TXM-900-HP-II Linx Technologies Inc, TXM-900-HP-II Datasheet - Page 5

• Manufacturer Part Number: TXM-900-HP-II
• Description: TRANSMITTER RF 900MHZ 8-CHANNEL
• Manufacturer: Linx Technologies Inc
• Series: HP2r

Specifications of TXM-900-HP-II

• Frequency: 902MHz ~ 928MHz
• Applications: ISM, RKE, Security and Fire Alarms
• Modulation Or Protocol: FM, FSK
• Data Rate - Maximum: 50 kbps
• Power - Output: -3dBm ~ 4dBm
• Data Interface: PCB, Through Hole
• Antenna Connector: Through Hole
• Voltage - Supply: 2.17 V ~ 16 V
• Operating Temperature: 0°C ~ 70°C
• Package / Case: SIP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -
• Memory Size: -
• Current - Transmitting: -
• Other names: TXM-900-HP2; TXM-900-HP2

THEORY OF OPERATION
The HP-II-TXM is a high-performance, eight-channel, FM transmitter capable of
transmitting analog or digital data.
Figure 12: HP Series-II transmitter block diagram
Digital information is modulated at the transmitter using FSK (frequency shift
keying), the binary fo rm of frequency modulation. FSK offers significant
advantages over AM-based modulation methods, i.e., increased noise immunity
and the ability of the receiver to “capture” in the presence of multiple signals.
These advantages will be particularly appreciated in crowded bands like those in
which the HP-II operates. While FSK modulation is not the most bandwidth-
efficient manner of modulating digital data, it is an excellent choice for reliable,
low-cost, low-power RF products such as the HP Series-II.
To transmit analog information the module reverts to FM modulation. In this
mode simple to complex waveforms can be introduced at the transmitter’s data
pin and recovered with minimal distortion at the receiver’s analog output pin.
The user-supplied antenna is connected at pin 2 (see Figure 1).The HP Series-
II transmitters are designed to operate with a 50-ohm load.
An accurate 12.00MHz VCXO (voltage-controlled crystal oscillator) serves as the
frequency reference for the transmitter. The modulation input pin is connected to
the VCXO through a two-pole low-pass filter. The low-pass filter is used to shape
the incoming data and limit the transmission bandwidth to 25kHz.
The reference frequency is directly modulated.This method affords two benefits.
First, it eliminates the need for a frequency conversion in the transmitter,
reducing size, cost, and current consumption. Second, it allows the modulation
to occur within the loop bandwidth of the frequency synthesizer allowing a wide
modulation bandwidth of 50Hz to 25kHz.
The modulated 12.00MHz reference frequency is applied to the Phase-Locked
Loop (PLL). The PLL, combined with a 902-928MHz VCO, forms a stable
frequency synthesizer that can be programmed to oscillate at a number of preset
frequencies.
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