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Beginners Guide to Radio Scanners

If you’re a complete beginner/novice to scanning, I hope this guide will give you some useful advice and point you in the right direction to get you started.

This guide will be updated time to time to add new subjects and teach you more about your scanner and various scanning activities.

First off, I’ll start with the basics of what a scanner is and does in its simplest form.

The Basics

1: What is a scanner?

A scanner is a radio that covers a far wider frequency range than your average radio at home. Most radios you find in everyday use have a single purpose, i.e. the radio in your car/home is designed to only receive commercial radio stations. Scanners on the other hand, can receive signals transmitted on a wide range of frequencies, allowing the user to listen in to a huge range of different communications including air traffic control, emergency services (ambulance and fire), hobbyists (Citizens Band, Amateur radio), security guards, taxi’s and a lot more.

2: What does a scanner do?

A scanner has two main modes of operation; these are commonly known as ‘search’ and ‘scan’

In ‘search’ mode, you are searching for any transmissions within a certain frequency range specified by the user, i.e. 400-470 MHz. The scanner will quickly scan through the frequencies and if it detects a transmission it will stop immediately and let you listen to what it has found. At this point you can hold the scanner on this frequency and continue to listen or you can let it continue scanning for other transmissions. You can also store the frequency it stopped on into a memory channel for future reference. That brings me to the next mode on your scanner, ‘scan’

Once you start filling up your memory channels with frequencies of interest to you, you can set the scanner to scan through only the channels you’ve saved. This mode on most scanners is extremely quick so you never miss any action.

3: Types of scanners?

Scanners come in two types, handheld and base/mobile. Deciding which to buy is simply a case of knowing where you will use the radio most. If you only plan to use it at home, a home base unit would be a better option. If you plan to take your scanner out and about, a handheld unit will be the best option. Purchasing a handheld is probably the best option for beginners as you can use this at home and also outdoors so you get the best of both worlds.

Getting technical

Now that we’ve got what a scanner basically does, we’ll move onto some of the more technical aspects of scanning.

A lot of beginners seem to falter at this stage, they’ve bought a scanner, played around with it and can’t find anything to listen to and are disappointed and blame the scanner, when 90% of the time, it’s a user error, or just a lack of knowledge in regards to knowing where to scan and what to look for.

I’ll start with some of the other basic functions on a scanner, I’ll stick to the basics that every scanner will have, most scanners will have a lot more features but these will all be model specific.

1: Squelch

You need to set your squelch control properly for the scanner to search/scan. This is easy to do. To start off, turn the squelch right down so you get the constant hissing/white noise coming through the speaker, then slowly turn it back up, you want to set it just above the point where the hissing/white noise stops and that’s it, your squelch is set.

2: Modes

Nearly all scanners will have at least 2 modes, those being AM and FM. For the best part, you’ll be sticking to FM. There are some exceptions though, Air Band (108-136 Mhz) for example uses AM, so when searching through the air band range, make sure you’re using AM.

Some scanners will list FM as NFM and WFM, NFM stands for narrow fm and WFM stands for wide fm. You only need WFM for listening to commercial radio stations, for everything else stick to NFM.

There is also USB and LSB, upper and lower sideband, these modes are used mainly on the HF bands (3-30 MHz) by radio amateurs, ships, aircraft etc. You will only find these modes on more advanced scanners.

3: Step size

You’re scanner will usually have various step sizes for you to choose from (on cheaper/older scanners you may find these are locked and you have no choice) these will typically range from 5/6.25/8.33/10/12.5/25/50khz steps. Choosing the correct step size is essential for searching efficiently and making sure you don’t miss any transmissions, and also to make sure that when the scanner stops, it’s accurately tuned to the frequency.

A general guide is to stick to 12.5 kHz steps for VHF, and 6.25 kHz steps for UHF.

4: Scan delay

Most scanners will have an option for you to choose how long the scanner will stop on a frequency after the transmission ends, before it starts scanning or searching again. The times will vary from scanner to scanner, usually 2-30 seconds and it’s entirely up to you which you choose. This is a handy feature as the other radio user may take a few seconds to respond to the first person, so without this feature, the scanner would just immediately move on without waiting for the response.

5: Lock out

Again, this is a feature most scanners have. This enables you to lock out certain frequencies you want to skip past/ignore. In “search” this is useful as you will occasionally come across a transmission which is constantly there making the scanner stop, so instead of having to manually make the scanner continue, with the lock out feature the scanner will simply ignore it and continue scanning. In ‘scan’ mode, you might not want to listen to some of your stored channels while scanning through them, so if you lock them out, the scanner will ignore any activity found on them. Any channels locked out, can be unlocked at any time as well, refer to your manual on how to unlock the channels (usually just the same way you locked them to start with)

6: Hold

Most scanners have a ‘hold’ button, pressing this will indefinitely hold the scanner on the current channel/frequency until you press it again which is handy for monitoring one channel if something interesting is happening, this will ensure you miss nothing.

Using your scanner

Now that you have a basic understanding of what your scanner can do, and what the basic functions do, it’s time to put it to use.

You will need to refer to your scanners manual to find out how to get it into search mode (to find frequencies in your area) or scan mode (to scan frequencies you’ve stored)

Here is a rough guide of where to search and what you may find using your scanner.

31.000 – 32.000 MHz FM – Cordless phones

70.500 – 71.500 MHz AM – Fire Brigade

85.000 – 88.000 MHz – PMR (Private Mobile Radio)

117.975 – 136.000 MHz AM – Civil Air band.

144.000 – 146.000 MHz FM – Amateur Radio 2m Band

156.000 – 163.000 MHz FM – Marine band

163.000 – 185.000 MHz FM – PMR (security,taxis,ambulance etc)

200.000 – 399.000 MHz AM – Military airband

430.000 – 440.000 MHz FM – Amateur Radio 70cm band

440.000 – 446.000 MHz FM – PMR

446.000 – 446.500 MHz FM – PMR (including licence free pmr)

446.500 – 470.000 MHz FM – PMR (security etc)

It’s now simply a case of searching through the various ranges over and over and finding transmissions within range, listening to them and trying to identify them.

Have patience when you’re searching and don’t get frustrated if you pick up nothing the first few times you scan through, just keep on searching and you will come across transmissions eventually! Once you do, you can start adding them to your memory channels and building up your own database of frequencies in your area.

