4G USB Modem SIM Card Detection Issues Through Extension

The main problem with a 4G USB modem when connected via a USB extension cable is almost always related to voltage drop in the cable, which leads to insufficient power supply to the modem, especially during peak data transmission loads. The SIM card is not detected precisely due to unstable power caused by wire resistance in the long cable, which causes significant voltage drop when the cellular module is operating.

Table of Contents

• Main causes of the problem
• Power and cable checking
• Solutions without buying a new extension
• SIM card and modem checking
• Technical aspects of voltage drop
• Conclusion and recommendations

Main causes of the problem

Voltage drop in the cable is the primary reason why a 4G USB modem doesn’t detect the SIM card when connected via an extension cable. As explained in the Keenetic documentation, you should not use a USB cable longer than 2 meters, as voltage drop can occur in the cable, which negatively affects the modem’s operation.

The wires in the cable have electrical resistance, which causes a proportional voltage drop depending on the device’s power consumption. This drop is usually insignificant for a typical cable and consumption, but it can become a problem for devices with high peak power consumption, such as 4G modems.

During data transmission, modems require peak currents up to 2A, which with the resistance of a long cable causes a noticeable voltage drop. As noted on Electronics StackExchange, voltage drops significantly when transmitting RF signals, so special measures need to be taken to compensate for this drop.

Power and cable checking

You can use the following methods to diagnose the problem:

1. Voltage measurement - Purchase a USB current/voltage meter for $5 on Amazon and measure the voltage at both ends of the extension cable while the modem is operating, as recommended on Reddit.

2. Visual cable inspection - Check the cable for overheating, melting traces, or damage. A damaged cable should be replaced immediately.

3. Standards compliance check - If the cable requires adapters, it doesn’t meet standards. Replace it with a certified USB 2.0 cable, as advised on SuperUser.

4. Using a shorter cable - Temporarily connect the modem with a short cable (less than 2 meters) to confirm that the problem is specifically with the length of the extension.

Solutions without buying a new extension

There are several ways to solve the problem without purchasing a new extension:

1. Using an external powered USB hub

Connect the USB extension cable to an external powered USB hub that will provide additional power. As explained on Raspberry Pi forums, the situation with reduced voltage really requires using an external powered hub, as USB devices consume too much current, lowering the voltage.

2. Improving cable quality

Use a cable with thicker wires (larger cross-section). As recommended on Electronics StackExchange, try to get an extension with heavier wires if your charging current is high.

3. USB 3.0 cables with repeaters

Consider using a USB 3.0 cable with built-in repeaters. As mentioned on Overclockers UK forums, you can use a USB 3.0 cable with built-in repeaters that compensate for losses.

4. Active solution with external power

For critical cases, you can modify the cable by adding external power. As explained on Electronics StackExchange, to compensate for voltage drop in the cable, you will need a circuit with voltage feedback (“sense” feedback).

SIM card and modem checking

Although the main issue is power supply, it’s also worth checking:

1. Correct SIM card installation - Make sure the SIM card is properly inserted into the modem slot, as recommended on HowTo-Connect.

2. SIM card compatibility - Check if the SIM card works in another device. As shown by Reddit users’ experience, sometimes a SIM card works in a phone but not in a specific modem.

3. Modem operating mode - Some modems may require switching between operating modes, as mentioned on Reddit: “You may need to switch the card mode from PCIE mode to USB mode.”

Technical aspects of voltage drop

Understanding the physical processes will help better solve the problem:

• Voltage drop calculation: Typical converters are designed for a maximum output current of 2.1A, which means a voltage drop of 0.6V at maximum current, as explained by West Florida Components. With a 5V input, this will result in a drop to 4.4V at the end of the cable.

• Modem peak currents: 4G modems have a 25% duty cycle, so a 2A peak current corresponds to an average current of 500mA. However, during RF signal transmission, the current can increase significantly.

• Critical voltage: Research from Netnode.de shows that USB modem issues are mainly caused by voltage below 5V, rather than insufficient power supplies.

Conclusion and recommendations

Main conclusions:

1. The problem with recognizing the SIM card via a USB extension cable is almost always related to voltage drop, not to damage to the SIM card or modem itself.

2. The most effective solution without buying a new extension is to use an external powered USB hub, which compensates for voltage losses in the cable.

3. For diagnosis, it’s useful to measure the voltage at both ends of the cable using a USB current/voltage meter.

4. When working with long cables (5m and more), always consider voltage drop and use either reinforced cables or additional power sources.

Recommended actions:

• First, try connecting the modem with a short cable to confirm the diagnosis
• If necessary, use an external powered USB hub
• For a permanent solution, consider purchasing a quality USB extension with repeaters or limit the cable length to 2 meters

Sources

1. Recommendations for LTE/4G/3G connection diagnostics – Keenetic
2. USB modem cannot be recognized via USB extension cord – Super User
3. Usb 3G, 4G modems, power supply – Electronics Stack Exchange
4. How To Compensate Cable Voltage Droops? – West Florida Components
5. USB modem power issues – Netnode.de
6. under voltage due to usb dongles – Raspberry Pi Forums
7. How can I guess if a USB cable will power my devices? – Super User
8. USB Extension Cable Power Loss – Reddit
9. How can USB extension cords affect of USB charging? – Electronics Stack Exchange
10. Voltage Regulator: how to compensate for voltage drop in cable? – Electronics Stack Exchange