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Radio Astronomy Service · 1 of 16
The Radio Astronomy Service
Listening to the universe
Protected by ITU rules
A complete overview
Radio Astronomy Service · 2 of 16
What is RAS?
Astronomy from radio waves
Signals of cosmic origin
A receive-only service
Defined: RR No. 1.58
Radio Astronomy Service · 3 of 16
Why RAS is different
It only listens
Cannot transmit around interference
Extremely faint signals
Harmed through side lobes
Radio Astronomy Service · 4 of 16
How RAS is protected
Frequency allocations
Interference criteria
Recording in the MIFR
Radio quiet zones
Radio Astronomy Service · 5 of 16
The key rules
No. 11.12 — notify frequencies
No. 4.4 — unallocated bands
No. 11.31 — examination
Appendix 4 — required data
Radio Astronomy Service · 6 of 16
How to file
1. Capture in SpaceCap
2. Submit via e-Submission
3. Receivability examination
4. Publication in Part I-S
5. Registration in MIFR
Radio Astronomy Service · 7 of 16
What you must provide
Station name and location
Antenna characteristics
Observed band and bandwidth
Receiver noise temperature
Radio Astronomy Service · 8 of 16
Appendix 4 items
The formal data list
23 required items
Almost all mandatory
Radio Astronomy Service · 9 of 16
AP4 — general characteristics
Station name and location
Antenna site coordinates
Notifying administration
Date reception begins
Beam elevation and azimuth
Radio Astronomy Service · 10 of 16
AP4 — antenna (item B.6)
Antenna type
Antenna dimensions
Effective area
Radio Astronomy Service · 11 of 16
AP4 — frequency and observations
Centre of observed band
Observed bandwidth
Class of station
Receiver noise temperature
Observation class and type
Radio Astronomy Service · 12 of 16
Outside an allocated band?
Request No. 4.4
Recorded for information only
No protection given
Radio Astronomy Service · 13 of 16
Smart filing tip
Split large bands
Match each allocation
Keep more protection
Radio Astronomy Service · 14 of 16
The protection toolchain
RA.314 — which frequencies
RA.769 — harmful level
RA.1513 — how often
RA.1631 — antenna pattern
RA.611 — spurious emissions
Radio Astronomy Service · 15 of 16
Good to know
Filing is free
Administrations submit notices
BR examines everything
Radio Astronomy Service · 16 of 16
Questions?
brmail@itu.int
spacehelp@itu.int
itu.int/wrs-24
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What is the Radio Astronomy Service?
Radio astronomy is astronomy based on the reception of radio waves of cosmic origin (RR No. 1.13). The radio astronomy service (RAS) is the radiocommunication service involving its use (RR No. 1.58). A radio astronomy station is a station providing that service.
RAS is fundamentally different from other radio services in three ways that shape everything about how it is regulated:
PassiveRAS only receives. It cannot transmit its way around interference, so protection depends entirely on other services limiting their emissions.
Extremely sensitiveRadio telescopes detect signals far weaker than any communications receiver — so emissions harmless to other services can swamp them.
Side-lobe exposedInterference is almost always received through the antenna side lobes, not the main beam — which drives the 0 dBi reference used throughout the criteria.
Because it receives only, RAS is protected mainly by (a) frequency allocations in the Table of Frequency Allocations, (b) interference criteria (the RA-series Recommendations), and (c) recording observation frequencies in the Master International Frequency Register (MIFR) so they gain regulatory protection. Notifications of RAS stations have risen over the past decade, reflecting growing awareness of the value of formal registration.
Regulatory foundationsThe Radio Regulations (RR) provisions that govern RAS
Provision
What it does
RR No. 1.13 / 1.58
Definitions: radio astronomy is astronomy based on reception of radio waves of cosmic origin; the radio astronomy service (RAS) is a service involving its use.
RR No. 11.12
Any frequency to be used for reception by a radio astronomy station may be notified for inclusion in the Master International Frequency Register (MIFR).
