Answer first: the CD100 repeats Band 20 (800 MHz) and Band 3 (1800 MHz) simultaneously through one 5 dBi omni outdoor antenna and one 3 dBi indoor whip, which is why one budget unit covers all four UK network families rather than serving a single operator. Band 20 at 800 MHz is the long-range rural 4G layer for O2, Vodafone and Three, using an uplink of 832 to 862 MHz and a downlink of 791 to 821 MHz; Band 3 at 1800 MHz is the capacity layer for EE 4G and the home of EE's 2G voice, using an uplink of 1710 to 1785 MHz and a downlink of 1805 to 1880 MHz. The amplifier adds at least 45 dB of uplink gain and at least 50 dB of downlink gain on each band, holds output at or above the regulated >=10 dBm ceiling, and carries UKCA, CE and RoHS certification under Ofcom's licence-exempt rules. It does not tune 3G Band 1 at 2100 MHz, does not tune any 5G band, and covers only 100 m2 for up to 10 simultaneous users.

This guide assumes you have already checked which band your SIM actually uses: an O2, Vodafone or Three customer lives on Band 20 for 4G, an EE, ASDA, BT, Virgin, Orange or T-Mobile customer lives on Band 3 for 4G and 2G voice, and the MVNO list below maps each pay-monthly and pay-as-you-go SIM to its host network. The CD100's value is that it buys both layers in one chassis instead of choosing one operator's band and leaving the other at zero bars indoors.

Every figure in this guide comes from the CD100 specification sheet: frequency Band 20 and Band 3 FDD LTE, uplink gain >=45 dB, downlink gain >=50 dB, maximum output power >=10 dBm, noise figure <=5 dB, indoor coverage up to 100 m2, 10 simultaneous users, 5 dBi omni outdoor antenna, 3 dBi whip indoor antenna, 10 m included outdoor low-loss coax, AC 100 to 240 V 50/60 Hz to DC 5 V adapter with a UK 3-pin plug, and operating temperature -10 C to +55 C. Where the guide compares the CD100 to a single-band sibling, it compares tuned bands, coverage and networks rather than price.

Quick Answer: What Exactly Does the CD100 Repeat, and Which UK Networks Does It Cover?

The CD100 repeats two frequency bands and their services at the same time, so the answer splits into ten factual points that set the technical baseline before the deep-dive sections.

1. Band 20 at 800 MHz carries O2, Vodafone and Three 4G LTE. Its paired block runs 832 to 862 MHz uplink and 791 to 821 MHz downlink; this is the long-range rural layer that bends over hills and through stone.
2. Band 3 at 1800 MHz carries EE 4G LTE and EE 2G voice. Its paired block runs 1710 to 1785 MHz uplink and 1805 to 1880 MHz downlink; this is the capacity layer that fills towns and cities.
3. Uplink gain is at least 45 dB and downlink gain at least 50 dB on each band, restoring the faint phone transmit signal and the tower signal after wall loss.
4. Maximum output power is at least 10 dBm, the ceiling Ofcom sets for licence-exempt mobile repeaters, so the unit never interferes with the macro network.
5. Noise figure is no more than 5 dB, meaning the amplifier adds little extra noise between the donor antenna and the re-radiated indoor signal.
6. One chassis covers all four UK network families: O2, Vodafone, Three on Band 20; EE on Band 3; plus their MVNO partners listed later.
7. VoLTE works where the network offers it, and 2G circuit-switched voice and SMS remain boosted on Band 3 for EE partner SIMs.
8. The unit is Ofcom licence-exempt and carries UKCA, CE and RoHS, so no frequency licence, annual fee or registration is required.
9. The CD100 does not tune 3G Band 1 at 2100 MHz and does not tune any 5G band, so legacy 3G fallback and 5G speeds are outside its design.
10. Rated coverage is 100 m2 for up to 10 simultaneous users, which fits one room, a small flat, a cottage or a home office, not a whole house or commercial floor.

