Aeroflex 2945B User manual

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Application
Note
Testing live EDACS repeater stations is made quick and
easy using the IFR 2945B Communications Service
Monitor. A step by step guide to a typical measurement
application
EDACS repeater testing using the
IFR 2945B Communications Service
Monitor
Introduction
The IFR 2945B Communications Service Monitor is ideal-
ly suited to the testing of trunking repeaters. It provides
an extensive array of tests, allowing verification of per-
formance, and rapid diagnosis of faults.
This application note will assist the first time users by lead-
ing them through the initial stages in setting up the 2945B
and testing an EDACS repeater.
The majority of this document is concerned with using the
2945B test set off-air, that is with no physical connection
to the repeater. The limitations of this method will be
explained, but the method does allow rapid set up and
quick verification.

Trunked radio concepts
The idea behind trunking comes from the telephone system - the
'Trunk' line connecting telephone exchanges. This line is shared
by the telephone users, without them being aware that it is hap-
pening. The process of "Trunking" is transparent to the telephone
user.
The operation of a trunked radio system is very similar, as the use
of the available radio channels is shared amongst the system
users by a site controller, without them being aware of the
process. As far as the radio system users are concerned, they
each have a channel all to themselves.
What is EDACS?
EDACS is a computer controlled trunked radio system, that is
geared towards one person calling a group of others. Additional
services provide individual to individual calls, telephone intercon-
nects, data transmission and secure speech calls.
The IFR 2945B Communications Service Monitor, when set up in
EDACS repeater test mode, behaves as an EDACS radio on the
system, but allows complete control over the identities it uses on
the system.
The 2945B Communication Service Monitor can function in two
major modes: either as a trouble shooting tool, in manual mode;
or to run automatic tests, either for verification or remotely to
ensure optimum performance of the installed systems.
What do you need to know?
In order for the 2945B test set to work on your system, it needs to
be told some details about the system - EDACS is a custom made
trunked radio system and each installation is different from all
other EDACS systems in some details.
The first thing that you need to know is the frequency plan of the
system you are going to test. One way to find this information is
to get a radio that works on the system and use the manufactur-
er programming tools to read the 'personality' from the radio. The
frequency plan can be examined and then entered into the test
set.
Next, you need to know the data rate. EDACS can operate at two
different data rates - 9600 baud (or bits per second), with a chan-
nel spacing of 25 kHz per channel, or 4800 baud with channel
spacing of 12.5 kHz.
As a general rule, if the frequencies in the frequency plan are in
the 900 MHz band, then the data rate will be 4800 baud. If they
lie in the 400 MHz or 800 MHz bands, they are usually 9600
baud.
Finally, you need to know the control channel for the system you
are testing. This isn’t a problem for the radios on the system - they
will scan all the channels until they find a control channel. The
2945B does not scan, allowing you to test a particular channel, so
you have to find the control channel yourself. This can be done
using the instrument's spectrum analyzer.
How to set up the 2945B
Selecting the EDACS repeater test system.
First of all, you need to tell the test set that you want to test EDACS
repeaters - so press the blue [SYSTEM] key, the left [SYSTEM] soft-
key, and then select [EDACS repeat] from the list of available sys-
tems.
Now select [SET-UP], and the system parameters set-up screen
shown below should appear. If it doesn’t, keep pressing the [SET-
UP] key as there are four set-up screens, selected in turn.
The system parameters set-up screen.
The screen for entering system details.
In order to enter details of the system you are going to test, you
then need to select [select system] and [edit current].
Press [system title] to enter the text title that identifies the system
you are setting up - the title is used at the top left of the display
and the first 7 letters are used on the soft key label for the stored
system.
[channel edit] allows you to set up the frequency plan of your sys-
tem. It requires you to know the TX frequency of the repeater, and
the duplex offset. If you know the TX and RX frequencies, the
duplex offset is the RX frequency minus the TX frequency. You will

