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The Definitive DAS Guide: Active vs Passive, Installation, & Recommendations

Posted by James N on

In a wireless world, poor wifi & cellular signal is more than about convenience. Like electricity, plumbing and refrigeration, it’s now a modern necessity for us to connect to literally everything.

From phone calls, instant messaging, emails, high-speed data, streaming apps, and internet, any disruption can affect workflow, critical information, and professional reliability.

Think about the effects of poor cellular signal at home or work and the myriad of problems and helplessness that come with poor cell coverage & reception.

Multiply that by the hundreds to thousands of people at a busy workplace or commercial venue… that’s a lot of inefficiency and thousands of lost hours.

21st century problems depend on 21st century solutions.

How You Connect to The Web

When it comes to wireless solutions: broadband landline internet & cellular 3G & 4G (and soon to be 5G) internet are the two biggest technologies used to connect to the web & cloud.

While wifi from landline internet is the prevalent go-to technology in homes & offices, there are certain limitations, especially with the influx of wireless users, changes in wireless device habits, and the evolution of cellular technology.

First, wifi from landline internet has less security and more potential privacy issues with data being monitored by the employer/host at workplaces and other unsecured commercial or public areas.

Second, in commercial high-traffic areas like hotels, airports, and stadiums, the building operator often pays for the lowest data speed plan available. When multiplied by the hundreds to thousands of users and cellular devices on the same network, it’s common to have very slow internet speeds.

With a lack of personal security and lesser download & upload speeds, many building operators are opting to use cellular connectivity to assist, complement, or even supplant their wifi landline internet. And with the upcoming promise of 5G and aggressive carrier competition to keep their unlimited data plans at low prices, there’s mounting evidence that supports of a cord-cutting generational shift.

That’s where a DAS system comes into play.

What is DAS?

DAS stands for distributed antenna system. In layman’s terms, it’s a system of antennas that improve cellular & other radio frequencies for better coverage and more reliable service.

There two main types of DAS known as iDAS (indoors) and oDAS (outdoors). However, a vast majority of DAS installations are in-building. And the two most popular indoor DAS solutions are known as Active DAS & Passive DAS.

These two DAS systems are now being deployed across the country in many buildings by SMBs and enterprises to boost cellular signal strength to maintain workplace efficiency.

What’s the Difference Between Active & Passive DAS?

In general all DAS systems come with 3 main parts:

  1. Signal Source
  2. Central Amplification Unit
  3. In-Building Distribution

Both have the same objective to improve indoor coverage; however, several major differences separate the two systems and therefore creates a different set of pros & cons for both active & passive DAS systems.

Let's learn more about them in detail:

Active DAS

The signal source for Active DAS comes directly from the carrier networks. 

Those signals are then converted from an analog radio frequency to a digital signal to maintain signal strength regardless of cable run and coverage area. Getting signal directly from the carrier base station resembles something like having a mini-cell tower inside the building.

The signal on Active DAS is often best-in-class in terms of signal boosting coverage range; however, time & cost are the biggest limiting factors.

Permission to connect to the carrier network is often a long bureaucratic process involving paperwork, budgeting, and lengthy time delays. And that’s only for one carrier. For each additional carrier, the same process has to be repeated.

Also, specialized equipment & cabling (fiber optic cables) are needed to re-convert digital signal to radio frequency for the area in need of coverage. While this adds to the performance, it also adds to the cost.

Typically, Active DAS solutions average about $5-10 per square feet of coverage. So a 50,000 sq ft building could expect costs from $250,000 to $500,000 dollars for a complete Active DAS installation including product and installation service fees. Installation can take several months up to a year.

As a general rule, any high-traffic building over 500,000 sq ft needing complete wall-to-wall coverage (like a stadium or airport) should consider Active DAS.

