When residents can watch some channels but not others, the fault usually sits in certain frequencies of the building TV system, not the whole system. There is no need to rip out the system: check from the unit back to the rooftop headend. The first two steps cost nothing.
Executive summary
- One unit affected: usually fixed in the unit by retuning or replacing the TV lead.
- A whole floor or riser affected: check that riser's amplifiers, taps and splitters.
- The whole building affected: check the headend, which may still be set for frequencies used before the digital TV re-plan.
Why some channels disappear
Digital TV carries several channels on one frequency (a MUX). If one frequency falls below threshold, every channel in that MUX drops together while the others still work. Five common causes:
- Receivers still hold old frequencies. In 2020 the NBTC moved digital TV frequencies to release the 700 MHz band for 5G; sets never retuned miss some channels.
- Channel-specific headend. Channel amplifiers or frequency filters pass only the frequencies they were set for, so moved frequencies vanish building-wide.
- Higher frequencies lose more in cable. Without correct amplifier slope/tilt, end-of-line units see dropouts first.
- 4G/5G interference. The 700 MHz band now belongs to mobile; wideband legacy antennas and amplifiers amplify it and overload.
- Loose or ageing connectors. Corroded F-connectors or worn taps and splitters weaken certain frequencies locally.
Five-point check
- Log complaints by unit, floor, riser and channel.
- Check the unit: retune, check the TV lead, and test another set on the same outlet.
- Measure at the outlet and floor tap across all frequencies.
- Check riser amplifiers: power, gain, slope and connectors.
- Check the headend: antenna alignment, channel amplifier settings and an LTE/5G filter.
Symptoms and where to look first
| Symptom | Likely cause | Check first |
|---|
| Some channels missing in a few units | Old frequencies stored, unit cable or outlet | The unit (retune) |
| Channels missing on upper floors or end of line | High-frequency cable loss, wrong slope | Riser amplifiers and taps |
| Channels missing building-wide | Channel amplifiers set to old frequencies, antenna misaligned | Headend |
| Intermittent freezing on many channels | 4G/5G interference, amplifier overload | Headend (add LTE/5G filter) |
| Channels lost after rain or repairs | Water in connectors, crushed or cut cable | Rooftop connectors and repair areas |
Notes for engineers
- Outlet level: 65–75 dBµV; follow the project TOR where it differs.
- MER: keep several dB of margin above receiver threshold; a frequency clearly below the others is the one to fix.
- Level difference across frequencies: keep it small at each outlet; adjust amplifier slope if not.
- Compare with handover records, or keep this survey as the new baseline.
- Re-measure at the same points at every maintenance visit.
Free consultation and system check
JJSATs has surveyed, repaired and upgraded MATV and SMATV systems for condominiums, apartments, dormitories, hotels and hospitals for over 25 years.
Source: InfoQuest, 19 Aug 2020 (NBTC 700 MHz re-plan)
