ICAO ACP WG/F WP13
International Civil Aviation Organization
INFORMATION PAPER
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
FIFTEENTH MEETING OF WORKING GROUP F
Nairobi, Kenya, 19 – 25 September 2007
Agenda Item 7: Any Other Business
DIGITAL BROADCASTING SYSTEMS IN THE 87.5-108 MHZ BAND
Presented by
Felix Butsch, Germany
Prepared by
Felix Butsch, Helmut Günzel, DFS Deutsche Flugsicherung GmbH
Thomas Hasenpusch, German Federal Network Agency, BNetzA
SUMMARY
This working paper raises the awareness that the introduction of new, digitally or partly digitally
modulated broadcast signals in the band 87.5 to 108 MHz is going on. While the compatibility of
analogue FM-modulated broadcast signals is this band with aeronautical systems above 108 MHz is
already well specified ITU-R Recommendations SM.1009-1 and IS.1140, there is a need to amend
these recommendations to cover also the new broadcast signal types.
As one step in the direction of these new amendments, this WP presents various digital modulation
types currently being tested in Germany as well as first results of laboratory measurements of the
interference impact of such signals to the ILS- and VOR-components of one combined ILS/VOR
receiver type which is common in commercial air transport.
Page 1 of 19
1
INTRODUCTION
The compatibility between analogue sound-broadcasting services in the band 87 to 108 MHz and
Aeronautical Services in the band 108 to 137 MHz is specified in ITU-R Recommendation SM.1009-1.
Pertaining susceptibility test procedures are contained in ITU-R Recommendation IS.1140.
Recently the German broadcasting community, as well as broadcasting operators in other countries started
the preparation of broadcasting digitally modulated signals in the band 87.5-108 MHz. Therefore,
amendments of the aforementioned ITU-R Recommendations in order to cover the new broadcast signal
types are deemed necessary.
This WP presents various digital modulation types currently being tested in Germany as well as first results
of laboratory measurements of the impact of such signals to the ILS- and VOR-components of one combined
ILS/VOR receiver type (Collins ILS/VOR/MB-900), which is common in commercial air transport.
1.2
General considerations
VHF Band II covers 87.5 - 108 MHz and is generally used for FM broadcasting. The current channel spacing
is 100 kHz in ITU Region 1 (Europe) and 200 kHz in ITU Region 2 (North and South America). The
narrower channel spacing in Europe makes it harder to make broadband modulation types compliant with
existing services in the band (e.g. FM) and adjacent bands (e.g. aeronautical services). The probability that a
new digital broadcasting modulation type will be successfully implemented is higher, if the spectrum of the
considered modulation fits into the current channels spacing scheme. To facilitate between the transition
between the classic analogue FM broadcast service and new digital broadcast signal, several – in a strict
sense – not pure digital, but rather “hybrid” signals are proposed. Such signals consist of a combination of the
classic FM-broadcast signal and an “In-band on channel” (IBOC) digital signal.
The following three digital modulation types are currently under consideration in Germany:

DRM+ / DRM120

HD Radio

FMeXtra
1.3
DRM+ and DRM120
DRM+ and DRM120 are modulation techniques, similar to the Digital Radio Mondial (DRM) modulation
applied in the HF-band, however with a higher bandwidth. They use Orthogonal Frequency Division
Multiplexing (OFDM) with either a Quadrature Amplitude Modulation (QAM) or a Quadrature Phase Shift
Keying Modulation (QPSK). The various options for the sub-carrier modulations are possible (Tab. 1, Ref. 6,
Ref. 8).
Tab. 1: Characteristics of various DRM+ modulation types (Ref. 8).
Modulation type (main carrier)
COFDM
Modulation (data carriers)
4-QAM
16-QAM
16 QAM
64-QAM
Number of sub-carriers
266
132
213
66
Sub-carrier spacing
375 Hz
750 Hz
444 Hz
1500 Hz
Crest factor
tbd
tbd
9 dB
tbd
Note (if applicable)
Modulation type which
was used for the German
interference measurements (Ref. 6)
Page 2
Fortunately the proposed emission masks Fig. 1 for the various DRM+ modulation types (Ref. 8) are all
below the standardised emission mask for FM-broadcast (European Standard, ETSI EN 302 018-1, Ref. 4).