Pros & Cons of Active DAS

Pros:

  1. Most powerful cellular boosting solution
  2. Coverage area is virtually limitless

Cons:

  1. Much more expensive than other solutions
  2. Longer deployment time

Recommendations:

  1. For much larger venue over 500,000 sq ft.
  2. If strong signal is needed for almost 95-99% of entire area.

Reputable Manufacturers & Models

The most reputable Active DAS manufacturers are  CommScopeCorningSOLiD, and TE Connectivity.

Passive DAS

The signal source for Passive DAS comes from amplifying cellular signal to and from the carrier cell towers.

Therefore it by boosting off-air signals instead of a direct connect, it requires an adequate amount of outside signal.

The signal on Passive DAS is often the best in terms of economical value since it is significantly cheaper than Active DAS; however, whole building coverage and a contingency of having adequate outside signal are limiting factors.

Passive DAS (also known as bi-directional amplifiers or cell phone signal boosters) are highly dependent on having a decent outside signal from the cell tower to work. Generally, this is ok for most cases in urban areas. However, rural areas will need stronger amplifiers & antennas to achieve any significant boost.

Typically, Passive DAS solutions average about $0.50-$1 per square feet of coverage. So a 50,000 sq ft building could expect costs from $25,000 to $50,000 dollars for a complete Passive DAS installation including product and installation service fees. Installation ranges from days to weeks to a few months. 

As a general rule, any building up to 500,000 sq ft needing only spot coverage (possibly with multiple units) should consider Passive DAS.

Pros & Cons of Passive DAS

Pros:

  1. Inexpensive option for cellular coverage
  2. Faster deploy time (weeks compared to months)

Cons:

  1. Dependent on having strong outside signal
  2. Spot coverage for main areas instead of whole building coverage

Recommendations:

  1. For buildings at 10,000 up to 500,000 sq ft (with multiple units)
  2. Spot coverage for priority areas

Reputable Manufacturers & Models

The most reputable passive DAS manufacturers are  WilsonProSureCall, and HiBoost.

First Conclusions: Active vs Passive DAS

Nearly 94% of commercial buildings are 50,000 sq ft or less. Including buildings up to 100,000 sq ft, the percentage goes up to 98%.

This means a vast number of buildings are less than 100,000 sq ft. In fact, 88% of all commercial buildings in America are under 25,000 sq ft.

Passive DAS is able to scale up to 100,000 sq ft and is very economical compared to Active DAS generally at 10-25% the cost.

However for bigger & more populated areas in need of wall-to-wall signal, Active DAS is the preferred choice.

Bottom line?

As a general rule of thumb, Passive DAS is the best choice for buildings up to 100,000 sq ft (with multiple antennas) but also capable of scaling up to 500,000 sq ft (with multiple units). It’s more cost-effective and can provide signal coverage when priority areas are more important than wall-to-wall coverage.

Active DAS is best for the other 2% of large commercial buildings: complex, sprawling high-traffic areas like airports, stadiums, convention centers, and structures over 500,000 sq ft.


Things to Know Before Investing in a DAS System

1. Causes of Poor Cellular & RF Signal

Cell phone signal is basically a radio frequency. Like most radio frequencies, cellular signal is fickle and can easily be redirected, absorbed, and blocked by literally everything under the sun. Let’s look at some of the biggest causes of weak cellular signal.

Cell Tower Distance

There are two things to think about when considering cell tower distance.

First, there’s the physical distance between the cell tower and your building. Second, there’s the transmitting distance of the cell tower.

In theory, a cell tower is able to broadcast signal for dozens of miles. However, carriers often reduce the power of their transmitters to avoid interference with other local cell towers using the same frequencies. This potentially reduces cellular reach from miles to a few hundred yards. Factor in other outside interference and that leads to extremely spotty signal.

So while many users think cell tower distance is a problem in mostly rural areas, it’s equally prevalent in urban areas, too when factoring in transmitting distance.

External Impediments

Before reaching your building, cellular signals have to fight through external interference. This includes mountains, hills, valleys, tall trees, man-made structures, and even weather since atmospheric changes are able to alter RF patterns.

