COMMAND RANGING & TELEMETRY UNIT CORTEX
CRT QUANTUM USER'S MANUAL
Ref. DTU 100042
Is.Rev. 5.17
Date: Dec.
03, 2021Sept. 30, 2021
This document is the property of Safran Data Systems.
It cannot be duplicated or distributed without expressed written consent.
3.4.2. Noise Generator Option
3.4.2.1. IFM Output Stage Architecture
Interpolation &
IF conversion
Digital IF
filtering
(Option) (Option)
modulated
signal
DAC
Analog
LP filtering
NOMINAL
IF out
Analog
BP filtering
ALTERNATE
IF out
0-90 MHz 50-90 MHz
Noise gen.
Variable
attenuator
C/No adjust
Variable
attenuator
Figure 61: IFM Output Stage Architecture
3.4.2.2. C/No Adjust
The Noise Generator is not designed to be used without a carrier. Using the noise generator with the carrier
disabled may result in a remnant signal at 70 MHz, thus causing the IF receiver to lock on this remnant signal.
The carrier-to-noise ratio in a 1-Hz bandwidth (C/No) can be programmed between 15 and 100 dB.Hz.
When the IF carrier is modulated at least by a video signal, the noise energy remains fixed and the carrier level is
automatically adjusted to the required C/No value.
When the IF carrier is exclusively modulated by a PCM signal:
If the symbol rate (SR) is higher than 1 Msps, the noise energy remains fixed and the
carrier level is automatically adjusted to the required C/No value.
Below 1 Msps and for very low noise conditions (for instance C/No > 70 dB.Hz @ 100
ksps), the noise energy will be automatically adjusted to the required C/No value.
3.4.2.3. Noise Bandwidth
The noise spectrum is centered on 70 MHz and its bandwidth depends on the IFM setting (video mode or PCM
mode).
In video mode, the peak-to-peak noise bandwidth is fixed (50 MHz).
In PCM mode, the peak-to-peak noise bandwidth depends on the symbol rate:
50 MHz if the symbol rate is higher than 3.125 Msps,
Between 8 and 12 times the symbol rate (with a minimum of 800 kHz) when the latter is
less than 3.125 Msps.
To Next Page
Loading...