Product Manual

© MiMOMax Wireless Ltd
Tornado Product Manual
15
3.2.8 Dual Serial
The two serial ports, ‘Serial 1’ and ‘Serial 2’ on the front panel, operate as RS232 ports can either operate via a terminal server
application (NDL and MDL) or providing a transparent end to end RS232 connection (NDL only). In a NDL system the serial
ports are also able to provide X-21, RS422, G703, C37.94 or MiMOMax HSSI2 via external interface converters.
3.2.9 GPIO
Four GPIO ports are provided, these are able to be open collector digital outputs capable of withstanding 70 VDC, and sinking
up to 100mA. Or they can be used as either digital or analogue input ports, making use of a 12-bit Analogue to Digital converter.
The direction and mode of each can be set independently.
3.2.10 Alarm
A single set of voltage free change over contacts are provided as an alarm indication, these are current limited to 750mA. The
alarm port is also on the GPIO connector.
3.2.11 Front Panel LEDs
LEDs on the front panel indicate Power, RF link status and Alarm. A green LED by the power connector is on when the internal
3.3 Volt power supply is on. A green LED labelled ‘Link’ is on when a RF link is active. A red LED labelled ‘Alarm’ flashes
during boot up. It will also flash when the alarm is active.
3.3 RECEIVER RF/IF SECTIONS
The receiver has two identical channels, each with separate RF, mixer and IF stages. A common local oscillator feeds both
channels simultaneously. RF input to each channel is by means of a PCB-mounted 50Ω SMB connector. With the exception
of the VCO/synthesiser sections the descriptions below apply equally to either receive channel.
3.3.1 Front End
The Front End resides on the duplexer board. Incoming signals are fed through a band pass duplexer which provides effective
rejection of out-of-band frequencies beyond the centre frequency (approximately +/-3MHz). Following the filter, is the receiver
Low Noise Amplifier (LNA). This is followed by a fixed image reject filter to remove noise attributed to the LNA as the majority
of image rejection comes from the internal duplexers.
3.3.2 Mixer and LO Buffer
The RF signal from the front end is converted down to an Intermediate Frequency (IF) by means of a mixer and LO Buffer.
3.3.3 IF and AGC Circuitry
The signal from the mixer feeds a 45.1MHz 4-pole crystal filter. It then passes via a buffer amplifier to a second IF filter which
is a 2-pole crystal unit. This gives a total of 6 poles of analogue IF filtering. Primary rejection of adjacent channels is provided
by post-IF DSP filtering further down the receive chain.
Following the second IF filter are two-stage variable-gain AGC amplifiers which provide >100dB effective gain adjustment,
using a DC control voltage derived from a 10-bit DAC. The balanced output from the second stage amplifier is fed via an anti-
aliasing band pass filter to an analogue-to-digital converter (ADC) and subsequent digital processing circuitry.
At maximum gain the 45.1MHz IF amplifier chain provides >90dB gain from 1st IF filter input to the balanced IF output (total
receiver gain from RF input to IF output: >100dB). In operation, the post-IF receiver processing circuitry adjusts the AGC
control voltage via the DAC to maintain the signal level into the receiver ADC within its linear operating region.
3.3.4 Local Oscillator
The receiver local oscillator consists of a programmable fractional-N phase-locked loop (PLL) frequency synthesiser, using a
stable reference frequency from an internal 40MHz temperature-compensated crystal oscillator located on the DPS PCB. The
required local oscillator frequency (i.e. receive frequency minus 45.1MHz) is programmed by the unit central processing
system which controls the synthesiser via a 3-wire serial interface bus. The frequency is settable in 6.25 kHz increments (5
kHz optional).