BBC North Hessary Tor -

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The North Hessary Tor Transmitting Station is a significant communications facility located on North Hessary Tor, one of the highest hills in Dartmoor, Devon, England. It is an important part of the UK’s broadcasting infrastructure and serves as a landmark visible from miles around. Here’s everything you need to know about this transmitter:

Overview:

Construction: The transmitting station was built in 1955 by the BBC as part of the post-war expansion of television broadcasting across the UK. It was originally designed to improve television reception for the people of South West England, particularly those in Devon and Cornwall.
Location: Situated on North Hessary Tor, which stands at 517 meters (1,696 feet), the station takes advantage of the high altitude, which provides ideal conditions for broadcasting over a wide area.

Physical Structure:

Mast Height: The most striking feature of the transmitting station is its 196-meter (643-foot) tall guyed mast. This steel structure is one of the tallest masts in the region and is clearly visible on the Dartmoor skyline.
Elevation: Including the height of North Hessary Tor, the total elevation of the mast’s top is approximately 713 meters (2,339 feet) above sea level, making it one of the highest points for broadcasting in the UK.

Broadcasting History:

Television Broadcasting:
- North Hessary Tor Transmitting Station began transmitting BBC Television in 1956. At that time, it broadcast the BBC’s 405-line VHF television service.
- It continued to provide BBC 405-line black-and-white television until the service was discontinued in 1985.
- Today, the mast is primarily used for Digital Terrestrial Television (DTT) services, offering Freeview, the UK’s free-to-air television service, to a wide audience across the region.
Radio Broadcasting:
- In addition to television, the North Hessary Tor Transmitting Station is a key hub for radio transmissions. It broadcasts FM radio for BBC networks such as:
  - BBC Radio 1
  - BBC Radio 2
  - BBC Radio 3
  - BBC Radio 4
  - BBC Radio Devon, the local service for the region.
- These stations are transmitted on VHF/FM, which is ideal for covering the hilly and remote terrain of Dartmoor and surrounding areas.
Digital Radio:
- The station also broadcasts DAB (Digital Audio Broadcasting) services, which provide high-quality digital radio across Devon and parts of Cornwall.

Coverage Area:

Due to its elevated position, North Hessary Tor Transmitting Station has an extensive coverage area. It serves a large portion of:

South Devon
Eastern Cornwall
Parts of Somerset
Exeter and Plymouth, two of the region’s largest cities, are also within its broadcast range.
The station is particularly important for rural and remote communities in these areas, where the topography makes signal reception from other masts challenging.

Technical Specifications:

Broadcast Frequencies: North Hessary Tor uses a range of frequencies to transmit both digital television and radio signals. Here’s a breakdown of the services:
- Digital TV (Freeview): Uses UHF bands to broadcast Freeview services. It replaced the analog television signals in the 2000s when the UK switched to all-digital television broadcasting.
- FM Radio: Broadcasts on the VHF/FM band. The main frequencies are:
  - BBC Radio 1: 98.7 MHz
  - BBC Radio 2: 89.3 MHz
  - BBC Radio 3: 91.5 MHz
  - BBC Radio 4: 93.7 MHz
  - BBC Radio Devon: 95.7 MHz
- DAB Radio: Broadcasts digital radio services with improved sound quality and more channels.

Significance in Broadcasting History:

First in the Southwest: North Hessary Tor Transmitting Station was one of the first major television transmitters in the Southwest of England, helping to bring television to a previously underserved region.
Expansion of BBC Services: The station played a crucial role in expanding the BBC’s broadcasting footprint in rural areas like Dartmoor, where the rugged landscape made it difficult for traditional transmitters to reach.
Part of National Infrastructure: Along with other major transmitting stations, North Hessary Tor is part of the UK’s national broadcast infrastructure, ensuring that people in remote and rural areas can access television and radio services.

Upgrades and Modernisation:

The station has undergone several upgrades over the decades to keep up with changes in broadcasting technology:

From 405-Line to 625-Line: When colour television was introduced, the station shifted from the older 405-line VHF system to the modern 625-line UHF system to support colour broadcasts.
Digital Switchover: In 2009, the UK underwent the digital switchover, during which analogue television signals were switched off, and all television services were converted to digital. North Hessary Tor was upgraded to transmit Freeview digital TV services as part of this process.
DAB Radio: As digital radio became more widespread, the station began broadcasting DAB signals in addition to its FM services.

