SDRplay Bias Tee - OneSDR - A Technology Blog

Understanding and Utilizing the Bias T Function in SDRplay Devices

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Table of Contents

Introduction

SDRplay, one of the prominent manufacturers in the Software-defined Radio community, offers a range of devices that are highly regarded for their performance and versatility. One valuable feature available in many SDRplay models is the Bias T function.

This article explores what Bias T is, how it works in SDRplay devices, and why it is beneficial for radio enthusiasts.

What is Bias T?

Bias T is a technology used in SDRs, radio receivers and other radio equipment to supply power to active antennas, low noise amplifiers and other external RF components directly through the coaxial cable that carries the RF signals. This eliminates the need for a separate power supply for these devices, simplifying setups and reducing cable clutter.

How Bias T Works in SDRplay

In SDRplay devices, the Bias T function enables the user to activate a +4.7 Volt DC source @ 100 mA that is sent up the antenna cable.

This voltage powers pre-amplifiers, active antennas, or other inline devices that require power without needing an external power source.

Key Features of SDRplay’s Bias T

Ease of Activation: In SDRplay devices, activating the Bias T function can typically be done via the provided software, such as SDRuno. This allows users to easily switch the power on and off as needed without physically accessing the hardware.

Protection: SDRplay designs its Bias T with circuit protection to prevent damage to the SDR or the powered device, safeguarding your equipment during operation.

Benefits of Using Bias T

Simplified Setup: By powering devices directly through the coaxial cable, Bias T removes the need for additional power wires, making the setup cleaner and simpler.
Enhanced Performance: For applications like receiving weak signals from far-off satellites, using an active antenna with Bias T can significantly improve signal strength and quality.
Versatility: Bias T supports a variety of RF devices, making SDRplay units extremely versatile for different applications, from amateur radio to satellite watching.

Practical Applications

Amateur Radio: Ham radio operators can use Bias T to power pre-amplifiers at the antenna, optimizing signal reception without the noise typically introduced by longer cable runs.
ADS-B Reception: For those tracking aircraft, Bias T can enhance the capabilities of active antennas, and filtered LNAs improving ADS-B signal reception quality.
Satellite Radio: Enthusiasts tracking weather satellites or receiving other satellite signals can benefit from the improved signal integrity provided by powered antennas.

Comparison of Bias T’s

Here is how Bias Tee’s in other SDRs compare. The RTL-SDR is able to support a higher level of current and both RTL and SDRplay have over-current protection as a plus over the HackRF.

SDR	Bias Tee Voltage (V)	Bias Tee Current (mA)	Over-current Protection
RTL-SDR	4.5	180	Yes
HackRF	3.3	50	?
SDRPlay RSPdx	4.7	100	Yes

Notes

RSP1 does not have a bias-t
RSP2, RSP2 Pro have Bias T’s on Port B only
RSP1A, RSP1B have Bias T
RSPdx, RSPduo have Bias T on Antenna Port B only

Conclusion

Bias T is an essential tool in a radio receiver. Including this subsystem gives the user the ability to improve the sensitivity of the SDRplay software defined radio system and detect weaker signals.