Therefore it is likely, but has still to be proven that the impact to aeronautical services operating in the
adjacent band is not more severe than the impact of the classic FM broadcast.
0
-10
-20
P/Pmax [dB]
-30
-40
-50
-60
-70
-80
-90
-400
-300
-200
-100
0
100
200
300
400
Frequency offset [kHz]
FM
4-QAM
16-QAM
64-QAM
Fig. 1: Standardised emission masks for FM and proposed emission masks for various DRM+ modulation types
The characteristics of the DRM120 modulation are given in Tab. 2 (Ref. 9 and Ref. 6).
Tab. 2: Characteristics of the considered DRM120 modulation type (Ref. 6, Ref. 9)
Modulation
COFDM, 16QAM, QPSK or 64-QAM
Number of sub-carriers
111
sub-carrier spacing
857 Hz
Channel Spacing
100 kHz
Crest factor
11.5 dB
As can be seen in Fig. 2 (Ref. 6), also the proposed emission masks for the various DRM120 (Ref. 6, Fig. 2)
is below the standardised emission mask for FM-broadcast (European Standard, ETSI EN 302 018-1, Ref. 4).
Page 3
Fig. 2: Proposed emission mask for DRM120 in comparison with the ETSI FM emissions mask
1.4
HD Radio
HD Radio, (“hybrid digital”) is a brand-name of the iBiquity Digital Corporation, a company, which
developed this signal type. This hybrid signal type allows transmitting simultaneously FM, as well as digital
data streams (e.g. high quality audio and a variety of text-based services). The Federal Communications
Commission selected HD Radio as the standard for AM and FM broadcasting in the United States. According
to Ref. 10 as of July 25, 2007, more than 1360 stations are broadcasting HD Radio signals in the USA.
A HD Radio signal consists of the classic analogue FM broadcast spectrum with two additional OFDM
blocks approximately between +/- 130 kHz (exactly 129.4 kHz) and +/- 200 kHz (exactly 198.4 kHz) (Fig. 3,
Ref. 6, Fig. 4). Further detailed parameters of this signal type are given in Tab. 3.
Tab. 3: Characteristics of the considered HD-Radio modulation type (Ref. 6)
Modulation
COFDM, QPSK
Number of sub-carriers
2 x 191
sub-carrier spacing
363 Hz
Bandwidth
2 x 69 kHz
Crest factor
8.5 dB
Page 4
Fig. 3: Spectral components of the HD radio hybrid mode signal (Ref. 6)
Note: DSB denotes the term “Digital Sideband Block”
60
130
200
FM-Signal
Power Spectral Density [dBm/kHz]
70
80
90
digital
100
110
120
300
200
100
0
100
200
300
Frequency Offset [kHz]
Fig. 4: Measured Power Spectral Density of HD-Radio signal
In contrast to for the various DRM modulation types, which are all below the standardised emission mask for
FM-broadcast, HD-Radio does not comply with this mask (data-sub-bands depicted with red dash-dotted
lines in Fig. 5 exceed blue line representing the applicable mask for FM broadcast).
Page 5
Fig. 5: Comparison of HD-Radio spectrum with various emission masks
1.5
FMeXtra
FMeXtra is an “in-band on-channel” (IBOC) digital radio broadcasting technology created by the company
Digital Radio Express. Unlike the HD Radio system, it uses any FM radio station's existing equipment and
transmitter plant to transmit digital audio data on sub-carriers instead of sidebands (Ref. 10). The gap
between 62 and 99 kHz in the base-band spectrum of a classic FM signal is used for a digital signal with a
data rate of 40 to 48 kBit/sec (Fig. 6, Ref. 7).
