KNX RF (Radio): KNX Basic exam questions with worked answers

Practice questions from the KNX RF (Radio) block of the KNX Basic certification. Detailed corrections, public sources, free to read without sign-up.

46 questions~ 41 minFree · no sign-up

Questions for the "KNX RF (Radio)" topic

Q01
Up to what voltage do the mains-power-system regulations apply that must be observed for a KNX RF installation?
- A.400 V.
- B.1000 V.
- C.690 V.
- D.1500 V.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
B — 1000 V.
Learning tip
Correct: the regulations for mains power systems up to 1000 V are to be observed.
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Q02
How are KNX RF E-Mode devices usually commissioned?
- A.Only with ETS and a full project database.
- B.By assigning individual addresses over an IP backbone.
- C.Via DIP-switches or push-button actions after mounting (ETS optional).
- D.Automatically, with no user action of any kind.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
C — Via DIP-switches or push-button actions after mounting (ETS optional).
Learning tip
Correct: E-Mode teaching-in is usually done with DIP-switches or push-buttons, or by ETS.
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Q03
In the E-Mode Push Button example, how is the desired function confirmed on the receiver?
- A.By briefly tapping the fct button once.
- B.By holding the cfg button for 10 seconds.
- C.By pressing the fct and cfg buttons simultaneously.
- D.By holding the fct button pressed for longer than 2 seconds.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
D — By holding the fct button pressed for longer than 2 seconds.
Learning tip
Correct: the function is confirmed by holding the fct button longer than 2 seconds.
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Q04
How does commissioning KNX RF S-Mode devices compare with commissioning KNX TP S-Mode devices?
- A.It requires no ETS at all, only push-buttons.
- B.It is to a large extent similar to commissioning KNX TP S-Mode devices.
- C.It is completely different and shares no procedures with TP.
- D.It can only be performed over an IP connection.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
B — It is to a large extent similar to commissioning KNX TP S-Mode devices.
Learning tip
Correct: the RF S-Mode procedure is largely similar to the TP S-Mode procedure.
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Q05
Why does each KNX RF line or segment receive its own unique domain address?
- A.To increase the physical radio range of the line.
- B.To set the 868 MHz carrier frequency for that line.
- C.To avoid logical interference between adjacent KNX RF lines.
- D.To supply bus power to the RF devices.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
C — To avoid logical interference between adjacent KNX RF lines.
Learning tip
Correct: the domain address gives each RF line a unique identity to prevent logical interference.
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Q06
What is the maximum number of receivers that may be linked to the same KNX RF sender?
- A.64 (a 65th receiver is prohibited).
- B.128.
- C.32.
- D.Unlimited.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
A — 64 (a 65th receiver is prohibited).
Learning tip
Correct: since the 65th receiver is prohibited, the maximum is 64.
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Q07
What does the functional test of a KNX RF installation involve?
- A.Measuring only the bus voltage at a single point.
- B.Checking the 868 MHz frequency with a spectrum analyser.
- C.Testing only one in ten devices as a representative sample.
- D.Triggering the sensors and observing that the corresponding actuators react, for every taught-in connection.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
D — Triggering the sensors and observing that the corresponding actuators react, for every taught-in connection.
Learning tip
Correct: sensors are triggered/pressed and the actuator reactions observed for all connections.
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Q08
Why must the correct functioning of a KNX RF installation be recorded in a test/acceptance report?
- A.For warranty reasons, to document that the installation functions correctly.
- B.Because ETS refuses to download the project without it.
- C.Only if the customer explicitly requests it.
- D.It is optional and mainly for aesthetics.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
A — For warranty reasons, to document that the installation functions correctly.
Learning tip
Correct: the report documents correct functioning and is kept for warranty reasons.
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Q09
Why is it recommended to record the E-Mode configuration in a list?
- A.Because ETS deletes the project immediately after download.
- B.Because E-Mode sensor-actuator links can be changed very easily, so the installation may no longer match the ordered version.
- C.Because E-Mode devices lose their configuration at every power failure.
- D.Because the domain address changes automatically each day.
KNX RF (Radio)· RF commissioning & checks· Medium
▸
Correct answer
B — Because E-Mode sensor-actuator links can be changed very easily, so the installation may no longer match the ordered version.
