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Amateur Radio Info & Exams - VHF FM - Repeater and Simplex Operation

Repeater Operation

Repeaters are automatic stations which receive a signal, and simultaneously retransmit it on a second frequency. Most are in the 10 metre to 23 cm range. TV ones may receive on a higher band, and retransmit on 70 cm. For voice 2 metres and 70 centimetres are popular for repeaters.

Repeaters can be located on hill-tops / mountains, communications towers, tall buildings, and grain silos. These can be stand-alone, or integrated into a commercial site, even sharing antennas through combiners. Small cross-band repeaters (below) are sometimes flown on re-purposed weather balloons.

A variation of the repeater theme is the "digipeater", a device which receives packets of data, including location information, and retransmits them.

Repeaters transmits on the advertised frequency, such as 147.250 MHz (Hornsby), or 146.650 MHz (Mt Bindo). Australian repeaters use 25 kHz spacing, European may be 12.5 kHz, as the band has been restricted to 144 to 146 MHz. US systems use a 30 kHz spacing, sometimes 15 kHz. The input has to be offset from the output, and this is traditionally by 600 kHz. Below 147 MHz this is a negative offset, so for Bindo, you transmit at 146.050 MHz, and above 147 MHz, a positive offset, so for Hornsby it is 147.850 MHz. In some places 147.000 goes up, to 147.600 MHz; some down, to 146.400 MHz. Dural is negative. As there are stupidly large numbers of repeaters in small US states, there are also systems in the 144 - 145 MHz area, some using 600 kHz offsets, and some (including DMR ones) using larger offsets into the 147.4 to 147.6 MHz segment normally used for simplex.

On 70 cm the offset is typically 5.00 MHz. This can be upward or downward, depending whether the repeater is at the bottom or top of the 440 to 450 MHz. In Australia repeater outputs are in the 438-440 MHz segment, with downward offsets, including 5 MHz. However, as idiot bureaucrats here not only allowed low duty cycle devices , such as car door openers, and wireless door-bells, like in Europe, but small walkie-talkies, wireless headphones, and even crane controllers to be used in the 433.050 - 434.790 segment, repeaters are now using -5.4 and -7 MHz offsets. Some remain at -5 MHz, especially if the input is outside this segment.

For technical reasons, there is an upwards trend in the offset with increasing frequency. These include the special filtering devices called cavities, used to isolate transmitter and receiver signals. Cavity filters can be around 30 cm in diameter, and 2 metre high for the lowest bands, down to maybe 10cm by 40 cm, and several are needed.

Some repeaters are part of a network, or are linked on-site to repeaters on different bands. These function as, say, a normal 2m repeater, and a normal 70 cm repeater, although there is an option to transmit on one band, and listen on the other. These are different to a purely cross-band device. On these one might transmit on 70 cm, and listen on 2m. A benefit of such systems is that there is usually no need for heavy cavity filters, so they can be set up in a vehicle, or even operate on a space station. Some hand-helds and mobile radios have a cross-band repeat mode.

Some repeaters have an Internet linking, where it is possible to dial into other repeaters or conference servers. Many DMR repeaters are also linked into networks.

VHF  folded dipoleThis is a (rather grotty) folded dipole for VHF High band, which covers 2 metres. These are mounted vertically, using the bar. The spacing from the mast determines the radiation pattern of the antenna. Also, important, they must NOT be mounted at the top of a pole, but with maybe 10 cm above the top of the antenna, otherwise the pattern will also be distorted vertically, probably with a high angle of radiation, in at least some directions.
These antennas are often used on properly engineered repeaters, including because they are structurally strong, and are at DC ground.

FM Simplex

This is what computer type call "half duplex", as one station transmits, then the other. However the term Simplex is used when the station is transmitting and receiving on the same frequency. This is how most HF and SSB VHF operation occurs, but is less common for FM in areas with repeaters. It is however a good idea when two stations can hear each other directly. Many transceivers have a "Reverse" button, which allows a quick check on the repeater input frequency, to see if this is possible.

On 2m, simplex is used the area between 146.400 and 146.600, or thereabouts; with 146.520 MHz being the "National Simplex Calling Frequency" in the US. In Australia this is 146.500 MHz. In Australia WICEN uses simplex at or around 147.500 MHz.

