23 cm in Belgium: Radar, the New Band Plan and the Future of ATV

What changes when the band plan and radar are considered together?

A receiver improvement can recover a link lost to interference. It cannot preserve an ATV channel that no longer fits the coordinated band plan. Equally, moving a transmitter to a compliant channel does not make the receiver immune to radar. Belgian 23 cm repeaters now face both problems.

The Vienna 2026 changes concentrate practical television and broadband data below 1257 MHz, move the main voice-repeater inputs, and give weak-signal work a new home around 1299 MHz. The radar environment then determines how reliably the remaining channels can serve their intended users.

My engineering conclusion is that a conventional regional 23 cm ATV system cannot simply carry on with a new frequency programmed into the same equipment. Narrow DATV remains worth developing where measurements support it. For a regional television output still on 23 cm, a coordinated move to 13 cm or 10 GHz deserves serious consideration. Existing cross-band systems may need only a specific output or incoming relay feed changed. ON0MCL illustrates why an input dependency must be distinguished from the output that serves its viewers.

Three documents answer three different questions

• ECC Decision (25)01: technical measures to protect radionavigation-satellite reception, including Galileo, from amateur transmissions. It does not protect amateur receivers from radar.
• The IARU Region 1 supplemental band plan: coordination of amateur modes and channels when those measures are implemented nationally. The Vienna C5 recommendation is VIE26_C5_Rec_02; its table and notes appear in the official conference documents, under C5, In conference documents. This is a supplement for changed national conditions; it does not itself cancel every country's existing permissions.
• Belgian implementation and station licences: the applicable legal conditions. CEPT's implementation register lists Belgium as planned, with implementation expected at the end of 2026. That entry is an announced intention, not an enacted Belgian licence amendment.

In my UBA coordination proposal, we are seeking voluntary migration while discussing with BIPT how to retain the present allocation where there is no actual interference. That request, the proposed station moves and any fee waiver remain under discussion. An Off plan label in the ON0 register identifies a coordination mismatch; by itself it does not establish that a station has lost its licence.

What the Galileo power limits actually mean

ECC Decision (25)01, Annex 1 distinguishes bandwidth and power reference. For terrestrial amateur emissions up to 150 kHz wide, 1258–1296 MHz is limited to approximately 20 mW EIRP (−17 dBW). Above that, the annex gives transmitter-power limits of about 50 W at 1296–1298 MHz and 158 W at 1298–1300 MHz. Those are not interchangeable with radiated-power limits.

For emissions wider than 150 kHz, including ATV, the annex instead specifies −17 dBW per 1 MHz, approximately 20 mW EIRP/MHz, throughout 1258–1300 MHz. Moving a normal broadband television signal to 1299 MHz therefore does not gain the narrowband power allowance.

The annex has separate satellite-uplink conditions, including an elevation-dependent provision at 1260–1262 MHz, and a higher-power EME provision at 1298–1300 MHz with antenna and elevation conditions. These are not terrestrial-repeater exceptions. National transitional arrangements may be provided; the annex's expectation of up to three years is not an automatic Belgian grace period. Check the national implementation and station authorization.

The revised 23 cm plan: frequencies, widths and uses

This operational summary follows the Vienna C5 supplemental table and its notes. Frequencies are in MHz. A channel centre is not a band edge, and channel spacing is not occupied bandwidth. National conditions and coordination still apply.

The repeater-input notes specify RS channels up to 1257.975 MHz, including the upper part of the 1257–1258 MHz segment. Use the explicit pairing notes when programming equipment. At every segment boundary, allow for the complete emission and filter skirts; a centre frequency exactly on a boundary does not give a wide signal permission to straddle neighbouring uses.

What the Belgian migration proposal means for actual stations

The following are the proposed moves I am discussing with the station groups as UBA repeater manager. They are coordination proposals, not completed conversions or final BIPT decisions.

ON0TLO: preserve the output, rebuild the input arrangement

For ON0TLO in Zichem, the output remains 1297.200 MHz, RM8. The input changes from 1291.200 to 1257.200 MHz: a −40 MHz shift instead of −6 MHz. This can require different duplexer hardware, revised filters and checks of the receiver, local oscillator, antenna and user equipment tuning ranges.

