hp 8921a cell site test set product note 8921-1

HP 8921A Cell Site Test Set

Product Note 8921-1

AMPS Base Station Testing

This product note describes man-ual operation of the HP 8921ACell Site Test Set (or HP 8920A RFCommunications Test Set withoptions 001, 002, 003, 004, 005,013, 014) for testing AdvancedMobile Phone System (AMPS)Cellular Base Station equipment.It will lead you through the stepsrequired to set-up the instrumentin the proper state to make par-ticular measurements. Storingthese instrument states in mem-ory registers allows you to quicklyrecall them without having to gothrough the laborious task of cre-ating them each time you want tomake a measurement on yourbase station equipment.

For automated base station test-ing, Hewlett-Packard offers HP 11807B Cell Site Test Softwarefor use with the HP 8921A CellSite Test Set. The HP 11807B soft-ware has options that cover themost widely used AMPS base sta-tions. Each option uses test andadjustment procedures derivedfrom the manufacturers mainte-nance manuals. For more infor-mation on this and otherHewlett-Packard products, con-tact your local Hewlett-Packardrepresentative.

Cell Site Overview

A cell site contains three types ofradios: control, voice, and locate.When a mobile originates a call oris paged, the cell site control radiosets up the call. This control radiocommunicates with the centralswitch (Electronic Mobile Ex-change (EMX), Mobile SwitchingCenter (MSC), and Mobile Tele-phone Switching Office (MTSO))to connect the call to another mo-bile or landline phone. The mobileis then instructed by the cell sitecontrol channel to tune to a par-ticular voice channel.

The conversation takes place onthe voice radios with the voicesignals traveling back to the MSCand routed to the other party.

The locate, or scanner, radio isused to monitor the signal levelsof the channels and notifies theswitch enabling it to make hand-off decisions. This radio is receiveonly and, like the voice and con-trol radios, is controlled by dis-tributed control functionsbetween the MSC and local cellsite controller. Communication ofthese control functions takesplace via either a landline or mi-crowave transmission data link.

Cell sites are configured as omni-directional, sectored, or somecombination of the two. In gen-eral, an omni-directional cell willhave two receive antennas and onetransmit antenna.

2


Cellular System Overview

The two receive antennas arephysically separated to get betterimmunity to multipath fading con-ditions and are typically space diversity antennas. Other omnisites may have only two receiveantennas to save money. In thiscase, one receive path is coupledto the same antenna as the trans-mit path. A tuned cavity duplexer(combined receive and transmitfilter) is then used to keep the sig-nal paths separated.

A directional, or sectored, cellsplits the coverage into sectorswhich are served by different an-tennas. Typically, a directionalcell will have three sectored re-ceive antennas, one omni receiveantenna, three sectored transmitantennas, and one omni transmitantenna. Voice radios are config-ured on one face of the cell forboth transmit and receive and thelocate radio accepts inputs fromall of the receive antennas. Theone omni-transmit antenna is usedfor control channel transmit.When testing base station equip-ment in directional cells, you willbe working with radios

configured to different antennas.Gain/loss for each antenna pathwill have to be taken into consid-eration for power measurementsand switching between receiveantennas for testing receiver sen-sitivity may also be necessary.

3

Basic Omni Cell Site Setup

3 - Sector Directional Site

Base Station Tests

Standard tests to make on basestation equipment include receive,transmit, and system tests. Thisproduct note outlines the follow-ing tests for cell site transceivers:

The following System Test proce-dures are NOT INCLUDED in thisproduct note. However, you canfind detailed procedures for thesetests in the HP 8920A RF Commu-nications Test Set ApplicationsHandbook (Hewlett-Packard PN08920-90126).

Cell Site Connections

The basic connections requiredfor performing the manual tests inthis application note include TX,RX, and audio. Because eachmanufacturers base station equip-ment may connect to the HP8921A Cell Site Test Set differ-ently, it will be up to you to deter-mine how best to connect yourtransceivers to the HP 8921A.