RR No. 29.5 §2
Locations of RAS stations to be protected and their observation frequencies are notified to the Bureau under No. 11.12 and published under No. 20.16.
RR No. 4.4
Must be requested if the RAS station operates in a band not allocated to RAS in the Table of Frequency Allocations (Article 5). Recording is then for information only, with no protection.
RR No. 11.31
Basis of the regulatory examination: conformity with the Table of Frequency Allocations and other provisions.
RR No. 8.4 / Table 13B
Assignments overlapping unallocated bands get an unfavourable finding but may be recorded under No. 8.4 with No. 4.4 conditions; overlaps with a lower-category allocation are recorded at that lower category (symbols R/S).
RR Appendix 4
Specifies the mandatory data items captured in the notification notice (the SNS file).
Resolution 55 (rev. WRC-19)
Governs as-received publication of submitted notices.
Council Decision 482
Notifications of radio astronomy stations are exempt from the cost-recovery fee.
Key idea. Recording an observation frequency in the MIFR is what confers protection. The protection an RAS station actually receives matches the allocation status of the band it observes in — primary, secondary, or none.
How to submit a filing to the ITUNotification of a radio astronomy station — the five-step process
Under RR No. 11.12, any frequency used for reception by a radio astronomy station may be notified for inclusion in the MIFR. An administration (not an individual observatory) submits on behalf of its stations.
1 · Submission
The administration captures the station's characteristics in SNS data format using BR's SpaceCap software (select notice type "RAST"), then submits the SNS file — plus any attachments — to BR through the e-Submission system (a user account is required). BR publishes the notice as-received.
2 · Receivability examination
BR checks the notice for completeness and correctness against Appendix 4 and the Rules of Procedure. If mandatory data are missing or incorrect, the notice is returned; BR may request clarifications, giving the administration 30 days to respond.
3 · Publication of Part I-S
Once receivability is confirmed, the notice is published in Part I-S of the BR IFIC within no more than two months. This publication is the formal acknowledgement of receipt (No. 11.28).
4 · Regulatory examination
BR examines the notice under No. 11.31 and the Rules of Procedure to formulate findings — checking the observation band against the Table of Frequency Allocations.
5 · Registration or return
Favourable findings → Part II-S and the observation frequencies are recorded in the MIFR (and thereby protected). Unfavourable findings but with No. 4.4 requested → Part II-S, recorded for information only. Otherwise → Part III-S and the notice is returned to the administration.
Mandatory data (RR Appendix 4)
Captured in the SNS file using SpaceCap:
Name of station
Country or geographical area of the station
Geographical coordinates of each antenna site (lat/long, degrees and minutes)
Notifying administration
Date of bringing into use
Operating administration or agency
Minimum / maximum antenna main-beam elevation
Operating azimuths of the antenna main beam
Antenna characteristics — type, dimensions, effective area (data item B.6)
Centre of the observed frequency band
Bandwidth of the observed frequency band
Class of station
Overall receiving system noise temperature
Characteristics of the observations
Antenna characteristics
The antenna radiation pattern (type, dimensions, effective area — item B.6) is required. SpaceCap auto-fills these when an antenna-pattern ID is selected from Table 6 of the Preface to the BR IFIC. If no suitable ID exists, notify code 999 (Other), supply the type/dimensions/effective area plus azimuth and elevation coverage, and BR assigns a new ID during examination.
Operating outside an RAS-allocated band? If the station observes in a band not allocated to RAS in Article 5, provision No. 4.4 must be requested. The assignment can then be recorded only for information — it receives no protection.
Protection strategy — split the band. Instead of notifying one large observation band, split it into several smaller bands aligned with the underlying allocations. Each sub-band then receives the finding (primary / secondary / none) matching its allocation, so the parts in allocated bands keep their protection instead of the whole notice being dragged down.
Cost. Notifications of radio astronomy stations are exempt from the cost-recovery fee (Council Decision 482).
