GDI SS900FH series, User Manual, Page: 11 / 40

GDI Communications Inc. LLC
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Introduction
The GDI SS900FH series of wireless modems employ a frequency hopping spread spectrum system (FHSS)
integrated with selectable RS232, 485, 422 devices. The most common type is RS 232, and it is the one referred
to in this manual. It is assumed that the user has a basic understanding of serial RS232 communication principles.
The frequency hopping spread spectrum system is implemented in the SS900FH via a method of transmitting the
traffic communications information within the ISM 900 MHz frequency band .
The RF carrier is switched between 50 distinct frequencies between 902Mhz and 928MHz. This switching
sequence which is referred to as the “Hop Pattern” is pseudorandom to minimize the chance of interference with
other wireless systems. To further isolate different networks, the SS900FH can be configured to 10 different Hop
Patterns
The SS900FH unit is a Data Communications Equipment (DCE) device, ready to be connected to a Data
Termination Equipment (DTE) device via a 9-pin D serial cable, or a USB to 9-pin D serial cable..
This method of implementing a FHSS communication system helps to mitigate the most significant challenges to
all radio communication systems. Namely, interference causes by other transmitters, multipath interference,
interception and jamming, and noise associated with nearby transmitters. The result is a frequency hopping
spread spectrum transmission system that is affordable, reliable, with a high data throughput rate. The GDI
SS900FH system is:
1. Highly resistant to noise and interference. The process of re-collecting a spread signal
statistically spreads out the noise and interference thereby causing them to recede into the
background.
2. The FHSS signals are difficult to intercept. A FHSS signal sounds like a momentary noise
burst or a temporary increase in the background noise to a narrowband receiver.
3. The GDI SS900FH can share the unlicensed frequency band with many types of conventional
transmission systems with minimal interference. This is due to the statistical nature of the
FHSS system, and the power limiting requirements of Part 15 unlicensed devices.