UKHemel Hempstead
England · TV, FM and DAB
- Position
- 51.728581, -0.426217
- Grid reference
- TL08790449
- Nation
- England
- Ground height
- 142 m
- Antenna height
- 73 m
- Aerial group
- Group K — C21–48, wideband across the post-clearance band
- Polarisation
- Vertical
- BBC region
- London
- ITV region
- London
- ITV news region
- London
- Parent transmitter
- Crystal Palace
- Ofcom site numbers
- 10105, 10108
How far it reaches
Two different questions, and the map below can be switched between them. Reaches is everywhere this mast puts a usable signal; strongest is the much smaller slice where nothing else does it better.
| Band | Reaches | Strongest in | |
|---|---|---|---|
| Television | 10.9% of UK Output Areas | 0.6% of UK Output Areas | a substantial transmitter |
| FM radio | 2.5% of UK Output Areas | 0.2% of UK Output Areas | a substantial transmitter |
| DAB radio | 7.1% of UK Output Areas | 0.4% of UK Output Areas | a substantial transmitter |
More detail
Most places can receive several transmitters — a median Output Area hears twelve — and only one of them can be the best, which is why the two columns are so far apart. Reach counts an area once the model clears the reception threshold there at all, and it inherits the sweep's screen: only the strongest twenty candidates per area are stored, so a mast lying twenty-first somewhere does not count as reaching it. Both are a share of areas, deliberately, and not a number of homes: checked against Ofcom's own coverage the model ranks transmitters correctly (Spearman 0.861) but over-states how far each one gets by a median factor of 2.5. A share is a ranking statement and survives that; a household count would not. How this is worked out.
On the map
Everywhere Hemel Hempstead is predicted to reach for television, FM radio and DAB radio, shaded by how much signal is left over. Other transmitters reach most of this ground too.
Only the areas where Hemel Hempstead is the strongest option for television, FM radio and DAB radio — the ones the postcode lookup would send here. A smaller picture than its reach, and a different question.
The lines are how far the signal is modelled to get: solid while the margin still clears 10 dB, dashed out to where it last clears 0 dB. The real edge sits inside them — every point inherits the model's measured optimism of about 17 dB.
How the rings were drawn
It is an envelope, not a boundary: terrain can still block reception well inside it, and it is an edge, not a fill — the colour says how far the signal gets, not that every spot under it works. The traced outline is smoothed across 12 degrees of bearing, so no single ray can spike or notch it; the ground it encloses moves by well under a percent [V]. Zoom in and the shading gives way to the per-area prediction, which is the same question answered Output Area by Output Area. The television ring was traced assuming an omnidirectional transmitting aerial, because Ofcom publish no radiation pattern for this site [I]. The DAB radio ring was shaped by Ofcom's published radiation pattern [D]. The FM radio ring was contoured from the stored predictions, which keep only the strongest candidates for each area — the true edge can extend beyond what is drawn [I].
The modelled outer edge drawn above: television about 74 km toward the south-west but only 16 km toward the north-west; FM radio about 54 km toward the south but only 16 km toward the north-west; DAB radio about 74 km toward the south-west but only 16 km toward the north-west [I].
Open this transmitter on the full mapreach, the aerial direction, and everything else within range
Television
| Mux | Freeview name | Channel | Frequency | ERP | System | Operator | Ofcom row |
|---|---|---|---|---|---|---|---|
| PSB1 | BBC A | C40 | 626 MHz | 2.0 kW | DVB-T | BBC | Hemel Hempstead |
| PSB2 | D3&4 | C43 | 650 MHz | 2.0 kW | DVB-T | Digital 3&4 (ITV/Channel 4) | Hemel Hempstead |
| PSB3 | BBC B | C46 | 674 MHz | 2.0 kW | DVB-T2 | BBC | Hemel Hempstead |
| COM4 | SDN | C37 | 602 MHz | 2.0 kW | DVB-T | SDN (ITV plc) | Hemel Hempstead |
| COM5 | ARQ A | C31 | 554 MHz | 2.0 kW | DVB-T | Arqiva | Hemel Hempstead |
| COM6 | ARQ B | C29 | 538 MHz | 2.0 kW | DVB-T | Arqiva | Hemel Hempstead |
| LTV | Local | C34 | 578 MHz | 200 W | DVB-T | Comux / local operators | Hemel Hempstead |
FM radio
| Station | Frequency | ERP (H) | ERP (V) | Height | RDS name | PI code | Pattern |
|---|---|---|---|---|---|---|---|
| BBC Three Counties Radio (FM) | 92.1 MHz | — | 50 W | 65 m | BBC_3CR | C617 | V |
| Heart | 96.6 MHz | 500 W | 500 W | 80 m | Heart | C360 | HV |
BBC Three Counties Radio (FM) — radiation pattern
Radiates most strongly toward the north (0°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
Heart — radiation pattern
Radiates most strongly toward the north-east (50°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for. Solid is horizontal polarisation, dashed is vertical.
DAB radio
| Ensemble | Block | Frequency | ERP | Height | Area | EId | Services |
|---|---|---|---|---|---|---|---|
| Herts Beds Bucks | 10D | 215.072 MHz | 3.9 kW | 69 m | Home Counties | C1B2 | 11 |
| SDL National | 11A | 216.928 MHz | 3.1 kW | 69 m | North London | C1CE | 31 |
| London 3 | 11B | 218.640 MHz | 244 W | 69 m | London | C199 | 21 |
| D1 National | 11D | 222.064 MHz | 3.1 kW | 69 m | North London | C181 | 30 |
| London 2 | 12A | 223.936 MHz | 250 W | 79 m | Pimlico | C186 | 18 |
| BBC National DAB | 12B | 225.648 MHz | 4.0 kW | 79 m | North London | CE15 | 16 |
| London 1 | 12C | 227.360 MHz | 391 W | 69 m | London | C185 | 19 |
Herts Beds Bucks — block 10D
SDL National — block 11A
London 3 — block 11B
D1 National — block 11D
London 2 — block 12A
BBC National DAB — block 12B
London 1 — block 12C
Herts Beds Bucks — radiation pattern
Radiates most strongly toward the north-east (60°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
SDL National — radiation pattern
Radiates most strongly toward the north-east (60°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
London 3 — radiation pattern
Radiates most strongly toward the north-east (60°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
D1 National — radiation pattern
Radiates most strongly toward the north-east (60°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
London 2 — radiation pattern
Radiates most strongly toward the north-east (60°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
BBC National DAB — radiation pattern
Radiates most strongly toward the north-east (60°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
London 1 — radiation pattern
Radiates most strongly toward the north-east (60°), as published by Ofcom.
More detail
Each ring is 10 dB of attenuation below the pattern's own peak; the outer rim is the peak itself and anything 30 dB down or deeper is drawn at the centre rather than off the edge of the chart, so a very deep null reads as “weak” and not as a hole in the picture. The shape says which direction radiates harder relative to the mast's own peak, not the absolute field strength there or how far it reaches — that is what the coverage map and the postcode lookup are for.
Other transmitters nearby
Every structure Ofcom list within 40 km, nearest first. Close is not the same as an alternative: most of these are single-service relays, and one of them may radiate a thousandth of this mast's power in a direction that misses you.
Ofcom's notes
London L-DTPS