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also need to enable each channel.
When you press the [return] key, the display will show you which
channels are enabled. Check this is correct before you continue.
Pressing the [data rate] key toggles between 9600 and 4800
baud data. If you aren’t sure what speed data is used on your sys-
tem, try 9600, and if this doesn’t work, try 4800.
The [RF port select] key allows you to change which of the ports
on the front panel of the test set will be used for RF input and out-
put. For simplicity, we’ll start with off-air tests, so this should be
set to [BNC out ANT in]. If the RF signal is very strong, such as the
area immediately around a repeater, then you should select [BNC
out N in] which greatly reduces the test set sensitivity. You should
also connect an antenna to both the input and output ports since
using two antennas avoid problems where the test set signal gen-
erator swamps reception of channels that have small duplex off-
sets.
Finally, you can set what data deviations are to be used by the test
set. Altering these values is not really necessary at this stage - the
values of 3 kHz for high speed deviation and 750 Hz for low speed
deviation will work for all EDACS systems.
When you press the [return] key the system is set up, and your fre-
quency plan is loaded into the instrument.
The manual test screen with a valid control channel.
Press [MANUAL] to access the manual testing screen. Now you
have to establish which channel is the control channel. The eas-
iest way is to step through the enabled channels in the frequency
plan using the [control channel] key. When the correct control
channel is found, the SERVICE indicator will change from NO SER-
VICE to a percentage figure, in inverse text.
If this doesn’t work, first check that the system is available, using
a radio programmed for that system. If it indicates service, and
will make a call, then either the data rate is incorrect, the signal is
too weak to be picked up by the test set, or the frequency plan is
incorrect.
To check the data rate, you should turn the sound volume up on
the front panel, and then step through the channels using the
[control channel] key. When you hear a continuous drone, select
[Tx TEST], and press [Scope /Bar] until the large ‘scope display
appears. Press the [Persistence] key until High is highlighted
when you should see an ‘eye’ diagram of the modulation from the
repeater. This then allows you to calculate the system data rate.
An ‘eye’ diagram produced off-air from an EDACS control
channel.
Press [SYSTEM], and noting the channel, change the data rate
using the [SET-UP], [edit current] and [data rate] keys. Then press
[return] and [MANUAL], and select the channel again (altering the
current system will force the test set to re-initialise the system).
If the test set still doesn’t indicate service, or no channel gives a
droning noise, then you should check the entered frequency plan
again and ensure that there is reasonable signal strength present
- the 2945B service monitor will detect a signal reliably at levels
of around -40 dBm to -50 dBm using the ANT port. EDACS radios
are far more sensitive, however, and if you are working without a
direct connection you should get closer to the repeater and try
again.
Once the service indicator shows that the control channel is 'visi-
ble' to the test set, the next step is to get the test set to commu-
nicate with the repeater. To do this, you need to use the data per-
formance test, in the manual test screen, by pressing [mode],
[data perform].
The MANUAL TEST screen showing a data performance test in
progress.
In data performance mode the test set sends messages to the
repeater on the control channel, and gets acknowledgement
responses back. This allows you to check that you have set the
duplex offset correctly for the channel that is currently the control
channel.
Set the RF generator level to maximum (+5 dBm using the BNC
output port), and when the SUCCEEDED count reads above 0%,
contact is established.
Finally, you should check that the other channels are correct. This
involves making a call on the system, which will then assign the
test set to a working channel

