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T-Mobile 5G Internet Gateway (Sagemcom Fast 5688W) External Antenna Guide

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Looking to get the best possible data rates from your T-Mobile 5G Internet Gateway?

You’ll want to purchase and connect external MIMO antennas to the device’s internal U.FL ports.

In this guide, we'll:

  • Recommend the best external antennas to use.
  • Show you how to access the internal U.FL antenna ports, and how to install adapters for external antennas.
  • Explain how to aim the antennas for best results.

Got either of T-Mobile's older gateways? If you have the boxier gateway with the display on the front, check out our guide for that device here. If you have the cylindrical gateway with the display on the top, check out our guide for that device here.

In this guide

Important Note: To connect external antennas you'll need to open your T-Mobile Gateway. Read our instructions for doing so carefully to avoid damaging the device. Gateways are owned by T-Mobile, and they may charge you a repair fee if you return a damaged gateway device.

The Best External Antennas For the T-Mobile 5G Internet Gateway

Using a MIMO antenna outside your building, pointed at the nearest tower, can help you get the fastest 4G LTE and 5G data rates possible.

The T-Mobile 5G Internet Gateway has four internal U.FL ports, which allow for two 2x2 MIMO antennas or a 4x4 MIMO antenna to be connected to the device.

Since a 4x4 MIMO antenna offers superior performance and would allow more of the internal cellular antenna ports to be used than a 2x2 MIMO antenna, we highly recommend our 4x4 MIMO antenna kits over our 2x2 MIMO antenna kits.

Accessing the antenna ports does require some disassembly. And we recommend being careful: if you damage the device and then later return it, T-Mobile can charge you a damage fee. Our instructions below guide you through how to connect and test antennas without damaging the device.

We recommend two different 4x4 MIMO antenna options for use with the T-Mobile 5G Internet Gateway:

Best for Most Users

This 4x4 MIMO Panel Antenna kit will provide a meaningful signal improvement possible data rates, even if you're surrounded by trees, hills, or tall buildings.

For users surrounded by trees, hills, or tall buildings, the best external antenna choice is our 4x4 MIMO Panel Antenna kit. While still directional, this antenna doesn’t require line-of-sight to the tower.

Best with line of sight

This 4x4 MIMO Log Periodic Antenna kit includes four cross polarized log periodic antennas to provide an even more meaningful signal improvement. They work best if you have direct line-of-sight to the tower.

However, if you have line of sight to the nearest tower, we recommend using a 4x4 MIMO Log Periodic Antenna kit instead. The higher gain on these antennas can also get you better performance, but only when you have a straight shot to the tower.

Why External Antennas Are Critical for Improving Data Rates

There's one big misconception about external antennas.

Most people think that external antennas primarily help you increase your data rates by increasing the signal strength.

But that's not the case.

An increase in signal strength is actually probably the third most important way that external antennas help.

Here are the three main ways that external antennas help you increase your data rates:

1.They Improve Signal Quality

In 4G LTE and 5G networks, signal quality is measured as SINR (Signal to Interference plus Noise Ratio) or sometimes as RSRQ (Reference Signal Received Quality).

Improving signal quality has a huge impact on your data rates.

Higher data rates allow your hotspot to communicate using "higher order modulation schemes." That means they can use the same wireless spectrum to send more data per second.

However, there's one big caveat:

In order to improve your signal quality, you need to both aim and shield your outdoor antenna properly. We talk more about this in the next section.

2.They Allow You To Connect On More Bands

Hotspots like the T-Mobile 5G Internet Gateway support a feature called "carrier aggregation."

Carrier aggregation allows the Gateway to connect on multiple cellular bands simultaneously.

The more bands you're connected on, the greater the bandwidth, and the higher your data rates.

However, many of the higher frequency bands aren't able to penetrate into buildings. Using external antennas allows you to access higher frequency bands, which are often less congested and offer higher speeds than lower frequency bands.

3.They Increase Your Signal Strength

As you might expect, using outdoor directional antennas can help increase the signal strength.

This helps increase data rates, but only up to a point.

If your signal strength (called "RSRP" in 4G and 5G networks) is stronger than about -100 dBm, stronger signal won't speed up your connection any further.

Installing External Antennas to the T-Mobile 5G Internet Gateway

Before getting started, it's always a good idea to run a couple of speed tests indoors from a device connected to your Gateway's WiFi. The results will fluctuate a little, but this is the baseline you're trying to improve.

