide a number
of data pins to which switches can be directly connected. In addition, address bits
are usually provided for security and to allow the addressing of multiple receivers
independently. These IC’s are an excellent way to bring basic Remote
Control/Status products quickly and inexpensively to market. Additionally, it is a
simple task to interface with inexpensive microprocessors such as the Microchip
PIC or one of many IR, remote control, DTMF, and modem IC’s.