Fig. 6: Baseband spectrum of classic FM-Stereo signal and digital data sub-band of FMeXtra (Ref. 7)
In contrast to DRM+/DRM120 and HD-Radio, for FMeXtra, the whole baseband including the digital subchannel between 62 and 99 kHz is frequency-modulated to the RF-carrier. This helps to make sure, that the
RF-spectrum does not deviate very much from the spectrum a pure FM radio signal (Fig. 7, Ref. 7).
Page 6
Fig. 7: Comparison of spectra of pure FM (blue), FM with RDS (black), FM with RDS and FMeXtra (green)
Notes: RDS denotes the Radio Data Signal.
For the lab-test, a coloured noise according to ITU-R IS.1140 (Ref. 2) was used to generate the FM
signal.
2
Susceptibility measurements
In August 2007, the German Air Traffic Service Provider DFS carried out measurements of the impact of
aforementioned new digital broadcast signal to a combined ILS/VOR receiver (Collins ILS/VOR/MB-900) in
collaboration with the following organisations:
• German Federal Network Agency for Electricity, Gas, Telecommunications, Post and Railway, BNetzA,
• University of Applied Science (FH) Kaiserslautern, Germany
• Technical University of Kaiserslautern, Germany
• University of Hannover, Germany
Notes: The detailed description of the measurement setup and the results are presented in Ref. 6 and Ref. 7.
These reference documents can be obtained from the authors of this working paper on request by Email.
2.2
Measurement procedure
For VOR and ILS, ITU-R IS.1140 (Ref. 2) specifies a set of desired signal power levels at which the
protection ratio (i.e. the necessary difference between desired and undesired signal level) has to be measured
to check the linearity of the aeronautical receiver under test. The minimum desired signal power levels are
-79 dBm for VOR and -86 dBm for ILS. The lowest VOR frequency is 108 MHz (100 kHz above the highest
FM broadcast frequency of 107.9 MHz) and the lowest ILS frequency is 108.1 MHz (200 kHz above the
highest FM broadcast frequency of 107.9 MHz).
For the test, starting from this minimum occurring frequency offset the frequency of the interference signals
signal was shifted towards lower frequencies, in this way increasing the offset to the desired signal (VOR
tuned to 108 MHz and, ILS, tuned to 108.1 MHz).
Page 7
The desired signal and interference signal/s was/were fed into the radio navigation receiver (Collins
ILS/VOR/MB-900) the test-setup specified in ITU-R Recommendations SM.1009-1 and IS.1140.
The VHF FM broadcast interference thresholds for analogue aeronautical radionavigation receivers are
defined in ITU-R Recommendations SM.1009-1. According to this recommendation, the maximum allowable
error in the course display for VOR is 0.5°. For the ILS (respectively the ILS component of the tested
combined VOR/ILS receiver), the maximum tolerable course error is defined as 7.5 µA in the analogue
course indicator display measured at a deflection 90 µA, corresponding to 0.093 DDM. (For comparison, the
full scale deflection is 150 µA).
Most modern receivers, like the type used here, output data messages with course information via an
ARINC-429 bus to a multifunctional display. To have similar failure criteria than for analogue receivers,
ITU-R Recommendation IS.1140 indicates a statistical method for determining the maximum allowable
course error.
The statistical method for determining the maximum on-course errors of ILS localizer receivers based on a
95% probability and limits centring error to 5% of the standard deflection. Receiver compatibility is analysed
using a similar technique. Five per cent of the standard localizer deflection is given by (0.05  0.093 DDM)
or 4.5  (0.00465 DDM) and a 95% probability may be achieved by utilizing plus or minus two standard
deviations, 2, of the normal distribution.
An equivalent deflection of 4.5 A for the VOR is 0.3 change in bearing indication.
The measurements are conducted by collecting a number of output-deflection samples from the ARINC-429
bus) and then computing the mean and standard deviation of the data. The standard deviation for the baseline
case (no interfering signals) is multiplied by two to get the baseline 2 value and 4.5  (0.00465 DDM) is
added to the baseline 2 value to get an upper limit for the 2 value with interfering signals present. The
interference threshold is defined as the point where the 2 value exceeds the upper limit.
