Pira P275 User manual

P275
FM Broadcast Analyzer
User Manual
Firmware version 2.2b
Hardware version 10.2016
Web: http://www.pira.cz E-mail: m[email protected]

2
Table of Contents
Related Documents...........................................................................................................................................................2
Introduction ......................................................................................................................................................................3
Main highlights...................................................................................................................................................................................3
Measurements, indications and outputs...............................................................................................................................................3
Electromagnetic compatibility ............................................................................................................................................................4
Technical Specifications...................................................................................................................................................5
General................................................................................................................................................................................................5
Antenna (RF) Input.............................................................................................................................................................................5
Measurements .....................................................................................................................................................................................6
MPX Input ..........................................................................................................................................................................................6
Alarm Outputs.....................................................................................................................................................................................6
Headphones audio output....................................................................................................................................................................7
Internal RDS/RBDS Decoder..............................................................................................................................................................7
Side connectors and controls...............................................................................................................................................................8
Power supply.......................................................................................................................................................................................9
Mainboard composition ....................................................................................................................................................................10
Alarm outputs....................................................................................................................................................................................12
Operating Instructions ...................................................................................................................................................13
Power-up...........................................................................................................................................................................................13
Control buttons..................................................................................................................................................................................13
Menu.................................................................................................................................................................................................13
RF Measurements...........................................................................................................................................................16
Signal quality ....................................................................................................................................................................................16
Overall frequency deviation (peak frequency deviation)...................................................................................................................19
Pilot deviation...................................................................................................................................................................................19
RDS deviation...................................................................................................................................................................................19
Pilot-to-RDS phase difference...........................................................................................................................................................20
Modulation power (MPX power, Pm)................................................................................................................................................20
Frequency deviation histogram.........................................................................................................................................................21
Service details...................................................................................................................................................................................22
Simple stereo balance meter..............................................................................................................................................................22
Carrier frequency offset ....................................................................................................................................................................23
Radio Data System decoding ............................................................................................................................................................24
USB and COM Port Communication ...........................................................................................................................28
Connecting the FM analyzer to a PC.................................................................................................................................................28
Communication speed selection (autobaud feature)..........................................................................................................................28
List of commands and configuration registers...................................................................................................................................29
Data format .......................................................................................................................................................................................33
Other Features................................................................................................................................................................35
Firmware update ...............................................................................................................................................................................35
Precise carrier frequency offset measurement...................................................................................................................................35
Annexes............................................................................................................................................................................36
Memory map.....................................................................................................................................................................................36
Mainboard mechanical drawing........................................................................................................................................................37
Control interface (J3) connection example........................................................................................................................................38
Related Documents
Visit the Website for the latest documentation version and the following additional documentation:
FM Scope - User Guide (http://pira.cz/fm_broadcast_analyzer/fmscope.pdf)
RDS Spy - RDS Decoder for Windows (http://rdsspy.com/download/mainapp/rdsspy.pdf)

3
Introduction
The P275 FM Broadcast Analyzer is a stand-alone low-cost solution for FM broadcast analysis. It
provides complete FM modulation and basic AF spectrum measurements in FM radio band through the
combined antenna and MPX input.
Built-in LCD display and control interface allows to measure and collect data in terrain without need of
any PC computer. Serial interface and the control software provide a possibility of remote control, data
viewing and automated data logging.
This kind of analyzer is essential equipment for all FM radio stations to ensure compliance with basic
technical broadcast standards and to accomplish the highest audio quality possible.
Main highlights
Stand-alone design, completely DSP based from IF to outputs
Compliant with CEPT/ERC REC 54-01 E and ITU-R SM.1268
Dual-conversion receiver
Built-in LCD display and RS-232 interface
Built-in USB interface
Firmware updates are free
Easy to use
Measurements, indications and outputs
Overall frequency deviation incl. histogram
Modulation power (MPX power)
Baseband spectrum, RF carrier spectrum
Pilot deviation, RDS deviation
Pilot-to-RDS phase difference
FM carrier frequency offset
Reception quality and signal strength
Stereo balance meter
MPX peak to peak voltage
Headphones audio output
Alarm logic or general purpose outputs
RDS/RBDS decoder
Please read this entire manual and familiarize yourself with the controls before attempting to use this equipment.
The equipment has been thoroughly tested and found to be in proper operating condition when shipped. The
manufacturer is not liable for any damages, including but not limited to, lost profits, lost savings, or other incidental or
consequential damages arising out of the use of this product.
No part of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical,
including photocopying, recording or information storage and retrieval systems, for any purpose other than the
purchaser's personal use.
It is our intention to provide you with the best documentation possible to ensure successful use of the product. If you
wish to provide your comments on organization, clarity, subject matter and ways in which our documentation can better
serve you, please mail us your comments.
Information in this document is subject to change without notice.
Revision: 2018-05-12
Copyright © 1999-2018 PlRA DigitaI s.r.o.