NA-771 SMA-Female Dual Band UV 144/430Mhz 10W High-gain Antenna For Baofeng BF-UV5R

Type : NA-771
Connector : SMA Female Connector
Frequency : 144 / 430MHz
Gain : 2.15db(144MHz) / 3.0db(430MHz)
Max power : 10 Watts
V.S.W.R : Less 1.5
Impedance : 50 OHM
Color : Black
Length : About 400mm
Weight : 29g
Package weight : 37g
This antenna is also compatible with the following radios.
BAOFENG: UV5R/Plus, UV5RA/Plus, UV5RE/Plus, UV5RB, UV5RC, UV5RD, UV3RPlus, BF-320, BF-480, BF-490, BF-520, BF-V6, BF-V8 etc…
WOUXUN: KG-UVD1P, KG-816, KG-818, KG-819, KG-869, KG-889, KG-833, KG-659/E, KG-699, KG-669, KG-669plus, KG-689, KG-679, KG-659, KG-689plus etc…
LINTON: LT-2288, LT-3288, LT-5288, LT-3188, LT-2188, LT-3260, LT-2268, LT-3268 etc…
PUXING: PX-777, PX-666, PX-3288, PX-555, PX-666, PX-888, PX-6288 etc…
QUANSHENG: TG-K4AT, TG-2AT, TG-45AT, TG-42AT, TG-22AT, TG-25A
WEIERWEI: VEV-3288S ,VEV-3288 V-1000 etc…
FEIDAXIN: FD-6288, FD-268, FD-288, FD-150A, FD450A, FD160A, FD450A, FD-460A etc…
TYT: TH-UV3 etc…

 

Low profile SMA-Female Dual Band Antenna for BaoFeng 888s UV-5R

A low profile antenna that is great for vehicle communications that works better on UHF 400-520Mhz than VHF 136-174Mhz.

Specification:
 Max. Power :10W
Impedance:50ohms
Magnet diameter: approx. 30mm
Connector:SMA-Female
Length: 3 meters
Antenna height: approx. 140mm
Frequency: 136-174MHz 400-520MHz
Gain: 3.0 dB
Weight: 46g
This antenna is also compatible with the following radios.
BAOFENG: UV5R/Plus, UV5RA/Plus, UV5RE/Plus, UV5RB, UV5RC, UV5RD, UV3RPlus, BF-320, BF-480, BF-490, BF-520, BF-V6, BF-V8 etc…
WOUXUN: KG-UVD1P, KG-816, KG-818, KG-819, KG-869, KG-889, KG-833, KG-659/E, KG-699, KG-669, KG-669plus, KG-689, KG-679, KG-659, KG-689plus etc…
LINTON: LT-2288, LT-3288, LT-5288, LT-3188, LT-2188, LT-3260, LT-2268, LT-3268 etc…
PUXING: PX-777, PX-666, PX-3288, PX-555, PX-666, PX-888, PX-6288 etc…
QUANSHENG: TG-K4AT, TG-2AT, TG-45AT, TG-42AT, TG-22AT, TG-25A
WEIERWEI: VEV-3288S ,VEV-3288 V-1000 etc…
FEIDAXIN: FD-6288, FD-268, FD-288, FD-150A, FD450A, FD160A, FD450A, FD-460A etc…
TYT: TH-UV3 etc…

NAGOYA UT-106 10w Antenna for BAOFENG UV5R / UV5RA / UV5RE HIYG

This great little vehicle mounted antenna will provide extra coverage when out and about.

Specifications:
Length: Approx. 43cm/16.9″
Diameter: Approx. 3cm/1.18″
Frequency range: 136-174 400-520 (MHz)
Impedance: 50 (Ω)
Gain: 2.15 (dB)
Max power: 10W
Applicable models: Baofeng all models
Center frequency: 144 / 430MHZ
Weight: 60g
This antenna is also compatible with the following radios.
BAOFENG: UV5R/Plus, UV5RA/Plus, UV5RE/Plus, UV5RB, UV5RC, UV5RD, UV3RPlus, BF-320, BF-480, BF-490, BF-520, BF-V6, BF-V8 etc…
WOUXUN: KG-UVD1P, KG-816, KG-818, KG-819, KG-869, KG-889, KG-833, KG-659/E, KG-699, KG-669, KG-669plus, KG-689, KG-679, KG-659, KG-689plus etc…
LINTON: LT-2288, LT-3288, LT-5288, LT-3188, LT-2188, LT-3260, LT-2268, LT-3268 etc…
PUXING: PX-777, PX-666, PX-3288, PX-555, PX-666, PX-888, PX-6288 etc…
QUANSHENG: TG-K4AT, TG-2AT, TG-45AT, TG-42AT, TG-22AT, TG-25A
WEIERWEI: VEV-3288S ,VEV-3288 V-1000 etc…
FEIDAXIN: FD-6288, FD-268, FD-288, FD-150A, FD450A, FD160A, FD450A, FD-460A etc…
TYT: TH-UV3 etc…

BAOFENG UV-5R review

The radio snob in me wants to start off by saying that there are other radios out there – and many of them are a lot more reliable than the Baofeng UV-5R. Icom, Motorola,  & Yaesu make excellent HT (Handy Talkie) radios. And you might be much better served by having a more substantially reliable radio like one of those. If I had to put my life on the line I would prefer to have a radio I know I can count on to work when I need it to.

But as these are so inexpensive, and easy to get (on BANGGOOD) and since you’re usually looking at around $150 to get one of the better brands I decided to write this article to discuss the entry-level Baofeng so folks can understand what this radio can and can’t do. And since we now own 2 of them we shouldn’t talk too much smack about them now, should we.

The Baofeng uv5r review & Guide

Lets set your expectations. This is not a top-of-the line radio. Its not supposed to be. Its cheap, so you can rest assured that problems with these radios can arise from time to time. We’ve had one that cannot receive or transmit if the channel is changed unless you turn the unit on/off.

Versions

There are several known variants of this radio. All of them are the same hardware, the only difference is the firmware (software) they ship with. If you buy on Amazon you are probably getting the latest firmware, but there’s no guarantee. Its not a game changer, they all pretty much run the same from what I can tell.

Durability

Don’t drop these. They aren’t cream-puffs but they are not meant to be roughed up like some other radios are. But the build feels solid enough for what its meant to do.

Expendabilty

Our suggestion is to get a good HT from Icom or Yaesu if you can spring the +$150, and get a few Baofengs as beaters and backups. Strength in numbers. But if you want something today buy the Baofeng and you rest easy that at least you covered it.