Appendix 4 data items for radio astronomyEvery AP4 item flagged in the “Radio astronomy” column, from RR (2024) Appendix 4, Annex 2, Tables A–D
These are the characteristics an administration captures in the SNS file (via SpaceCap) when notifying a radio astronomy station. An item appears here only if the “Radio astronomy” column of the Appendix 4 master table carries a symbol; items with no symbol do not apply to RAS notices. Tables A–D were reviewed in full — only Tables A, B and C contain RAS items (Table D, relating to the Appendices 30/30A/30B Plans, has none).
X Mandatory information+ Mandatory under the condition specified for that itemC Mandatory if used as a basis to effect coordination with another administrationO Optional information
Table A — General characteristics of the station
Items A.7.x fall under the heading “Specific earth station or radio astronomy station site”.
Item
Description
Req.
A.1.e.2
Name of the station
X
A.1.e.2bis
Country or geographical area in which the station is located (using the symbols from the Preface)
X
A.1.e.3.b
Geographical coordinates of each transmitting or receiving antenna site constituting the station (latitude and longitude in degrees and minutes)
X
A.1.f.1
Symbol of the notifying administration (see the Preface)
X
A.2.c
Date (actual or foreseen) on which reception of the frequency band begins, or on which any of the basic characteristics are modified
X
A.3.a
Symbol for the operating administration or agency in operational control of the station (see the Preface)
X
A.3.b
Symbol for the address of the administration to which communication should be sent (see the Preface)
X
A.7.b.1
Planned minimum angle of elevation of the antenna’s main beam axis, in degrees, from the horizontal plane
X
A.7.b.2
Planned maximum angle of elevation of the antenna’s main beam axis, in degrees, from the horizontal plane
X
A.7.c.1
Start azimuth for the planned range of operating azimuthal angles of the antenna’s main beam axis, in degrees clockwise from True North
X
A.7.c.2
End azimuth for the planned range of operating azimuthal angles of the antenna’s main beam axis, in degrees clockwise from True North
X
Table B — Radio astronomy station antenna characteristics
Item B.6 is headed “Radio astronomy station antenna characteristics”.
Item
Description
Req.
B.6.a
Antenna type (see the Preface)
X
B.6.b
Antenna dimensions (see the Preface)
X
B.6.c
Effective area of the antenna (see the Preface)
X
Table C — Frequency assignment and observation characteristics
Item C.13 is headed “Characteristics of observations for radio astronomy stations”.
Item
Description
Req.
C.2.b
Centre of the frequency band observed
X
C.2.c
If the frequency assignment is to be filed under No. 4.4, an indication to that effectRequired when the assignment is filed under No. 4.4
+
C.3.b
Bandwidth of the frequency band, in kHz, observed by the station
X
C.4.a
Class of station (using the symbols from the Preface)
X
C.4.b
Nature of service performed (using the symbols from the Preface)
X
C.5.c
Overall receiving system noise temperature, in kelvins, referred to the output of the receiving antenna
X
C.13.a
Class of observations to be taken on the frequency band shown under C.3.b
X
C.13.b
Type of radio astronomy station in the frequency band shown under C.3.b
X
C.13.c
Minimum elevation angle θmin at which the radio astronomy station conducts single-dish or VLBI observations in the frequency band
X
All RAS items are mandatory (X) except C.2.c, which is mandatory only when the assignment is filed under No. 4.4. In the source table, a blank cell means the item does not apply to radio astronomy notices.
Source: Radio Regulations (Edition of 2024), Volume 2, Appendix 4, Annex 2 — “Characteristics of satellite networks, earth stations or radio astronomy stations”. Symbol definitions per the key to Tables A, B, C and D.
How the protection criteria fit together
Five in-force Recommendations form the core toolchain used to judge whether something interferes with radio astronomy. Read them as a chain:
RA.314 defines the frequencies the science needs; RA.769 sets the interference level that counts as harm; RA.1513 sets how often that level may be exceeded; RA.1631 supplies the antenna pattern that converts satellite-constellation geometry into an epfd value to compare against RA.769; and RA.611 extends protection to spurious/harmonic emissions from transmitters outside RAS bands. Full summaries of all five are in the Recommendations panel.