2.3
Out-of-Band (OOB) emission measurements
Out-of-Band emissions from VHF broadcast signals in the band below 108 MHz can cause interference into
the Aeronautical Radio Navigation band above to 108 MHz (called “A1 interference” in ITU-R Recommendations SM.1009-1). This is illustrated for the case of a DRM120 signal operated in the highest VHF Band-II
broadcast channel at 107.9 MHz in Fig. 8 and Fig. 9.
20
107.9
108.0
Power Spectral Density [dBm/kHz]
40
DRM120
60
VOR
80
100
120
107.7
107.8
107.9
108
108.1
108.2
108.3
Frequency [M Hz]
Fig. 8: Out-of-band emissions by a DRM120 signal into the lowest VOR channel
Page 8
20
107.9
108.1
DRM120
Power Spectral Density [dBm/kHz]
40
60
ILS
80
100
120
107.7
107.8
107.9
108
108.1
108.2
108.3
Frequency [M Hz]
Fig. 9: Out-of-band emissions by a DRM120 signal into the lowest ILS channel
For the sake of briefness, in this WP only the results of the determination of the necessary protection ratio to
avoid intolerable VOR and ILS course-deflection due to by the various above mentioned new digital/hybrid
broadcasting signal types are presented. It is obvious, and was also confirmed by the measurements that the
appearance of the flag requires higher interference power level than to reach the interference criterion
expressed as maximum course-deflection.
2.3.1
Results of the DRM120 OOB-emission measurements
Fig. 10 (Ref. 6) depicts the measured necessary protection ratio to avoid intolerable VOR course-deflection
due to DRM120 interference compared with the case of interference due to pure FM-broadcast interference.
Fig. 10: Necessary protection ratio to avoid intolerable VOR course-deflection due to DRM120 interference
Page 9
It can be seen from Fig. 10, that the FM broadcast has a stronger impact for offset up to 200 kHz (below
108.2 MHz, where the DRM120 signals has as stronger impact for offsets between 200 and 100 kHz.
Variation of the carrier frequency of the DRM120 signal in steps of 20 kHz did not have any additional
effect. Therefore it can be concluded that the various sub-carriers of the digital signal do not have an impact
that is different to the impact of noise (Ref. 6).
Fig. 11: Necessary protection ratio to avoid intolerable ILS course-deflection due to DRM120 interference
Fig. 11 (Ref. 6) depicts the measured necessary protection ratio to avoid intolerable ILS course-deflection
due to DRM120 interference compared with the case of interference due to pure FM-broadcast interference.
The interference impact of DRM120 on ILS seems to be higher than that of a pure FM broadcast signal (Fig.
11). Also for the case of ILS that the various sub-carriers of the digital signal did not have an impact that is
different to the impact of noise (Ref. 6).
2.3.2
Results of the DRM+ OOB-emission measurements
Fig. 12 (Ref. 6) depicts the measured necessary protection ratio to avoid intolerable VOR course-deflection
due to DRM+ interference compared with the case of interference due to pure FM-broadcast interference and
DRM120. It can be seen, that apart from offsets smaller than 200 kHz, the interference impact of DRM+ to
the VOR reception is roughly the same as from DRM120. This is the result of the slightly different shape of
sidebands of the signals. This indicates that the interference potential of DRM modulation is in general nearly
independent from signal parameters like carrier spacing and crest factor.
Page 10
Fig. 12: Necessary protection ratio to avoid intolerable VOR course-deflection due to DRM+ interference
Fig. 13 (Ref. 6) depicts the measured necessary protection ratio to avoid intolerable ILS course-deflection
due to DRM+ interference compared with the case of interference due to pure FM-broadcast interference and
DRM120. It can be seen in Fig. 13, that the interference impact of DRM+ to the ILS reception is roughly the
same as from DRM120. This is the result of the slightly different shape of sidebands of the signals. This
indicates again, that the interference potential of DRM modulation to ILS/VOR is in general nearly independent from signal parameters like carrier spacing and crest factor.