4
Electromagnetic compatibility
The manufacturer declares that the product complies with the essential requirements of applicable European
Directives and carries the CE marking accordingly and in conformity with the following product standards:
EMC Standard
Test conditions
Notes
EN 55011:2009
Class B
In line with EN 61326-1:2013:
EN 61000-3-2:2014
1)
EN 61000-3-3:2013
1)
EN 61000-4-2:2009
Contact discharge ±4 kV
Air discharge ±8 kV
EN 61000-4-3:2006
3 V/m (80 MHz - 1 GHz)
3 V/m (1.4 GHz - 2 GHz)
1 V/m (2 GHz - 2.7 GHz)
EN 61000-4-4:2012
L, N conductors ±1 kV
Capacitive way (antenna cable) ±1 kV
1)
EN 61000-4-5:2006
L, N conductors ±0.5 kV
1)
EN 61000-4-6:2009
3 V, 150 kHz - 80 MHz
EN 61000-4-11:2004
0% UT during half cycle
0% UT during full cycle
70% UT during 25 cycles
short interruption: 0% UT during 250 cycles
1)
Test report no.: 414103294AE1
Issued by: Testing laboratory no. 1004.3, ITC, a.s., CZ
Date: 2016-10-25
Notes:
1) With standard power supply.

5
Technical Specifications
Parameter
Condition
Value
General
Supply voltage
USB, J2
5.0 V DC ±10 %
battery
2.3 –4.3 V DC (2x or 3x AA NiMH)
internal (J17)
5.0 V DC ±5 %
Supply current
LCD off
80 mA
LCD on
140 mA
battery
Up to 280 mA @ 2.4 V
External power supply connectors
USB Micro, pin header
Mainboard dimensions
115 x 65 mm
CPU
70 MIPS DSP
Data connector
RS-232 (DCE, 9 pins), bidirectional,
USB (FTDI based, virtual serial port)
Communication speed
19200 or 115200 bps (autodetect)
Communication mode
1 stop bit, 8 data bits, no parity, (no flow control)
RX buffer length
40 bytes
Signal input
BNC type,
combined antenna (RF) and MPX input with
internal switch.
Antenna (RF) Input
Recommended source impedance
50 Ω
Frequency range
guaranteed
76.0 –108.0 MHz
extended
64.0 –108.0 MHz
Tuning step
selectable 50 kHz or 100 kHz
Input sensitivity
S/N 26 dB
4 μV
basic measurements
30 μV
full measurements
70 μV
Maximum input level
1000 mV (20 mW)
Intermodulation immunity
basic (single input LC circuit with coil tap)
Intermediate frequency (IF)
1st IF
10.7 MHz
2nd IF
0.325 MHz ± 0.005 MHz
Image rejection
+ 21.4 MHz
23 dB
IF bandwidth
280 kHz
Never connect RF power output from the transmitter directly to the device's antenna input!