The sections below explain each point with the exact frequencies, gain maths, network mapping and regulatory context, and the comparison table later in this guide shows why choosing both bands matters versus a Band 20-only or Band 3-only unit.

What Is Band 20 at 800 MHz, and Which UK Networks Use It for 4G?

Band 20 is the LTE band that sits in the 800 MHz sub-gigahertz region. In 3GPP terms it is a Frequency Division Duplex (FDD) block, meaning the phone transmits on one fixed frequency and receives on a separate fixed frequency at the same time, rather than sharing one channel in time. The CD100 tunes the Band 20 pair exactly: uplink 832 to 862 MHz for the phone-to-tower direction, and downlink 791 to 821 MHz for the tower-to-phone direction. A 31 MHz uplink block and a 31 MHz downlink block sit 41 MHz apart, the standard guard that keeps transmit and receive from colliding inside the same repeater.

Why 800 MHz reaches further than 1800 MHz

Lower frequency means a longer wavelength, and a longer wavelength bends over hills, around buildings and through thick stone, slate and brick that absorb 1800 MHz more heavily. That is why Ofcom allocated the 800 MHz digital dividend spectrum, freed after the analogue TV switch-off, to rural coverage: O2 and Vodafone built much of their deep-country 4G on Band 20 so a village in a valley gets LTE where higher bands cannot reach. Three also receives Band 20 4G through a shared network arrangement with O2, so a Three SIM in a rural spot often attaches to an O2-hosted Band 20 cell, and the CD100 boosts that cell the same way.

Which primary networks and MVNOs ride Band 20

Primary 4G customers on Band 20 are O2, Vodafone and Three. The MVNOs that lease capacity from those hosts follow the same band: giffgaff, Tesco Mobile, Lycamobile and Sky Mobile run on the O2 network; Lebara runs on Vodafone; iD Mobile, Smarty and FreedomPop run on Three. A CD100 owner on any of those SIMs benefits from the Band 20 path whether the visible mast carries the O2, Vodafone or Three carrier.

What the CD100 does on the Band 20 path

The outdoor omni captures the weak Band 20 downlink at 791 to 821 MHz, the >=50 dB downlink gain stage restores the signal after plasterboard, brick and double-glazed loss, and the 3 dBi whip re-radiates it indoors. On the return path, the phone's faint Band 20 transmit at 832 to 862 MHz reaches the whip, the >=45 dB uplink gain stage boosts it back through the omni toward the serving mast, and the >=10 dBm output ceiling keeps the transmitted power inside the licence-exempt limit so the repeater behaves as a small indoor cell rather than a competing tower.

What Is Band 3 at 1800 MHz, and Why Does It Carry EE 4G Plus 2G Voice?

Band 3 is the LTE block at 1800 MHz, another FDD pair the CD100 tunes exactly: uplink 1710 to 1785 MHz and downlink 1805 to 1880 MHz. Here the uplink block spans 75 MHz and the downlink block spans 75 MHz, separated by the 95 MHz guard, which gives Band 3 a much wider channel allocation than Band 20 and is why EE runs most of its urban capacity on it. EE's 2G GSM network also lives in or adjacent to this 1800 MHz region, which is why the same Band 3 path carries both fast LTE data and legacy circuit-switched calls and SMS for EE partner SIMs.

Why 1800 MHz feels faster but reaches less far

Wider channels and higher frequency give Band 3 the capacity to carry more simultaneous users at higher data rates in towns and cities, but the shorter wavelength loses energy faster across long distances, foliage and thick walls. That trade-off defines the CD100's role: Band 20 rescues a rural O2, Vodafone or Three customer with a bar-count problem at the property edge, while Band 3 rescues an EE customer indoors where capacity signal fails to penetrate a concrete or stone home. The unit treats both independently and never forces a phone from one band to the other.