Learning tip
Correct: easy changeability means the as-built state can drift, so it should be recorded.
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Q10
KNX RF allows the wireless transmission of telegrams by means of the medium Radio Frequency, so a separate bus cable is not required.
TrueFalse
KNX RF (Radio)· RF transmission medium· Easy
Correct answer
True
Learning tip
The source defines KNX RF as wireless telegram transmission via radio frequency, removing the need for a dedicated bus cable.
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Q11
KNX RF is especially interesting when an existing TP installation has to be extended and no additional cables can be installed due to building regulations or aesthetic reasons.
TrueFalse
KNX RF (Radio)· RF transmission medium· Easy
Correct answer
True
Learning tip
The source names this as the key use case: extending a TP installation where new cables cannot be laid (e.g. museums, public buildings).
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Q12
How does the free-field range of KNX RF compare with the distance achievable inside a building?
- A.The free-field range is significantly lower than the in-building distance
- B.They are always exactly equal
- C.The free-field range is significantly higher than the in-building distance
- D.The in-building distance is unlimited
KNX RF (Radio)· RF transmission medium· Medium
▸
Correct answer
C — The free-field range is significantly higher than the in-building distance
Learning tip
Correct: free field is the open-space best case and is significantly higher than what is achievable inside a building.
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Q13
The free-field range of KNX RF is limited to approximately 100 m.
TrueFalse
KNX RF (Radio)· RF transmission medium· Easy
Correct answer
True
Learning tip
The source gives the free-field range as limited to approximately 100 m.
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Q14
Why is the KNX RF free-field range limited to approximately 100 m?
- A.Because of the maximum allowed transmission power and the limited energy available in battery-operated or battery-free devices
- B.Because the 868 MHz band physically cannot travel further
- C.Because ETS caps the transmission distance at 100 m
- D.Because encryption of telegrams shortens the range
KNX RF (Radio)· RF transmission medium· Medium
▸
Correct answer
A — Because of the maximum allowed transmission power and the limited energy available in battery-operated or battery-free devices
Learning tip
Correct: the source names transmission-power limits and the limited energy of battery/battery-free devices.
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Q15
KNX RF uses the 868 MHz frequency band.
TrueFalse
KNX RF (Radio)· RF transmission medium· Easy
Correct answer
True
Learning tip
The source states that KNX RF uses the 868 MHz frequency band.
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Q16
How do walls, ceilings and furniture affect KNX RF signals?
- A.They pass through without any hindrance
- B.They are amplified as they pass through
- C.They are attenuated during penetration and partially reflected
- D.They are converted into a wired telegram
KNX RF (Radio)· RF transmission medium· Medium
▸
Correct answer
C — They are attenuated during penetration and partially reflected
Learning tip
Correct: the source states signals are attenuated on penetration and partly reflected.
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Q17
What happens to KNX RF signals around metallic objects?
- A.Metal has no effect on 868 MHz signals
- B.Metal always amplifies the signal
- C.Metal converts the signal to a lower frequency
- D.They are shielded or reflected, creating a radio shadow on the reverse side where direct reception is not possible
KNX RF (Radio)· RF transmission medium· Medium
▸
Correct answer
D — They are shielded or reflected, creating a radio shadow on the reverse side where direct reception is not possible
Learning tip
Correct: metallic objects shield/reflect signals and produce radio shadows behind them.
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Q18
Which statement about reflections of KNX RF signals is correct?
- A.Reflections can have both a positive and a negative effect
- B.Reflections are always beneficial
- C.Reflections are always harmful
- D.Reflections never occur in the 868 MHz band
KNX RF (Radio)· RF transmission medium· Medium
▸
Correct answer
A — Reflections can have both a positive and a negative effect
Learning tip
Correct: the source says reflections may be positive or negative depending on the situation.
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Q19
When should structural interfering factors for KNX RF be taken into account?
- A.Only after commissioning, if problems appear
- B.They never need to be considered
- C.Already during the building planning stage, when carefully selecting the device mounting sites
- D.Only automatically by the ETS during programming
KNX RF (Radio)· RF transmission medium· Medium
▸
Correct answer
C — Already during the building planning stage, when carefully selecting the device mounting sites
Learning tip
Correct: the source says interfering factors must be considered at the planning stage and mounting sites chosen carefully.