Programming

Not horrible, but only if done on a computer. If all you care about is 4-5 frequencies then you can do it on the unit. You need the computer program CHIRP to program the HT. You also need a special USB cable. Avoid the cheap knockoffs. Been there done that.

You can download a greatly improved version of the Owners Operating Manual here. Its a good idea to save a copy of this to your emergency USB stick with all your other emergency documents. You DO have an emergency USB drive, don’t you?

 

Citizen Band radio

The Citizen Band Radio Service (CBRS) is a two-way, short distance, voice communications service that provides a cheap, reliable means of communication.

The service operates in two frequency bands:

  • high frequency (HF) band – (26.965 – 27.405 MHz)
  • ultra high frequency (UHF) band – (476.4125 – 477.4125 MHz)

The service is for public access and available to everyone. If a company chooses to use the service for business, they have no rights of exclusivity and must accept other users on the same channel.

Do I need a licence?

No. The operation of CB radios is authorised under the Radiocommunications (Citizen Band Radio Stations) Class Licence 2002. Class licences do not have to be applied for and no licence fees are payable.

The CBRS class licence does not authorise the operation of 27 MHz marine equipment.

What channel do I use to contact other travellers?

There are specific calling channels in the CB bands.

HF band:

  • channel 11 (AM – 27.085 MHz)
  • channel 16 (SSB – 27.155 MHz)

UHF band:

  • channel 11 (476.675 MHz)

Once you have established contact with another traveller, switch to another channel to continue talking. This frees the call channels for other users. If travelling in a convoy of vehicles, select a usual ‘working’ channel prior to setting out.

Can I use my CB radio to transmit data?

Yes. Data can only be transmitted on UHF channels:

  • 22 (476.950 MHz)
  • 23 (476.975 MHz)

Transmission must comply with the restrictions imposed in the CBRS class licence. These channels are dedicated to data purposes and should not be used for voice communication.

In an emergency

There are specific emergency channels that you can use:

  • channel 9 (27.065 MHz) in the HF band
  • channel 5/35 (476.525/477.275 MHz) in the UHF band

These channels are emergency channels and non-urgent traffic must be confined to other channels.

Organisations voluntarily monitor the emergency channels and may assist you in contacting the appropriate service in an emergency.

Conditions of operation

CB operators do not have to be licensed to operate their equipment, but the CBRS class licence imposes a number of operating conditions:

Compliance with mandatory standardsDevices operating under the CBRS class licence must comply with the relevant mandatory standards specified in the licence.

Operating frequenciesCB radios must only be operated on the channels that are detailed in the CBRS class licence. Operation on a channel that is not specified in the class licence is a breach of the licence conditions.

Proper conductThere are specific conditions regarding personal conduct during operation of a CB radio station, and penalties apply for improper conduct. In particular, the CBRS class licence states that:

A person must not operate a CB station:

  • in a way that would be likely to cause a reasonable person, justifiably in all the circumstances, to be seriously alarmed or seriously affronted; or
  • for the purpose of harassing a person.

Transmitter power levels

CB radio equipment must not exceed the maximum output power specified in the class licence. Attaching any external device, such as linear amplifiers, increase power is not allowed.

Other conditions

The operation of a CB radio is also subject to the provisions of the Radiocommunications Act 1992.

Breaches of licence conditions

CB radio users must comply with conditions in the class licence. If any condition of the licence is breached the operator will be liable for prosecution.

What if I cause interference?

Interference to television and radio receivers and other electronic equipment may occur when a CB radio transmitter is used nearby. Such interference is unlikely when mobile, but may occur in campsites, caravan parks or home base situations. Users should cooperate with the affected person and take reasonable steps to fix the problem.

Selective calling

Selective calling (selcall)-a technique used to enable the reception of calls from particular CB radios without having to listen to other users-is permitted under the class licence. Selcall uses the transmission of audio tones that are recognisable to receivers fitted with a compatible decoder. It can be used on either HF or UHF CB radios. Some CB radios come fitted with a selcall facility using continuous tone coded squelch system (CTCSS) techniques. CTCSS is only authorised on UHF CB bands.

CBRS repeaters

A repeater is a station established at a fixed location that receives radio signals from one CB station and automatically retransmits the signal to another station using the corresponding output channel. UHF CBRS repeaters can be found in all states and enable the range of vehicle to vehicle communications to be significantly increased.

CB repeaters are not authorised under the CBRS class licence. The repeater stations are usually located at hilltop radiocommunication sites and require specific frequency assignments and the issue of an individual apparatus licence.

Repeater channels

Channels 1 to 8 and 41 to 48 are designated as repeater output channels, with channels 31 to 38 and 71 to 78 the corresponding designated repeater input channels.

A repeater that transmits on channel 1 will always receive on channel 31. When operated in duplex/repeater mode the CB radio automatically selects the corresponding transmit/receive frequencies.

These designated repeater channels may be used for single frequency communications provided they are not used in the locality of repeaters.

Channels 5 and 35 are dedicated for emergency communications.

Please note: this document is intended as a guide only and should not be relied on as legal advice or regarded as a substitute for legal advice in individual cases.

Original Article

UNDERSTANDING UHF CB RADIO – WHICH CHANNELS SHOULD YOU USE?

What is UHF?

Simply put, UHF CB or citizen band radio is a two-way radio system that uses the 476.4250–477.4125MHz, radio spectrum for short-distance communications.
It is divided into 80 channels for various uses. The service is for public access and available to everyone but not all channels can be used by anyone for just any reason – there are significant penalties for misuse of channels.

For example, the Australian Government has legislated that channels 5 & 35 on the UHF CB Band are reserved for emergency use only 

As at January 2007 the maximum penalties for the misuse of the legally allocated CB emergency channels are:

  • For general misuse – if an individual 2 years imprisonment, otherwise $165,000 (a $220 on-the-spot fine can be issued in minor cases); or
  • For interference to an Emergency call – if an individual 5 years imprisonment, otherwise $550,000

LEGALLY RESTRICTED CHANNELS

The following channels are legislated as a part of the ACMA UHF CB Class Licence.

  • Channel 5 and 35 are the designated emergency channels, and are not to be used except in an emergency. To make an emergency call, switch your radio to Channel 5 with duplex on, if there is no response, try again with duplex off.
  • Channel 11 is the ‘call channel’ and is only to be used for initiating calls with another person, you should quickly organise another vacant channel to continue your discussion on.
  • Channel 22 and 23 are only to be used for telemetry and telecommand, packet data and voice transmission are not allowed.
  • Channel 61, 62 and 63 are reserved for future allocation and transmission on these channels is not allowed.