Building Material

All types & sizes of building material are known to cause interference. Steel, tin, metal, concrete, brick, and low-e glass (energy efficient material) easily block, alter, or absorb cellular frequency.

Internal Impediments

Even when signal reaches inside your building, it has to deal with inside interference such as drywall, plaster, wood, thick walls, metal, and electrical or magnetic appliances or machinery.

2. Forget the Bars: Understanding dB Gain

Most cellular signals operate with the 700 to 2100 Mhz frequency grouped into 5 bands we know as LTE, Cellular, AWS, and PCS. That level of signal strength is measured in dB (decibels).

-50 dB is considered strong signal, what most users would call full bars. -120 dB is poor signal, almost a dead zone. This is universally true for all cellular devices.

However, it’s up to the carriers to subjectively match dB readings to the number of bars on their own networks. This means what are 2 bars on T-Mobile could be 3 bars on Sprint or full bars on Verizon despite receiving the exact same signal and performing at the same speeds.

That’s why being able to read dB for all carriers is important to gauge true cellular signal strength.

dB Gain vs dB Loss: How a DAS system Boosts Signal

We’ve already established two facts:

First, -50 dBm is consider good signal and -120 dBm is considered poor signal. Second, cellular signal is easily manipulated by almost everything under the sun.

With each interference (outside, building material, inside, and cell tower distance), a tiny or sizable amount of dB is lost. This is called dB loss.

When people walk outside to avoid interference, get to higher ground, get closer to a signal source, or use a cellular repeater, a tiny or sizable amount of dB is gained. This is called dB gain.

The push and pull of obtaining enough signal strength all boils down to dB gain minus dB loss.

For example, cellular signal starts out strong from the cell tower at -50 dB. Distance, trees, mountains and other tall structures interfere with the signal. It’s now at -85 dB. Building material such as concrete walls and low-e glass obstructs most of the signal. It’s now at -100 dB. Factor in thick drywalls inside the building and other internal impediments and now we’re at -115 dB.

This is barely working signal.

Considering that the outside signal is at -85 dB (good signal), it’s frustrating to that a few feet and a few materials could cause this much disruption.

That’s where a DAS system comes in. All obstructions are bypassed with the head unit (amplifier) where dB gain is achieved. Typically, most DAS amplifiers are capable of +60 to +70 dB gain. Factoring in signal loss through cable, equipment, and open air path loss (distance from the inside antenna to your phone), it’s possible for a -115 dB inside signal to reach to -80 dB or better.

This is a huge improvement. Even better than signal outside.

This is only a generalized example. Other factors such as type of cables, cable run, amplifier quality, and severity of internal impedance can change outcomes.

Some Other Things to Know About dB

dB is measured exponentially. For every +3 dB equates to 2x the power. So even if you see an improvement of “only” +3 to +5 dB, you’re looking at 2-3x the signal strength.

Below are three helpful tables: dB gain and power explained, typical dB signal needed outside for proper passive DAS installation, and type of materials that absorb radio frequency.


dB Gain Power Amplified 
+ 3 dB 2x
+ 6 dB 4x
+10 dB 10x
+15 dB  32x
+20 dB 100x
dBm Outside Signal Needed for Passive DAS Installation
-50 dB to -70 dB Great working signal for coverage.
-71 dB to -80 dB Good working signal for LTE & Cellular, not so much for PCS and AWS.
-81 dB to -95 dB Average working signal.
- 95 dB to below Poor working signal, expect lesser coverage.
Materials That Disrupt Cellular Signal 
Drywall -2 dB
Fiberglass -2 dB
Solid pine (1/2 inch) -3 dB
Plywood - 4 dB
Solid oak (1/2 inch) - 5 dB
Solid wood door  - 6 dB to -12 dB
Brick - 7 dB to -14 dB
Plaster - 8 dB to - 16 dB
Concrete (6 inches) -10 dB to -19 dB

Low-e Glass

-30 dB to -34 dB

DAS Components

1. Signal Source

For Active DAS, the signal source comes directly from the carrier network.