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Q20
If RF device mounting sites cannot be freely selected, how is a good radio connection usually achieved?
- A.By increasing the mains voltage at the device
- B.By switching the devices to the 2.4 GHz band
- C.By removing every possible reflection from the room
- D.By using a KNX RF repeater
KNX RF (Radio)· RF transmission medium· Medium
▸
Correct answer
D — By using a KNX RF repeater
Learning tip
Correct: the source recommends a KNX RF repeater when mounting sites are constrained.
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Q21
What must be ensured for mains-operated KNX radio devices?
- A.That the mains voltage is available at the selected mounting site
- B.That a twisted-pair bus cable reaches the device
- C.That the device is within 10 m of the receiver
- D.That the device is battery-free
KNX RF (Radio)· RF transmission medium· Easy
▸
Correct answer
A — That the mains voltage is available at the selected mounting site
Learning tip
Correct: the source requires mains voltage to be present at the chosen mounting site for mains-operated RF devices.
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Q22
In the KNX RF system, 868.30 MHz is used as the middle (centre) frequency.
TrueFalse
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Easy
Correct answer
True
Learning tip
The source states that 868.30 MHz is used as the middle frequency, around which the '0'/'1' states are formed by a slight frequency deviation.
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Q23
What bit rate does the KNX RF description give for the information to be transferred?
- A.16384 bits per second
- B.16384 bits per minute
- C.1638 bits per second
- D.163840 bits per second
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
A — 16384 bits per second
Learning tip
Correct: the source states a bit rate of 16384 bits per second, modulated with Manchester coding.
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Q24
What is the stated advantage of the Manchester coding used in KNX RF?
- A.A larger available frequency band
- B.Increased transmission reliability, with an edge transition in the centre of each bit
- C.Higher maximum transmission power
- D.Elimination of the need for a preamble
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
B — Increased transmission reliability, with an edge transition in the centre of each bit
Learning tip
Correct: the source names increased transmission reliability, thanks to the mid-bit 0/1 transition that keeps clocks synchronised.
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Q25
What is the maximum transmission power in the KNX RF (single-channel) system?
- A.25 W
- B.250 mW
- C.25 mW
- D.2.5 mW
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Easy
▸
Correct answer
C — 25 mW
Learning tip
Correct: the source states a maximum transmission power of 25 mW.
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Q26
The KNX RF duty cycle limits how long a device may transmit. What is that limit?
- A.10 %, i.e. a maximum of about 6 minutes per hour
- B.1 %, i.e. a maximum of 3.6 seconds per hour
- C.100 %, with no time limit
- D.1 %, i.e. a maximum of 36 seconds of transmission per hour
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
D — 1 %, i.e. a maximum of 36 seconds of transmission per hour
Learning tip
Correct: the duty cycle is 1 %, equal to a maximum transmission duration of 36 seconds per hour.
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Q27
What distinguishes KNX RF-Multi from KNX Ready?
- A.RF-Multi is single-channel while KNX Ready is multi-channel
- B.RF-Multi transmits over several fast and slow channels, while KNX Ready uses only a single channel
- C.RF-Multi removes the duty-cycle limit entirely
- D.RF-Multi uses a completely different frequency band from KNX Ready
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Easy
▸
Correct answer
B — RF-Multi transmits over several fast and slow channels, while KNX Ready uses only a single channel
Learning tip
Correct: KNX Ready is single-channel; RF-Multi spreads transmission over several fast and slow channels for better coexistence.
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Q28
How does the data rate of KNX RF-Multi slow channels compare with the fast channels?
- A.It is one quarter of the fast-channel data rate
- B.It is the same as the fast channels
- C.It is half the data rate of the fast channels, mainly because of the extended preamble
- D.It is double the data rate of the fast channels
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
C — It is half the data rate of the fast channels, mainly because of the extended preamble
Learning tip
Correct: slow channels run at half the speed of fast channels, mainly due to the longer preamble.
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Q29
By how much can sleep mode reduce a KNX RF-Multi device's energy consumption?
- A.Up to 99 % for both fast and slow channels
- B.Up to 99 % for fast channels and up to 80 % for slow channels
- C.Up to 80 % for fast channels and up to 99 % for slow channels
- D.Up to 50 % for fast channels and up to 70 % for slow channels
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
C — Up to 80 % for fast channels and up to 99 % for slow channels
Learning tip
Correct: sleep mode saves up to 80 % on fast channels and up to 99 % on slow channels, the device being woken periodically to receive.
