The Sydney suburbs where 5G struggles – and why reception bars lie

How is it that we can beam a high definition cat video into deep space, but a phone call can barely survive a short trip in an elevator, and it’s often a battle to load Instagram on the train?

NSW alone is also blighted by 4000 mobile black spots, including one which seems to rob commuters of cellular data as trains sail over the Sydney Harbour Bridge (although at least the view is nice when you’re forced to look up).

And, according to new data, there’s one suburb 10 kilometres from the CBD battling a chronic case of bad coverage. So what dictates where these dead zones lie? And will the shutting of 3G – which is almost complete – make the problem better or worse?

The suburbs where 5G struggles

A national audit of mobile black spots is under way.

The data from the audit so far shows that most Sydney suburbs are covered by “good” or “excellent” 5G coverage. But there are a few patches where the coverage drops to “modest”, according to data crowdsourced for the government by Accenture from 150,000 people.

There’s a patch of bad Optus coverage in the centre of Marrickville, according to the data, while patches of lower-quality Telstra coverage have also been recorded in Beacon Hill, Concord, Chatswood, Lane Cove and a few streets of Maroubra.

But the most obvious patch of “modest” coverage – defined by frequent service failure, call drops and noticeable distortion – lies around Tennyson Point and parts of nearby Gladesville and Putney. The audit data shows 5G from all three major telcos struggles in these areas.

Scores of residents in those areas told the Herald they were frustrated by terrible coverage, dead spots and calls cutting off despite being 10 kilometres from the CBD.

Audit data shows no mobile cells within the Tennyson Point 5G black spot. Areas away from urban centres near water can struggle with mobile service because the steep hills towards the shore create “shadows” of tower coverage patches where mobile coverage doesn’t land because it’s blocked, and the signal is directed towards busier roads and business strips.

The problem could be improved by installing new towers but that can prove commercially challenging and their installation often faces backlash from nearby residents.

The telcos didn’t say whether the audit data matched up with their own, although Telstra said the visualisation tool is in its early phases and is “indicative only of relative performance in the general area”.

As for testing a phone signal, disregard reception bars. They’re an all but useless indication of signal strength. To get a proper reading, you need to access Field Test Mode, which is accessible via settings on an Android or by calling *3001#12345#* on an iPhone.

That will give you a reading of signal strength in decibels, under the RSRP or RSRQ measures. The closer to zero, the better your signal.

For RSRP, anything between 0 and -115 decibels (dBm) is regarded as good coverage, according to Accenture’s metrics, while anything below -115 will begin to give you trouble. For RSRQ, anything between 0 and -15 dBm is decent, while signal heading towards -20 is getting patchy.

Data shows the network of cell towers (black points), which are most dense in the CBD. Blue and green locations show strong coverage while yellow and orange show locations with weak 5G signal – including the Tennyson Point patch (circled in red) – according to Accenture’s crowdsourced data.

What dictates whether you have good signal?

Where you are in relation to mobile cell towers is a major factor. Towers also aim signals towards urban centres and roads, so even if you’re close to one it may be beaming its signal in the opposite direction.

The geographical area covered by a base station is called a “cell”, and these cells create a patchwork of reception across the country.

Smaller antennas and booster cells attached to skyscrapers, power poles and bus stops help amplify the signal through built-up urban areas.

But there are many things that can disrupt a wave carrying your phone call or YouTube video, including buildings, trees and hills. Even dust and water in the air can wreak havoc.

“If you talk to people up in the north – Darwin, Cairns – during the monsoon, every afternoon when it starts pouring with rain, mobile signal in most areas will drop out,” Associate Professor Mark Gregory, a telecommunications expert at RMIT, said.

Wood, glass and concrete will also degrade a signal, so if you’re inside a building your signal has to work harder. But metal is the worst offender. Houses with metal roofs often require mobile boosters to funnel a signal inside.

A solid or mesh enclosure of metal – called a Faraday cage – disrupts radio waves because metal, as a conductor with free-flowing electrons, interferes with electromagnetic radiation.