Fig. 13: Necessary protection ratio to avoid intolerable ILS course-deflection due to DRM+ interference
Page 11
2.3.3
Results of the HD-Radio OOB-emission measurements
One of the most interesting cases is, when a HD-Radio signal is broadcast at the highest FM-broadcast
channels at 107.8 MHz and a VOR is operated on the lowest VOR-channel, at 108.0 MHz (Fig. 14).
60
HD-Radio
107.8
VOR
108.0
Power Spectral Density [dBm/kHz]
70
80
90
100
110
120
107.5
107.6
107.7
107.8
107.9
108
108.1
Frequency [M Hz]
Fig. 14: Emissions of an HD-Radio signal into a VOR-channel
Fig. 15 (Ref. 6) presents the results of the determination of the interference impact by HD-Radio on a
VOR receiver, in comparison to the impact by pure FM broadcast. It can be seen from Fig. 15, that the
impact of HD-Radio on a VOR receiver is very much stronger than the impact of pure FM broadcast. It
should be noted that for the HD-Radio frequencies 107.9 and 107.8 the lowest VOR-frequency (108 MHz) is
still inside the normal spectrum range of the HD-Radio emissions (Ref. 6). It can be recognized, that
interference impact from the upper digital sideband is noticeable up to a frequency-offset of 500 kHz.
To ensure compatibility with the VOR-reception, HD-Radio transmitters should not be operated above
107.7 MHz, otherwise the on-channel emissions of the HD-Radio signals fall into the VOR-band!
Fig. 15: Necessary protection ratio for VOR against interference due to HD-Radio
Page 12
Fig. 16 (Ref. 6) depicts the results of the determination of the interference impact by HD-Radio on an ILS
receiver, in comparison to the impact by pure FM broadcast. It can be seen from Fig. 16, that the impact of
HD-Radio on an ILS receiver is very much stronger than the impact of pure FM broadcast. It should be noted
that for the HD-Radio frequencies 107.9 and 107.8 the lowest ILS-frequency (108.1 MHz) is still inside the
normal spectrum range of the HD-Radio emissions (Ref. 6). It can be recognized, that interference impact
from the upper digital sideband is noticeable up to a frequency-offset of 300 kHz.
To ensure compatibility with the ILS-reception, HD-Radio transmitters should not be operated above
107.8 MHz, otherwise the on-channel emissions of the HD-Radio signals fall into the ILS-band!
Fig. 16: Necessary protection ratio for ILS against interference due to HD-Radio
2.3.4
Results of the FMeXtra OOB-emission measurements
Fig. 17 depicts the obtained measured necessary protection ratio for a VOR receiver (desired signal power
-79 dBm) interfered by pure FM broadcast and FMeXtra signal (Ref. 7).
Fig. 17: Measured necessary protection ratio for VOR interfered by pure FM broadcast and FMeXtra signal
Page 13
Fig. 18 depicts the obtained measured necessary protection ratio for an ILS receiver (desired signal power
-86 dBm) interfered by pure FM broadcast and FMeXtra signal (Ref. 7).
It can be seen from Fig. 17 that the impact of the FMeXtra signal to the VOR reception is slightly higher than
pure FM for frequency-offsets between 150 and 500 kHz. From Fig. 18 one can conclude that the
susceptibility of the tested ILS receiver against interference by FMeXtra is nearly as the impact of a pure
FM-signal.
Fig. 18: Measured necessary protection ratio for ILS interfered by pure FM broadcast and FMeXtra signal
2.4
Intermodulation measurements
High-level emissions from broadcast signals in the band below 108 MHz can overload the input stage of an
aeronautical ILS- or VOR-receiver. In this way generated intermodulation products interfering with the
reception of the desired navigation signal. This mechanism is called B1-interference. (For comparison, the
desensitisation of the ILS- or VOR-receiver due to an overload by a broadcast signal is called B2interference. This intermodulation type was not measured).
To asses the impact of the new digital; respective hybrid VHF broadcast signal, the susceptibility of an
ILS/VOR receiver to the third order intermodulation product of such a signal with two CW-signals with
suitable frequencies according to ITU-R IS.1009 (Ref. 1) has been carried out.
