¶ Introduction
An air traffic controller shall communicate with pilots in command of all aircraft in his airspace. In real aviation, all aircraft and all air traffic controllers are equipped with radio transmitters and antennas.
Each radio transmitter uses one unique frequency at a time and performs half duplex communication (this frequency is sometimes also called a radio channel).
The radio transmitter can be tuned to the selected frequency manually by its user. In half-duplex communication, each party can communicate to the other, but not simultaneously; the communication has one direction at a time : ATC to pilot(s), or Pilot to ATC.
The radio spectrum of frequencies is divided into bands with conventional names designated by the International Telecommunications Union (ITU): A frequency band is an interval in the frequency domain, delimited by a lower frequency and an upper frequency. The term may refer to a radio band or an interval of some other spectrum.
The frequency band definition:
| Frequency band | ITU designation | ITU abbreviation |
|---|---|---|
| 30–300 kHz | Low frequency | LF |
| 300 kHz – 3 MHz | Medium frequency | MF |
| 3–30 MHz | High frequency | HF |
| 30–300 MHz | Very high frequency | VHF |
| 300 MHz – 3 GHz | Ultra high frequency | UHF |
| 3–30 GHz | Super high frequency | SHF |
¶ In the real world
In the real world, the pilot uses mainly radio communication in the very high frequency band (VHF) in order to use voice communication.
On oceanic flight, with the long distance involved between ATC and pilots, the High frequency (HF) communication band is selected by using the long range communication property of this frequency.
Example of a VHF/HF communication panel in a 737 aircraft:
Military aircraft can use the ultra high frequency band (UHF). These bands are not simulated in IVAO.
¶ 8.33 kHz
The aviation VHF communication band ranges from 118.000 MHz to 136.995 MHz.
The "standard" spacing used to be 25KHz or 0.025 MHz between each channel.
118.000 / 118.025 / 118.050 / 118.075 / 118.100 / 118.125 / 118.150 / 118.175 / 118.200
With traffic increasing, it was necessary to create more channels. It was impossible to assign lower channels, as VOR & ILS uses frequencies from 108.00 to 117.95 MHz. Also it was impossible to assign higher channels, as they are used for satellite communications and military operations.
The solution was to reduce channel spacing from 25MHz to 8.33MHz. Hence, within each 25KHz channel we can have three 8.33KHz channels (25/3=8.33).
Therefore, with 8.33KHz spacing within each channel it gives the following table :
| Diplayed frequency | Real frequency | Frequency spacing |
|---|---|---|
| 118.000 | 118.0000 | 25KHz |
| 118.005 | 118.0000 | 8.33KHz |
| 118.010 | 118.0083 | 8.33KHz |
| 118.015 | 118.0166 | 8.33KHz |
| 118.025 | 118.0250 | 25KHz |
| 118.030 | 118.0250 | 8.33KHz |
| 118.035 | 118.0333 | 8.33KHz |
| 118.040 | 118.0416 | 8.33KHz |
| 118.050 | 118.050 | 25KHz |
You may have noticed that frequencies 118.000 and 118.005 use the same real frequency but with a different spacing. If you select on your 8.33 radio frequency 118.000, it will automatically operate as an old 25KHz radio. Now, if you select 118.005 it will operate in 8.33 mode. Only 8.33 receivers tuned on 118.005 will be able to hear you.
The new 8.33 kHz channel width for radio communication frequency is already integrated in the Pilot client and ATC client and the IVAO network servers.
In your cockpit, you must setup only the first 2 digits after the decimal and the 3rd digit is automatically tuned by the system to either a 0 or 5.
The 8.33 kHz spacing channel is mandatory in some countries in upper airspace.
As the IVAO pilot software interface is compatible with 8.33kHz, please add the letter Y to the equipment in your flight plan.
¶ In IVAO network
In the IVAO network, users must not use any real radio transceiver.
- The use of aeronautic radio transmitters is reserved for real world flights.
- It is forbidden to use them for any IVAO activities.
In IVAO, radio communications are simulated using IVAO Pilot and ATC software.
In order to make communications more realistic, you can choose the VHF frequency in your flight deck or IVAO Pilot Client interface and the software will do the rest to connect you to the correct channel.
The IVAO Pilot Client interface is an IVAO tool which synchronizes the pilot frequency in the cockpit and the interface with the air traffic controller frequency. An air traffic controller in IVAO is responsible to tune the frequency of his position in the IVAO ATC software radar software.
¶ Use of frequency in IVAO for air traffic controller
Before you can control an active position, you must set the VHF frequency of your controller position in your IVAO ATC software radar scope.
ATTENTION This frequency tuning may not automatic!
This frequency can be taken from:
- The IVAO database (HQ database or your division database)
- Real charts if the database was not available.
We advise you not to take any real frequencies you may have heard on a real radio receiver. These frequencies are subject to changes in the functionality of many parameters that IVAO does neither use nor simulate.
¶ How to tune the frequency in ATC Client?
Follow the procedure below:
- Click on the COM1 tab in the IVAO ATC software COMMbox window
- Type double bars
//followed by the VHF frequency wanted
Example: //130.275
As long you connected with CONNECT TO VOICE option marked, the frequency is properly setted up.
¶ Use of frequency in IVAO for pilots
Once connected, the first step is to tune IVAO pilot software to UNICOM 122.800MHz as the active frequency.
The 122.800 MHz frequency is the unique worldwide self-announcement air to air frequency for all airfields in IVAO.
When you are ready to begin your flight, check in the IVAO pilot software interface if there are any air traffic controllers available in your zone.
Any air traffic controller requires 2 way radio communication contact prior to any movement:
- If an Air Traffic Controller is available, set the VHF frequency on the IVAO pilot software as the active frequency. You will receive the ATIS information by text and automatically connect to the frequency (except if you have deactivated voice mode or the air traffic controller is in text only mode).
- If there are no air traffic controllers in your area, you must remain on the Unicom frequency 122.800MHz and perform self-announcement text messages .
Be aware that when there is any technical problem that does not permit two way voice communication, you shall communicate using the IVAO pilot software scratchpad using text as secondary mode. You are not permitted to ignore the text mode procedure in that case.
- none
- Apr/23 - Text adpation to Voice UNICOM and removed TS2 mentioning.
- VID 150259 - Creation - Wiki integration
- VID 450012 - Update April 2020
- VID 496402 - Wiki.js Integration and Updates (Apr/23)