Interference formulas — from first principlesHow to decide whether an emission harms a radio telescope, built up one step at a time
Everything in this section answers one question: is a given emission strong enough to harm a radio-astronomy observation? We build the answer from basic physics — noise, power, and geometry — and arrive at the exact criteria used in Recommendations ITU-R RA.769, RA.1513 and RA.1631. No prior radio-astronomy knowledge is assumed; each symbol is defined where it appears.
How faint can we hear? (sensitivity)→What counts as harm? (10% rule)→Turn it into flux (pfd)→Add up satellites (epfd)→How often? (% time)
0. Building block: power spread over a sphere
The one geometric idea behind flux density and epfd
S = P · G ⁄ (4π d²) [W/m²]
Where
S power flux density — how much power crosses one square metre at the telescope (W/m²)
P power radiated by the transmitter (W)
G gain of the transmitting antenna toward the telescope (a pure ratio; 1 = isotropic)
d distance from transmitter to telescope (m)
Why. A transmitter radiating power P outward spreads it over the surface of an expanding sphere. The surface area of a sphere of radius d is 4π d², so an isotropic transmitter delivers P⁄(4π d²) watts per square metre. A directional antenna concentrates the beam, multiplying that by its gain G in the chosen direction. This single relation reappears everywhere below.
1. How faint can a telescope hear? — the radiometer equation
Basis of all RAS sensitivity figures
ΔTrms = Tsys ⁄ √(Δf · τ) [K]
Where
ΔTrms smallest change in received power the telescope can distinguish, expressed as a temperature (K)
Tsys system noise temperature — the receiver's own noise, in kelvins (a good dish + cooled receiver ≈ 20–50 K)
Δf bandwidth of the measurement (Hz)
τ integration (averaging) time (s)
Why. A radio receiver's own noise is random. Any single instant is dominated by that noise, but if you average many independent samples the random ups and downs cancel out. The number of independent samples collected is roughly Δf · τ (bandwidth × time), and random averaging improves as the square root of the sample count. So the leftover uncertainty falls as 1⁄√(Δf · τ). Widen the band or integrate longer and the telescope hears fainter things. RA.769 fixes a reference integration time of τ = 2000 s so that every band is compared on equal terms.
2. What counts as “harmful”? — the 10% criterion
Recommendation ITU-R RA.769, core definition
ΔTA = 0.1 × ΔTrms = 0.1 · Tsys ⁄ √(Δf · τ) [K]
Where
ΔTA the largest interference the observation may tolerate, expressed as an equivalent antenna temperature (K)
Why 10%. Interference adds to the natural noise. If the added power is much smaller than the telescope's own noise fluctuation ΔTrms, it barely shifts the measurement. RA.769 draws the line at one tenth of that fluctuation: interference below 10% of the noise wobble is deemed negligible; above it, the data are considered degraded. This one decision — the factor 0.1 — converts a physics quantity (ΔTrms) into a regulatory limit (ΔTA).
3. From temperature to power — the Nyquist relation
Connects noise temperature to watts
P = k · T · Δf [W]
Where
P noise power in the band (W)
k Boltzmann's constant = 1.38 × 10⁻²³ J/K
T temperature representing the noise (K)
Δf bandwidth (Hz)
Why. In radio engineering, any noise source is described by the temperature a resistor would need to generate the same noise power — that is the meaning of “noise temperature.” The available noise power is simply k · T · Δf. This lets us swap freely between the telescope's natural units (kelvins) and the regulator's units (watts). Applying it to the tolerance from step 2 gives the threshold interfering power PH = k · ΔTA · Δf.