 

UHF’s distinct advantage over mobile phones is that it can work anywhere and requires little to no infrastructure to be in place. At the user end, all that is required is a basic radio set. The key disadvantage is that it operates on a line-of-sight basis, and therefore has very short reach. Under normal conditions, you can expect a good signal over a distance of 5 to 8km; in a high position (such as a hill), this can be increased to up to 25km. The upside is that you’re always communicating with those who are in your immediate vicinity.

UHF channels

Each of the 80 UHF channels has the following accepted use:

  • Channels 1–8 and 41–48: duplex channels (output).
  • Channels 31–38 and 71–78: duplex channels (input).
  • Channels 5 and 35: duplex channels strictly used for emergency communications.
  • Channels 9, 12 -17, 19–21 24–28, 30, 39, 49-60, 64-70, 79 and 80:general chat channels, simplex use.
  • Channel 10: 4WD Clubs or Convoys and National Parks.
  • Channel 11: Call Channel used for locating friends – a general meeting point for when communications are lost or beginning, before moving to another channel.
  • Channel 18:Caravanners and Campers Convoy Channel.
  • Channel 40: Australia Wide road safety channel used primarily by truckies and oversized load pilot vehicles.
  • Channels 22 and 23 (25kHz):Telemetry & Telecommand used for automated data communications only.
  • Channel 29: Road safety channel Pacific Hwy, Pacific Mwy (NSW & QLD).
  • Channels 61–63: reserved for future use

What is Duplex?

The ‘duplex’ function of the UHF system helps increase the range of UHF radios using repeater stations set in ideal locations, such as hills. In duplex mode, the fixed position station forwards the signal it receives from repeater input stations 31-38/71-78 to the corresponding output stations 1-8/41-48.

Any transmissions sent on non-duplex channels are sent in simplex mode, or directly between radio sets without the use of a repeater.

Changes from 12.5kHz vs. 25kHz band spacing

In 2011 the channel bandwidth or frequency spacing was split in two from 25kHz to 12.5kHz. This effectively doubled the number of available channels from 40 to the current 80. While most older radio units are not compatible, it is still possible to use them until the end of the 5-year transition period (2016).

Etiquette

It is important to remember that channels 5 and 35are strictly for emergency communications, as emergency services monitor channel 5 for requests for help. People found to be misusing these or any other designated channels can face hefty fines.

Once communication is established, it’s accepted that both parties continue on another channel to free the channel up. If they’re taking place over a short distance, these ‘one on one’ conversations can continue on any of the general-use channels.

It’s important to understand that all communications on every channel are public. Anyone within range of you or a repeater that you’re using can hear you and join in. For the most part, users are well behaved and respect the rules, but you may encounter trolls who want to cause trouble or new users who are unaware of the etiquette.

UHF radio is a great way of staying in touch with your convoy or just to see who’s about. Most importantly, it is a vital link to the outside world when things go wrong.

UHF CB 80 Channel Frequency List

Channel Frequency Duplex Frequency Use Channel Spacing
Channel 1
476.4250
477.1750 Duplex – Repeater Output 12.5 KHz
Channel 2
476.4500
477.2000 Duplex – Repeater Output 12.5 KHz
Channel 3
476.4750
477.2250
Duplex – Repeater Output
12.5 KHz
Channel 4
476.5000
477.2500
Duplex – Repeater Output
12.5 KHz
Channel 5
476.5250
477.2750
Duplex – Repeater Output (Emergency use only)
12.5 KHz
Channel 6
476.5500
477.3000
Duplex – Repeater Output
12.5 KHz
Channel 7
476.5750
477.3250
Duplex – Repeater Output
12.5 KHz
Channel 8
476.6000
477.3500
Duplex – Repeater Output
12.5 KHz
Channel 9
476.6250
Simplex
12.5 KHz
Channel 10
476.6500
Simplex 4WD Drivers – Convoy, Clubs & National Parks
12.5 KHz
Channel 11
476.6750
Simplex Call Channel
12.5 KHz
Channel 12
476.7000
Simplex
12.5 KHz
Channel 13
476.7250
Simplex
12.5 KHz
Channel 14
476.7500
Simplex
12.5 KHz
Channel 15
476.7750
Simplex
12.5 KHz
Channel 16
476.8000
Simplex
12.5 KHz
Channel 17
476.8250
Simplex
12.5 KHz
Channel 18
476.8500
Simplex Caravan & Campers Convoy Channel
12.5 KHz
Channel 19
476.8750
Simplex
12.5 KHz
Channel 20
476.9000
Simplex
12.5 KHz
Channel 21
476.9250
Simplex
12.5 KHz
Channel 22
476.9500
Data Only (No Voice)
25 KHz
Channel 23
476.9750
Data Only (No Voice)
25 KHz
Channel 24
477.0000
Simplex
12.5 KHz
Channel 25
477.0250
Simplex
12.5 KHz
Channel 26
477.0500
Simplex
12.5 KHz
Channel 27
477.0750
Simplex
12.5 KHz
Channel 28
477.1000
Simplex
12.5 KHz
Channel 29
477.1250
Simplex Pacific Hwy (NSW) & Bruce Hwy (Qld) Road Channel
12.5 KHz
Channel 30
477.1500
Simplex UHF CB Broadcasts
12.5 KHz
Channel 31
477.1750
476.4250
Repeater Input
12.5 KHz
Channel 32
477.2000
476.4500
Repeater Input
12.5 KHz
Channel 33
477.2250
476.4750
Repeater Input
12.5 KHz
Channel 34
477.2500
476.5000
Repeater Input
12.5 KHz
Channel 35
477.2750
476.5250
Repeater Input (Emergency Use Only)
12.5 KHz
Channel 36
477.3000
476.5500
Repeater Input
12.5 KHz
Channel 37
477.3250
476.5750
Repeater Input
12.5 KHz
Channel 38
477.3500
476.6000
Repeater Input
12.5 KHz
Channel 39
477.3750
Simplex
12.5 KHz
Channel 40
477.4000
Simplex Highway Channel
12.5 KHz
Channel 41
476.4375
477.1875
Duplex – Repeater Output
12.5 KHz
Channel 42
476.4625
477.2125
Duplex – Repeater Output
12.5 KHz
Channel 43
476.4875
477.2375
Duplex – Repeater Output
12.5 KHz
Channel 44
476.5125
477.2625
Duplex – Repeater Output
12.5 KHz
Channel 45
476.5375
477.2875
Duplex – Repeater Output
12.5 KHz
Channel 46
476.5625
477.3125
Duplex – Repeater Output
12.5 KHz
Channel 47
476.5875
477.3375
Duplex – Repeater Output
12.5 KHz
Channel 48
476.6125
477.3625
Duplex – Repeater Output
12.5 KHz
Channel 49
476.6375
Simplex
12.5 KHz
Channel 50
476.6625
Simplex
12.5 KHz
Channel 51
476.6875
Simplex
12.5 KHz
Channel 52
476.7125
Simplex
12.5 KHz
Channel 53
476.7375
Simplex
12.5 KHz
Channel 54
476.7625
Simplex
12.5 KHz
Channel 55
476.7875
Simplex
12.5 KHz
Channel 56
476.8125
Simplex
12.5 KHz
Channel 57
476.8375
Simplex
12.5 KHz
Channel 58
476.8625
Simplex
12.5 KHz
Channel 59
476.8875
Simplex
12.5 KHz
Channel 60
476.9125
Simplex
12.5 KHz
Channel 61
Reserved for Future Expansion
Channel 62
Reserved for Future Expansion
Channel 63
Reserved for Future Expansion
Channel 64
477.0125
Simplex
12.5 KHz
Channel 65
477.0375
Simplex
12.5 KHz
Channel 66
477.0625
Simplex
12.5 KHz
Channel 67
477.0875
Simplex
12.5 KHz
Channel 68
477.1125
Simplex
12.5 KHz
Channel 69
477.1375
Simplex
12.5 KHz
Channel 70
477.1625
Simplex
12.5 KHz
Channel 71
477.1875
476.4375
Repeater Input
12.5 KHz
Channel 72
477.2125
476.4625
Repeater Input
12.5 KHz
Channel 73
477.2375
476.4875
Repeater Input
12.5 KHz
Channel 74
477.2625
476.5125
Repeater Input
12.5 KHz
Channel 75
477.2875
476.5375
Repeater Input
12.5 KHz
Channel 76
477.3125
476.5625
Repeater Input
12.5 KHz
Channel 77
477.3375
476.5875
Repeater Input
12.5 KHz
Channel 78
477.3625
476.6125
Repeater Input
12.5 KHz
Channel 79
477.3875
Simplex
12.5 KHz
Channel 80
477.4125
Simplex
12.5 KHz