6
Measurements
Frequency deviation range
min.
0 –121 kHz
Frequency deviation error
1 kHz sine
< ± 1.5 kHz
typical content
< ± 2 kHz
Modulation power range
min.
-12 –14 dBr
Modulation power error
-6 –6 dBr
± 0.2 dBr
Pilot deviation error
6.8 kHz
± 0.2 kHz
RDS deviation range
0.8 –17.9 kHz, note 4
RDS deviation error
full signal
± 5% ± 0.5 kHz
Pilot-to-RDS phase difference error
± 4 deg.
Baseband frequency response flatness
10 Hz –60 kHz
± 0.3 dB
Stereo balance error
± 0.5 dB
Signal level (RSSI) range
typical
0 –90 dBµV
battery pwr supply
20 –90 dBµV
Signal level (RSSI) error
60 dBµV
± 3 dBµV
30 –75 dBµV
± 5 dBµV
0 –90 dBµV
not specified
MPX Input
Input impedance
2.3 kΩ
Recommended source impedance
600 Ω or less
Maximum MPX level
peak to peak
8.0 Vpp
Bandwidth
-1 dB
100 kHz
Vertical resolution
12 bits
Peak to peak voltage error
1 kHz sine
± 2% ± 0.010 Vpp
Pilot level range
0.010 –2.250 Vpp
RDS level range
0.002 –3.400 Vpp
Alarm Outputs
Maximum current from pin 1
100 mA
Maximum current from/to pin 2, 3, 4, 5
15 mA (internally limited by 390R serial resistor)
Don’t open the cover (boxed versions)! No user adjustable parts inside! Risk of damage!
Never use the equipment if there's any visible damage on its electrical parts! In that case
disconnect all cables, remove accumulators and contact the vendor or manufacturer.

7
Headphones audio output
Audio channels
2 (left and right)
Output impedance
typ.
100 Ω
Output level
no load
adjustable 0.1 –4.0 Vpp @ 75 kHz
Signal to noise ratio
75 kHz dev.
60 dB
Stereo decoder separation
1 kHz
>26 dB
Distortion
1 kHz
1 %
Internal RDS/RBDS Decoder
RDS filter and demodulator
DSP based
RDS source
Antenna (RF) or MPX input
RDS groups detected
All RDS groups 0A-15A, 0B-15B
RDS services supported
PS, PI, PTY, PTYN, TP, TA, M/S, DI, AF, EON,
ECC, LIC, PIN, RT, CT, AID, RT+
RDS groups decoded
0A, 0B, 1A, 2A, 2B, 3A, 4A, 10A, 14A
Minimum RDS deviation (ΔFrds)
antenna (RF) input
1.0 kHz
Minimum RDS level
MPX input
4 mVpp
Antenna input sensitivity
(average BER = 5 % or less,
single station, no interference)
ΔFrds=2.0 kHz
25 μV
ΔFrds=3.4 kHz
18 μV
ΔFrds=6.8 kHz
9 μV
Notes (Technical specifications):
1. pp = peak-to-peak value; BER = Block Error Rate
2. Due to inherent reception the unit may have reduced sensitivity at 102.4 MHz.
3. Very strong el. field intensity (above 130 dBμV/m) may cause additional measuring error or may disallow
the measurement.
4. If pilot and RDS are not synchronized, the range reduces to 1.5 –17.9 kHz. Spurious RDS detection may
occur on stations without RDS if the station's signal is noisy or specific static sine tones are transmitted.
If ARI system is used simultaneously with RDS on the same transmitter, the RDS deviation value should
not be taken into consideration. Instead of this the Windows application and MPX spectrum graph gives an
image about signal level of each component.

8
Side connectors and controls
Following figure applies to the Al-boxed version only.
1
Input
BNC 50Ω input connector.
Accepts RF as well as MPX signal.
See section ‘Menu’ for details.
See section ‘Antenna input’ and ‘MPX input’ for specifications.
2
USB Micro
Allows connection of external 5V power supply or connection to a PC.
See section ‘Power supply’ for details.
See section ‘USB and COM Port Communication’ for details.
3
Battery holder
A space for optional battery.
Open the cover using a coin. Press and rotate clockwise to close the cover.
The unit accepts R6 AA size NiMH cells (2 pieces).
4
RS-232
Serial RS-232 connector female type.
See section ‘USB and COM Port Communication’ for pin assignment.
5
Battery off/on
Activates built-in battery voltage converter –turns on the unit if the NiMH
cells are inserted. Does not have any effect on external power supply.
See section ‘Power supply’ for details.
6
Alarm outputs (J2)
Optional alarm outputs 2.54mm (0.1") pitch pin header.
See section ‘Alarm outpus’ for details.
See section ‘Mainboard composition’ for pin assignment.
7
Headphones output
2-channel audio output provided on 3.5mm Jack.
See section ‘Headphones audio output’ for specifications.
1
76543
2