Test Set Operation

This product note assumes theuser has some familiarity with thegeneral use of the HP 8921A CellSite Test Set (or HP 8920A RFCommunications Test Set). If thisis not the case, please refer to theHP 8921A Cell Site Test Set User’sGuide and the HP 8920A RF Com-munications Test Set ApplicationsHandbook for an overview of itsfunctions, features, andcapabilities.

This product note also assumesthat the user is familiar with theoperation of the Base Station un-der test. It is not the intent of thisnote to show the step-by-step set-ups required for setting up allbase stations for particular meas-urements since many base sta-tions have unique setups andcontrol options. However, when aparticular base station setup isrequired, it will be called out inthe setup procedure.

4

Transmitter Tests

Frequency Error/OffsetOutput PowerSAT Frequency Error and

DeviationVoice DeviationData Deviation

Receiver Tests

Sensitivity (SINAD)Squelch Threshold

System Tests

(not included)Antenna Return Loss (VSWR)Cable Fault LocationField Strength Measurements


HP 8921A Cell Site TestSet Overview

The HP 8921A Cell Site Test Set isa single instrument that combinesthe features of 22 individual radiotest instruments. The HP 8921A is designed to meet thecommunication needs of bothservice and manufacturing envi-ronments, and has the capabilityto test AMPS and TACS Base Sta-tions, cellular phones, and variousother communications systems.

Test and troubleshooting time isdecreased by simplifying standardmeasurement tasks and providingthe required measurement capa-bility in a single instrument.Transmitters and receivers arecharacterized with single-key RX,TX, and duplex tests. Each ofthese tests displays a specializedscreen that provides access to thenecessary controls and measure-ment results. Measured resultsmay be displayed as digital read-outs and/or bar graphs. All set-tings and measurements are easilyaccessed and changed using thefront panel knob and keys. If de-sired, all settings can be saved innonvolatile save/recall registersfor future access.

The various ports on the HP8921A allow thereceiver/transmitter being testedto be quickly connected. A re-ceiver with 2 µV sensitivity (typi-cally <1 µV) is available throughthe ANT IN port, for off-the-airmonitoring of low-level signals.Transmitters of up to 60 W (100 Wintermittently for 10seconds/minute) can be con-nected to the RF IN/OUT portwithout the use of externalattenuators.

Global MeasurementConsiderations

Saving and RecallingInstrument Setups

The Save and Recall functionsallow you to store different instru-ment setups and retrieve themlater eliminating the task of re-configuring the HP 8921A eachtime you wish to make a measure-ment. You can name save regis-ters anything you want providedthe name does not exceed 9characters. If there is a particularsetup you would like the instrument to be in whenever youpower it up, save the setup withthe name POWER ON.

To save an instrumentsetup:

1. Make any changes to theinstrument that you want toSAVE in a register.

2. Press, ’shift’, SAVE.3. Using the front panel knob,

create a new name orchoose an existing namefrom the ’SAVE’ menu.

4. Scroll to the top of the’SAVE’ menu and choose’DONE’. The currentinstrument state is now saved.

Configuring the HP8921A for AMPS BaseStation Testing

The Configure screen defines anumber of general functions, suchas date and time, screen intensity,and beeper volume. It is also usedto define some RF signal parame-ters, such as RF Generator / Ana-lyzer offset, channel standardsand characteristics, and signalloss/gain compensation. Changesmade to the "Configure" screenwill be saved when you saveinstrument setups.

5

HP 8921A Cell Site Test Set

Explanations:

The RF Display fieldselects the format forentering the RF Analyzer

frequencies:

* When Freq. is selected,you enter the RFGenerator and RFAnalyzer frequenciesdirectly using the keypador knob.

* When Chan is selected,the RF Gen Freq andTune Freq fields on allscreens are replaced bythe RF Channel field,and only the channelnumber is entered anddisplayed.

The RF Chan Std field al-lows you to select thechannel standard for the ra-dio under test. The RF Gen-erator and RF Analyzerfrequencies will be auto-matically set to correspondto the channel number en-tered in the RF Channel

field. This field also sets thecorrect TX/RX frequencyoffset (45 MHz for AMPS).