NATO phonetic alphabet

The International Radiotelephony Spelling Alphabet, commonly known as the ICAO phonetic alphabet, sometimes called the NATO alphabet or spelling alphabet and the ITU radiotelephonic or phonetic alphabet, is the most widely used radiotelephonic spelling alphabet. Although often called “phonetic alphabets”, spelling alphabets are not associated with phonetic transcription systems such as the International Phonetic Alphabet. Instead, the International Civil Aviation Organization (ICAO) alphabet assigned codewords acrophonically to the letters of the English alphabet, so that critical combinations of letters and numbers can be pronounced and understood by those who exchange voice messages by radio or telephone regardless of language barriers or the quality of the communication channel.

The 26 code words in the NATO phonetic alphabet are assigned to the 26 letters of the English alphabet in alphabetical order as follows: Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.

Code words

The final choice of code words for the letters of the alphabet and for the digits was made after hundreds of thousands of comprehension tests involving 31 nationalities. The qualifying feature was the likelihood of a code word being understood in the context of others. For example, football has a higher chance of being understood than foxtrot in isolation, but foxtrot is superior in extended communication.

The pronunciation of the code words varies according to the language habits of the speaker. To eliminate wide variations in pronunciation, recordings and posters illustrating the pronunciation desired by the ICAO are available. However, there are still differences in pronunciation between the ICAO and other agencies, and the ICAO has conflicting Roman-alphabet and IPA transcriptions. Also, although all codes for the letters of the alphabet are English words, they are not in general given English pronunciations. Assuming that the transcriptions are not intended to be precise, only 11 of the 26—Bravo, Echo, Hotel, Juliet(t), Kilo, Mike, Papa, Quebec, Romeo, Whiskey, and Zulu—are given English pronunciations by all these agencies, though not always the same English pronunciations.