Which primary networks and MVNOs ride Band 3

The primary 4G and 2G customer on Band 3 is EE, together with EE's partner brands ASDA Mobile, BT Mobile, Orange, T-Mobile, The People's Operator and Virgin Mobile, all of which run on the EE network. A Plusnet Mobile SIM also sits on the EE host network and benefits from the Band 3 path. Because the Band 3 amplifier repeats the 1800 MHz layer regardless of which EE-family brand the SIM displays, a pay-as-you-go ASDA handset and a contract EE handset both get boosted indoors.

2G voice on Band 3 for handsets without VoLTE

EE still maintains a 2G GSM layer for circuit-switched voice and SMS, and the CD100 repeats that layer alongside LTE. An older feature phone, an elderly relative's handset, or a phone in an area where VoLTE has not been enabled still completes a normal voice call over the boosted 1800 MHz path rather than dropping to no service. This is why the spec sheet lists supported services as 4G LTE data plus 2G voice calls plus SMS, with VoLTE where available, rather than claiming a universal 3G or 5G call fallback.

UK Network and MVNO Mapping: Which SIM Works on Which CD100 Band

The table below maps every SIM named on the CD100 product page to its host network and the band the booster repeats for it. Before ordering, check your SIM's host carrier rather than the shop brand, because the MVNO brand name itself does not appear on the tower.

Two households on different hosts therefore benefit from different halves of the CD100: the O2 household sees the Band 20 path light up, the EE household sees Band 3 light up, and a shared home where one person uses giffgaff and another uses BT Mobile gets both bands boosted at once, which is the practical reason a dual-band chassis beats buying two single-band boxes.

Uplink and Downlink Frequencies: The Exact 832-862, 791-821, 1710-1785 and 1805-1880 MHz Pairs

A repeater works on a paired FDD block: the phone transmits (uplink) on one block and receives (downlink) on another, and the amplifier must repeat both directions without mixing them. The table below lists the exact CD100 tuned ranges from the specification sheet.

Why uplink and downlink gain differ

The CD100 lists >=45 dB uplink gain and >=50 dB downlink gain rather than equal numbers, and the asymmetry is deliberate. A tower transmits with high power while a phone transmits at low power from a battery, so the uplink path loses more energy on the way back and the amplifier still only needs to restore the faint phone signal to a level the tower can decode. The larger downlink figure restores the tower signal after indoor wall loss before the whip re-radiates it. The 5 dB gap between the two figures is normal for a home repeater and is not a defect.

What a 31 MHz or 75 MHz block means on a phone screen

Those ranges are the spectrum the network may allocate channels inside, not a single wide pipe. A phone attaches to one channel of typically 5, 10 or 20 MHz within the block, and the repeater repeats the whole tuned range transparently, so any channel the network chooses inside 791 to 821 MHz or 1805 to 1880 MHz passes through regardless of future channel reallocation, as long as it stays inside the band.

Gain Explained: >=45 dB Uplink and >=50 dB Downlink on Both Bands

Gain, measured in decibels, is the factor by which the amplifier boosts the weak signal before re-radiating it. A decibel is logarithmic: +10 dB multiplies power by ten, +20 dB by one hundred, +30 dB by one thousand, +45 dB by roughly thirty-one thousand, and +50 dB by one hundred thousand. The CD100's >=45 dB uplink and >=50 dB downlink figures mean the faint donor signal picked up by the omni is amplified tens of thousands of times before the whip releases it indoors.

How the gain budget pays for wall loss

Every indoor surface costs signal: a plasterboard partition costs a few dB, an external brick wall costs 10 to 20 dB, a stone cottage wall costs more, and double glazing and a solid floor add their own loss. The >=50 dB downlink margin absorbs that cumulative loss so the phone still shows bars inside the room. The same budget also covers the passive loss in the 10 m included coax and any 20, 30, 40 or 50 m upgrade cable, which is why longer cable lengths are affordable in the gain math but never free.

