Answer first: the CG250 is a plug-and-play Band 20 + Band 8 home repeater for 250 m² that repeats Band 20 at 800 MHz for O2, Vodafone and Three 4G data and Band 8 at 900 MHz for O2 and Vodafone 2G calls and SMS, with ≥60 dB uplink and ≥65 dB downlink gain, a higher ≥17 dBm output than a 10 dBm home unit, a ≤5 dB noise figure and 25 active sessions. The whole job needs only a drill, a screwdriver, a spirit level and cable clips, takes 10 to 15 minutes for the basic one-antenna setup, and can grow to three indoor antennas through a splitter when the outside donor is strong between -70 and -90 dBm. Follow the ten numbered steps below, keep the donor and server 10 m apart, connect power last, and leave the bracket on an exposed rooftop after the test.

CG250 Snapshot Before You Mount the Outdoor Antenna

A short spec table keeps every number this guide relies on in one place. The CG250 repeats Band 20 4G and Band 8 calls, recovers a weak rural donor with ≥60 dB uplink and ≥65 dB downlink gain, and spreads a higher ≥17 dBm field than a 10 dBm unit across the rated 250 m² for 25 phones.

Step 1: Read the Outdoor 4G Signal in dBm at the Wall Before Fixing Anything

A home repeater can only amplify the signal the outdoor antenna actually receives; brick, reinforced concrete, solid stone and a tiled roof hide the tower from a handheld phone. The pre-mount check happens outside the house, not on the sofa, and it decides where the omni sits and whether the included 5 dBi aerial is enough or the optional Yagi earns its place.

The dBm ranges the CG250 expects at the outdoor antenna

A reading of -97 dBm on 4G reads as a healthy rooftop donor that the ≥65 dB downlink gain and ≥17 dBm output turn into a usable indoor signal across both floors. -105 dBm sits at the edge of the recommended band and still produces a stable data session once the omni clears the wall, rendered stone and the pitch-side shelter more comfortably than a lower-rated unit; with a lower rated unit it produces a fragile session only. -112 dBm on 4G is the practical antenna near ceiling: roughly -112 dBm the LTE receiver loses the control channel, the phone falls back to a slower service or shows no service, and no booster manufacturer can pull a donor never received. The ≥60 dB uplink gain covers a weak outdoor antenna better than holding a phone to the glass, but it cannot invent a band the survey never picked up.

How to read dBm rather than bars in a home survey

Phone bars are subjective and differ between iPhone and Android; the dBm figure is the measurement the amplifier actually sees. On an iPhone, enter field-test mode from the dialer and watch the RSRP value while standing beside the house. On Android, use an engineering or network diagnostics menu, or a free field-test app that lists RSRP by band. Hold the phone away from your body, because a hand and head absorb 3 to 5 dB, and read on the side of the house facing the nearest mast rather than the sheltered courtyard side.

Where to survey: roadside, side wall, garden gable, layby

Stand on the road-facing side, the open garden side at the rear, and the far side of the driveway; record the reading for your own SIM and a household member on a different network, because the strongest combined spot is where the omni goes. On a rural lane the open gable or roof edge beside a hedge or a barn; on a town house the hard side facing the street typically beats the enclosed courtyard. Survey carefully: if your Band 20 reads -112 dBm at every position beside the house, the CG250 cannot manufacture that band inside, though it may still improve voice on the other network's service, but the missing 4G stays missing; re-check facing the proper mast rather than expecting the amplifier to close the gap by itself.

Step 2: Mount the 5 dBi Omni-Directional Antenna for an Open Horizon

The 5 dBi outdoor antenna gathers signal equally from all horizontal directions rather than focusing one narrow beam, which suits a home where the usable O2 or Vodafone mast can sit in any compass direction. On a tiled or slate roof it fixes without drilling tiles; on a chimney stack, gable wall or fascia it uses the supplied bracket; on a flat roof the weighted base or adhesive pad settles in the clear air.

Roof edge or gable: clear sky line over 3 to 5 metres height

Wrap the roof or stock stack, peel the adhesive pad or bolt the small bracket, and press or fix the omni to the roof edge, chimney breast or gable, away from roof rails, satellite dishes, vent pipes and the TV aerial. Keep the omni at least 3 metres above any roof-mounted clutter, ideally 3 to 5 metres up, because the metal roof absorbs the 5 dBi pickup. The roof edge position favours an all-round donor on a rural lane; the central ridge balances all directions for a town house; keep the omni at least a metre clear of roof-mounted air horns, spotlights and satellite dishes, because metal near the base defeats the omni pickup.