The RF Level Offset fieldenables/disables the effectsof the RF In/Out, Duplex

Out, and Antenna In fieldsbelow it. These fields areused if you wish to take intoaccount losses due to cablesand/or splitters in yoursetup.

* When set to ’Yes’, the RFGenerator amplitude andRF Analyzer powermeasurement are offsetby the values entered inthese fields.

* When set to ’No’, thevalues in these fields areignored. The values can,however, be left in thethree fields.

For example, enter "-3.5"into the RF In/Out field forthe approximate total lossdue to a 1 meter cable and 3dB splitter.

From the front panel of theHP 8921A, enter the "Config-ure" screen. Set the RF Dis-

play and RF Chan Std asseen here and the RF Level

Offset as desired.

6


Screen Configuration

C

B

A

PerformingMeasurements

The following measurement pro-cedures assume the HP 8921AConfigure screen is setup as de-scribed in the previous section. Ifthe instrument has been presetsince then, you will need to re-configure that screen.

7

Transmitter Tests

Transmitter Frequency Error/Offset and Power . . . page 8Transmitter SAT Frequency and Deviation . . . . . . . page 9Transmitter Maximum Voice Deviation . . . . . . . . . . page 10Transmitter Data Deviation . . . . . . . . . . . . . . . . . . . page 11

Connect the Base Station to the HP 8921A according to the following diagram.

RX Audio Out

TX Audio InRX Input

TX OutputFrom Base Station

From BaseStation

Channel: As desiredTX Power Level: As desiredTX Power: OnSAT: OffData: Off

Step 1:Press the TX key on the HP 8921A to enter the transmitter test screen.

Step 2: Change the settings in the TX screen as seen in the highlighted areas.

Key instrument considerations

With the front panel keys, enter the same RF Channel as set on the base station.

Disable the FM Deviation and AF Freq measurements by scrolling to their units fields and pressing the On/Off key.

Step 3:The transmitter frequency error and power should now be displayed in theappropriate result fields. For TX Output Power in units other than Watts,scroll to and highlight the TX Power units field and press the appropriateunits key.

Step 4:Save this measurement setup as FREQ.

8

Base Station Setup

HP 8921A Cell Site Test Set Setup

A

Transmitter Frequency Error/Offset

and Power

B

Channel: As desiredTX Power Level: As desiredTX Power: OnSAT: OnData: Off


Step 2:Change the settings in the TX screen as seen in the highlighted areas.


Enter the same RF Channel as set on the base station.

If you are using an HP 8920A RF Communications Test Set, you must have Option 014 (6 kHz BPF) in order to choose this filter. If not, you can use the 15 kHz LPF. The 6 kHz BPF is standard on the HP 8921A.

AFGen1 Lvl must be "OFF" or it may interfere with the SAT measurement.

Disable the TX Freq Error and TX Power measurements by scroll-ing to their units fields and pressing the On/Off key.

Step 3:The SAT frequency and deviation should now be displayed in the appropri-ate result fields. For AF Freq in units other than Hz, scroll to and highlightthe AF Freq units field and press the appropriate units key.

Step 4:Save this measurement setup as SAT.

9

Transmitter SAT Frequency and Deviation

Base Station Setup


A

B

C

D

Channel: As desiredTX Power Level: As desiredTX Power: OnSAT: OffData: Off





For AFGEN1 Lvl, enter an initial value of 50 mv and set an incre-ment for this field of 20 dB.

Disable the TX Freq Error and TX Power by scrolling to their units fields and pressing the On/Off key.

Step 3:Scroll to the AFGen1 Lvl field and depress the Up-Arrow key once. Thiswill increment the AFgen1 Lvl by 20 dB (as set above).

Step 4:The maximum voice deviation should now be displayed in the FM Deviation result field.

Step 5:Save this setup as MAX_VOICE.

