External Communications Flashcards
What is the purpose of a communication system?
To create an acceptable reproduction of the source message at the destination.
In communication systems, why do we modulate?
1) Efficiency
2) Hardware limits
3) Resist noise and interference
4) Frequency assignments
5) Multiplexing
Where is noise most significant?
At the receiver where the transmitted signal is weakest.
What is the difference between noise and interference?
1) Noise is random and unpredictable
2) Interference is a structured, human-made signal such as someone else’s transmission.
What can affect received signal strength?
1) Attenuation
2) Free space loss
3) Fading
4) Reflection
5) Refraction
6) Diffraction
7) Scattering
What is an analog signal?
Analog signals are waveforms where the voltages vary over time. This means that at a given time, there are infinite possible amplitude values.
What is a digital signal?
A digital signal is discrete in amplitude.
What is a modulated signal?
A baseband signal combined with a carrier frequency.
What is modulation?
The information of the message (baseband) is imbedded in a carrier signal. Modulation occurs by altering the amplitude, frequency or phase of the carrier.
What is the purpose of “band limiting”?
Restrict signal bandwidth to fit assigned channel
What is the difference between analog and digital signals?
1) Analog - continuous in time and amplitude
2) Digital - discrete in amplitude and continuous in time.
What is the transmission frequency for coaxial cable?
1kHz to 4 GHz
What are some advantages of fiber optic cables?
1) Immune to EMI
2) High data rates
3) Lightweight
4) No sparks
5) Difficult to intercept
6) Small cables
What are some disadvantages of fiber optic cables?
1) Cost
2) Difficult to repair and install
What is attentuation?
Decrease in signal strength as a function of distance as it travels through the medium.
What is the 3dB loss?
3dB loos is equivalent to losing half the power. If a 1W signal is attenuated to 0.5 W in 1 meter, the attenuation of the signal is 3dB/m
What is the Hartley Shannon Law
Maximum channel capacity for a finite bandwidth, continuous time channel.
What is the Voltage Standing Wave Ratio?
Ratio of the maximum amplitude to the minimum amplitude of the standing wave in a transmission line.
Define reflection, refraction and diffraction.
1) Reflection - EM waves bouncing off a surface
2) Refraction - EM wave bending due to changes in propagation velocity
3) Diffraction - tendency of a wave to bend around a boundary.
What is Snell’s Law?
Gives the relationship between the angles of light as it passes from one medium to another.
Do any of the LINK systems require keys?
1) LINK-11 - No
2) LINK 16 - Yes key goes in cabinet in OPS
3) LINK 22 - No
How does LINK interface with GCCS - M?
What is MSCU?
MSCU is another source of internet. It requires a lease, I am not sure if STJ currently has one.
The AE is in the middle of the hangar top.
It functions in X and K band.
The user laptop is located in the CCR next to the NMT laptop.
What is JREAP-C and where is it located?
Joint Range Extension Application Program. Hardware is located in the CCR, aft bulkhead on the bottom shelf.
What is river city?
A protocol to control outgoing information systems and communication.
What is River City 1?
It is the most restrictive state and is assumed automatically when the ship encounters or responds to an emergency.
What is river city 2?
This is a restricted state. Only members in user group BRAVO have access during this state. It is used when VIPs are on board, higher threat port visits and during operations.
What is river city 3?
This is a restricted bandwidth state. Used when larger than normal BW is required such as transferring large files. In this state you can’t web browse or send UNLAS email. USER group BRAVO has full access.
What is river city 4?
This is the least restrictive state and is used during normal operations.
If the CCMS HDD fails an you need to switch to your tape drive, does your recovery time change?
It would increase when using the tape drive. However, there are spare drives on board. No one uses CCMS anymore anyway.
Can you change circuits using the TSCU?
If you have to isolate cooling to HF, can you still operate safely?
The system would begin to overheat and would eventually fail. In theory you could use it until it started to burn up.
Can you use HF Emergency when the EMCON panel is enabled?
Yes you can by using the EMCON bypass key in the ERR.
Can you control LINK 11 via CMS?
Yes, you can access the Data Link Processing System (DLPS) via the MCT at any MFW. (check with the operators about this)
Where to the Naval Communicators operate NMT from?
They operate NMT from the CCR via the Remote Operating Unit.
Does anyone from CSED go to the ERR for action stations?
Yes, a communications technician will go there to monitor UHF emergency and be available for quick reaction fault finding.
Is there any redundancy for NMT to switch between the FWD and AFT navigation feeds?
Does LINK 16 physically connect to the external communications system?
LINK 16 has its own transceiver and antenna with its own radio.
Explain the power triangle.
It can transmit:
1) One circuit up to 4kW
2) Two circuits up to 1kW
3) Four circuits up to 250W
4) Eight circuits up to 100W
HF Emergency allows one circuit up to 1kW
What is the purpose of the Communications Plan
The communications plan is to assign communication frequencies, channels and radio assignments to manage the frequency bands and control emissions when operating in a task group. This prevents communication interference and reduces enemy ability to interrupt communications.
Where is the HF emergency equipment located?
1) Transmitter and Receiver - ERR
2) Antenna - STBD side of funnel
What is the impact of losing the HF ISDU?
If we lose WADS what is the impact?
Unable to automatically configure circuits through CCMS. However, circuits can be manually configured at the BPP.
How do operators know which circuit is associated with which channel?