A wider separation can make transmitter rejection easier in a suitable design. It does not establish that the old duplexer can be retuned. RM8 also shares its proposed input with RS8, whose output would be 1298.200 MHz; that RS channel is not in Belgian use in the coordination proposal. Future assignments must preserve compatibility.

ON0ANR: move the data channels as a group

ON0ANR's six listed 200 kHz data channels cannot remain at their present centres. The 1299.400, 1299.500, 1299.550 and 1299.650 MHz assignments conflict with the new narrowband/beacon use. The 1299.900 and 1299.950 MHz assignments are too wide for the upper FM/DV channels. At 1299.950 MHz, a nominal ±100 kHz emission reaches 1300.050 MHz, beyond the amateur-band edge.

The proposed shared data block is 1243.250–1245.250 MHz: ten nominal 200 kHz slots with centres from 1243.350 to 1245.150 MHz in 200 kHz steps, shared with the two UBA data stations also leaving 1299 MHz. Ten adjacent slots do not provide extra guard bands; actual occupied spectra, filtering and simultaneous operation need checking before ten stations can be assumed to coexist.

For modes no wider than 150 kHz, 1298.125 or 1298.875 MHz may be alternatives: these are the two DD positions identified as free of Belgian repeater outputs in the proposal. Confirm the actual mode, bandwidth, number of required channels and neighbouring assignments first.

ON0TVO and ON0CTV: the 23 cm outputs that need migration

The affected television outputs are ON0TVO on 1,275 MHz and ON0CTV on 1,280 MHz. Both lie within the constrained 1258–1300 MHz region and need migration out of that region under the proposed implementation. These are digital television examples; their problem is not simply that an analogue picture occupies too much spectrum.

The OVRC ATV repeater listing, dated 24 September 2023, records ON0TVO's 23 cm output at SR 2000 and FEC 2/3. It also lists outputs on 5,710 MHz and 10,180 MHz, so changing the 23 cm output does not imply replacing the complete repeater. Its listed 23 cm inputs at 1,250 MHz digital and 1,252 MHz FM are below 1258 MHz; their occupied bandwidth and coordination still need assessment.

For ON0CTV, the listed output is 1,280 MHz, DVB-S, 50 W, SR 4000 and FEC 3/4. The 50 W is a reported station figure, not an independently verified measurement or an ERP/EIRP calculation. Its listed 436 MHz and 2,335 MHz inputs are outside this 23 cm rearrangement. Changing its output therefore requires a coordinated transmit channel and compatible reception at its viewers, rather than automatically moving those inputs.

SR 4000 denotes 4 Msymbol/s. With a roll-off factor of 0.35, the nominal shaped width is approximately 5.4 MHz. FEC 3/4 changes the available payload and decoding trade-offs; it does not make a 4 Msymbol/s carrier fit a 150 kHz channel. ON0CTV's television output remains a broadband application under the ECC provisions.

ON0MCL: preserve the 10 GHz output and identify the relay input

ON0MCL's output to retain is 10,375 MHz, SR 2500 (2.5 Msymbol/s), with the reported operating period of 10:00–22:00. Its 2,330 MHz / 13 cm channel is an input. This input is outside the 23 cm rearrangement and does not need to move merely because the 23 cm band plan changes.

There is a separate path to examine: the OVRC listing identifies an ON0TVO feed among ON0MCL's inputs, but gives no receive frequency for that feed. If MCL receives TVO's 1,275 MHz output, moving that output also requires MCL to retune or replace the corresponding receive path. That is a change to MCL's incoming relay feed, while its 10,375 MHz output can remain. If MCL receives one of TVO's other outputs, that particular dependency does not follow.

This distinction matters for both migration and radar diagnosis. A failed 23 cm feed from TVO can disrupt the programme reaching MCL while MCL's 10 GHz transmitter and its local 13 cm input remain functional. Confirm the actual inter-repeater receive frequency before specifying a replacement converter, filter or antenna. MCL's own night-time shutdown says nothing about whether the radars operate at night.