Solid chimney, rendered wall or fascia: bracket rather than suction

A suction cup holds on a smooth tiled roof for short jobs but weathers; a permanent fix uses the small screw bracket on a brick gable, chimney stack or painted fascia. Drill a 6 mm pilot hole through the rendered wall, fit the bracket level, then clip the omni onto it. Never rely on an adhesive pad on a windy exposed ridge without the bracket as backup. The omni points straight up and does not tilt; tilting the omni usually leaves you uncovered unless you have switched to the directional Yagi, because tilting an omni cancels part of its circular pattern.

When the omni falls short: the optional high-gain Yagi

Where the donor sits at -105 to -112 dBm on one identifiable mast, the omni's all-round pattern wastes half its pickup in open sky; the optional high-gain Yagi focuses a narrow beam straight at that tower and recovers several decibels more. This is the weak-donor upgrade, not a requirement for a normal suburban home, and this guide returns to the Yagi trigger in the rural optimisation section below.

Step 3: Run the 10 m Outdoor Cable to BS and the 5 m Indoor Cable to MS

The CG250 ships two different feeds for two different jobs, and keeping them straight prevents feedback that shuts the amplifier down. The 10 m outdoor low-loss coax runs from the roof omni down to the chassis BS (base station / donor) port; the 5 m indoor coax runs from the chassis MS (mobile station / server) port to the 3 dBi whip inside.

What each length does and where it routes

Clip the outdoor feed every 40 cm along the fascia, drop it through a purpose-made wall gland rather than a loose window gap, and seal the entry with exterior silicone so rain cannot chase the cable in. Keep bends gentle; a tight right-angle fold crushes the coax and costs decibels. The indoor 5 m feed reaches the whip placed in the central living space or hallway; a split system routed through the splitter uses extra runs to the second and third antennas, covered in Step 5.

Cable upgrades for a long roof-to-chassis distance

If the chassis lives in a garage and the omni on a two-storey roof beyond 10 m, replace the outdoor feed with the 20, 30, 40 or 50 m length rather than splicing two cables; every metre of coax costs signal, and joined sections invite water and mismatch. Keep the indoor whip feed short, because lengthening the server side also spends recovered power before it radiates.

Step 4: Match BS and MS Ports Before Any Power

The chassis labels BS and MS on their ports. BS stands for base station, the outdoor donor side facing the tower; MS stands for mobile station, the indoor server side facing the phones. Swapping the two creates a feedback loop between antennas that the automatic gain control treats as a dangerously loud signal and throttles back, leaving the home weaker than before.

Connect in this fixed order

First fit the roof omni, second fix the whip indoors, third lay the 10 m outdoor coax from omni to BS, fourth lay the 5 m indoor coax from MS to whip, fifth confirm both labels match, and only then prepare power. A physical check before the adapter goes in avoids the common fault where the indoor whip feeds the donor port and the outdoor omni feeds the server port. On the split version, the splitter sits on the MS side after the chassis, never on the BS donor side, because splitting the faint incoming feed wastes recovery headroom.

Step 5: Hold the Two Antennas 10 m Apart and Split to a Third Indoor Whip

Minimum isolation keeps the donor antenna from hearing the server antenna directly, which causes oscillation and automatic shutback. The CG250 calls for a 10 m vertical separation: outdoor omni high on the roof, indoor whip low in the hallway, with a floor and walls between rather than facing across a window.

10 m vertical isolation and the alternative horizontal gap

On a two-storey home the roof omni above and the ground-floor whip below already supplies the vertical gap; measure straight down through the floors rather than around the furniture. Where vertical separation falls short, place the omni at one end of the property and the whip at the far end on the same floor, giving roughly 10 m of horizontal distance with solid walls in between. Bringing the whip within 5 m of the omni, especially through a single glass pane, invites the AGC to mute the output.

Expanding to 3 indoor antennas through a splitter on a strong donor

The CG250 states plainly that coverage expands by adding an indoor antenna, splitter and cable when the outside signal is strong. This expansion only works on a donor between -70 and -90 dBm, because a weak donor cannot spare extra split loss; on a strong donor, fit a two-way or three-way splitter on the MS side, run extra coax to a second whip in the far bedroom and a third whip in the home office or cafe counter, and let the ≥17 dBm output feed all three. Each split divides the radiated field, so add antennas only where a single whip leaves a dead corner rather than blanketing every room by default. The split path is what lets a 250 m² open-plan cafe or three-bedroom house serve 25 phones without one whip fighting corner after corner.