Letters

Letter Code word Conflicting accounts of the pronunciation
U.S. Army
standard
ICAO and ITU
Roman standard
FAA
standards
ICAO
IPA standard
SIO
(France)
ICAO recording
(1955)
Consolidated transcription
A Alfa
ATIS: Alpha
AL fah AL FAH ALFAH or
AL-FAH
ˈælfɑ al fah [ˈælfʌ] /ˈælfɑː/ al-fah
B Bravo BRAH voh BRAH VOH
(1955: BRAH VOH)
BRAHVOH or
BRAH-VO
ˈbrɑːˈvo bra vo [brɑˈvoʊ] /ˌbrɑːˈv/ brah-voh
C Charlie CHAR lee CHAR LEE CHARLEE or
CHAR-LEE
ˈtʃɑːli  or
ˈʃɑːli
tchah li,
char li
[ˈtʃɑ˞li],
[ˈʃɑ˞li]
/ˈɑːrl/ char-lee or
/ˈʃɑːrl/ shar-lee
D Delta DEL tah DELL TAH DELLTAH or
DELL-TAH
ˈdeltɑ del tah [ˈdɛltʌ] /ˈdɛltɑː/ del-tah
E Echo EKK oh ECK OH ECKOH or
ECK-OH
ˈeko èk o [ˈɛkoʊ] /ˈɛk/
F Foxtrot FOKS trot FOKS TROT FOKSTROT or
FOKS-TROT
ˈfɔkstrɔt fox trott [ˈfɑkstrɑt] /ˈfɒkstrɒt/ foks-trot
G Golf Golf GOLF GOLF ɡʌlf [sic] golf [ˈɡʌl(f)] /ˈɡɒlf/ golf
H Hotel HO tell HOH TELL HOHTELL or
HOH-TELL
hoːˈtel ho tèll [hoʊˈtɛl] /hˈtɛl/ hoh-tel
I India IN dee ah IN DEE AH INDEE AH or
IN-DEE-AH
ˈindiˑɑ in di ah [ˈɪndi.ʌ] /ˈɪndɑː/ in-dee-ah
J Juliett
ATIS: Juliet
JEW lee ett JEW LEE ETT JEWLEE ETT or
JEW-LEE-ETT
ˈdʒuːliˑˈet djou li ètt [ˌdʒuliˈɛt] /ˈlɛt/ jew-lee-et or
/ˌlˈɛt/ jew-lee-et
K Kilo KEY loh KEY LOH KEYLOH or
KEY-LOH
ˈkiːlo ki lo [ˈkiloʊ] /ˈkl/ kee-loh
L Lima LEE mah LEE MAH LEEMAH or
LEE-MAH
ˈliːmɑ li mah [ˈlimʌ] /ˈlmɑː/ lee-mah
M Mike Mike MIKE MIKE mɑik maïk [ˈmʌɪk] /ˈmk/ myk
N November NOH vem ber NO VEM BER NOVEMBER or
NO-VEM-BER
noˈvembə no vèmm ber [noʊˈvɛmbɹ̩] /nˈvɛmbər/ noh-vem-bər[17]
O Oscar OSS car OSS CAH OSS-SCAR or
OSS-CAR
ˈɔskɑ oss kar [ˈɑskɹ̩] /ˈɒskɑː/ os-kah
P Papa PAH pah PAH PAH PAHPAH or
PAH-PAH
pəˈpɑ pah pah [pəˈpɑ] /pɑːˈpɑː/ pah-pah
Q Quebec keh BECK KEH BECK KEHBECK or
KWUH-BECK
keˈbek bèk [kɛˈbɛk] /kɛˈbɛk/ ke-bek
R Romeo ROW me oh ROW ME OH ROWME OH or
ROW-ME-OH
ˈroːmiˑo ro mi o [ˈɹoʊmi.oʊ] /ˈrm/ roh-mee-oh
S Sierra see AIR ah SEE AIR RAH SEEAIRAH or
SEE-AIR-AH
siˈerɑ si èr rah [siˈɛɾʌ] /sˈɛrɑː/ see-err-ah
T Tango TANG go TANG GO TANGGO or
TANG-GO
ˈtænɡo tang go [ˈtæŋɡoʊ] /ˈtæŋɡ/ tang-goh
U Uniform YOU nee form YOU NEE FORM or
OO NEE FORM
YOUNEE FORM or
YOU-NEE-FORM or
OO-NEE-FORM
ˈjuːnifɔːm  or
ˈuːnifɔrm
you ni form,
ou ni form
[ˈjunɪ̈fɔ˞m],
[ˈunɪ̈fɔ˞m]
/ˈjuːnfɔːrm/ ew-nee-form or
/ˈnfɔːrm/ oo-nee-form
V Victor VIK ter VIK TAH VIKTAH or
VIK-TAR
ˈviktɑ vik tar [ˈvɪktəɹ] /ˈvɪktɑː/ vik-tah
W Whiskey WISS key WISS KEY WISSKEY or
WISS-KEY
ˈwiski ouiss ki [ˈwɪski] /ˈwɪsk/ wis-kee
X X-ray
or Xray
EKS ray ECKS RAY ECKSRAY [sic] or
ECKS-RAY
ˈeksˈrei èkss [ˈɛksɹeɪ] /ˈɛksr/ eks-ray or
/ˌɛksˈr/ eks-ray
Y Yankee YANG kee YANG KEY YANGKEY [sic] or
YANG-KEY
ˈjænki yang ki [ˈjæŋki] /ˈjæŋk/ yang-kee
Z Zulu ZOO luu ZOO LOO ZOOLOO or
ZOO-LOO
ˈzuːluː zou lou [ˈzulu] /ˈzl/ zoo-loo
– (hyphen) Dash /ˈdæʃ/ dash

Digits

Digit Code word Pronunciation SIO Wikipedia transcription
0 Zero (FAA, USMC)
Nadazero (ITU, IMO)
ZE-RO (ICAO), ZE RO or ZEE-RO (FAA)
NAH-DAH-ZAY-ROH (ITU, IMO)
zi ro /ˈzr/ zee-roh
/ˌnɑːˌdɑːˌzˈr/ nah-dah-zay-roh
1 One (FAA), Won (USMC)
Unaone (ITU, IMO)
WUN (ICAO, FAA)
OO-NAH-WUN (ITU, IMO)
ouann /ˈwʌn/ wun
/ˌˌnɑːˈwʌn/ oo-nah-wun
2 Two (FAA), Too (USMC)
Bissotwo (ITU, IMO)
TOO (ICAO, FAA)
BEES-SOH-TOO (ITU, IMO)
tou /ˈt/ too
/ˌbˌsˈt/ bee-soh-too
3 Three (FAA), Tree (USMC)
Terrathree (ITU, IMO)
TREE (ICAO, FAA)
TAY-RAH-TREE (ITU, IMO)
tri /ˈtr/ tree
/ˌtˌrɑːˈtr/ tay-rah-tree
4 Four (FAA), Fo-wer (USMC)
Kartefour (ITU, IMO)
FOW-ER (ICAO), FOW ER (FAA)
KAR-TAY-FOWER (ITU, IMO)
fo eur /ˈf.ər/ foh-ər
/ˌkɑːrˌtˈf.ər/ kar-tay-foh-ər
5 Five (FAA), Fife (USMC)
Pantafive (ITU, IMO)
FIFE (ICAO, FAA)
PAN-TAH-FIVE (ITU, IMO)
fa ïf /ˈff/ fyf[19]
/ˌpænˌtɑːˈfv/ pan-tah-fyv
6 Six (FAA, USMC)
Soxisix (ITU, IMO)
SIX (ICAO, FAA)
SOK-SEE-SIX (ITU, IMO)
siks /ˈsɪks/ siks
/ˌsɔːkˌsˈsɪks/ sok-see-siks
7 Seven (FAA, USMC)
Setteseven (ITU, IMO)
SEV-EN (ICAO), SEV EN (FAA)
SAY-TAY-SEVEN (ITU, IMO)
sèv n /ˈsɛvɛn/ sev-en
/ˌsˌtˈsɛvɛn/ say-tay-sev-en
8 Eight (FAA), Ate (USMC)
Oktoeight (ITU, IMO)
AIT (ICAO, FAA)
OK-TOH-AIT (ITU, IMO)
eït /ˈt/ ayt
/ˌɔːkˌtˈt/ ok-toh-ayt
9 Niner (FAA, USMC)
Nine or niner (ICAO)
Novenine (ITU, IMO)
NIN-ER (ICAO), NIN ER (FAA)
NO-VAY-NINER (ITU, IMO)
naï neu /ˈnnər/ ny-nər[20]
/ˌnɔːvˌˈnnər/ nov-ay-ny-nər
100 Hundred (ICAO) HUN-dred (ICAO) hun-dred /ˈhʌndrɛd/ hun-dred
1000 Thousand (ICAO) TOU-SAND (ICAO) taou zend /ˌtˈsænd/ tow-zend[21]
. (decimal point) Point (FAA)
Decimal (ITU, ICAO)
DAY-SEE-MAL (ITU) (ICAO) si mal /ˌdˌsˈmæl/ day-see-mal
. (full stop) Stop (ITU) STOP (ITU) /ˈstɒp/ stop