Coordinate the transmitting station and every receiving endpoint

For TVO and CTV, the proposed options are a suitable output on 13 cm or 10 GHz, or a coordinated digital output within the lower 23 cm broadband segment if bandwidth, isolation and interference tests support it. Where a 23 cm input is needed, the proposed narrow DVB-S2 window is 1245.5–1255 MHz. Existing inputs and outputs outside the affected segment should be assessed on their own merits.

An output migration affects home viewers and any repeater that receives that output. Record each path as transmitter frequency, receiver frequency, mode, symbol rate and bandwidth. This avoids changing an unrelated 13 cm input while overlooking the actual 23 cm relay receiver.

Within the 13.75 MHz broadband envelope, the proposed 2 MHz data block, a 0.25 MHz separation before the ATV input window and the 1255–1257 MHz buffer leave a 9.5 MHz ATV planning window. Keeping the buffer helps protect the new FM inputs beginning at 1257 MHz. This is a national coordination proposal, not an additional IARU allocation.

Why conventional analogue FM-ATV no longer fits the proposal

Analogue FM television bandwidth depends on both the video spectrum and peak deviation. Carson's estimate is B ≈ 2(Δf + f_m,max). As an illustration, ±4 MHz deviation and a 5 MHz highest modulating frequency already give approximately 18 MHz, before deciding how audio subcarriers, the emission mask and neighbouring-channel protection will be handled.

That illustrative analogue example exceeds the entire 13.75 MHz broadband envelope, and still more the proposed 9.5 MHz television window. It does not describe the digital outputs listed for ON0TVO and ON0CTV. Merely reducing deviation trades away FM noise improvement; reducing video bandwidth changes the service. A specially restricted analogue signal can be narrower, so “no possible FM video waveform fits” would be too absolute. The practical conclusion is that conventional wideband analogue FM-ATV is not a drop-in fit for this digital ATV/data plan.

For DVB-S/S2 with raised-cosine shaping, the nominal occupied width is approximately B = R_s(1 + α), where R_s is symbol rate and α is roll-off. At 1 Msymbol/s and α = 0.35 this is 1.35 MHz. At 4 Msymbol/s it is 5.4 MHz: two such signals would require 10.8 MHz before any separation, already exceeding the 9.5 MHz window. Symbol rate, coding, picture bitrate and filtering must therefore be selected together.

An input/output pair of narrower DVB-S2 signals can fit arithmetically within that window. The repeater must still receive a weak input while transmitting nearby. Illustratively, a 10 W output is +40 dBm; 80 dB of combined antenna and filter isolation leaves −40 dBm at the receiver. Against a −100 dBm wanted signal, the residual transmitter is still 60 dB stronger. Whether that is acceptable depends on front-end blocking, transmitter noise at the receive frequency, phase noise and filter response. Frequency fit alone does not demonstrate a working duplex repeater.

Why moving below 1257 MHz does not solve radar reception

The lower-band move addresses spectrum use and Galileo protection. A radar receiver problem follows the actual radar emissions, the propagation path and the receiving chain. The documented SMART-L equipment range extends across the lower 23 cm segment too. That does not prove a specific channel is occupied, but it gives no basis for declaring the new ATV window radar-free.

A narrower digital channel can admit less noise and less interfering energy. It cannot prevent a wideband masthead amplifier from compressing before that channel filter. Nor can it remove a pulse that overlaps the wanted channel. This is why successful migration needs both a channel plan and a measured interference budget.

Which radars, and will they run 24 hours a day?

The Dutch SMART-L installations are a documented development relevant to this discussion. They must be distinguished by location and operating status. Their existence alone does not identify the source of a particular Belgian interference report.

Nieuw Milligen also needs careful identification: Defence names a temporary Ground Master 400 Alpha there. A replacement radar at one site is not automatically another SMART-L, and a photograph or an unfamiliar radar signal is insufficient to assign a source.

Twenty-four-hour operation does not mean an uninterrupted carrier. A radar can remain operational all day while transmitting pulses, rotating its beam and changing modes. Conversely, a small transmit duty cycle does not guarantee usable television between pulses.