In general, the third order intermodulation frequency of three signals can be determined as follows:
fintermod = f1 + f2 - f3
The following frequency combinations (from the various combinations recommended in ITU-R IS.1009)
were used for the intermodulation measurements:

Interference to the VOR-channels 108 and 108.2 MHz:
107.9 + 107.5 – 107.4 = 108 MHz (used for tests with DRM120, DRM+ and FMeXtra)
107.9 + 107.7 – 107.5 = 108.2 MHz (*used for B1 tests with HD-Radio)

Interference to the ILS-channel 108.1 MHz
107.9 + 107.5 – 107.3 = 108.1 MHz (used for B1 tests with DRM120, DRM+ and FMeXtra)
107.5 + 106.5 – 105.9 = 108.1 MHz (**used for B1 tests with HD-Radio)
Page 14
The f1 signal was frequency modulated with coloured noise according to ITU-R IS.1009. Its power was
set to -2 dBm. The f2 and f3 signals were pure CW-signals each with a power of -2 dBm. The power of the
desired signals was -79 dBm for VOR and -86 dBm for ILS (minimum desired signal levels).
The B1 intermodulation interference test is illustrated by Fig. 19. It shows the spectra of the three generated
interference signals (CW at 106.5 MHz and 107.5 MHz and HD-Radio signal at 105.9 MHz) which cause an
intermodulation product at the lowest ILS channel at 108.1 MHz.
*Note: For the B1 intermodulation tests of the VOR receiver with HD-Radio signals as f1 interference signal,
the frequency combinations, which were used for the same test with the other signals (DRM120, DRM+ and
FMeXtra), could not be used. A different frequency combination (107.9 + 107.7 – 107.5 = 108.2 MHz) with
an intermodulation product a 108.2 MHz centre rather than a 108.0 MHz (lowest VOR channel) had to be
used, to avoid strong OOB-interference into the VOR channel.
**Note: For the B1 intermodulation tests of the ILS receiver with HD-Radio signals as f1 interference signal,
the frequency combinations, which were used for the same test with the other signals (DRM120, DRM+ and
FMeXtra), could not be used. A different frequency combination (107.5 + 106.5 – 105.9 = 108.1 MHz), with
a centre frequency of 107.5 rather than 107.9 MHz (400 kHz lower) had to be used for the digital
interference signal, to avoid strong OOB-interference into the ILS channel 102.1 (like in Fig. 14).
0
105.9
106.5
HD-Radio
107.5
Power Spectral Density [dBm/kHz]
20
40
Intermod
108.1
60
80
100
104.5
105
105.5
106
106.5
107
107.5
108
108.5
Frequency [M Hz]
Fig. 19: One HD-radio and two CW signals causing interference to an ILS channel by intermodulation
2.4.1
Results of the B1 intermodulation measurements
Tab. 4 presents the results of the measurement of the necessary protection ratio against B1 intermodulation to
course information due to DRM120 in comparison with the FM modulation. Determined protection ratio for a
VOR receiver against interference by a DRM120 signal is -71 dB, i.e. 7 dB less than, what is necessary for
the protection against interference by a pure FM signal. This means that the B1-intermodulation interference
potential of a DRM120 signal is lower than that of a FM signal. This is due to the fact that the power of a
DRM120 signal is evenly distributed over a higher bandwidth than in the case of FM.
Tab. 4: Necessary protection ratio against B1 intermodulation to course information due to DRM120
DRM120
FM
Determined protection ratio for a VOR receiver (108.2 MHz, -79 dBm)
-71 dB
-64 dB
Determined protection ratio for an ILS receiver (108.1 MHz, -86 dBm)
-77 dB
-73 dB
Page 15
Tab. 5 presents the results of the measurement of the necessary protection ratio against B1 intermodulation to
course information due to DRM+ in comparison with the FM modulation. Also in this case it turns out that
the B1-intermodulation interference potential of a DRM+ signal is lower than that of a FM signal.