For Passive DAS, the signal source comes from pulling in and amplifying signal from the carrier cell tower. An outside antenna known as the donor antenna is used to capture cellular signal. Typically, a donor antenna comes in two forms: omnidirectional & yagi antenna.

Omni Antenna

An omni-directional antenna has a 360 degree throw range with a +2 to + 5 dB gain. It’s a multi-purpose antenna when needing to boost signal for multiple carriers and if carrier towers are within range.

Yagi Antenna

A yagi antenna has a 110 degree throw range with a +7 to +10 dB gain. It’s a specialized antenna when needing to boost a particular carrier and if the carrier tower is much further away.

Note: It is possible with a use of splitter to use both antennas for all-around boost while focusing on a specific carrier.

2. Central Amplification Unit

For Active DAS, the central amplifier is called the base station (also called BTS, NodeB, and eNode B).

For Passive DAS, the central amplifier is simply called the amplifier (also called repeater and signal booster).

Signal is passed to the amplifier where it is multiplied then passed along to the in-building distribution. Most passive DAS amplifiers are capable of +60 to +70 dB gain.

3. In-Building Distribution

Both DAS systems use indoor antennas to broadcast the boosted signal. Typically, broadcasting antennas come in two types: dome & panel antenna.

Dome Antenna

A dome antenna has a 360 degree throw with a broadcasting range of 50 feet. It’s a multi-purpose indoor antenna when needing to broadcast signal evenly across the open office.

Panel Antenna

A panel antenna has a 70 degree throw with a broadcasting range of 75 feet. It’s a specialized indoor antenna for priority areas, high ceilings, and corridors. They can be hid behind drywalls for aesthetic reasons.

4. Cables

For Active DAS, fiber optic and ethernet cables are generally used.

For Passive DAS, LMR400 up to 100 ft, LMR600 up to 200 ft, and AL4 up to 400 ft.


Full Walkthrough of DAS Installation

1. Site Survey

For Passive DAS installation, a site survey consists of locating the area on the roof that has the strongest signal (for outside antenna installation), measuring signal strength in all areas inside the building, talking to the client about problem areas, and listening to other requests & details.

2. Floor Plan Analysis

Looking at the building layout and floor plans, an RF or certified signal boosting technician plans for the best DAS layout, calculating dB gain & loss, potential coverage, cable runs, and accessories.

3. Client Consultation

The Floor Plan Analysis is delivered to the client and discussed in detail about coverage expectations, products, and pricing. Multiple solutions are provided, and redesigns are possible to accommodate client’s preference. Once client agrees to plans & pricing, installation begins.

4. Donor Antenna Installation

The outside antenna is installed on the roof. Cable is run into the building. A good installer or integrator should know how to run cable in an aesthetically-pleasing and organized way.

5. Amplifier Installation

The central amplification unit is installed in an area (usually IT room) where tech has easy access to service the booster. A short test confirms that the amplifier is boosting signal.

6. Broadcast Antenna Installation

The inside antennas are installed. Dome antennas are installed in ceilings. Panel antennas are installed on walls. Cable is run from the inside antennas to the amplifier.

7. Testing

Once everything is installed. The installer or integrator will turn on the amplifier and do a full walkthrough with the Floor Plan Analysis, accounting for dB readings before and after the installation. Data is recorded. Fine-tuning and cleanup is done here. Client is shown results and asked to do a live performance test.

8. Post-Installation Support

Customer support follows up a few days to a week later to confirm DAS solution is working to client’s expectations.


Need to Talk to a DAS or signal boosting expert?

Cellular boosting needs a thorough and fine touch. Our in-house cellular technicians are able to solve any unique problem with the best technology and prices.

From free consultation to post installation support, we provide end-to-end service. Contact us today and see how our wireless experts can provide instant answers.

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