Before you make a call, you should set up the identity of the test
set and of the radio you want to call, to avoid calling anyone else
on the system. The test set has default values for group and log-
ical identities of 1.
The radio parameters set-up screen.
Press the [SET-UP] soft key until the screen above appears. The
radio logical ID is the identity of the radio the test set will call. The
IFR ID is the identity that the test set will use when it makes or
responds to calls. The group identity is both the group that the test
set will call, and the group identity that it will respond to.
If you now go back to the Manual test screen, and select [mode],
[individ call] the test set will attempt to make a call to the radio
whose identity is in the RADIO LOGICAL ID field. The mode
should change to WC CONFIRMATION, and then to WORKING
CHANNEL.
The MANUAL TEST screen after a successful individual call.
Selecting [mode], [clear down] will return the test set to the con-
trol channel.
You should now have a working EDACS repeater test system,
ready to go! The system parameters are stored internally in non-
volatile memory, but you may also like to take this opportunity to
save the settings on to a PCMCIA memory card.
Measuring off-air
The IFR 2945B test set has several tests built in to allow monitor-
ing and diagnosis of EDACS repeaters. These are designed to be
used off-air, and on a live system, so that the condition of the
repeater can be continuously monitored, without disrupting the
system traffic, as well as being connected physically to the
repeater RF and audio connections.
Distortion measurements can be performed on a channel with-
out requiring audio access to that channel. Three different dis-
tortion measurements are available - SINAD, signal to noise and
distortion, which should not be used in isolation. The values
returned by these tests should be used to detect degradation in
performance, with relative results being important, and not the
absolute values.
Data deviation tests are provided for both low and high speed
data, with the tests using advanced DSP (Digital Signal Processor)
filtering.
A data performance test is also provided, to allow the receiver on
the control channel to be tested.
All of these tests have test limits and parameters stored in mem-
ory so that you can tailor the test and the limits to your particular
system. The parameters are set up using the AUTORUN PARA-
METERS screen.
Additionally, one of the built in test programs, the QUICK TEST, is
designed specifically for use off-air.
The AUTORUN PARAMETERS set-up screen.
As an example, in order to set up the Quick test, we need to alter
the RF generator levels for all the signalling tests, and set the data
deviations to those in use on the system.
1) Set the RF GEN LEVEL to be +5 dBm for the:
CALL FROM IFR,
CLEAR FROM IFR and
DATA PERFORMANCE tests.
2) To do this, use either the up and down arrow keys, or the rotary
control.
3) Highlight the test required (the DATA PERFORMANCE test in
this example).
4) Now press [select] and a list of the test’s parameters is given.
5) Select the RF GEN LEVEL entry, and press 5.
6) Then press either the [dBm] softkey, or the orange
[dBm/ENTER].
7) Pressing [return] returns you to the list of tests.
You should also set up the data deviations initially with either a
generous error tolerance (say 30%) or the known correct values
for your system.
Finally, the Tx LEVEL test is of little use in off-air measurement, and
should be turned off. The problem is caused mainly by the vari-
ability of the environment around the antenna (people, vehicles,
and buildings appearing between the antenna and the repeater),