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Q30
What preamble length does a KNX RF-Multi sender use in a slow channel (compared with 15 ms fast and 5 ms Ready)?
- A.50 ms
- B.5 ms
- C.15 ms
- D.500 ms
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
D — 500 ms
Learning tip
Correct: a slow-channel RF-Multi sender uses a 500 ms preamble, letting receivers sleep longer and save battery.
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Q31
From which ETS version are KNX RF Multi S-Mode devices supported?
- A.ETS6
- B.ETS3
- C.ETS4
- D.ETS5
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Easy
▸
Correct answer
A — ETS6
Learning tip
Correct: the source states RF Multi S-Mode devices are supported from ETS6 onwards.
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Q32
Why does KNX RF natively support long frames?
- A.To remove the need for a domain address or serial number
- B.To support the KNX Secure Application Layer (authentication and encryption), so the media coupler is not the security weak point
- C.To let unidirectional devices receive telegrams
- D.To raise the maximum transmission power above 25 mW
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
B — To support the KNX Secure Application Layer (authentication and encryption), so the media coupler is not the security weak point
Learning tip
Correct: long frames carry the KNX Secure Application Layer, giving authentication and encryption and removing the media coupler as the weak point.
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Q33
How does a unidirectional KNX RF device handle bus access and collisions?
- A.It waits for the channel to be free, then transmits
- B.It never resends, so a collided telegram is simply lost
- C.It sends immediately; on a collision it resends, but the 1 % duty cycle makes collisions nearly excluded
- D.It requests a time slot from a central controller first
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
C — It sends immediately; on a collision it resends, but the 1 % duty cycle makes collisions nearly excluded
Learning tip
Correct: unidirectional devices transmit at once and resend if a collision happens, which is rare thanks to the 1 % duty cycle.
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Q34
How does a bidirectional KNX RF device access the bus?
- A.It transmits immediately regardless of channel state
- B.It transmits continuously until an acknowledgement arrives
- C.It can only receive and never transmits
- D.It checks whether the channel is free; if it is occupied it waits until free, then transmits
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
D — It checks whether the channel is free; if it is occupied it waits until free, then transmits
Learning tip
Correct: bidirectional devices listen first and only send once the channel is free.
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Q35
Which statement best describes the structure of a KNX RF telegram?
- A.It consists of several data blocks separated by checksum bytes; the blocks at the start and end synchronise the receivers to the transmitter
- B.It is a single continuous block with no internal checksums
- C.It contains only useful data and no addressing information
- D.Its start and end blocks carry the switching command
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
A — It consists of several data blocks separated by checksum bytes; the blocks at the start and end synchronise the receivers to the transmitter
Learning tip
Correct: a KNX RF telegram is several data blocks separated by checksums, with start/end blocks used for synchronisation.
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Q36
Which information does the control field of the first data block carry?
- A.Only the CRC used for error detection
- B.The switching or dimming command to be executed
- C.Telegram length, device type (uni-/bidirectional), transmission quality (signal strength) and battery status
- D.The group address assigned by ETS
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
C — Telegram length, device type (uni-/bidirectional), transmission quality (signal strength) and battery status
Learning tip
Correct: the control field holds the telegram length, the device type, the transmission quality and the battery status of battery-operated devices.
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Q37
In the first data block, which identifier is sent after the control field for an RF S-Mode device?
- A.The group address
- B.The KNX serial number
- C.The individual (physical) address
- D.The domain address
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
D — The domain address
Learning tip
Correct: for RF S-Mode devices a domain address is sent after the control field (E-Mode devices send the serial number).
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Q38
For KNX RF devices in E mode, which statement about the KNX serial number is correct?
- A.It is a unique identifier programmed during manufacturing, is not modifiable, and is stored in the receiver as the source address
- B.It is assigned by the installer with ETS during commissioning
- C.It changes each time the device transmits
- D.It is only used inside one installation and cannot distinguish neighbouring installations
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
A — It is a unique identifier programmed during manufacturing, is not modifiable, and is stored in the receiver as the source address
Learning tip
In E mode, the unique factory-programmed KNX serial number is transmitted and stored in the receiver as the source address. In S mode, distinguish the transmitted domain address from this serial number.