In the US 446.00 MHz is the National simplex frequency, in Australia it is 439.000 MHz.

In communities without a local repeater, a specific frequency might be selected by the locals. 147.475 MHz is/was used in the upper Hunter Valley, for example. 147.525 is also used in Australia.

For 6 metres 52.525 MHz is used for calling in most countries, and it is possible for such signals to travel significant distances.

CTCSS, DCS, Toneburst

Repeaters inputs can suffer interference from several sources. These include the so-called Low Interference Potential Devices (LIPDs) on 70 cm, inter-modulation products, where a rusty wire against a galvanised pole creates a diode which mixes two signals together, generating an interfering signal, and distant Ham stations using a different repeater. Pre-dating SMS, high powered VHF pager transmitters used to be a problem in some areas.

To stop unwanted signals triggering repeaters, several advances tone systems used to activate the repeater.

CTCSS, continuous tone-coded squelch system, uses a a range of low frequency tones to activate the repeater. In some cases, such as teh system in Hornsby, where Optus pay TV signals leaked out of the cables at poor joints, a tone is sent to operate the users radio. In this case, its use is optional, as carrier squelch still works. The operator sending a tone can also be used to turn on linking from one band to another band not permitted for some classes of licence, say 2m to 6m, an Australia-only issue.

DCS, digital coded squelch uses a low speed data stream, consisting of 3 digits, and some ancillary numerals to open the repeater.

Tone-burst is primarily a European system, where an audible tone, often of 1750 kHz is transmitted at the beginning of the over, and the repeater then stays open until the carrier ceases. If someone had this on by accident, you will hear something like "BEEEEEP! VK2DOH listening".

Systems which don't use these are said to use "carrier squelch".

DTMF, dual tone multi-frequency signalling is NOT used for accessing repeaters, but can be used for dialling between Echolink and IRLP nodes. Similar 5-tone, and other "Selcall" systems do use voice-frequency tones to signal radios.


SSB (Single sideband) is legally permitted in all bands above 50 MHz, except in segments where Morse only or data only are mandated. Operation should, however be restricted to segments listed as SSB or All-modes in the ARRL bandplan, or those of the country you are in. USB is the normal sideband.

SSB is used during contests, and by stations trying to set distance records, or make contact with stations in as many gridsquares a possible; as the bandwidth is narrower. You can also use it for chatting, as long as you avoid the various calling channels.


Not on the exam, but AM can also be used in voice segments on VHF and UHF, ideally the all-mode parts, but no one should get upset if you use it in the 147.500 segment. Most modern multi-mode transceivers have an AM mode. The Yaesu VX-7R hand-held has an AM mode on 6 metres; and the air-band plus 2 meters Vertex-Standard VXA-700 Spirit, which sometimes pops up on ebay has AM on 2 metres.

AM modulation generates an envelope where the level of the RF signal, viewed on an oscilloscope, varies in level with the input signal. If the modulating signal is too great, at the negative swing of the audio signal, the modulator attempts to go below zero, resulting in a highly distorted signal.

One of the distractors is "Asymmetric modulation" - it has no place in an FM question, but is used in broadcast AM transmitters, to give a louder sound, but modulating upwards greater than 100%, but avoiding downwards modulation greater than 100%.


A number of three letter Q-codes feature in the exam. Originally used in Morse code, these usually function as both questions and statements. "QRM?" thus asks, "Are you suffering from man-made interference?", and without the question make, indicates "I am suffering interference". "QSY?" asks "Shall I change frequency?".

Examples are:

QRM - Man-made interference
QRN - Natural interference, such as lightning crashes, or atmospheric Noise.
QSY - Change frequency, can be a frequency, repeater name, or suggesting to move up by, say 10 kHz from the call channel.
QSB - Your signal is fading
QTH - Location
QRZ - Who is calling me?
QRU - Have you anything for me? Used on manual / Morse message forwarding networks.
QSL - Can you confirm reception? Relates to a message in formal and emergency communications support, but also to QSL cards.

Relevant Questions

Actual exam questions, from the published NCVEC Technician pool.