4. From power to flux density — the antenna aperture
Recommendation ITU-R RA.769 / RA.1631 — the 0 dBi assumption
Prec = S · Aeff , Aeff = G · λ² ⁄ (4π)
Where
Prec power the antenna delivers to the receiver (W)
S power flux density arriving at the antenna (W/m²) — or per Hz for spectral pfd
Aeff effective collecting area of the antenna (m²)
G antenna gain in the direction the interference comes from (ratio)
λ wavelength = c ⁄ f (m); c = 3 × 10⁸ m/s
Why the side lobe matters. An antenna behaves like a net of effective area Aeff: the power it captures is flux density × area. Aeff is tied to gain by Aeff = G λ²⁄4π. Interference almost never arrives down the main beam — it sneaks in through the far side lobes, where the gain is roughly isotropic, G = 1 (0 dBi). RA.769 therefore evaluates the threshold at 0 dBi, giving Aeff = λ²⁄4π. (For satellite constellations, RA.1631 supplies the actual side-lobe gain at each angle instead of assuming 0 dBi.)
5. Putting it together — the detrimental flux-density threshold
Recommendation ITU-R RA.769, Tables 1–3
SH = 2k · ΔTA ⁄ Aeff = 8π · k · ΔTA ⁄ λ² [W·m⁻²·Hz⁻¹]
How the pieces combine
Step 2 gives the tolerable interference as a temperature ΔTA
Step 4 converts flux to captured power; invert it to get the flux that produces ΔTA
The factor 2 appears because a radio telescope receives only one polarization of the (randomly polarized) interference
Setting G = 1 (side lobe) gives Aeff = λ²⁄4π, hence the 8π⁄λ² form
What you get. SH is the spectral power flux density (per hertz) at which interference becomes harmful. It is exactly what RA.769 tabulates band by band. Multiply by the bandwidth to get total pfd. Because the numbers are astronomically small, they are quoted in decibels: dB(W/m²/Hz) = 10 · log₁₀(SH).
Worked example — 1.4 GHz continuum. Take Tsys = 20 K, Δf = 20 MHz, τ = 2000 s, f = 1.4 GHz so λ = 0.214 m.
• ΔTrms = 20 ⁄ √(2×10⁷ × 2000) = 20 ⁄ 2×10⁵ = 1.0 × 10⁻⁴ K
• ΔTA = 0.1 × 1.0×10⁻⁴ = 1.0 × 10⁻⁵ K
• SH = 8π × 1.38×10⁻²³ × 1.0×10⁻⁵ ⁄ (0.214)² ≈ 7.6 × 10⁻²⁶ W/m²/Hz ≈ −251 dB(W/m²/Hz)
This lands within a couple of dB of RA.769's tabulated value for this band — the small difference comes from the exact Tsys and constants the Recommendation assumes.
6. Adjusting for observing time
Scaling the RA.769 tables (τ ≠ 2000 s)
SH(τ) = SH(2000) × √(2000 ⁄ τ)
Why. Sensitivity improves as 1⁄√τ (step 1), so a longer observation can be spoiled by weaker interference. A spectral-line study running τ = 10 h = 36 000 s is √(2000⁄36000) ≈ 0.24 times the tolerance, i.e. about 6 dB more stringent than the 2000 s table value. This is exactly the offset RA.769 lists for longer integrations.
7. How often is too often? — the percentage-of-time criterion
Recommendation ITU-R RA.1513
data loss = (time SH is exceeded ⁄ total observing time) × 100%
Limits (bands where RAS is primary)
≤ 2% of time — from any single interfering network
≤ 5% of time — aggregate, from all networks combined
Why a time budget. A moving satellite only occasionally lines up badly with a telescope, so the threshold from step 5 is not exceeded continuously. RA.769 sets how strong; RA.1513 sets how often. An observation is judged harmed only when the flux exceeds SH for more than the allowed fraction of time. Both conditions together define real harm.