The COMM PLAN is posted on the TV on the forward bulkhead of the OPS ROOM.
Which channels are monitored all the time?
VHF - Channel 16 (121.5 MHz)
UHF - 243 MHz
HF 2182 KHz
What is the minimum safe at sea requirements WRT communication systems?
1) 1 x VHF
2) 1 X UHF
3) 1 X HF
4) 1 X internet source
5) SHINCOM
6) Public Address
Why are HF keys in the major emitter keyboard?
Due to the potential to create contact currents or a re-radiator.
What are the restrictions when using HF with LINK 11?
Can only use exciters 1,2,7,8 due to upper and lower side bands.
What is extended line of sight?
It is when you can use a line of sight system and extended beyond line of sight such as scattering off the troposphere. Theoretically, you could piggyback another unit signals to extend your range too. How likely is this? I have no idea.
What is the frequency range and power output of PRC 117
Power - 1-10W
Frequency - 30 to 500MHz
What is the maximum bandwidth of NMT?
10Mb dependent on lease.
What is the main difference between LINK 11 and 16?
LINK 16 gives a warning before broadcasting information and LINK 11 does not.
What is the maximum power output of UHF?
1) In AM the power is 30W
2) In FM the power is 100W
Why are there SFC feeds required for NMT and UHF SATCOM?
Navigation feeds are required for synchronization and to stabilize the UHF SATCOM antennas.
What is the CCMS printer used for?
It will print the B-switch for BPP configuration.
What is the HF frequency range?
Tx - 2-30MHz
Rx - 10KHz - 30 MHz
EMERG - 2-30 MHz
What is the UHF frequency range?
UHF - 225-400 MHz
UHF EMERG - 225-400 MHz
UHF SATCOM - 240MHz - 318 MHz
What is the LINK 16 frequency range?
960 KHz - 1215 MHz
What is the GMDSS frequency range?
Tx - 156 - 161.45 MHz
Rx - 156 - 153.45 MHz
What is the PRC-117 frequency range?
30-512 MHz
What does loopback mean?
Can you loop back UHF and HF
Listen to what you have transmitted.
Yes you can loop back HF and UHF
What crypto techniques to we use?
What happens when we receive a distress call? Are there alarms?
1) Brief the CO about the call, they will decide how to respond.
2) There are alarms.
ASK about this!
What FMF organization assists us with Communication trials?
NESTRA - Naval Electronic Systems Test Range Atlantic
Where are crypto keys obtained from?
Trinity
What is the name of the paper crypto loader unit?
KOI-18
Is there only one BPF and AMU in the HF Tx system?
No, there is one for each antenna.
What is the EMRU?
1) EMCOM Relay Unit
2) Located in the middle forward cabinet in HFTR
3) Used to transfer all AE power to the dummy loads and grounds the antenna to provide safe access.
How would the failure of one HF power amplifier affect the power pyramid?
1) No 4k circuit
2) Only 1 1k circuit
3) only 3 250 W circuits
4) Only 7 100W circuits.
What HF component performs signal modulation?
HF exciter
What does the exciter generate?
A carrier signal
Why to we have a Remote Transmit Control Unit?
1) Signature Management
2) Safety
At what HF power does the upper deck get piped OOB?
2Kw
Do UHF LOS and EMERGENCY use air driers?
Air is supplied to the antennas and the couplers for prevent condensation and corrosion.
How many UHF patch panels are there?
Two
What satellite constellation does UHF SATCOM use?
UHF follow on (UFO)
What is a thru-line watt meter?
Measures peak and average power
If WADS and BPP are set up together, which one takes precedence?
BPP
If CCMS is down can we control WADS?
Yes, WADS can be used locally to connect and disconnect circuits but the BPP would be uses.
What is CCMS and what type of processors does it use?
Communications Control and Monitoring System and it used a UYK 507 processor.
When can signals go to the BPP from the Red Patch Panel?
When the data is secured
How many COMPLANS do we store?
We store five and have one active.
What is the printed version of the COMPLAN called?
The B-switch
What is the HF range at full power?
Potential to go around the planet three times.
What are the distress receivers?
1) HF - 2182 KHz (maritime distress)
2) UFH LOS - 243 (military air distress)
3) PRC-117 - 121.5 MHz civilian air distress
4) GMDSS - Ch 16 156.8 MHz(international distress)
What is the purpose of the technical COMSEC inspection?
To ensure equipment on board is installed IAW the Emissions Control Policy.
Which systems can you “loop back”?
Any system where Tx and Rx are separate.
1) HF
2) UHF
3) PRC 117 with UHF
What is special about KIV-7M?
It is programmable
What happens when a signal is received outside the receive band?
Potential exists to pick it up, however it would be severely attenuated and it may not be readable.
Why does GMDSS have a larger Rx band?
So that our transmissions don’t interfere with the users of VHF between 161.5 and 163 MHz.
What is impedance matching?
Impedance matching in a communications system is matching the impedance (the resistance to alternating current) of the transmitter and the antenna to maximize power transfer and mitigate the losses.
What are the differences between LINK 11 and LINK 16?
1) Tech: 11-HF/UHF +polling. 16- UHF+TDMA
2) Data Rate: 11-slow 16 - high
3) Range: 11 - global 16 - LOS
4) Real Time: 11 - limited 16 - yes
5) Encryption: 11 - limited 16 - advanced
6) Apps: 11 - legacy sys 16 - modern ops