Once you've tested your baseline internet speeds, you're ready to install external antennas. The T-Mobile 5G Internet Gateway doesn't have any external antenna ports, but it's possible to access the internal ports and install adapters that allow you to connect antennas.

In the next section of this guide, we'll show you how to open up your Gateway, connect adapters for external antennas, and close it back up.

Before you get started, you will need the following:

  • A small phillips head screwdriver
  • A Torx T10 screwdriver
  • A small/thin flat-head screwdriver
  • A thin plastic prying tool, needle-nose pliers, or tweezers
  • Two U.FL-male to N-female pigtail adapters (included in our External Antenna kit)
  • Tape for securing and labeling cables. Painters or Electrical tape works best.
  • A secure container to keep screws and small parts safe while you work
Important note:

Be careful not to damage your T-Mobile Home Internet Gateway while disassembling.

As part of your agreement with T-Mobile, you "borrow" this equipment from them. When you end your service, you'll likely need to return the gateway to T-Mobile. If there's damage to the device they are contractually able to charge you up to $370 in damage fees.

Waveform does not make any guarantees nor take any responsibility for damage caused to your unit when following these instructions. Please proceed at your own risk.

If you do decide to return your unit to T-Mobile, make sure to reconnect the existing internal antenna connectors before doing so.

Step-by-Step Guide to Installing Adapters for External Antennas

Step 1: Power off the T-Mobile 5G Internet Gateway and unplug the power cable.

Step 2: Using a pliers, remove all four rubber feet from the bottom of the device to obtain access to each T10 screw underneath.

Step 3: Break the warranty seal to obtain access to the T10 screw underneath.

Step 4: Remove the four T10 screws revealed in Step 2 and the fifth T10 screw revealed revealed in Step 3, as shown below:

Unscrew the five T10 screws from the bottom cover

Step 5: Use the flat head screwdriver or prying tool to pry the back plate from the outer cover of the device.

Tip: There is a clasp every third of the way up on each side of the back plate, for a total of six clasps.

Remove the back plate

Step 6: Once the right and left sides of the back plate are unclasped from the outer cover of the device, lift up the bottom side of the back plate (1) and pull it down towards the bottom cover of the device (2), as shown below. Doing so should fully free the back place from the outer cover.

Removing the back plate from the outer cover.

Step 7: Use a prying tool to unclasp the outer cover from the bottom of the device and then remove it from the inner enclosure by lifting it away from the bottom of the device.

Tip: There is a clasp in the center of each side of the outer cover, for a total of three clasps.

Releasing the clips securing the outer cover to remove it from the device

Step 8: Rotate the gateway to see a series of five cables connected to the board by small U.Fl connectors.

  • The red, green, orange, and blue cables located on the U.FL ports labeled "5GNR P", "LTE D", "MIMO 1", and "LTE M", respectively, are used for cellular antennas. Depending on a 2x2 or 4x4 MIMO Antenna kit, two or four of these cables will need to be disconnected, respectively.
  • The brown cable located on the U.FL port labeled "GPS" is used by device's the GPS antenna. This cable will remain in place.
The T-Mobile Gateway's five U.FL cables and ports

Step 9: Depending on your situation, as listed below, use a prying tool or pair of tweezers to very carefully disconnect the two or four of the colored cables:

  • If you have a 2x2 MIMO Antenna Kit and 5G cell service is available at your location, disconnect the red cable and the orange cable. Do not alter the remaining cables.
  • If you have a 2x2 MIMO Antenna Kit and 5G cell service is not available at your location, disconnect the green cable and the blue cable. Do not alter the remaining cables.
  • If you have a 4x4 MIMO Antenna Kit, disconnect the red, green, orange, and blue cables cables.

NOTE: Be very careful. U.Fl connectors can be quite fragile. Make sure you're very gentle to avoid breaking the connector when disconnecting it from the board.

NOTE: These pairings are preliminary and based on the names of the ports (5GNR P, LTE D, MIMO1, and LTE M). Due to this uncertainty, we highly recommend that users test other port-pairings to see if other configurations can provide even better results. If so, please let us know here so we can further improve this guide!

Step 10: Once the U.Fl cables for the internal antennas are fully disconnected, tape them together and move them to the side of the inside the inner enclosure and out of the way.

Taping together the stock U.Fl antenna cables.

Step 11: Route each pigtail adapter through its corresponding vent port on the bottom of the device, as shown below:

Route your pigtail adapters through the vent ports.

NOTE: Routing the pigtails through the vent ports shown above helps prevent the pigtail adapters from laying against the internal heatsink. This heatsink can get hot during normal gateway operations and could potential damage the cables if they are laid directly against it.