Why a radar can be relevant across a national border

A TNO document places SMART-L operation in the 1.2–1.4 GHz range, which encompasses the 1240–1300 MHz amateur band. That broad equipment range does not mean that every frequency is occupied simultaneously, or that every mode overlaps every ATV channel. TNO supplementary location study, letter page 7/11.

More troublesome reception after a radar change does not, by itself, prove that peak transmitter power increased. Pulse duration, repetition, occupied spectrum, beam scheduling and receiver recovery can change the effect substantially. Comparing only the old and new transmitters' kilowatt figures misses those mechanisms.

The relevant path runs from the radar to the affected receiving antenna. Its strength depends on terrain, antenna heights, both radiation patterns, polarization, obstructions, atmospheric refraction and the radar's instantaneous emissions. A national border contributes no RF attenuation. Elevated repeater sites and clear paths can expose receivers to distant signals; terrain screening can protect other sites.

Tropospheric enhancement can improve an amateur path and the interference path at the same time. Which improves more determines whether reception gets better. A quiet afternoon is therefore a weak basis for promising regional service throughout the year.

Do not turn a radar's aircraft or missile detection range into an ATV interference radius. Detecting a target normally involves a transmitted signal, scattering from that target and a return path. Interference at an amateur receiver can arrive directly over a one-way path, with an entirely different receiving threshold.

Two different ways the picture disappears

Radar energy inside the wanted channel

When appreciable radar energy passes through the ATV channel filter, it directly competes with the wanted modulation. Analogue FM television may show streaks, tearing, loss of synchronization or bursts of noise. Digital ATV may exhibit transport errors, frozen pictures, audio interruptions or loss of lock. None of those symptoms uniquely identifies radar.

A linear filter cannot separate two signals that occupy the same frequencies simply because one is television and the other is radar. Narrowing the accepted bandwidth may reduce the intercepted interference, but only within the bandwidth required by the selected television mode. A notch through the wanted signal can damage its modulation and group-delay response.

The receiver is overloaded before channel selection

A strong signal outside the tuned ATV channel may compress a masthead amplifier, drive a mixer into an unsuitable operating region, trigger gain reduction or clip an analogue-to-digital converter. Several otherwise clear channels may then deteriorate together. A spectrum display can appear to show wideband interference that is partly being created inside the receiving chain.

Filtering protects the stages after the filter. A narrow demodulator filter cannot repair distortion created in an earlier wideband amplifier. A filter after the masthead preamplifier cannot stop that preamplifier overloading. This is why the receiver's complete signal path matters more than the bandwidth shown on its display. Analog Devices: receiver front-end gain, preselection and blockers.

The two mechanisms can occur together. Reciprocal mixing with local-oscillator phase noise and intermodulation can add further impairment. A low noise figure is useful, but it does not specify blocking tolerance, pulse recovery or converter headroom.

Why a low average reading can conceal a serious problem

Defence describes normal SMART-L search operation as one rotation in approximately five seconds, with transmission during about 10% of the operating time. It also describes a stationary mode with different signal behavior. These are public operating descriptions, not a complete waveform specification. Defence: how the radar works.

For equal rectangular pulses with duty fraction D, at a fixed reference plane:

At D = 0.1, the power during a pulse is 10 dB above the time average. Beam rotation, frequency changes and measurement bandwidth can further change the relationship between an instrument's displayed average and the largest input excursions. This simple calculation is not a measurement of either Dutch site.

Modern pulse-compression radar can use modulation within a relatively long transmitted pulse. The short resolved echo in the radar's matched processing does not mean an unrelated ATV receiver experiences only that short duration. Keysight: modulation and pulse compression.

Receiver recovery adds another time scale. A short RF disturbance can produce a longer video outage if gain control, carrier recovery, frame synchronization or decoding must recover. The fraction of corrupted television is consequently not equal to the radar's transmitter duty cycle. Repeating interference every few seconds can make a programme unusable even when many individual RF samples remain clean.