9
Power supply
Several power supply inputs are provided. They can be combined together in general but some limitations may exist.
Please read carefully all the specifications below.
USB Micro connector
Use this connector for supplying the FM analyzer from a PC computer or +5V power supply (DC wall adapter).
Maximum ripple of the power supply voltage shall not exceed 100 mVpp.
This connector is polarity protected for currents up to 2 A. Connecting the power supply the unit is always turned
on, i.e. the power off/on switch, if present, has no effect if the unit is powered via the USB connector.
The USB micro connector allows the device to be powered from various sources. To keep this
advantage, avoid strong force when using this connector. To remove dirt and restore good
conductivity, use compressed air.
Never exceed specified voltage value at this connector! It may cause permanent damage to the
device! Do not pull in and out the cable with strong force! Do not let the cable hang freely from
tables or shelves!
The USB port should be rated to full 500 mA current! When supplying the unit from USB bus, it
is a better choice to connect the unit to the USB interface on the main board. Supplies for pocket
USB hubs and for some USB interfaces of lap-top and desk top computers may not be sufficient.
Battery power supply connector
Use this connector (J13) for supplying the FM analyzer from 2x or 3x 1.2V NiMH accumulator or another low
voltage power supply (see the device specifications). When powered via the battery connector, an optional off/on
switch may control the device. Due to safety reasons, the unit does not charge the accumulators.
Performance may be impaired when the device is powered this way.
Never exceed specified voltage value at the battery power supply connector! It may cause
permanent damage to the device!
Disconnect or remove accumulators from the unit when it is not in use!
Disconnect the USB cable in order to allow operation from the battery.
Be careful not to lose the battery holder cover!
Internal power supply connectors
For embedding purposes the board provides power supply inputs at some internal connectors. These connectors are
polarity protected for currents up to 2 A. Maximum ripple of the power supply voltage shall not exceed 50 mVpp.
Connector
Pin number
Meaning
Notes
J2
(Alarm outputs)
1
+5V
Fused.
6
Ground
J3
1
Ground
4
+5V
J17
1
+5V
Preferred. Automatically disconnects USB power supply.
2
Ground
The USB Micro connector and the J2 or J3 power supply connector cannot be used at the same time (in such a case,
place a serial Schottky diode to the internal power supply path).
Never exceed specified voltage value at these connectors! It may cause permanent damage to
the device!

10
Mainboard composition
J2 –Alarm outputs / General purpose outputs *
1
+5V
2
Alarm 1 (Signal lost)
3
Alarm 2 (Silence)
4
Alarm 3 (Overmodulation)
5
Alarm 4 (Pilot or RDS level error)
6
Ground
CONLCD1 –Opt. LCD connector (HD44780, 20x4)
1
Ground
3
+5V
5
V0
7
RS
9
Ground
11
E
13
Ground
15
Ground
17
Ground
19
Ground
21
DB4
23
DB5
25
DB6
27
DB7
29
LED+
31
LED-
CONRS1 –RS-232 communication port
2
TxD
3
RxD
5
Ground
J15 –Internal RS-232 communication port
1
TxD
2
RxD
3
Ground
J1 –Internal TTL RS-232 communication port
1
RxD (TTL)
2
TxD (TTL)
3
Ground
J13 –Battery power supply connector
1
+2.2 to +4.3 V input
2
Ground
J17 –Internal 5V power supply connector
1
+5 V input
2
Ground
* Notes (Alarm outputs / General purpose outputs):
The Alarm outputs can be used as independent general purpose logical outputs or as an RDS TA output. See the
section "List of commands and configuration registers" for more details.
Maximum current from/to pins 2-5 is limited by internal 390R serial resistors.
Combined
antenna (RF)
and MPX
input
LCD
Control
interface
Alarm or
general
purpose
outputs
USB Micro
RS-232 TTL
Battery power
supply input
RS-232

11
J3 –Optional control interface (see the Annexes for connection example)
1
Ground
2
Battery converter on/off switch:
Leave unconnected for enabling the converter.
Tie to ground for disabling the converter.
3
Optional 10 MHz REF input for precise carrier offset measurement
4
+5V
5
Reserved, do not connect.
6
Auxiliary port TxD (Reserved)
7
Audio output Left
8
Auxiliary port RxD (Reserved)
9
Audio output Right
10
Button OK (pull-up resistor already on board)
11
Button DOWN (pull-up resistor already on board)
12
Button UP (pull-up resistor already on board)
13
Ground
14
Ground
J4 –Optional CPU control
1
+5V
2
Reset –hold low for at least 2 µs to reset the device.
Equivalent to ASCII command RESET*X
3
Ground
4
Reserved - do not connect
5
Reserved - do not connect
Adjusting elements
There are no adjusting elements on the board.
Note: The device provides four serial communication ports (USB, RS-232, J15 and J1). These ports are internally
linked together so the user may select any of these ports that best fits the communication requirements. When
requesting data via any port, all ports will send the reply. The user must ensure that different ports on the board will
not receive requests at the same time.
Note for boxed version: There are no user-adjustable elements inside! Don’t open the cover!