Step 12: Install your U.FL to SMA-Female pigtail adapters by very carefully aligning and pressing them down into the ports you opened up in Step 9. A quiet "click" can often be heard once the connectors are pressed down and fully connected.

Installing the U.FL to SMA-female pigtail adapters.

Tip: If you are struggling to get the pigtail connected, we recommend using a tweezers to spread the petals of the U.FL connector further apart, as shown in the image below:

Spreading the U.FL connector petals

Step 13: On each pigtail adapter, tag and label its port number (1, 2, 3, or 4) by looping a piece of tape around the cable and writing down the name in pen/marker. This will help denote which adapters connects to each internal port for later referencing.

Step 14: Reassemble everything in reverse order. Make sure that your power button is in the off position before reconnecting the battery.

Fully completed installation.

Congrats! Your T-Mobile 5G Internet Gateway should now be fully re-assembled, with the pigtail adapters protruding from the bottom. You are now ready to connect your external antenna(s) to the adapters you installed into your Gateway.

Step 15: Connect your external MIMO Antenna(s) to the labeled adapters installed in your Gateway using either the cable connectors (used for testing in test mode) or the coaxial cables (used for the final installation) included in your kit.

  • If you have a 4x4 MIMO Antenna Kit, you will connect your adapters in the order shown below:
Antenna & Port Pairs.
  • If you have a 2x2 MIMO Antenna Kit, the order in which you connect your adapters to the external MIMO Antenna(s) does not matter.

Congrats! Your T-Mobile 5G Internet Gateway is now connected to your more powerful MIMO External Antennas.

Positioning and Aiming MIMO Antennas

Positioning and aiming MIMO antennas well is crucial to getting the best performance to your T-Mobile 5G Internet Gateway, or indeed any other hotspot.

We've actually compiled a detailed 2x2 MIMO instruction manual and 4x4 MIMO instruction manual to accompany our own MIMO Antenna Kits, where we go into depth on the best ways to aim the antennas.

The goal is to find the best location and direction for the antenna(s), to maximize data rates to the T-Mobile Gateway. It can take a little patience, but can have a huge impact – it’s worth a bit of extra effort!

Connect your MIMO external antennas to your modified T-Mobile 5G Internet Gateway via the newly installed pigtail adapters, and go outside with your "test-rig".

With each location and direction you try, run a couple speed tests, and make a note of the results. Here are all the locations and directions where we recommend testing your MIMO antenna:

Where to test your signal

Where to test your signal

Pro tip: Don’t just go to the highest point of the roof! While signal is generally stronger the higher you go, there’s also often more interference. We’ve found it’s often better to mount the antenna(s) on the side of the building where the structure can shield the antennas from interference.

Once you've found the position which gets you the highest data rates to the T-Mobile Gateway, that's where you'll want to install the MIMO antenna. Go ahead and mount the antenna, run cables inside, connect everything up, and enjoy superior data rates!

T-Mobile 5G Internet Gateway Technical Specifications

Supported T-Mobile bands in the US

  • 5G Bands: n25, n41, n66, n71, n77
  • 4G LTE Bands: B2, B4, B5, B12, B26, B41, B46, B66, B71

Cellular Modem

  • Model: Qualcomm Snapdragon X62
  • MIMO Support: 4x4 w/ internal antennas or external antennas
  • LTE-A Carrier Aggregation: Yes
  • LTE Performance Category: Cat 19 (Downlink), Cat 18 (Uplink)
  • Max Theoretical Speeds:
    • 5G SA: 2.4 Gbps Download, 900 Mbps Upload
    • 5G NSA: 3.4 Gbps Download, 550 Mbps Upload
    • LTE: 1.6 Gbps Download, 200 Mbps Upload

Wi-Fi

  • Technologies: Wi-Fi 6 - 802.11 ax
  • Bands: Simultaneous 2.4 GHz and 5 GHz

Ports

  • Cellular Antenna Ports: 4x internal U.FL
  • Ethernet Ports: 2x Gigabit LAN ports, 1x Gigabit WAN port
  • SIM Slot: 1x SIM (4FF)
  • Other Ports: 1x USB-C (Power), 1x USB-C (Data/Test Port)

Other Helpful Resources

T-Mobile Gateway (Sagemcom Fast 5688W) Documentation

A Helpful Guide on Installing and Maintaining U.FL Connectors

A Helpful Video of Disassembling the T-Mobile Gateway (Sagemcom Fast 5688W) by Nater Tater

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