10

Transmitter Maximum Voice Deviation

Base Station Setup


A

B

C

Channel: As desiredTX Power Level: As desiredTX Power: OnSAT: OffData: On





AFGen1 Lvl must be "OFF" or it may interfere with the DATA measurement.

Disable the TX Freq Error, TX Power, and AF Freq measure-ments by scrolling to their units fields and pressing the On/Off key.

Step 3:The Data Deviation should now be displayed in the FM Deviation resultfield.

Step 4:Save this measurement setup as DATA.

11

Transmitter Data Deviation

Base Station Setup

HP 8921A Cell Site

Test Set Setup

C

A

B

12

Receiver Measurements

Receiver Sensitivity (SINAD) . . . . . . . . . . . . . . page 13

Receiver Squelch Threshold . . . . . . . . . . . . . . . page 14

Connect the Base Station to the HP 8921A according to the following diagram. Note the Audio In connection. This must be connectedproperly for accurate receiver audio measurements

Using the front-panel knob, scroll to and select the AF ANL screen, and select 600 TO HI in the Audio INLO field. 600 TO Hi establishes a 600 Ω impedance between the center pins of the Audio IN LO and AudioIN HI connectors.

RX Audio Out

TX Audio InRX Input

TX OutputFrom Base Station

From Base Station

Audio IN

Channel: As desiredTX Power Level: As desiredTX Power: OffSAT: OffData: OffSquelch: Off

Step 1:Press the RX key on the HP 8921A to enter the receiver test screen.

Step 2:Change the settings in the RX screen as seen in the highlighted areas.



Enter an initial value in the amplitude field. This value will depend on the sensitivity of the receiver you are testing.

Step 3:Using the front-panel knob, adjust the Amplitude until the desired SINADis measured. To adjust the resolution of the amplitude adjustment, use theINCR SET, INCR 10, or INCR 10 keys.

Step 4:Save this measurement setup as SINAD.

13

Receiver Sensitivity (SINAD)

Base Station Setup


A

B

Channel: As desiredTX Power Level: As desiredTX Power: OffSAT: OffData: OffSquelch: On

Step 1:Press the RX key on the HP 8921A to enter the receiver test screen.

Step 2:Change the settings in the RX screen as seen in the highlighted areas.



Enter a starting amplitude. This initial amplitude value will de-pend on the squelch sensitivity of your receiver.

It is important to activate the Atten Hold function of the HP 8921A for this test. If this is not done, the RF signal to the receiver may drop out momentarily as you adjust its amplitude and an at-tenuator change is required. This will activate the squelch on the re-ceiver and make it difficult to measure the squelch sensitivity.

14

Receiver Squelch Threshold

Base Station Setup

HP 8921A Cell Site

Test Set Setup

A

B

C

Step 3:Adjust the volume on the HP 8921A to verify audio output. If no audio isheard, the base station may be in a squelched condition. In this case, in-crease the amplitude until the squelch de-activates and an audio signal isheard.

With the amplitude field highlighted, slowly decrease the amplitude of theRF signal and note the point at which the squelch activates and the audiosignal is muted. To adjust the resolution of the amplitude adjustment, usethe INCR SET, INCR 10, or INCR 10 keys.

For squelch hysteresis testing, slowly increase the RF level until thesquelch de-activates and an audio signal is present. Note the RF level atwhich this occurs. The squelch hysteresis is the difference between thislevel and the level at which the squelch activates.

Step 4:Save this measurement setup as SQUELCH.

Typical AMPS System Specifications

15

Parameter Specification

TX Frequency Error ±1.5 ppm

TX Sat

Frequency ±1 Hz

Deviation 2 kHz ±10%

TX Voice

Nominal Deviation 8 kHz ±10%

Maximum Deviation 12 kHz

TX Wideband Data

Deviation 8 kHz ±10%

RX Sensitivity (SINAD) < -116 dBm @ 12 dB SINAD

Appendix A

16

Data subject to change

© Hewlett-Packard Company 1997

Printed in U.S.A. 5/97

5962-9475E

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hp 8921a cell site test set product note 8921-1

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