Noise figure <=5 dB and why it matters

A perfect amplifier adds no noise; every real amplifier adds some, measured as the noise figure. The CD100's noise figure of no more than 5 dB keeps that added noise low enough that the amplified signal still decodes cleanly rather than arriving louder but garbled. A high noise figure would raise the indoor noise floor, cause the phone to see a louder but noisier cell, and reduce the usable uplink; a <=5 dB figure is the standard home-repeater quality level.

Gain is not the same as output power

Gain describes amplification factor, while output power, covered in the next section, describes the absolute ceiling the repeater may transmit at. A unit can have high gain but still keep output below the regulatory >=10 dBm ceiling, because the automatic gain control raises gain only until a stable indoor signal appears and then backs off rather than running at maximum into overload.

Why >=10 dBm Output Power Stays Within the Ofcom Licence-Exempt Limit

Maximum output power, listed as >=10 dBm on the CD100 spec, is the regulated ceiling the repeater may radiate from its indoor antenna. Ofcom's licence-exempt rules for mobile repeaters cap indoor output so the boosted cell behaves like a small local helper rather than a competing base station that could overwhelm the macro network, cause interference, or create uncontrolled roaming between the boosted signal and the tower.

What 10 dBm means in practice

10 dBm equals 10 milliwatts of radiated power, deliberately low enough to cover a room or small flat rather than the street. The rating is a permitted-class ceiling, not a claim that every unit outputs exactly that wattage; the automatic gain control dials output down further when the donor is strong, and pushes toward the ceiling only when the donor is weak. The unit never cranks past the Ofcom limit to chase coverage, which is what keeps it licence-exempt.

Why a higher dBm would not help a home anyway

More transmit power would only increase interference risk, heat and oscillation, while the indoor limit at 100 m2 comes from wall loss and antenna placement, not from raw watts. The correct lever for a weak donor is a better antenna position or the high-gain directional Yagi, not more output power, and the regulatory ceiling removes that temptation by design.

Ofcom licence-exempt status in plain terms

Because the CD100 sits inside the permitted output and band rules, Ofcom does not require a frequency licence, an annual fee, a registration number or a spectrum plan. The owner must still use the unit only on the licensed bands it repeats, keep separation high enough to avoid oscillation, and not modify the output stage; those obligations come with the licence-exempt class rather than a personal permit.

Why Dual-Band Beats Single-Band: CD100 vs C100 (Band 20 Only) and D250 (Band 3 Only)

The Boost4U home line includes single-band siblings: the C100 tunes Band 20 only for O2 and Vodafone 4G at about 100 m2, and the D250 tunes Band 3 only for EE 4G and voice at about 250 m2. The CD100 keeps both bands in one chassis. The table compares tuned bands, coverage, networks and users without pricing either sibling.

The mixed-household problem

Many UK homes are not single-network: one parent uses O2, another uses EE, a child's giffgaff rides O2, and a guest's EE SIM shows up on visits. A Band 20-only C100 leaves the EE side at zero bars, and a Band 3-only D250 leaves the O2 and Vodafone side cold. The CD100 repeats both layers with one omni, one whip and one power adapter, so the household does not need two boxes, two cables and two antenna pairs.

The coverage trade-off to understand honestly

The D250 reaches 250 m2 because it dedicates its budget to one band at a larger footprint, while the CD100 splits hardware across two bands and stays at 100 m2. A large single-network EE home that needs 250 m2 and nothing else may prefer the D250; a compact mixed-network home that needs all four families in one flat benefits from the CD100. Dual-band coverage at 100 m2 is a network-completeness purchase, not a larger-area purchase.

VoLTE and 2G Voice: How Calls Stay Connected on the CD100

Modern phones place calls over the 4G data layer using Voice over LTE (VoLTE), while older handsets and areas without VoLTE fall back to the circuit-switched 2G GSM network. The CD100 supports both routes where the network offers them, but its support differs by band.