8. Many satellites at once — equivalent power flux-density (epfd)
Pi transmit power in the RAS reference bandwidth (dBW)
Gt(θi) transmit-antenna gain toward the telescope (linear ratio)
di distance from satellite i to the telescope (m)
Gr(φi) the telescope's gain toward satellite i — supplied by RA.1631's antenna pattern (linear)
Gr,max the telescope's peak (main-beam) gain (linear)
N number of visible satellites; convert any dBi gain to linear via 10(dBi/10)
Reading the formula. Each term is just step 0 (P·G⁄4πd², the flux from one satellite) multiplied by Gr(φi)⁄Gr,max — a weighting for how well the telescope “hears” in that satellite's direction. A satellite in a deep side lobe contributes almost nothing; one drifting through the main beam contributes fully. Summing over all N visible satellites gives the aggregate flux the constellation delivers, normalized as if it all arrived through the main beam. The 10 log₁₀ expresses it in decibels.
How it's used. The epfd is compared against the RA.769 threshold, and the RA.1513 time limits are applied to the fraction of time it is exceeded. This chain — RA.1631 pattern → epfd → RA.769 level → RA.1513 time — is the standard method for assessing non-geostationary constellations against radio astronomy.
Reference — units & conversions
dB value in dB = 10 · log₁₀(linear ratio of powers); e.g. −250 dB(W/m²/Hz) = 10⁻²⁵ W/m²/Hz
dBi antenna gain relative to isotropic; linear G = 10(dBi/10), so 0 dBi = 1
jansky the astronomer's flux unit: 1 Jy = 10⁻²⁶ W·m⁻²·Hz⁻¹ (the RA.769 thresholds are only a few Jy or less)
λ = c ⁄ f wavelength from frequency; c = 3 × 10⁸ m/s
pfd vs spectral pfd multiply spectral pfd [per Hz] by the bandwidth [Hz] to get pfd [W/m²]
Formulas are standard results presented for teaching; consult Recommendations ITU-R RA.769, RA.1513 and RA.1631 for the authoritative definitions, assumptions and tabulated values.
These are the actual numbers the formulas produce: the interference levels considered harmful to radio astronomy, band by band. All values assume a 2000 s integration time and interference entering through a 0 dBi side lobe. The column that matters most for sharing assessments is the rightmost — spectral pfd SH, in dB(W/m²/Hz).
Reading the tables. An emission is harmful if its spectral pfd at the telescope exceeds the SH value for that band. Adjustments: for longer integration add the offset in the notes; for GSO transmitters subtract 15 dB; to convert SH to a 1 MHz reference bandwidth add 60 dB. 1 jansky = 10⁻²⁶ W/m²/Hz.
Download: the complete three-table set with all intermediate columns and notes is available as a spreadsheet — see the file shared alongside this page (RA769_Threshold_Tables.xlsx).
Table 1 — Continuum observations (21 bands)
Centre freq (MHz)
BW Δf (MHz)
TA (K)
TR (K)
ΔT (mK)
ΔP (dB W/Hz)
ΔPH (dBW)
pfd SHΔf (dB W/m²)
Spectral pfd SH (dB W/m²/Hz)
13.385
0.05
50000
60
5000
-222
-185
-201
-248
25.61
0.12
15000
60
972
-229
-188
-199
-249
73.8
1.6
750
60
14.3
-247
-195
-196
-258
151.525
2.95
150
60
2.73
-254
-199
-194
-259
325.3
6.6
40
60
0.87
-259
-201
-189
-258
408.05
3.9
25
60
0.96
-259
-203
-189
-255
611
6
20
60
0.73
-260
-202
-185
-253
1413.5
27
12
10
0.095
-269
-205
-180
-255
1665
10
12
10
0.16
-267
-207
-181
-251
2695
10
12
10
0.16
-267
-207
-177
