When designing or prototyping a new wireless design on an existing software-defined radio (SDR) system, its radio performance sets the limit of the targeted waveforms or applications that can be implemented. The prototype’s intended use may not just be for a controlled lab environment; it may also be intended for field trials or even final deployments. The conditions found in field trial and deployment environments further push the RF requirements of the radio head by emphasizing the need for higher sensitivity and better noise immunity to external unwanted RF signals.

Recently, Nutaq tested its Radio420x radio head that is being used in various SDR configurations (ZeptoSDR, PicoSDR and uSDR). The following test setup was used for the majority of measurements.

Radio420x - Perseus - uTCA Chassis

The results of these experiments were quite amazing. The shielded Nutaq Radio420x FMC design (based on the LMS6002D RF-IC) provided high-end performance in the entire 300 MHz to 3.8 GHz frequency range, with up to a 28 MHz baseband bandwidth.

Let’s look at some of the measurements performed on the receiver side.

1) Low-band section of the Radio420x’s LMS6002D:

Low-band section of the Radio420x’s LMS6002D

2) High-band section of the Radio420x’s LMS6002D:

High-band section of the Radio420x’s LMS6002D:

In addition to the multiple gain controls within the LMS6002D RFIC, Nutaq added external low-noise RF amplifiers. Playing with all these gains allows the radio designer to make educated decision settings and compromises (e.g. increasing the compression point (P1dB) while minimizing lost on the sensitivity side).

Another secret sauce included in the Radio420x is the ability to select an RF band-pass filter from its software-selectable RF filter bank. This feature lets you get out of a controlled, low-noise lab environment as it offers a very high noise immunity when in crowded real-world wireless environments. Additionally, the included mechanical shield provides heat dissipation and reduces the impact of high-energy signal sources (typically induced by DC-DC converter switching frequencies in close proximity). In other words, the shielding ensures maximum spurious-free dynamic range (SFDR) performance by minimizing spurious high energy signals that can drastically degrade the quality of service (QoS) and robustness of a wireless system.

Our Radio420x experiments demonstrated that the shielding provided around 40 dB of power supply noise rejection. The following test was performed at 900MHz with and without the mechanical shield installed:

Test Result At 900MHz With and Without The Mechanical Shield Installed

Now, let’s look at some of the measurements performed on the transmitter side.

1) Low-band:

Low-Band Transmitter P1dB IMD3 2nd Harmonic SB Carrier Suppression

2) High-band:

High-Band Transmitter P1dB, IMD3, 2nd Harmonic, SB Carrier Suppression

An interesting fact shown by these graphs is that the Radio420x has a better than –40 dBc single-sideband (SSB) suppression for the whole frequency range under 3.5 GHz. Above 3.5 GHz, the side-band suppression can be adjusted in software by modifying the phase and gain imbalance.

The included figures establish a good starting design chart for standard radio designs. When it comes to receiver design, the typical static sensitivity of –100 dBm makes the receiver chain lend itself well to GSM, WCDMA and LTE femtocell designs, while the compression headroom, as depicted by the 1 dB input compression point, sets a comfortable limit for out-of-band blockers when operating in crowded spectrum areas. The transmitted signal purity also allows standard radio designs to be tested over the air (when subject to license exemption) without causing harmful interference to neighboring systems.

The included graphs showing P1dB, IMD3, LO leakage rejection and unwanted SSB suppression demonstrate the Radio420x’s suitability for even high PAR waveforms such as LTE. These parameters are intimately related to key waveform performance metrics like EVM and ACLR (which we have discussed in previous blogs about radio physical impairments effects). We will therefore not hesitate to recommend the Nutaq Radio420x for designing prototypes with highly demanding waveforms like LTE.