Why choosing the correct USB interface matters

Ramsey Electronics provides six different options for USB interfaces.  This can make choosing an interface a little daunting.  The information and chart below should help you quickly choose the correct interface for your application.

Specifications:

• Maximum Port Speed.  By selecting the lowest required Maximum Port Speed, you can save on the cost of the interface.
• Effective Isolation Frequency Range.  This is important to ensure that the interface isolates at your required test frequencies.  You may have to go with a higher speed model to get your required RF isolation range.
• Minimum Conductive Insertion Loss.  This is important to ensure you have enough RF isolation for effective testing.  Most digital devices do not provide the same level of RF isolation as RF test equipment.  Digital cables do not provide the same RF Shielding Effectiveness as good quality RF cables.  This means that your digital devices and cables can pick up ambient RF and transfer it through an RF Shielded Test Enclosure.  To prevent this from happening, select a USB interface what will provide the Minimum Insertion loss necessary to provide accurate testing.
• Downstream Power.  Downstream power is used to directly power to devices inside the enclosure or charged devices like cell phones.   The chart below shows the voltages and maximum current each device can pass or provide.
• Input and Output Connectors.  This is the least important of all options to consider.   Cables can be purchased in all configurations to connect any interface to any device.

Interfaces:

• CONN278 with Adapters Sets.  The CONN278 is a 10pF capacitive filtered DB9 adapter.  It is available with two different adapter sets to allow the DB9 adapter to be connected to your USB devices.  The 10pF capacitive filter is a very poor filter that only offers a little conductive insertion loss at 1 GHz.  These options should only be used as an economic option where no filtering of the USB signal is required.
• STEUSB2071  This is our premium USB2.0 interface.  It provides good conductive insertion loss from 700MHz to 40GHz.  It is basically a complex low-pass filter designed to pass USB2.0 data.  If 4G LTE or low band 5G frequencies (600MHz and 700MHz bands) are important for your testing, you may want to consider moving up to the STEUSB312 or STEUSB3CC interfaces for their superior Effective Isolation Frequency Range.
• STEUSB3AA  This interface is an economical USB3.0 interface (5Gbps).  It provides good RF shielding but no conductive insertion loss.  This option should only be used as an economic option where no filtering of the USB signal is required.
• STEUSB312  This is one of our two premium USB3.1 GEN2 (10Gbps) interfaces.  This unit provides the Battery Charging Mode BC v1.2, 5VDC up to 1.5 Amps.  This unit also has a dedicated charge mode.  Dedicated charge mode is enabled when the USB Type B port has no connection, and the Type A port is connected to a device.   Dedicated Charge mode can provide 5VDC up to 2 Amps. 
• STEUSB3CC  This is the other of our two premium USB3.1 GEN2 (10Gbps) interfaces.  This unit has the same data speed as the STEUSB312.  The main difference is that this unit has USB Type C connectors and provides USB-C Power Delivery.  The STEUSB3CC’s USB-C Power Delivery can provide 5, 9, 15, and 20VDC up to 3 amps.  USB-C Power Delivery can be used to power devices and charge cell phones.  However, it will not work with all devices or cell phones.  The device must be compliant with USB-C Power Delivery standards.  If the device or cell phone are not compliant the STEUSB3CC will not power or communicate with the phone, even if the phone is powered separately.  If you have concerns that you need to test phones and they may not be USB-C PD compliant, opt for the STEUSB312.