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Q39
Which devices are typically unidirectional 'send-only' KNX RF devices?
- A.Mains-powered relay actuators controlling lighting
- B.Media couplers linking RF to TP
- C.Battery-operated sensors and detectors such as push-button transmitters, binary inputs and door/window contacts
- D.KNX RF repeaters
KNX RF (Radio)· KNX Ready, RF-Multi, bus access & telegram structure· Medium
▸
Correct answer
C — Battery-operated sensors and detectors such as push-button transmitters, binary inputs and door/window contacts
Learning tip
Correct: send-only unidirectional devices are mainly battery-operated sensors/detectors like hand-held or wall transmitters, binary inputs and door/window contacts.
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Q40
Which statement best describes the topology of devices in a KNX RF installation?
- A.They must be grouped into areas and lines joined by couplers, exactly like KNX TP.
- B.They are arranged in a star around a central RF controller that routes every telegram.
- C.They follow no fixed hierarchical arrangement; within radio range any sensor can communicate with any actuator.
- D.Each device may communicate with only one paired device, never with several actuators.
KNX RF (Radio)· RF topology & combination of media· Medium
▸
Correct answer
C — They follow no fixed hierarchical arrangement; within radio range any sensor can communicate with any actuator.
Learning tip
Correct: the source says RF devices are not subject to a hierarchical arrangement and each sensor within range can reach each actuator.
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Q41
In a KNX RF telegram, what does an E-Mode device use as its device identifier?
- A.Its domain address.
- B.Its individual (physical) address such as 1.1.5.
- C.The group address of the linked actuator.
- D.Its serial number.
KNX RF (Radio)· RF topology & combination of media· Medium
▸
Correct answer
D — Its serial number.
Learning tip
Correct: each KNX RF E-Mode device sends its serial number as device identifier.
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Q42
What does a KNX RF S-Mode device send as its device identifier?
- A.Its domain address.
- B.Its serial number.
- C.A hardware MAC address.
- D.Its area/line topology address.
KNX RF (Radio)· RF topology & combination of media· Medium
▸
Correct answer
A — Its domain address.
Learning tip
Correct: KNX RF S-Mode devices send their domain address as device identifier.
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Q43
With how many KNX RF repeaters can the radio range of an installation be extended?
- A.Up to 1.
- B.Up to 2.
- C.Up to 4.
- D.An unlimited number.
KNX RF (Radio)· RF topology & combination of media· Medium
▸
Correct answer
B — Up to 2.
Learning tip
Correct: the range can be extended with up to two KNX RF repeaters, across several floors.
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Q44
Which transmission media can be combined within a single KNX system?
- A.Only TP and powerline.
- B.Only RF and IP.
- C.Twisted Pair (TP), Radio Frequency (RF) and IP.
- D.Only a single medium may be used per system.
KNX RF (Radio)· RF topology & combination of media· Easy
▸
Correct answer
C — Twisted Pair (TP), Radio Frequency (RF) and IP.
Learning tip
Correct: KNX allows TP, RF and IP to be combined within one system.
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Q45
What is the function of a media coupler in a KNX installation?
- A.It converts 230 V mains into the bus voltage for RF devices.
- B.It stores telegrams and replays them after a fixed delay.
- C.It automatically assigns individual addresses to all RF devices.
- D.It transfers information and commands between devices on different transmission media (e.g. RF and TP).
KNX RF (Radio)· RF topology & combination of media· Easy
▸
Correct answer
D — It transfers information and commands between devices on different transmission media (e.g. RF and TP).
Learning tip
Correct: the media coupler passes telegrams from devices on one medium to devices on another.
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Q46
For KNX RF S-Mode devices, how is it defined which telegrams a media coupler transfers?
- A.Only via ETS, comparable to the function of a line coupler (bus line to RF line).
- B.Only by teaching-in with the coupler's push-buttons, without ETS.
- C.Automatically, based on measured signal strength.
- D.It is fixed by the manufacturer and cannot be configured.
KNX RF (Radio)· RF topology & combination of media· Medium
▸
Correct answer
A — Only via ETS, comparable to the function of a line coupler (bus line to RF line).
Learning tip
Correct: for S-Mode this is done only via ETS, like a line coupler.
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