Why nearby stations can survive while regional coverage disappears

Let C be wanted carrier power, N receiver noise in the measurement bandwidth, and I interference in that same bandwidth and at the same reference plane. A useful first calculation is C/(N + I). Add noise and interference as linear powers before converting back to decibels.

Consider an illustrative linear receiver with N = −100 dBm. A distant signal at −86 dBm initially has 14 dB C/N. If in-channel interference during an affected interval is −90 dBm, N + I becomes approximately −89.59 dBm and C/(N + I) becomes just 3.59 dB. A local signal at −64 dBm would have 25.59 dB under the same conditions.

These invented levels explain the mechanism; they are not Belgian field measurements or universal decoder thresholds. Actual pulse interference is non-Gaussian, and loss of lock, coding, interleaving and recovery must be measured. If the receiver saturates, this linear calculation is no longer sufficient.

A repeater can therefore become effectively local for dependable ATV service without its transmitter, antenna gain or licensed power changing. Occasional long-distance contacts during quiet intervals do not restore its former service availability.

A repeater has more than one vulnerable receive path

• User to repeater: interference at the repeater input can prevent distant users accessing it. Increasing repeater output power does nothing for this failure.
• Repeater to viewer: the relay may receive its input correctly while radar affects the viewer's receiver. A clean local test card at the repeater does not establish the remote downlink.
• Inter-repeater link: a microwave backbone receiver can be the failed stage even when both local access links are sound.

Compare a known clean local test source, the repeater's decoded input, its transmitted output and observations at several receiving sites. A clean internet stream alongside a damaged RF picture can help locate a downlink problem, provided the stream and RF output actually carry the same source at that time.

Voice and narrowband data repeaters have different occupied bandwidths and failure criteria. Their survival does not prove wideband ATV remains practical. Nor does ATV failure automatically mean every narrowband mode has failed.

What reduced-bandwidth DATV can achieve

At roughly 290 K, input-referred receiver noise is approximately −174 + 10 log₁₀(B_Hz) + NF dBm. With a 2 dB noise figure, a 2 MHz noise bandwidth gives about −109 dBm; 20 MHz gives about −99 dBm. That 10 dB difference helps explain why narrowband reception and wideband television face different margins.

For raised-cosine single-carrier modulation, nominal spectral width is approximately B = R_s(1 + α). At roll-off α = 0.35, 4 Msymbol/s occupies about 5.4 MHz, while 333 ksymbol/s occupies about 450 kHz. With similarly scaled receiving filters, the latter accepts roughly 10.8 dB less white noise.

At unchanged total wanted RF power, reducing symbol rate increases energy per symbol, at the cost of data capacity. Actual performance still depends on modulation, coding, implementation and accepted video quality. Nominal occupied width and equivalent noise bandwidth are not identical quantities.

Reduced bandwidth can also avoid some interfering frequencies. It cannot guarantee rejection of a radar signal inside the remaining channel, protect an amplifier that overloads ahead of the filter, or make arbitrarily long decoding outages disappear. Forward error correction has finite capability.

What I would change at an affected station

A passive loss ahead of the first amplifier adds approximately its loss in dB to the noise figure of that cascade when referenced at standard temperature. Accepting a modest sensitivity penalty can be worthwhile if it prevents a much larger blocking penalty. That decision needs measurements.

Increasing transmitter power is constrained by authorization and only addresses the wanted signal on the relevant link. It cannot make a saturated receiver linear. An internet feed can preserve access to pictures, but it does not restore the lost RF path.

Measure the failure before buying the cure

1. Record the path and receiver configuration. Include frequency, bandwidth or symbol rate, modulation/FEC, antenna heading, preamplifier, filters, analogue gain and the level reference plane.
2. Record time behavior. Correlate received RF bursts with MER, pre/post-FEC errors, transport continuity errors, loss of lock and video recovery. Save the spectrum, detector, resolution bandwidth and sweep or capture settings.
3. Check measurement overload. A spectrum analyser or SDR can itself produce the apparent interference. Use appropriately rated input protection and attenuation, keep within peak input limits, and verify results at more than one input level.
4. Try a calibrated receive-only attenuation step. Improvement with less input is evidence of a nonlinearity or gain-control problem downstream of that point, not proof of a particular radar. In a linear co-channel-limited receiver, attenuating wanted and unwanted signals equally does not improve their ratio.
5. Compare filter placement. A filter before the masthead amplifier and the same filter after it answer different questions. Keep DC bias paths and equipment ratings correct.
6. Compare sites and days. Distinguish a repeater input failure from a viewer failure. Record the distribution of outages, including propagation changes, before promising a service radius.