Challenges and Maintenance:

Operating in such an exposed location, North Hessary Tor Transmitting Station faces several challenges:

Weather Conditions: Dartmoor’s weather is famously unpredictable, with high winds, heavy rainfall, and fog, particularly in winter. The height and location of the mast make it vulnerable to these conditions.
Access: The remoteness of the tor means that reaching the mast for routine maintenance or repairs can be difficult, especially in poor weather.

Landmark Status and Visibility:

The transmitting station, with its towering mast, is a well-known landmark on Dartmoor. Due to its height, it is visible from a great distance, making it an important navigational point for hikers and travellers across the moor.
It is also a focal point of interest for locals and visitors to the area, often included in walking routes that take in North Hessary Tor and its surroundings.

Environmental and Conservation Considerations:

Dartmoor National Park: North Hessary Tor is located within Dartmoor National Park, which is a protected area known for its natural beauty and wildlife. The presence of the transmitting station must comply with environmental regulations to minimise any negative impact on the landscape.
Visual Impact: Some conservationists have raised concerns about the visual impact of the large mast on Dartmoor’s otherwise wild and untouched scenery. However, it has been generally accepted as a necessary structure for modern communications.

Interesting Facts:

Symbol of Modern Technology on Ancient Land: The juxtaposition of this tall, modern broadcasting mast against the ancient, rugged terrain of Dartmoor is striking. Dartmoor is famous for its prehistoric stone structures, and the mast represents the blend of ancient and modern in this area.
Nearby Attractions: Close to the mast is the village of Princetown, famous for Dartmoor Prison and the Dartmoor National Park Visitor Centre. These are popular tourist destinations for those exploring the area around North Hessary Tor.

Conclusion:

The North Hessary Tor Transmitting Station is a vital part of the UK’s broadcasting network, serving the southwest of England with television and radio services. Its towering mast is both a functional piece of infrastructure and a landmark on Dartmoor. Since its construction in 1955, the station has adapted to significant changes in broadcasting technology, ensuring that even the most remote parts of Devon and Cornwall can stay connected to national and local broadcasts.

Jump to 1954 Site Tests

NHT Background, Selection and Development

The meticulous selection process for the BBC VHF radio and television transmitting station in Devon and South-West England involved careful consideration and extensive testing conducted at two potential sites.

[Shortly before the Public Inquiry held at Exeter in September, 1953, to investigate the BBC’s proposal to build at North Hessary Tor, it was decided to carry out tests from a further site, King Tor Halt, about ¾ mile (approx. 1km) southwest of North Hessary Tor site. These tests were made to determine whether King Tor Halt might in any way be a satisfactory alternative to North Hessary Tor in the event of the proposals for the use of North Hessary Tor being rejected. The report with the addition of King Tor Halt is here.]

One of the prospective locations under examination was Horner Down. However, after thorough evaluation, the decision ultimately favoured the site at North Hessary Tor near Princetown on Dartmoor, positioned approximately thirteen miles north-north-east of Plymouth. The North Hessary Tor site proved to be the sole suitable option that could adequately cover Plymouth and its environs while also serving the majority of Cornwall, the Torbay district, and Exeter. However, the proposal to construct a broadcasting station featuring a towering 500-ft mast within the confines of the Dartmoor National Park faced significant opposition from the Dartmoor Preservation Society. As a result, a public inquiry was convened in Exeter to address the matter. Following the inquiry, a favourable decision was reached in support of the BBC, leading to the acquisition of the North Hessary Tor site.

Situated at an elevation of 1650 ft, the selected site initially housed a temporary station that commenced operations on 17th December 1954. The temporary setup employed an aerial system consisting of individual dipoles for vision, with one serving as the primary and another as a reserve, along with a separate dipole for sound transmission. These aerials were affixed to a 150-ft square-section mast. The vision transmitter employed was a converted television outside broadcast transmitter, originally used back in 1937 for the coverage of the coronation of King George VI. It boasted an output power of 1 kW, and a modified ET 4336 transmitter served as a backup. Similarly, modified ET 4336 transmitters were deployed for television sound transmission, with one in active service and another held as a spare. The programme content was obtained through direct reception from Wenvoe. Both the temporary and eventual permanent stations operated on Channel 2, utilising vertical polarisation and offsets of -16.875 kHz for vision and -20 kHz for sound.