-247
4995
10
12
10
0.16
-267
-207
-171
-241
10650
100
12
10
0.049
-272
-202
-160
-240
15375
50
15
15
0.095
-269
-202
-156
-233
22355
290
35
30
0.085
-269
-195
-146
-231
23800
400
15
30
0.05
-271
-195
-147
-233
31550
500
18
65
0.083
-269
-192
-141
-228
43000
1000
25
65
0.064
-271
-191
-137
-227
89000
8000
12
30
0.011
-278
-189
-129
-228
150000
8000
14
30
0.011
-278
-189
-124
-223
224000
8000
20
43
0.016
-277
-188
-119
-218
270000
8000
25
50
0.019
-276
-187
-117
-216
Table 2 — Spectral-line observations (14 lines)
Line freq (MHz)
Channel BW (kHz)
TA (K)
TR (K)
ΔT (mK)
ΔPS (dB W/Hz)
ΔPH (dBW)
pfd SHΔf (dB W/m²)
Spectral pfd SH (dB W/m²/Hz)
327
10
40
60
22.3
-245
-215
-204
-244
1420
20
12
10
3.48
-253
-220
-196
-239
1612
20
12
10
3.48
-253
-220
-194
-238
1665
20
12
10
3.48
-253
-220
-194
-237
4830
50
12
10
2.2
-255
-218
-183
-230
14488
150
15
15
1.73
-256
-214
-169
-221
22200
250
35
30
2.91
-254
-210
-162
-216
23700
250
35
30
2.91
-254
-210
-161
-215
43000
500
25
65
2.84
-254
-207
-153
-210
48000
500
30
65
3
-254
-207
-152
-209
88600
1000
12
30
0.94
-259
-209
-148
-208
150000
1000
14
30
0.98
-259
-209
-144
-204
220000
1000
20
43
1.41
-257
-207
-139
-199
265000
1000
25
50
1.68
-256
-206
-137
-197
Table 3 — VLBI observations (10 bands)
Centre freq (MHz)
Threshold spectral pfd (dB W/m²/Hz)
325.3
-217
611
-212
1413.5
-211
2695
-205
4995
-200
10650
-193
15375
-189
23800
-183
43000
-175
86000
-172
Notes. Integration-time adjustments to add to the dB values: 15 min +1.7 · 1 h −1.3 · 2 h −2.8 · 5 h −4.8 · 10 h −6.3. For GSO transmitters, adjust by −15 dB. TA = antenna noise temperature; TR = receiver noise temperature. Source: Recommendation ITU-R RA.769-2 (2003), Tables 1–3.
ITU-R RA Recommendations (15 — normative)Concise summary + why it matters. Source: itu.int/rec/R-REC-RA/en
in force · incorporated by reference in the RR · 2003
The foundational protection criterion. Defines harmful interference as a 10% error in the measured noise fluctuation (ΔPH = 0.1·ΔP·Δf) over a 2000 s integration, and tabulates detrimental pfd/spectral-pfd per band from ~13 MHz to 270 GHz at 0 dBi side-lobe gain. Handles the GSO case (5° spacing, −15 dB) and the non-GSO case (epfd, RR No. 22.5C).
Why it matters — The quantitative definition of 'harmful' that every sharing study and BR examination measures against.
in force · incorporated by reference in the RR · 2015
Adds the time dimension to RA.769: aggregate data loss to RAS ≤ 5% of time from all networks, and ≤ 2% from any single network, in primary RAS bands. Defines data loss, sky blockage (a source within 19.05° of the beam blocks 5.5% of sky), and how to compute the percentage via the epfd tools.
Why it matters — Pairs with RA.769 — the level plus the tolerable frequency together define harm.
in force · incorporated by reference in the RR · 2003
Supplies the standard RAS antenna radiation pattern (a closed-form average side-lobe model above 150 MHz) for epfd-based non-GSO compatibility analysis, plus per-band typical maximum gains (63–93 dBi). Uses average rather than peak-envelope side-lobe levels so aggregate interference from constellations is not overstated.
Why it matters — The antenna half of the non-GSO toolchain: pattern (1631) + methodology (S.1586/M.1583) + threshold (769) + time criterion (1513).