Tab. 5: Necessary protection ratio against B1 intermodulation to course information due to DRM+
DRM+
FM
Determined protection ratio for a VOR receiver (108.2 MHz, -79 dBm)
-70 dB
-64 dB
Determined protection ratio for an ILS receiver (108.1 MHz, -86 dBm)
-75 dB
-73 dB
Tab. 6 presents the results of the measurement of the necessary protection ratio against B1 intermodulation to
course information due to HD-Radio signal in comparison with the FM modulation. The B1-intermodulation
interference potential of a HD-Radio signal is only lower than that of a FM signal, different frequency
combinations were used to avoid strong OOB-emissions into the tested VOR and ILS channels
As aforementioned the combination was (107.9 + 107.7 – 107.5 = 108.2 MHz) for the VOR test
and (107.5 + 106.5 – 105.9 = 108.1 MHz) for the ILS test.
Tab. 6: Necessary protection ratio against B1 intermodulation to course information due to HD-Radio
HD-Radio
FM
Determined protection ratio for a VOR receiver (108.2 MHz, -79 dBm)
-67
-64 dB
Determined protection ratio for an ILS receiver (108.1 MHz, -86 dBm)
HD-Radio
within ILSchannel
-73 dB
The protection ratios obtained by the B1-intermodulation measurements with a pure FM broadcast and a
FMeXtra signal, combined with two suitable CW signals (aforementioned) are given in Tab. 7. The
B1-intermodulation interference potential of a FMeXtra signal is comparable (within the measurement
uncertainty) to that of a FM signal.
Tab. 7: Necessary protection ratio against B1 intermodulation to course information due to FMeXtra
FM
FMeXtra
Determined protection ratio for a VOR receiver (108.2 MHz, -79 dBm)
-64 dB
-64 dB
Determined protection ratio for an ILS receiver (108.1 MHz, -86 dBm)
-71 dB
-70 dB
Fig. 20 and Fig. 21 allow a comparison of obtained B1 intermodulation protection ratios for the case of VOR
(Fig. 20) and ILS (Fig. 21). DRM120 and DRM+ signals have nearly equal or even less interference potential
to the lower VOR and ILS channels. This is also true for HD-Radio signals, as long as the HD-Radio
transmitter does not use a channel above 107.7 MHz. FMeXtra has a similar interference impact to the tested
ILS- and VOR-receivers than pure FM. This is not surprising, since the impact of the FMeXtra modulation on
the RF-spectrum is almost negligible (Ref. 6).
Page 16
-80
FM
FMeXtra
HD-Radio
-65
DRM+
-70
DRM120
Protection Ratio [dB]
-75
-60
Fig. 20. Comparison of measured B1 intermodulation measurements with a VOR receiver
-80
FM
FMeXtra
HD-Radio
-65
DRM+
-70
DRM120
Protection Ratio [dB]
-75
-60
Fig. 21. Comparison of measured B1 intermodulation measurements with an ILS receiver
3
SUMARRY
The introduction of new, digitally or partly digitally modulated broadcast signals in the band 87.5 to
108 MHz is going on. While the compatibility of analogue FM-modulated broadcast signals is this band with
aeronautical systems above 108 MHz is already well specified ITU-R Recommendations SM.1009-1 and
IS.1140, there is a need to amend these recommendations to cover also the new broadcast signal types.
As one step in the direction of these new amendments, this WP presents various digital modulation types
currently being tested in Germany as well as first results of laboratory measurements of the impact of such
signals to ILS and VOR receivers.
The measurement results show, that DRM120 and DRM+ signals have nearly equal or even less interference
potential to the lower VOR and ILS channels (channels in the lower part of the band above 108 MHz) than a
standard FM broadcast signal. FMeXtra has no significantly higher interference impact to the tested ILS- and
VOR-receivers. The interference potential of HD-Radio to the lower VOR and ILS channels is only
manageable, as long as the centre frequency of the HD is not higher than above 107.7 MHz. Otherwise
considerable OOB-emissions will occur in the VOR/ILS-band due to the high bandwidth of the HD-Radio
signal.
Page 17
Caveat!