VoLTE on Band 20 for O2, Vodafone and Three

Where the host network has enabled VoLTE on Band 20, a modern O2, Vodafone or Three handset places the call inside the boosted 800 MHz LTE session, and the CD100 repeats that session like any other data call. The booster does not negotiate VoLTE itself; the phone and network do, and the unit simply carries the already-established 4G call.

2G circuit-switched voice on Band 3 for EE

EE maintains a 2G layer in the 1800 MHz region, and the CD100's Band 3 path repeats circuit-switched voice and SMS for EE, ASDA, BT, Orange, T-Mobile, The People's Operator and Virgin handsets that cannot or do not use VoLTE. A basic feature phone, an elderly relative's handset, or a phone in a VoLTE-not-yet-enabled area still rings and completes a normal call over the boosted 2G layer.

What the CD100 does not carry for calls

The unit does not tune 3G Band 1 at 2100 MHz, so a network that still routes voice or data fallback through 3G in your location receives no boost on that layer. Where VoLTE is unavailable and the network relies on 3G circuit fallback, a call may not complete indoors even though 4G data shows bars; checking VoLTE support on your handset before ordering avoids that surprise.

Ofcom Licence-Exempt, UKCA, CE and RoHS Certification Explained

Four marks sit on the CD100: Ofcom licence-exempt status, UKCA for the UK market, CE for European conformity, and RoHS for restricted hazardous substances. Each answers a different regulatory question.

Ofcom licence-exempt

Ofcom's permitted-class rules allow a low-power indoor repeater on licensed mobile bands without the owner holding a spectrum licence. The CD100 meets the output and isolation conditions of that class, so no application, fee or renewal is required, provided the unit is used as supplied, kept separated from its own donor antenna, and not modified to raise output.

UKCA

UKCA marking confirms the product meets the applicable UK safety, electromagnetic compatibility and radio equipment requirements for sale in Great Britain after the CE transition. It is the UK-market equivalent of the conformity declaration, and it appears on units supplied to UK customers.

CE

CE marking confirms conformity with the European Union's Radio Equipment Directive and related health and safety standards, which is why the same kit ships across the EU delivery list including Germany, France, Italy, Spain, the Netherlands, Belgium, Austria, Sweden, Denmark, Finland, Ireland, Portugal, Poland and the Czech Republic as well as the UK.

RoHS

RoHS restricts lead, mercury, cadmium and other hazardous substances in electronics, so the chassis, cable and adapter comply with the waste-electrical-equipment rules rather than containing banned materials. None of these marks changes how the bands are repeated; they confirm the unit may be sold and used without a separate permit.

Honest Limitations: No 3G Band 1, No 5G, and Only 100 m2

A guide that only lists benefits misleads a buyer. The CD100 has three clear limits that should match your situation before you order.

No 3G Band 1 at 2100 MHz

The CD100 tunes only Band 20 and Band 3. It does not repeat Band 1 at 2100 MHz, the 3G UMTS layer some networks still use for data fallback or circuit-switched voice. A home that relies on 3G where 4G fails will see that fallback unboosted indoors. This is the single most important technical limit, and it is why the unit suits areas already served by Band 20 or Band 3 4G rather than places that only hold 3G.

No 5G on any band

The CD100 does not tune n78 (3.5 GHz), n8 (900 MHz) or any other 5G band, and it does not convert 4G into 5G. A 5G phone still receives its normal unboosted 5G signal from the macro tower, and the CD100 only lifts the 4G Band 20 and Band 3 layers. Expect reliable 4G calls and data, not boosted 5G speeds.

Only 100 m2 for 10 simultaneous users

The rated footprint of 100 m2 (1,076 ft2) fits one room, a studio, a one-bedroom flat, a cottage or a home office, and up to 10 active sessions. A whole house across multiple floors, a large detached property, a shop floor or an office beyond a single room needs a larger unit or a second unit rather than more output from this chassis. The 10-user count means active calls and data sessions, not every registered device in the home, and beyond that ceiling the network itself schedules phones.

Frequently Asked Questions