12
Alarm outputs
The device provides four independent logic outputs that are set by specific alarm conditions. These outputs can be
used for direct LED driving, switching to backup transmission equipment, signalizing via GSM gateway etc.
The alarm outputs are active high. If the alarm condition is no longer actual, appropriate output is driven low when
the time hysteresis elapses. Almost all parameters are user configurable. With factory default values the alarm
behavior is as showed in this table:
Alarm output
Condition
Interpretation
Alarm 1:
Signal lost
Signal quality < 4
(time duration 30 seconds)
FM transmitter failure or signal for the P275 device
is too weak for permanent monitoring.
Alarm 2:
Silence
ΔF AVE < 25 kHz
(time duration 1 minute)
There's no audio or the audio level is too low.
Broadcast automation system has crashed or
studio's mixing console has been set improperly or
connection between studio and transmitter has been
lost.
Alarm 3:
Overmodulation
ΔF MAX Hold > 88 kHz
and
[Histogram Max At > 78 kHz
or
ΔF AVE > 78 kHz]
(time duration 1 minute)
Transmitter problem or sound processing problem
or unauthorized manipulation with the broadcast
equipment or signal too bad (alarm 1 interpretation
may apply).
Alarm 4:
Pilot or RDS level error
ΔF Pilot < 5.8 kHz
or
ΔF Pilot > 7.7 kHz
or
ΔF RDS > 8.5 kHz
(time duration 1 minute)
Stereo encoder fault or transmitter problem or
unauthorized manipulation with the broadcast
equipment.
The user must ensure that the device will receive the station's signal in appropriate quality. To resume the
monitoring on desired frequency automatically after eventual power drop out, save the settings using menu item
File/Save Settings. To configure the alarms see the section 'USB and COM Port Communication' in this document
and appropriate section in the FM Scope User Guide.
Alarm response example.
Application example –Logical sum (OR function) of alarm outputs.

13
Operating Instructions
Power-up
On power-up, the device requires no heating time. After a few seconds the unit is ready for operate. The antenna,
audio and data cables can be connected regardless of the operating state.
Control buttons
Button
Meaning
Go to previous page or menu item, tune up, volume up.
Go to next page or menu item, tune down, volume down.
OK, enter the menu, confirm the option.
Menu
Navigation in the menu
To enter the menu or submenu, press the OK button.
To leave the submenu, go to the Return item, then press the OK button.
To leave the menu entirely, select an option or go to the Return item, then press and hold the OK button.
List of menu items
Menu item
Meaning
1 –Tune
Tune to a desired frequency in FM band (manual tuning) or select the MPX input.
2 –Scan
Tune using a scan mode (automatic tuning, stops on each station).
3 –Page Context
Items in this submenu appear depending on what page is being active.
Show Peaks
Histogram Data
Set as Normal
More RDS Data
Selects between overall peak deviation and Pos/Neg representation.
Show frequency deviation histogram values.
Consider the 2nd IF as a normal (see Carrier frequency offset)
Show more Radio Data System information.
4 –File
Save Settings
Load Data
Save Data
Save settings (incl. actual frequency tuned)
Load measured data and RDS data from EEPROM.
Save measured data and RDS data into EEPROM.
5 –Clear Data
Clear all measured values in operational memory.
6 –Settings
Volume
Force Mono
MPX Input
Corrections
DIP Switches
Adjust audio volume in steps.
Disable the stereo decoder.
MPX options for correct voltage calculation: source impedance, load impedance
Power supply ripple suppressing, audio output deemphasis etc.
Further configuration options (LCD backlight, frequency range etc.)
7 –Measuring
Enable/Disable the measuring.