Step 6: Power-On Sequence, LEDs and the 3 to 5 Minute AGC Lock

Apply power last and let the automatic gain control settle before judging the result. Rushing the LED readout within the first 30 seconds shows transient levels that change as the unit locks the donor.

The fixed power-on order

Connect both antennas and both cables, confirm BS to outdoor and MS to indoor, then plug the 5 V DC UK adapter into the wall and last into the chassis. The LEDs light, the internal AGC listens for 3 to 5 minutes, backs off when the tower looms close and recovers when the donor fades, and only then holds a steady field. Never plug the adapter first and attach antennas live; the chassis can see an open port and push gain into nothing.

Reading the band LEDs after AGC settles

A steady green on the Band 20 channel means the 4G donor is recovered and repeating; a steady green on Band 8 means the 2G call layer is up. A blinking amber signals the AGC still balancing after a weather or traffic change; a red or unlit band means that layer is not being received at the omni, which points back to Step 1 rather than a chassis fault. Wait the full 5 minutes before concluding, because the rural donor swings between clouds and roof reflection.

Step 7: Split 250 m² into Zones and Test 25 Users Before Leaving

The final check proves the rating across the rooms rather than at the chassis. Divide 250 m² into four zones: living room, kitchen or office, master bedroom, and the far bedroom or upstairs landing. In each zone, place a phone on 4G, open a data session, and place or receive an ordinary O2 or Vodafone call.

Zone test for data, calls and concurrent users

Record the bar count and RSRP on each band in every zone, run a speed test on 4G, and keep a call open for 60 seconds to confirm no drop. To prove the 25-user rating, gather family members or staff on a mix of O2, Vodafone and giffgaff SIMs, hold a spread of calls and browser sessions at once, and check that none collapses into a drop when the busiest zone loads. A single perfect test at the whip position proves nothing; the far corner at floor level beside the furniture is the honest measurement.

Where a zone still falls short

If one far bedroom stays weak on a strong donor, add the second whip through the splitter; if the office and cafe counter both need a field, add the third. If the donor itself reads -112 dBm everywhere, more indoor antennas cannot fix the missing layer, and the optional Yagi or a larger commercial rating becomes the honest answer.

The 10 to 15 Minute Basic Timeline and the Tools You Need

The single-whip setup finishes in 10 to 15 minutes with hand tools; the split-to-three-antenna version adds the cable runs.

Tools for the basic install

A 6 mm masonry bit for the gable bracket, a Phillips screwdriver, a spirit level, cable clips, exterior silicone for the gland, and a phone with a field-test or speed-test app cover the whole job. No soldering, no network configuration, and no account registration with the carrier; the unit works on the licensed bands in Ofcom's permitted class as supplied.

Rural Weak-Signal Optimisation and the Yagi Trigger

On a village lane where one mast sits at -105 to -112 dBm, the omni's all-round pattern spreads energy in every direction and underfeeds that one tower. The optional high-gain Yagi focuses a narrow beam on the identified mast, recovers several decibels, and turns a marginal -108 dBm donor into a repeating signal the ≥17 dBm output can spread across 250 m².

When to switch from omni to Yagi

Switch when the survey shows a single clearly identified mast, RSRP between -105 and -112 dBm on 4G, and no second useful tower nearby. Aim the Yagi by walking the signal direction with the phone, peak the reading, then fix the boom at that compass bearing and a slight tilt upward for distance. Do not aim the Yagi at a town centre several valleys away; a closer weaker tower beats a distant strong one through a ridge.

Surge protection and long cable runs

A rooftop feed exposed to lightning paths benefits from the optional in-line protector on the BS side, and a chassis in a distant garage calls for the 20 to 50 m outdoor upgrade rather than a splice. Neither replaces a weak donor; they protect and carry what the survey found.

Honest Limits: What the CG250 Does Not Fix at 250 m²

Three boundaries stay fixed no matter how high the output. The CG250 tunes Band 20 and Band 8 only, so it does not repeat 3G Band 1 at 2100 MHz, does not repeat any 5G band, and does not convert 4G into 5G. EE 2G voice sits on Band 3 at 1800 MHz and is not carried, so an EE household gets boosted 4G data where reach applies but not a boosted EE circuit call. The rated space is 250 m² for a three-bedroom home or small office supporting 25 sessions; it does not blanket a farmyard, separate outbuilding or extension beyond the far wall, and a permanently sited space clearly larger calls for a commercial-rated unit rather than more home output.

Article Keywords

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