For the susceptibility measurements described in this report, only one single certified receiver type (Collins
ILS/VOR/MB-900) has been used. Without testing a considerable number of other aeronautical radionavigation receiver types, general requirements for the protection of ILS- and VOR receiver against the
impact of new digital respective hybrid VHF broadcast signals in the band 87.5 to 108 MHz can not be
derived. At least the comparison of the interference potential of the new, digital/hybrid VHF broadcast signal
in comparison with a standard FM broadcast signal can be drawn.
4
RECOMMENDATIONS TO THE GROUP / GROUP MEMBERS

Be aware of the introduction of new digital; respective hybrid VHF broadcast signals in the band 87.5 to
108 MHz in your country.

Carry out your own measurements of the susceptibility of ILS and VOR receivers, with as many receiver
types as possible.

Contribute to the drafting of requirements for the protection of ILS- and VOR receiver against the impact
of new digital; respective hybrid VHF broadcast signals in the band 87.5 to 108 MHz.

Contribute to the drafting of the necessary amendments of ITU-R Recommendations SM.1009-1 and
IS.1140 to cover these new protection criteria as well as the pertaining measurement procedures.
5
REFERENCE DOCUMENTS
Ref. 1: ITU-R Recommendation SM.1009-1: “Compatibility between the Sound-Broadcasting Service in the
band of about 87-108 MHz and the Aeronautical Services in the band 108-137 MHz”
Ref. 2: ITU-R Recommendation IS.1140: “Test procedures for measuring aeronautical receiver
characteristics used for determining compatibility between Sound-Broadcasting services in the band of about
87 – 108 MHz and the Aeronautical Services in the band 108 to 118 MHz”
Ref. 3: ITU-R Recommendation BS.641: “Determination of radio-frequency protection ratios for frequencymodulated sound broadcasting“
Ref. 4: ETSI, EN302 418-1, “Transmitting equipment for the Frequency Modulated (FM) sound broadcasting
service; Part 1: Technical characteristics and test methods”, European Telecommunication Standardisation
Institute, March 2006
Ref. 5: “Digitizing the FM band, FMeXtra Technology Overview”, presentation, D. D. Kumar, Digital Radio
Express Inc.
Ref. 6: “DRM120, DRM+ and HD Radio interfering with FM Broadcast, Narrowband FM (BOS) and
Aeronautical Radionavigation”, T. Hasenpusch, R. Effinger, German Federal Network Agency for
Electricity, Gas, Telecommunications, Post and Railway (BNetzA), Munich, Germany, F. Schad, University
of Applied Science (FH) Kaiserslautern, Germany, September 2007
Ref. 7: “FMeXtra interfering with Aeronautical Radionavigation”, T. Hasenpusch, R. Effinger, German
Federal Network Agency for Electricity, Gas, Telecommunications, Post and Railway (BNetzA), Munich,
Germany, F. Schad, University of Applied Science (FH) Kaiserslautern, Germany, September 2007
Ref. 8: “Abschlussbericht zur Untersuchung zur Implementierung eines digitalen Übertragungssystems auf
OFDM-Basis im UKW-Frequenzbereich”, F. Bernhardt, Fachhochschule Kaiserslautern, Germany, Nov.
2005
Ref. 9: “Verträglichkeitsuntersuchungen von OFDM-basierten Rundfunkformaten im UKW-FM-Band”, F.
Schad et. al., University of Applied Science (FH), Kaiserslautern, Germany, presentation at the “Workshop
digitaler Rundfunk”, 13th Sept. 2007
Page 18
Ref. 10: http://en.wikipedia.org/
6
ACKNOWLEDGEMENTS
The authors of this information paper express their gratitude for the contributions to the following people:

Mr. Thomas Hasenpusch, Mr. Roland Effinger, German Federal Network Agency for Electricity,
Gas, Telecommunications, Post and Railway (BNetzA), Munich, Germany

Mr. Felix Schad, University of Applied Science (FH) Kaiserslautern, Germany

Mr. M. Rosenbaum, Technical University of Kaiserslautern, Germany

Mr. Albert Waal, Mrs. Fiederike Meyer, University of Hannover, Germany
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