14
Switching between antenna (RF) input and MPX input
The input connector is shared by two internal modules - the RF module and the MPX module.
To enable the MPX input, tune the frequency to 0.00 MHz (following the end of the band in any direction).
The MPX label will appear instead of the signal quality indicator.
Where applicable, the device keeps all functionality for the MPX input (stereo decoder, audio output, RDS decoder)
except that measurement of FM deviation in kHz is replaced by peak-to-peak voltage measurement.
Save Data
The FM analyzer can store data from up to 30 measurements into internal EEPROM memory. This memory does
not lose the data after power-off.
Select the Save data menu item and choose unused file position (or rewrite any actual position).
In addition actual frequency and these RDS information are saved: PS, PI, PTY, TP, TA, M/S, RT, EON, AF, DI,
group statistics.
The Save Data feature also supplies a preset memory function for tuning frequencies.
Load Data
Select the Load data menu item and choose the file required. The data are identified by the frequency.
To use the file as a frequency preset:
Make sure the Measuring option in the menu is enabled
Load the file
To use the file for the purpose of reading all stored data:
Disable (uncheck) the Measuring option in the menu
Load the file
You may browse the data, send them via serial port or continue in measurement by enabling the Measuring
option.
106.10 MHz §££££¤ ¨4
//Load Data©©©©©©©©©
File 1 106.10 MHz
106.10 MHz §££££¤ ¨4
//Save Data©©©©©©©©©
File 1No Data
0.00 MHz §MPX ¨1
u: MAX 5.45 Vpp
AVE 3.61 Vpp
RMS 1.2 dBu

15
Headphones output volume
The menu item Volume allows adjusting of audio volume in steps. The volume can be set separately for the antenna
(RF) input and for the MPX input.
Note: The headphones output is not suitable for rebroadcast or streaming purposes.
Low battery indication
When the system voltage drops below 4.5 V, for example due to low battery, the “BATT”indicator is showed. It’s
on the user’s responsibility to finish the measurement and switch off the unit as soon as possible. When the system
voltage drops below 4.3 V, the CPU will stop operating. Actual system voltage is indicated on page 9.
Disregard for the low battery indicator may result in data loss and accumulator damage!
96.30 MHz §££££¤ ¨5
//Volume©©©©©©©©©©©©
[¤¤¤¤¤¤__]

16
RF Measurements
Signal quality
The signal quality indication does not reflect the signal strength directly. It’s a result of the following input
parameters and influences:
Noise level (measured in baseband above 100 kHz)
Multipath propagation
Intermodulation
Amplitude ripple (AM modulation)
2nd IF frequency (frequency offset) –"in-channel" check
The essential condition for the measurement is enough signal level on the antenna input and sufficient frequency
spacing between the stations. Not all signals that you can listen can be also measured. The following scale illustrates
it and it’s valid in general:
Signal level
1 μV
10 μV
100 μV
1000 μV
Reception on
typical receiver
Mono only
Poor quality
stereo
High quality stereo
Measurement
ability
Not possible
Basic
Full
The basic measurement includes modulation power, pilot level and RDS decoding. The full measurement includes
overall frequency deviation and RDS level. In noisy environment or in a location with many strong stations the
minimum signal level may increase.
It’s possible to say that optimal signal strength range and reception conditions for full measurement coincide with
the requirements placed on high quality stereo reception. This rule determines the demands closely.
Signal reception quality table:
Signal
Meaning
§
No signal.
§£
Weak signal detected.
§££
Signal still unusable for measurement.
§£££
Poor signal. Basic measurement is possible with reduced accuracy
for RDS level. Full measurement is not possible.
§££££
Good signal. Full measurement is possible with partially reduced
accuracy.
§££££¤
Excellent signal.
Note: For proper measurement of modulation characteristics, internal bandwidth for RF signal is fixed at 280 kHz.
In locations where stations are present in 200 kHz or even 100 kHz spacing, the device may indicate insufficient
signal quality unless signal of the adjacent stations is rejected enough by positioning of the receiving antenna.
106.10 MHz §££££¤ ¨1
¢F: MAX 74.5 kHz
AVE 69.6 kHz
Pm: 5.4 dBr ( 3.45)