Pronunciation

Pronunciations are somewhat uncertain because the agencies, while ostensibly using the same pronunciations, give different transcriptions, which are often inconsistent from letter to letter. The ICAO gives a different pronunciation for IPA transcription and for respelling, and the FAA also gives different pronunciations depending on the publication consulted, the FAA Aeronautical Information Manual (§ 4-2-7), the FAA Flight Services manual (§ 14.1.5), or the ATC manual (§ 2-4-16). ATIS gives English spellings, but does not give pronunciations or numbers. The ICAO, NATO, and FAA use modifications of English numerals, with stress on one syllable, while the ITU and IMO compound pseudo-Latinate numerals with a slightly different set of modified English numerals, and with stress on each syllable. Numbers 10–99 are spelled out (that is, 17 is “1–7” and 60 is “6–0”), while for hundreds and thousands the English words hundred and thousand are used.

The pronunciation of the digits 3, 4, 5, and 9 differs from standard English – being pronounced tree, fower, fife, and niner. The digit 3 is specified as tree so that it is not pronounced sri; the long pronunciation of 4 (still found in some English dialects) keeps it somewhat distinct from for; 5 is pronounced with a second “f” because the normal pronunciation with a “v” is easily confused with “fire” (a command to shoot); and 9 has an extra syllable to keep it distinct from German nein ‘no’.

Only the ICAO prescribes pronunciation with the IPA, and then only for letters. Several of the pronunciations indicated are slightly modified from their normal English pronunciations: /ˈælfɑ, ˈbrɑːˈvo, ˈʃɑːli, ˈdeltɑ, ˈfɔkstrɔt, ɡʌlf, ˈliːmɑ, ˈɔskɑ, siˈerɑ, ˈtænɡo, ˈuːnifɔrm, ˈviktɑ, ˈjænki/, partially due to the substitution of final schwas with the ah vowel; in addition, the intended distinction between the short vowels /o ɑ ɔ/ and the long vowels /oː ɑː ɔː/ is obscure, and has been ignored in the consolidated transcription above. Both the IPA and respelled pronunciations were developed by the ICAO before 1956 with advice from the governments of both the United States and United Kingdom, so the pronunciations of both General American English and British Received Pronunciation are evident, especially in the rhotic and non-rhotic accents. The respelled version is usually at least consistent with a rhotic accent (‘r’ pronounced), as in CHAR LEE, SHAR LEE, NO VEM BER, YOU NEE FORM, and OO NEE FORM, whereas the IPA version usually specifies a non-rhotic accent (‘r’ pronounced only before a vowel), as in ˈtʃɑːli, ˈʃɑːli, noˈvembə, and ˈjuːnifɔːm. Exceptions are OSS CAH, VIK TAH and ˈuːnifɔrm. The IPA form of Golf implies it is pronounced gulf, which is not either General American English or British Received Pronunciation. Different agencies assign different stress patterns to Bravo, Hotel, Juliett, November, Papa, X-ray; the ICAO has different stresses for Bravo, Juliett, X-ray in its respelled and IPA transcriptions. The mid back [ɔ] vowel transcribed in Oscar and Foxtrot is actually a low vowel in both Received British and General American, and has been interpreted as such above. Furthermore, the pronunciation prescribed for “whiskey” has no initial [h], although some speakers in both General American and RP pronounce an [h] (or [ʍ]) here, and an initial [h] (or [ʍ]) is categorical in Scotland and Ireland.

Usage

A spelling alphabet is used to spell parts of a message containing letters and numbers to avoid confusion, because many letters sound similar, for instance “n” and “m” or “f” and “s”; the potential for confusion increases if static or other interference is present. For instance the message “proceed to map grid DH98” could be transmitted as “proceed to map grid Delta-Hotel-Niner-Ait”. Using “Delta” instead of “D” avoids confusion between “DH98” and “BH98” or “TH98”. The unusual pronunciation of certain numbers was designed to reduce confusion.

In addition to the traditional military usage, civilian industry uses the alphabet to avoid similar problems in the transmission of messages by telephone systems. For example, it is often used in the retail industry where customer or site details are spoken by telephone (to authorize a credit agreement or confirm stock codes), although ad hoc coding is often used in that instance. It has been used often by information technology workers to communicate serial/reference codes (which are often very long) or other specialised information by voice. Most major airlines use the alphabet to communicate Passenger Name Records (PNRs) internally, and in some cases, with customers. It is often used in a medical context as well, to avoid confusion when transmitting information.

Several letter codes and abbreviations using the spelling alphabet have become well-known, such as Bravo Zulu (letter code BZ) for “well done”, Checkpoint Charlie (Checkpoint C) in Berlin, and Zulu Time for Greenwich Mean Time or Coordinated Universal Time. During the Vietnam War, the The U.S. government referred to the Viet Cong guerrillas and the group itself as VC, or Victor Charlie; the name “Charlie” became synonymous with this force.

USNO NAVSTAR Global Positioning System

The following Global Positioning System (GPS) information is obtained from the 1994 Federal Radionavigation Plan (FRP), prepared jointly by the Department of Defense (DoD) and the Department of Transportation (DoT) and other sources such as conferences, meetings and seminars.


GPS CAPABILITIES

The GPS is a DoD developed, worldwide, satellite-based radionavigation system that will be the DoD’s primary radionavigation system well into the next century. The constellation consists of 24 operational satellites. The U.S. Air Force Space Command (AFSC) formally declared the GPS satellite constellation as having met the requirement for Full Operational Capability (FOC) as of April 27, 1995. Requirements include 24 operational satellites (Block II/IIA) functioning in their assigned orbits and successful testing completed for operational military functionality.