What is the most common repeater frequency offset in the 2 meter band?
A. Plus 500 kHz
B. Plus or minus 600 kHz
C. Minus 500 kHz
D. Only plus 600 kHz

On 2 metres, the most popular offset is plus or minus 600 kHz, answer B.

What is the national calling frequency for FM simplex operations in the 70 cm band?
A. 146.520 MHz
B. 145.000 MHz
C. 432.100 MHz
D. 446.000 MHz

The first two are not 70 cm, so chuck them. SSB operators world-wide use 432.100 MHz, so no. In the US, the FM calling frequency is 446.000 MHz, answer D. (Note that outside the Americas, it is likely to be lower).

What is a common repeater frequency offset in the 70 cm band?
A. Plus or minus 5 MHz
B. Plus or minus 600 kHz
C. Minus 600 kHz
D. Plus 600 kHz

On 70 cm, plus or minus 5 MHz is a common offset, answer A.

What is an appropriate way to call another station on a repeater if you know the other station's call sign?
A. Say break, break then say the station's call sign
B. Say the station's call sign then identify with your call sign
C. Say CQ three times then the other station's call sign
D. Wait for the station to call CQ then answer it

"Hi Fred, this is Bill from the radio club." works on the 'phone, so how about saying Fred's callsign, follows by yours? "VK4FRED, this is VK2BIL.", yep, answer B. You can just use "VK4FRED VK2BIL".

How should you respond to a station calling CQ?
A. Transmit CQ followed by the other station’s call sign
B. Transmit your call sign followed by the other station’s call sign
C. Transmit the other station’s call sign followed by your call sign
D. Transmit a signal report followed by your call sign

Transmit THEIR call, followed by YOURS, answer C.

What must an amateur operator do when making on-air transmissions to test equipment or antennas?
A. Properly identify the transmitting station
B. Make test transmissions only after 10:00 p.m. local time
C. Notify the FCC of the test transmission
D. State the purpose of the test during the test procedure

What is the rule for any transmission? IDENTIFY! Answer A, "AG6LE testing".

Which of the following is true when making a test transmission?
A. Station identification is not required if the transmission is less than 15 seconds

B. Station identification is not required if the transmission is less than 1 watt
C. Station identification is only required once an hour when the transmissions are for test purposes only
D. Station identification is required at least every ten minutes during the test and at the end of the test

You must identify every 10 minutes, and at the end of the test, answer D. Identifying at the start is a good idea too.

What is the meaning of the procedural signal “CQ”?
A. Call on the quarter hour
B. A new antenna is being tested (no station should answer)
C. Only the called station should transmit
D. Calling any station

CQ means you are calling for any station, answer D.

What brief statement is often transmitted in place of “CQ” to indicate that you are listening on a repeater?
A. The words “Hello test” followed by your call sign
B. Your call sign
C. The repeater call sign followed by your call sign
D. The letters “QSY” followed by your call sign

On a repeater just saying your callsign is usually sufficient, answer B. The callsign of the repeater is rarely used on air.

What is a band plan, beyond the privileges established by the FCC?
A. A voluntary guideline for using different modes or activities within an amateur band
B. A mandated list of operating schedules
C. A list of scheduled net frequencies
D. A plan devised by a club to indicate frequency band usage

There are voluntary guides for modes and activities within the various bands, answer A. For example, 50.400 MHz is the 6 m AM calling frequency, 28.885 MHZ USB in the 10 m band is the liaison frequency for DX operations on 6 metres.

T2A11 [97.313(a)]
Which of the following is an FCC rule regarding power levels used in the amateur bands, under normal, non-distress circumstances?
A. There is no limit to power as long as there is no interference with other services
B. No more than 200 watts PEP may be used
C. Up to 1500 watts PEP may be used on any amateur frequency without restriction
D. While not exceeding the maximum power permitted on a given band, use the minimum power necessary to carry out the desired communication

People in New York probably don't want to hear two stations down the road from each other in California chatting, so only use the power necessary for the communications, within general and band-specific power limits, answer D.

Which of the following is a guideline to use when choosing an operating frequency for calling CQ?
A. Listen first to be sure that no one else is using the frequency
B. Ask if the frequency is in use
C. Make sure you are in your assigned band
D. All of these choices are correct

You should do all of these, answer D. These apply especially to HF, as a nearby station may be talking to a distant station, and one is having a long over. Sometimes it is only the local station you can hear, and sometimes it is only the distant station you can hear, as the local one, maybe a few hundred kilometres away is in the "skip zone".