17
Following tables illustrate approximate max. measuring distance as a result of transmitter’s ERP power and
measuring conditions:
Estate housing, telescopic antenna:
ERP
Max. distance
1 W
300 m
10 W
800 m
100 W
3 km
1 kW
8 km
10 kW
20 km
100 kW
40 km
Open space, hill, Yagi antenna:
ERP
Max. distance
1 W
800 m
10 W
3 km
100 W
7 km
1 kW
20 km
10 kW
50 km
100 kW
100 km
Selecting an antenna
There is no general choice for the antenna.
The requirements for the antenna differ with local conditions and kind of use.
The essential condition for the measurement is enough signal level of the desired station on the antenna input. Not
all signals that you can listen on any radio receiver can be also measured. It’s possible to say that optimal signal
strength range for full measurement coincides with the range which is required for high quality stereo reception.
From this observation it's clear that simple telescopic or whip antennas are not enough for some applications. On the
other hand special calibrated antennas for EMI and RF field applications have no reason for FM modulation
measurements.
In the transmitter's near field (up to 1 km distance from the transmitter) any piece of wire connected to the antenna
input should be always sufficient. When measuring other than only local stations or where number of stations
reaches a couple of tens, a single dipole or 3-element Yagi antenna will give considerably better results than simple
telescopic or whip antenna. In many cases this kind of antenna must allow positioning in horizontal plane in order to
boost signal of stations of interest and reduce signal of all other stations.
Always make sure there is no pulse interference source near the antenna. These sources especially include
computers, cars, electric motors, PWM regulators, high voltage lines etc. Assure stable antenna position during the
measurement so the device can examine the signal characteristics reliably. Especially the frequency deviation should
not be measured in motion like in ridden car.
Hint: Keep on mind that with fixed omni-directional antenna, the number of stations with excellent reception (full
measurement ability) usually does not exceed 15, regardless of how many strong stations are on air overall in the
location. This may be caused due to multipath propagation of many station signals, as well as by the receiver’s
limited selectivity (restricted by requirement of proper FM deviation measurement) and intermodulation
predisposition of the receiver’s simple front-end. If the station of interest is 30 dB or more below the strongest
stations, finding the best antenna position may be necessary to reduce this ratio and to ensure full measurement
ability.

18
Measurement using the transmitter’s test RF output
Many FM broadcast transmitters are equipped with a test RF output. This output is primarily not intended for
modulation characteristics measurement using an analyzer based on a receiver like the P275. In most cases the RF
test output can be used for this purpose but this usually does not bring any advantage.
Special care is required before connecting the analyzer to this output. Make sure the output signal power does not
exceed 20 mW (13 dBm). In some cases the test RF output gives 30 dBm (1 W) or more. That signal must be
attenuated to less than 20 mW before connecting to the analyzer!
It is sometimes better not to use the test output and get the signal "from air". The modulation characteristics are not
affected in near field. Another recommended way is to connect only the transmitter's and analyzer's ground
(shielding).
On the transmitter sites where many transmitters are operating the user may be forced to find one of the methods
mentioned that gives full quality result. It’s due to intermodulations caused by many strong signals and their
harmonics that are present in this environment.
Measuring when connected to a PC
Personal computer (PC) is a strong source of unwanted RF signals which may cause interference with the signal
being measured. Sometimes, when using telescopic aerial, the reception quality may decrease once a ‘live’ data
cable (USB or RS-232) is connected to the FM analyzer. This phenomenon does not occur when using external
antenna because well symmetrized antenna suppresses this kind of interference. However, a telescopic aerial is not
symmetrized, thus the device case as well as outer side of the data cable effectively becomes a part of the receiving
antenna, bringing all unwanted RF signals from the PC.
The solution is usually simple. Make a few coils on the data cable to cut off the RF path between the device and the
interference source:
3 coils
telescopic or whip antenna

