Application Note

Receiver Testing with the

Anritsu MS2830A Signal Analyzer,

MG3710A Vector Signal Generator,

and S412E LMR Master

™

Table of Contents

1. Receivers in Crowded Spectrum ............................1

2. Testing Digital Receivers ........................................2

3. Adjacent Channel Rejection ...................................3

4. Spurious Response Rejection ................................7

5. Intermodulation Rejection ......................................9

6. Blocking / Out-of-band Interference .....................10

7. In the Field Tests ..................................................14

8. Attenuation and Isolators ......................................15

9. Conclusion ............................................................15

Introduction – Receivers in the New Narrowbanded RF Space

Public safety receivers are built to perform in the harshest environments. Physically they appear to be up to any

challenge. Some even work under water. Unfortunately, it is not easy to see how they will perform in a harsh RF

environment. Narrowbanding moves adjacent channel performance to a new level. New spectrum allocations push

public safety radios up in frequency near 3G and 4G transmissions. Digital radios such as those that utilize the

APCO Project 25 (aka P25) standard react to interference differently from analog radios.

Figures 1 and 2 show likely spectrum scenarios where public safety P25 radios are close in frequency to 3G and

4G transmissions. This white paper discusses the common test procedures for analog and digital receivers and

proposes new procedures that can better predict digital receiver performance under the emerging narrowband

spectrum allocations.

Figure 1. New 700 MHz Band w/ FirstNet “D Block.”

2 Receiver Testing with the Anritsu MS2830A Signal Analyzer, MG3710A Vector Signal Generator, and S412E LMR Master�� Anritsu

Figure 2. 800 MHz Rebanding Plan.

Testing Digital Receiver Sensitivity

A common method to verify performance of an analog receiver is to send the receiver an RF test signal consisting

of a single audio tone with specific characteristics (e.g., deviation for an FM receiver). The audio output from the

receiver is brought back into an audio input on the test system for measurement of SINAD, the ratio of

Signal+Noise+Distortion divided by Noise+Distortion, expressed in dB. For public safety receivers, SINAD is

commonly measured using a 1 kHz tone modulation. A 1 kHz audio notch filter in the test set is used to remove the

tone from the received audio, the SINAD is then derived from the measurement ratio. Analog receiver sensitivity is

measured by monitoring the SINAD level as the RF signal power is lowered. The RF input power resulting in 12 dB

SINAD is typically considered the specified sensitivity of the receiver.

For a digital receiver, the key performance measure is BER (Bit Error Rate). Most public safety digital radios have a

test mode that provides BER measurement and display for a few BER test patterns. For P25 Phase 1 (as defined by

TIA-102.CAAA-C) the 1011 Hz pattern is used. The 1011 Hz pattern is a near Pseudo-Random Binary Sequence

(PRBS) that also provides an audio tone output from the vocoder. The tone indicates to anyone listening to a channel

that it is out of service, similar to the situation with the 1 kHz tone for SINAD testing of an analog receiver. If a BER

test mode is not available in the receiver, then the receiver needs to provide an output with the received data bit stream

so the test system can compare the transmitted data pattern with the received pattern. The specified sensitivity of

the receiver is typically the RF signal level for which the measured BER is 5%.

Digital receiver sensitivity is specified and measured with just the single test signal applied to the receiver. Receivers

in real-world use are impacted by a wide variety of other signals in addition to the desired signal. In testing and

predicting receiver performance in these real-world situations, the fundamental measure of the receiver performance

measure remains the 5% BER level.

One problem with receiver testing is that the desired signal level is very near the receiver sensitivity level. Interfering

signals must be generated and combined with as little distortion as possible. Careless management of interfering

signals can result in spurious signals larger than the desired test signal, fogging the test results. Refer to “Notes on

Attenuators and Isolators to reduce source-

generated intermodulation products” later

in the document.

Another problem with testing digital receivers

is that (unlike a CW signal) digital modulation

is very “noise like” and the displayed

spectrum analyzer level will change with

the resolution bandwidth setting. Figure 3

illustrates the test setup for a sensitivity

measurement on a P25 receiver.

MS2830A Signal Analyzer

RF Signal

Figure 3. P25 Sensitivity Measurement block diagram.