A roughly five-second recurrence may be consistent with the published SMART-L search rotation, but it is not a unique identification. Use measurements and competent spectrum investigation to establish attribution. In Belgium, the BIPT and the amateur association's spectrum specialists are the appropriate channels for a documented interference report.

Moving the output: what 13 cm and 10 GHz can offer

Moving the television output away from 23 cm separates that downlink from these L-band radar and Galileo constraints. It also removes the need to receive and transmit television a few MHz apart within the crowded lower 23 cm window. It does not automatically improve every path: each candidate channel needs its own allocation, interference, terrain, antenna, feeder-loss and availability assessment.

Where a 23 cm input is retained, it remains exposed. A perfect 10 GHz picture of a test card proves the output link; it does not prove that distant users can reach the repeater through its 23 cm receiver. Test both directions independently and provide another input path if the 23 cm one cannot meet the service requirement. ON0MCL's 2,330 MHz local input is outside 23 cm. Its separate ON0TVO feed must be checked against the frequency it actually receives.

A satellite dish is useful; an arbitrary LNB is not guaranteed

The proposal includes a DVB-S output around 10.4 GHz. A suitable dish and LNB/converter can make reception practical, but do not promise that every ordinary satellite-TV installation will work unchanged. For example, Inverto's universal PLL LNB specification covers RF from 10.7 to 12.75 GHz, with a 9.75 GHz low-band oscillator and a specified 950–2150 MHz output range.

With that oscillator, 10.400 GHz converts to 650 MHz; ON0MCL's reported 10.375 GHz converts to 625 MHz. Both the input frequency and resulting IF are outside those quoted ranges. Some hardware works beyond its nominal limits, and amateur adaptations or suitable converters can solve this, but sensitivity, stability, IF tuning range and the receiver's minimum supported symbol rate must be verified. Choose the converter and DVB receiver as one receive system.

Migration dates, licences and costs

The BIPT licensing FAQ and linked frequency table remain the starting point for existing Belgian permissions, alongside each unattended station's authorization. A band-plan change does not itself authorize a new output frequency, power or emission. Conversely, the existing BIPT table is not a guarantee that its conditions will remain unchanged after national implementation.

Amateur operation here is secondary: stations must protect primary services and cannot claim protection from their interference. Keeping an allocation therefore preserves opportunities for amateur work; it does not guarantee a quiet television channel.

The combined conclusion for Belgian ATV

The combined assessment must follow each station's actual signal paths. The supplemental plan concentrates practical television and broadband data below 1257 MHz and changes voice-repeater pairings. Radar can then reduce the reliability of affected 23 cm receivers. ON0TVO's 1,275 MHz output and ON0CTV's 1,280 MHz output require migration under the proposed implementation. ON0MCL's 10,375 MHz output can remain; its incoming ON0TVO feed needs a corresponding receiver change if it uses TVO's affected 23 cm output. MCL's separate 2,330 MHz input does not move for this reason.

I would retain suitable existing cross-band paths, address each affected 23 cm output and its dependent receivers, and consider a coordinated 13 cm or 10 GHz main output where the service still relies on a 23 cm downlink. A narrow 23 cm digital input should be retained or introduced only where site measurements support the required availability. A fully 23 cm digital repeater remains an option where bandwidth, isolation and radar tests demonstrate that it works. A conventional wideband analogue system simply retuned into the remaining space is a poor long-term plan.

This is an engineering recommendation, not a claim that every Belgian repeater has already become local-only. A strong local signal can survive while distant ones fail; severe overload can also defeat a nearby user. The useful question for each station is whether its proposed complete system can deliver the intended service under continuing radar operation and the new spectrum conditions.

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