Prior to FOC an Initial Operational Capability (IOC) was declared on December 8, 1993 when 24 GPS satellites (Block I and Block II/IIA) were operating in their assigned orbits, available for navigation use and providing the Standard Positioning Service (SPS) levels specified below.

GPS provides two levels of service, Standard Positioning Service and the Precise Positioning Service .

The Standard Positioning Service (SPS) is a positioning and timing service which will be available to all GPS users on a continuous, worldwide basis with no direct charge. SPS will be provided on the GPS L1 frequency which contains a coarse acquisition (C/A) code and a navigation data message. SPS provides a predictable positioning accuracy of 100 meters (95 percent) horizontally and 156 meters (95 percent) vertically and time transfer accuracy to UTC within 340 nanoseconds (95 percent).The Precise Positioning Service (PPS) is a highly accurate military positioning, velocity and timing service which will be available on a continuous, worldwide basis to users authorized by the U.S. P(Y) code capable military user equipment provides a predictable positioning accuracy of at least 22 meters (95 percent) horizontally and 27.7 meters vertically and time transfer accuracy to UTC within 200 nanoseconds (95 percent). PPS will be the data transmitted on the GPS L1 and L2 frequencies. PPS was designed primarily for U.S. military use. It will be denied to unauthorized users by the use of cryptography. PPS will be made available to U.S. and military and U.S. Federal Government users. Limited, non-Federal Government, civil use of PPS, both domestic and foreign, will be considered upon request and authorized on a case-by-case basis, provided:

  • It is in the U.S. national interest to do so.
  • Specific GPS security requirements can be met by the applicant.
  • A reasonable alternative to the use of PPS is not available.

For questions regarding GPS policy, the user is advised to refer to the regularly appearing FRP. The FRP is published every 2 years and is available from the National Technical Information Service, Springfield, VA 22161. The latest report number is DOT-VNTSC-RSPA-95-1/DOD-4650.5 for report date 1994.


GPS SIGNAL CHARACTERISTICS

The satellites transmit on two L-band frequencies: L1 = 1575.42 MHz and L2 = 1227.6 MHz. Three pseudo-random noise (PRN) ranging codes are in use.

  • The coarse/acquisition (C/A) code has a 1.023 MHz chip rate, a period of 1 millisecond (ms) and is used primarily to acquire the P-code.
  • The precision (P) code has a 10.23 MHz rate, a period of 7 days and is the principal navigation ranging code.
  • The Y-code is used in place of the P-code whenever the anti-spoofing (A-S) mode of operation is activated.

The C/A code is available on the L1 frequency and the P-code is available on both L1 and L2. The various satellites all transmit on the same frequencies, L1 and L2, but with individual code assignments.

Due to the spread spectrum characteristic of the signals, the system provides a large margin of resistance to interference. Each satellite transmits a navigation message containing its orbital elements, clock behavior, system time and status messages. In addition, an almanac is also provided which gives the approximate data for each active satellite. This allows the user set to find all satellites once the first has been acquired.


SELECTIVE AVAILABILITY, ANTI-SPOOFING

Selective Availability (SA), the denial of full accuracy, is accomplished by manipulating navigation message orbit data (epsilon) and/or satellite clock frequency (dither). Anti-spoofing (A-S)guards against fake transmissions of satellite data by encrypting the P-code to form the Y-code.

SA will be implemented on Block II at the SPS levels, as soon as each Block II satellite is operational. SA was activated July 4, 1991 at 0400 UT (ref: Notice Advisory to NAVSTAR Users 121-92282 DTG 011354Z JUL 91 ). A-S was exercised intermittently through 1993 and implemented on January 31, 1994 (ref: Notice Advisory to NAVSTAR Users 050-94042, DTG 112054Z FEB 94).


GPS SYSTEM SEGMENTS

The GPS consists of three major segments: SPACE, CONTROL and USER.

The SPACE segment consists of 24 operational satellites in six orbital planes (four satellites in each plane). The satellites operate in circular 20,200 km (10,900 nm) orbits at an inclination angle of 55 degrees and with a 12-hour period. The position is therefore the same at the same sidereal time each day, i.e. the satellites appear 4 minutes earlier each day.

The CONTROL segment consists of five Monitor Stations (Hawaii, Kwajalein, Ascension Island, Diego Garcia, Colorado Springs), three Ground Antennas, (Ascension Island, Diego Garcia, Kwajalein), and a Master Control Station (MCS) located at Schriever AFB in Colorado. The monitor stations passively track all satellites in view, accumulating ranging data. This information is processed at the MCS to determine satellite orbits and to update each satellite’s navigation message. Updated information is transmitted to each satellite via the Ground Antennas.

The USER segment consists of antennas and receiver-processors that provide positioning, velocity, and precise timing to the user.


GPS SYSTEM TIME

GPS system time is given by its Composite Clock (CC). The CC or “paper” clock consists of all operational Monitor Station and satellite frequency standards. GPS system time, in turn, is referenced to the Master Clock (MC) at the USNO and steered to UTC(USNO) from which system time will not deviate by more than one microsecond. The exact difference is contained in the navigation message in the form of two constants, A0 and A1, giving the time difference and rate of system time against UTC(USNO,MC). UTC(USNO) itself is kept very close to the international benchmark UTC as maintained by the BIPM, and the exact difference, USNO vs. BIPM is available in near real time.

The latest individual satellite measurements are updated daily. (Data format explanation.)

The best current measure of the difference, UTC(USNO MC) – GPS is based on filtered and smoothed data over the past two days.


GPS TIME TRANSFER

GPS is at the present time the most competent system for time transfer , the distribution of Precise Time and Time Interval (PTTI). The system uses time of arrival (TOA) measurements for the determination of user position. A precisely timed clock is not essential for the user because time is obtained in addition to position by the measurement of TOA of FOUR satellites simultaneously in view. If altitude is known (i.e. for a surface user), then THREE satellites are sufficient. If time is being kept by a stable clock (say, since the last complete coverage), then TWO satellites in view are sufficient for a fix at known altitude. If the user is, in addition, stationary or has a known speed then, in principle, the position can be obtained by the observation of a complete pass of a SINGLE satellite. This could be called the “transit” mode, because the old TRANSIT system uses this method. In the case of GPS, however, the apparent motion of the satellite is much slower, requiring much more stability of the user clock.