19
Overall frequency deviation (peak frequency deviation)
Frequency deviation (ΔF) is used in FM radio to describe the maximum (peak) instantaneous difference between an
FM modulated carrier frequency, and the nominal carrier frequency.
The overall peak frequency deviation shall not exceed 75 kHz.
The peak hold values of the deviation are taken during a measuring time of 50 ms, 20 times per one second. From
this array of values the MAX, AVE and MIN values are calculated and showed. These values represent signal
characteristics in last second. The measurement is fully continuous over the signal, without any gaps.
Moreover, MIN Hold and MAX Hold functions are provided. The MAX Hold value represents the maximum
deviation found in last 10 seconds. Since it may be affected by pulse interference, interpret it very carefully.
Remember that any "Hold" or "MAX" function based on a single number cannot fully and adequately
describe the FM modulation characteristics as the histogram function can (described thereinafter).
Pilot deviation
In FM stereo broadcasting, a pilot tone of 19 kHz indicates that there is stereophonic information. The receiver
doubles the frequency of the pilot tone and uses it as a phase reference to demodulate the stereo information. The
(L+R) main channel signal is transmitted as baseband audio in the range of 30 Hz to 15 kHz. The (L-R) subchannel
signal is modulated onto a 38 kHz subcarrier occupying the baseband range of 23 to 53 kHz.
The deviation range of the FM carrier caused by pilot tone is from 6.0 kHz to 7.5 kHz.
The recommended value is 6.8 kHz.
RDS deviation
Radio Data System (RDS), is a standard from the European Broadcasting Union for sending small amounts of
digital information using conventional FM radio broadcasts. Radio Broadcast Data System (RBDS) is the official
name used for the U.S. version of RDS. The two standards are nearly identical, with only slight differences. Both
use a 57 kHz subcarrier to carry data.
The deviation range of the FM carrier caused by RDS/RBDS is from 1.0 kHz to 7.5 kHz.
The most used value is around 3.0 kHz. This value should be considered as a minimum if
dynamic PS or TMC service is being broadcasted.
106.10 MHz §££££¤ ¨3
¢F: Pilot 6.8 kHz
RDS 3.4 kHz
Phase Diff.: 0 deg
106.10 MHz §££££¤ ¨3
¢F: Pilot 6.8 kHz
RDS 3.4 kHz
Phase Diff.: 0 deg
106.10 MHz §££££¤ ¨1
¢F: MAX 74.5 kHz
AVE 69.6 kHz
Pm: 5.4 dBr ( 3.45)

20
Pilot-to-RDS phase difference
The 57 kHz for RDS subcarrier was chosen for being the third harmonic of the pilot tone for FM stereo, so it would
not cause interference or intermodulation with it. The amount by which RDS subcarrier and third harmonic of pilot
tone are out of step with each other can be expressed in degrees from 0° to 360°. Since the RDS signal is based on
its carrier phase alternating, the full angle reduces to straight angle and we can equate 90 degrees = -90 degrees.
During stereo broadcasts the RDS subcarrier will be locked either in phase (0 degrees)
or in quadrature (90 or -90 degrees) to the third harmonic of the pilot-tone. The
tolerance on this phase angle is ±10 degrees.
A value out of the specification is however not to be considered as a critical failure, i.e. there's no need to solve that
situation promptly.
If no value is given, the RDS and pilot are not in stable phase relation. In that case check if pilot or MPX signal is
connected to the RDS encoder input and external synchronization is enabled. Follow the instructions supplied with
your transmission equipment.
Set the phase difference when the transmission equipment works under common conditions and after enough time of
warm-up. The phase difference depends a little on the transmission equipment temperature and other physical
quantities.
Modulation power (MPX power, Pm)
The modulation power is a relative power of the MPX signal averaged over 60 seconds according to the formula:
modulation power = 10 log {(2/60 s) (f(t)/19 kHz)2dt} [dBr]
0 dBr corresponds to an average power of a signal equivalent to the power of a sinusoidal tone which causes a peak
deviation of 19 kHz.
Intensive audio dynamics compression as well as increasing overall peak deviation causes the modulation power to
rise.
The modulation power limit, if defined in your country, is usually 0 dBr or +3 dBr.
Please refer to your local communications authority for more information.
Since the modulation power is averaged over last 60 seconds, first value can appear after one minute from power-up
or tuning to a new frequency. However the analyzer reduces this time using estimation method during first minute
so it shows an estimated value of the modulation power almost immediately, saving considerably the operator's time
but still keeping compliance with standards. This is indicated by the 'Pm:' symbol blinking. Relevancy and accuracy
of the modulation power value increases with each second. After the first minute elapses, the value is accurate from
this moment and the 'Pm:' symbol stops blinking.
106.10 MHz §££££¤ ¨1
¢F: MAX 74.5 kHz
AVE 69.6 kHz
Pm: 5.4 dBr ( 3.45)
106.10 MHz §££££¤ ¨3
¢F: Pilot 6.8 kHz
RDS 3.4 kHz
Phase Diff.: 0 deg