Provides methods to protect RAS from adjacent-band transmitters, including the projection of the geostationary orbit onto the sky as seen from observatory latitudes and the resulting frequency and angular-separation requirements.
Why it matters — Adjacent-band emissions are a primary leakage path into sensitive RAS bands; underpins the coordination geometry used elsewhere in the series.
Protects RAS from spurious, harmonic and intermodulation emissions of transmitters outside RAS bands. Notes RR Appendix 3 spurious limits are not directly applicable to digital modulation. Worked example: an airborne 2-PSK transmitter can produce pfd ~40 dB above RA.769 thresholds in a RAS band far from its carrier. Directs satellite cases to the epfd tools.
Why it matters — Shows a fully in-band-compliant neighbour can still ruin observations through out-of-band products.
Addresses interference to RAS from unwanted emissions of wideband digitally-modulated systems (including spread-spectrum), whose noise-like spectra spill far from the carrier and are hard to separate from cosmic signals.
Why it matters — Modern digital and spread-spectrum systems are a growing interference source that conventional masks handle poorly.
Sets criteria and methods for protecting RAS in bands it shares with active services, including the tolerable-interference time criterion (2% of time for a shared service) and guidance on when band sharing is feasible.
Why it matters — Most RAS bands are shared; this defines the practical terms of coexistence.
Establishes mutual planning arrangements between spaceborne EESS active sensors and RAS in the 94 GHz and 130 GHz bands, where both services have strong scientific interest.
Why it matters — Enables two high-value science services to share critical millimetre-wave bands rather than exclude each other.
in force · incorporated by reference in the RR · 2023
Catalogs the spectral-line rest frequencies and continuum bands radio astronomy needs below 1000 GHz, tied to atomic/molecular physics from the IAU list: neutral hydrogen at 1420.406 MHz, OH near 1612–1720 MHz, water vapour at 22.235 GHz, CO at 115/230 GHz. Bands widen to cover Doppler and redshift. Flags where current RR allocations are non-primary, too narrow, or absent.
Why it matters — Defines which frequencies the science actually requires — the demand side of every sharing and allocation decision.
Identifies the preferred frequency bands for radio astronomical measurements in the 1–3 THz range, extending RA.314's band designations into the terahertz regime.
Why it matters — Terahertz astronomy is a growing frontier; this formalizes its spectrum needs before the band is contested.
Addresses protection of observations made from the shielded zone of the Moon — the lunar far side, screened by the Moon's body from Earth-origin emissions — identifying it as a uniquely interference-free site and the bands warranting protection there.
Why it matters — The lunar far side is the quietest location in the inner solar system; matters increasingly as lunar and cislunar activity grows.
Recommends establishing a radio-quiet zone around the L2 Sun-Earth Lagrange point — a favoured location for space observatories — to preserve it from interference.
Why it matters — L2 hosts major space telescopes; protecting the region preempts future interference to irreplaceable missions.
Covers protection of RAS measurements above 60 GHz from ground-based interfering sources, reflecting the distinct propagation, attenuation and sharing conditions of the millimetre-wave regime.
Why it matters — Millimetre-wave astronomy is expanding rapidly, and its protection logic differs from lower bands.
Gives the technical and operational characteristics of ground-based optical/infrared astronomy systems for use in sharing studies with active services between 10 and 1000 THz.
Why it matters — Extends coexistence analysis into the optical/IR regime as that spectrum sees active use such as lidar.
Describes global geodetic VLBI networks, whose observations underpin the international terrestrial reference frame, Earth-orientation parameters and timekeeping.
Why it matters — Geodetic VLBI is critical infrastructure for GNSS, navigation and Earth science, so its spectrum needs carry weight beyond astronomy.
Provides methods to determine the coordination area around existing RAS stations relative to IMT stations in the 6650–6675.2 MHz band (a methanol spectral line).
Why it matters — Protects a specific important spectral-line band from IMT through defined coordination distances.