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as well as multiple paths to the receiver
Having set all this up, press [PROGRAM] and select [quick test].
The autorun Test Program selection screen.
Then press [AUTO] and [start] to start the automatic test, which
should run without any intervention, and give a result at the end.
The AUTORUN screen after the quick test has been run.
Now it is up to you to adjust the limits of the tests for your system,
to detect problems before they become noticeable (for example,
the RF distortion measurement will pick up problems on a partic-
ular channel’s audio circuits before the system users notice any-
thing wrong).
Remote control
The 2945B has remote control facilities available both from the
built-in RS-232 serial interface, as well as the optional GPIB
(IEE488.2) interface. It also features a built in MI-BASIC inter-
preter, for user defined programs which can be downloaded from
a PC.
Detailed explanation of the remote operation of the test set is
beyond the scope of this document, but briefly, if you wished to
run a test remotely, you would first put the instrument into remote
mode, then put it into systems mode and finally run the test you
are interested in.
As an example, to check the high speed data deviation using the
RS-232 serial interface, the following commands are sent to the
test set (explanations in brackets):
<ctrl A> (Put the test set into remote mode)
:TESTMODE SYSTEMS
:STEST:HSDEVN? (The test returns 1 for pass, 0 for fail)
<ctrl D> (Put the test set back to local mode)
Data Displays and Decode Only
Since the data displays and decode only facilities may not be
available for all systems the IFR 2945B product is normally sup-
plied with this functionality disabled. For further information please
contact the Aeroflex help desk [phone].
Data Display
The purpose of this screen is to show the data frames that make
up the EDACS signalling - this allows you to check that the data
that was set in the repeater is actually being transmitted, as well
as letting you see exactly how EDACS works.
As an example, with the service indicator showing 100%, the data
display would look something like this:
The DATA display screen showing a control channel.
With this you can see that the channel is made up of SID (site ID)
and DRB (dynamic regroup) frames. Each frame shows a quantity
of C for continuous. The test set regards any frame that occurs
more than 99 times as being effectively continuous.
You can use this screen to see that in this case, the repeater is
operating in 'failsoft' mode (the 'F' bit in the frame is set to 1), the
current channel is channel 1, it is the main control channel (the 'A'
or auxiliary bit is 0), the site ID is 1, and so on.
For more information about how the frames are made up, refer to
the "Enhanced Digital Access Communications System (EDACS)
Digital Air Interface Specification".
Decode only mode
Decode only mode allows you to monitor what is actually hap-
pening on the control channel. To use it, select [MANUAL],
[mode], [more], [decode only]. The mode changes to DECODE
ONLY, with a service indicator and events that happen are dis-
played on the screen in real time.

The MANUAL TEST screen in decode only mode.
This isn’t very useful if there is a large amount of traffic on a heav-
ily loaded system, so there are two other options that can be
used. You can log the text that appears to either the internal
results store (visible under the autorun screen) or you can log the
results out to a printer. If you log the results to the results store
(press [mode], [log to store]) then the test set will store about 200
events. Subsequent events will be discarded when the store is
full.
The AUTORUN screen in decode only mode with logging to
store enabled
For a complete record, you should connect a printer or a com-
puter to the test set’s serial port. To do this, first set the printer
type to RS-232 (press [HELP/ SETUP], [Setup], [Setup Page 2],
[Printer Setup] and ensure that the printer port is set to RS-232)
To log the results to a computer you need to connect the test set
serial port to the computer, using a Null modem cable. You will
also need a terminal program, such as the terminal program that
comes with Microsoft Windows.
You need to set up the serial transfer parameters, both in the ter-
minal program, and also on the test set. On the test set, the seri-
al configuration is changed using the serial setup screen (press
[HELP/SETUP], [Setup], [Setup Page 2], [Serial Setup]).
Finally, log the transfer on the computer to a file - if you are using
the Windows terminal program, select 'Transfer', 'Receive Text File'
and enter the filename.
Summary
The 2945B test set is an ideal tool for both monitoring and fault
finding on EDACS repeater systems, allowing rapid diagnosis of
both programming problems and hardware failure.
The remote control operation, together with the built in MI-BASIC
programming language allows long term, remote monitoring of
distant repeater sites, which can be tested and monitored off-air,
removing the need to close a repeater down for maintenance.
The data display and logging features also allow long term moni-
toring for badly set up radios, as well as greatly easing the initial
commissioning of a new EDACS installation.
References
2945B Operating Manual Supplement for Communications
Service Monitors for EDACS Repeaters
[Aeroflex Part No. IFR46882-300]
Enhanced Digital Access Communications System (EDACS) Digital
Air Interface Specification" [Telecommunications Industry
Association December 28 1995, Doc #TSB69.3]

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Part No. 46891/944, Issue 1, 05/05
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As we are always seeking to improve our products,
the information in this document gives only a general
indication of the product capacity, performance and
suitability, none of which shall form part of any con-
tract. We reserve the right to make design changes
without notice. All trademarks are acknowledged.
Parent company Aeroflex, Inc. ©Aeroflex 2005.