That’s why your signal cuts off when the doors of an elevator close. A train is also essentially a metal cylinder and even metallic tints on the windows can deflect signals.

Some speculate the Sydney Harbour Bridge also acts as a Faraday cage, further robbing train scrollers of signal, but Gregory said it’s probably due to phones disconnecting from one cell tower and trying to connect with the next cell.

A spokesperson for Telstra had the same explanation. “Your phone sometimes needs a moment to cut through some ‘noise’, especially in city centres and exposed areas like along the Harbour Bridge. Your device can see literally hundreds of different cell signals from all directions, which can cause interference and brief disruptions.”

Telstra has a project under way to address such interruptions in the CBD and on the bridge, while signal-boosting infrastructure was built into the newly opened M1 metro line, affording passengers better mobile coverage underground.

Selling the spectrum

Mobile phones, Wi-Fi and radio harness waves of energy on the electromagnetic spectrum, or EMS, to transmit data. The EMS is the range of electromagnetic radiation frequencies, from radio waves through to infrared, visible light, X-rays and gamma rays.

All waves on the EMS travel at or close to the speed of light, which make them useful for rapid, wireless communication.

The EMS is arranged by wavelength and frequency. Wavelength is the distance between each crest of an electromagnetic wave; the length can span from 100,000 kilometres for radio waves to a trillionth of a metre for gamma rays.

Related to wavelength is frequency, measured in hertz, which refers to the number of waves that pass a given point in a second.

Newer forms of 5G utilise higher frequencies on the electromagnetic spectrum.Credit: EMF Guide

When you listen to a radio station, you are tuning in to the frequency of the EMS that station is broadcasting on. If two radio stations broadcast on the same frequency, the data would clash, resulting in glitchy interference.

That’s why the government, through the Australian Communications and Media Authority, controls who uses which part of the spectrum by licensing slices of the EMS for use.

We can only exploit certain parts of the EMS for telecommunications, therefore “spectrum”, as it’s referred to in the industry, is a limited resource.

“If you talk to a telco, you’ll learn one golden rule: there’s never enough spectrum,” Gregory said.

Why kill 3G?

That’s why telcos are in the middle of shutting down 3G; to free up spectrum for more advanced 5G technology. TPG/Vodafone cut it off last year while Telstra and Optus have delayed their shutdown to the end of October.

The delay came after the government flagged concerns about a subset of devices that mostly use 4G but rely on 3G for emergency calls. More than 100,000 people could lose access to triple zero once 3G is fully retired, according to a July update from Communications Minister Michelle Rowland.

But the process of shutting down older generations will continue into the future as new technology emerges. 6G tech is already nipping at the heels of 4G and 5G with the announcement of a 6G silicon chip by University of Adelaide scientists last month.

5G can supply more data at faster speeds and more precisely than 3G and 4G, and it can use the “millimetre wave” part of the spectrum where the wavelength is between 1 and 10 millimetres, aka mmWave.

“One of the big advantages of 5G is being able to massively exploit the higher frequencies,” Gregory said.

The higher the frequency of the wavelength you’re using, the more information you can transmit, faster. Australia’s 3G and 4G networks use frequencies between 700 megahertz (MHz) and 2.1 gigahertz (GHz), while the mmWave harnesses frequencies of 26 GHz.

The mmWave band was once used for satellite internet, but in 2021 the 26 GHz mmWave band became available for telcos to license. ACMA auctioned off 358 slices of the spectrum band for almost $650 million and the vast majority was snapped up by Optus and Telstra.

These high-frequency wavelengths can transmit a large amount of data over a short distance, so it suits high-density urban areas.

“If you look at shopping centres, sporting grounds, Bourke Street in Melbourne, George Street in Sydney, you’ve got hundreds of people in a small area, so you only need a signal that goes 20 metres and you might be covering hundreds of people,” Gregory said.

“The telco industry sees that type of spectrum as being vital for the industry moving forward.”

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