What is the term used to describe an amateur station that is transmitting and receiving on the same frequency?
A. Full duplex communication
B. Diplex communication
C. Simplex communication
D. Multiplex communication

The common term for this simplex, answer C.

What is the term used to describe the use of a sub-audible tone transmitted with normal voice audio to open the squelch of a receiver?
A. Carrier squelch
B. Tone burst

CTCSS signals are continuous low audio frequency tones, such as 91.5 MHz, which open the squelch on a receiver, such is that on a repeater, although some (also) transmit to the user; answer D. Radios generally filter these out, and small speakers have a poor response here anyway.

Which of the following describes the muting of receiver audio controlled solely by the presence or absence of an RF signal?
A. Tone squelch
B. Carrier squelch
D. Modulated carrier

This is called carrier squelch, as it needs only the carrier to open, answer B.

Which of the following common problems might cause you to be able to hear but not access a repeater even when transmitting with the proper offset?
A. The repeater receiver may require an audio tone burst for access
B. The repeater receiver may require a CTCSS tone for access
C. The repeater receiver may require a DCS tone sequence for access
D. All of these choices are correct

Depending on the system, different tones or codes are needed. Tone burst is a European system which wakes up the repeater, which stays up while the carrier remains present, often using 1750 Hz. Depending on the repeater, any one of these might be required for access, answer D.

What determines the amount of deviation of an FM (as opposed to PM) signal?
A. Both the frequency and amplitude of the modulating signal
B. The frequency of the modulating signal
C. The amplitude of the modulating signal
D. The relative phase of the modulating signal and the carrier

The greater the amplitude, the further it deviates the FM signal, answer C.

What happens when the deviation of an FM transmitter is increased?
A. Its signal occupies more bandwidth
B. Its output power increases
C. Its output power and bandwidth increases
D. Asymmetric modulation occurs

Greater deviation means greater bandwidth is occupied, answer A.

What could cause your FM signal to interfere with stations on nearby frequencies?
A. Microphone gain too high, causing over-deviation
B. SWR too high
C. Incorrect CTCSS Tone
D. All of these choices are correct

In a home-brew or modified FM system, microphone gain set too high, and without "limiting", will cause over-deviation into the next channel, answer A.

Which of the following applies when two stations transmitting on the same frequency interfere with each other?
A. Common courtesy should prevail, but no one has absolute right to an amateur frequency
B. Whoever has the strongest signal has priority on the frequency
C. Whoever has been on the frequency the longest has priority on the frequency
D. The station which has the weakest signal has priority on the frequency

The answer is A, common courtesy should apply.

T2B09 [97.119(b)(2)]
Which of the following methods is encouraged by the FCC when identifying your station when using phone?
A. Use of a phonetic alphabet
B. Send your call sign in CW as well as voice
C. Repeat your call sign three times
D. Increase your signal to full power when identifying

(Proper NATO) phonetics are a good idea, as they make the callsigns more intelligible, answer A.

Which Q signal indicates that you are receiving interference from other stations?

It is QRM, answer A. I suppose the M stands for Man-made.

Which Q signal indicates that you are changing frequency? A. QRU

It is QSY, answer B.

Under what circumstances should you consider communicating via simplex rather than a repeater?
A. When the stations can communicate directly without using a repeater
B. Only when you have an endorsement for simplex operation on your license
C. Only when third party traffic is not being passed
D. Only if you have simplex modulation capability

If you can communicate directly, you should considering doing so, answer A. The others are just silly.

Which of the following is true of the use of SSB phone in amateur bands above 50 MHz?
A. It is permitted only by holders of a General Class or higher license
B. It is permitted only on repeaters
C. It is permitted in at least some portion of all the amateur bands above 50 MHz
D. It is permitted only on when power is limited to no more than 100 watts

It is legally permitted in at least some (actually, most) of ALL bands above 50 MHz, answer C. The rest are really rather silly.

On to: Public Service

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Written by Julian Sortland, VK2YJS & AG6LE, January 2018.

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