The permanent station established at North Hessary Tor closely resembled earlier medium power stations in its design and specifications. Notably, great care was taken to ensure that the building’s elevation harmonised seamlessly with the natural landscape of the surrounding area. The permanent station’s construction was completed in May 1956, marking a significant milestone in the project. The fully operational permanent mast and station were unveiled on 7th August 1956, heralding a notable advancement in 405-line television transmissions with a maximum output of 15 kW for vision, measured in terms of effective radiated power.

Source:

BBC Engineering 1922 – 1972 Edward Pawley OBE, MSc(Eng), CEng, FIEE (ISBN: 0 563 12127 0) (https://www.bbceng.info/Books/books.htm)

The Big Tower https://www.thebigtower.com/live/NHT/Index.htm (Historic feature: https://www.thebigtower.com/live/NHT/501P06200319060.htm)

South Devon Television Site Tests

Second Interim Report – 1954 Version

1. Summary

The results from additional site testing for the television transmitter intended to serve the South Devon area have been compared with results from other sites, as previously reported. These earlier results are documented in report K.091, issued in May 1953. The original recommendation from May 1953, which proposed that North Hessary Tor should be selected as the site for this transmitter, has been upheld by these new tests.

2. Introduction

The South Devon site tests were conducted with the aim of identifying the best location for a television transmitter that could provide coverage to South Devon and Cornwall from a single medium-power transmitter. An earlier Interim Report, No. K.091, was released in May 1953, which presented the results from tests conducted at two potential sites: North Hessary Tor, near Princetown, and Horner Down, near Totnes. Based on these tests, North Hessary Tor was deemed the most suitable of the two sites.

However, prior to a Public Inquiry held in Exeter in September 1953 to review the BBC’s proposal to build at North Hessary Tor, it was decided to carry out additional tests from a third site: King Tor Halt, situated approximately half a mile (about 1 km) southwest of North Hessary Tor. These extra tests were undertaken to determine whether King Tor Halt could be a feasible alternative in the event that the proposal to build at North Hessary Tor was rejected. This report presents the results of the tests from King Tor Halt and compares them with the earlier results from the other two sites.

3. General

Initially, it was planned that the South Devon transmitter would use horizontal polarisation to help reduce co-channel interference in the service area. Specifically, it would have reduced interference from the vertically polarised high-power transmitter operating on Channel 2 at Holme Moss by at least 10 decibels. However, due to international agreements under the Stockholm Plan, vertical polarisation was ultimately chosen. Moreover, the effective radiated power (ERP) towards Caen was restricted to 10 kW to meet international transmission limitations.

Due to the adoption of vertical polarisation, the radiation in the westerly direction towards the Holme Moss service area had to be reduced to avoid interference with existing services. To achieve this, a directional aerial was proposed to ensure that the ERP towards Cheshire and North Wales did not exceed 1 kW.

For all three sites being considered, the directional aerial was assumed to have the same horizontal radiation pattern. However, as the sites are located at different longitudes, adjustments were made to account for the reduced radiation towards the western part of the Holme Moss service area. In the case of Horner Down, reorienting the aerial to meet these restrictions would have resulted in a slightly higher output than the allowed 10 kW in the direction of Caen. This could have been corrected with minor adjustments to the aerial design if Horner Down had been deemed the most suitable site.

The following table shows the assumed ERP for the three sites with their directional aerials:

North Hessary Tor:
True Bearings (degrees): 2-10°, 60°, 130°, 205°
ERP (kW): 1, 8, 10, 12
Horner Down:
True Bearings (degrees): 332-340°, 30°, 100°, 175°
ERP (kW): 1, 8, 10, 12
King Tor Halt:
True Bearings (degrees): 2-10°, 60°, 130°, 205°
ERP (kW): 1, 8, 10, 12

4. Results

The results obtained from the three sites are presented in the form of field strength contour maps for the service areas of each site (see Figures 1, 2, and 3, not provided here). The mean field strength for the main towns from each site is shown in Table 1 (see below). Table 2 presents a comparison of the mean field strengths from North Hessary Tor to those from Horner Down and King Tor Halt, expressed in decibels.

Table 1: Comparison of Predicted Field Strengths from Transmitter Sites
This table shows the mean field strengths (in millivolts per metre, measured 30 feet above ground level) for North Hessary Tor, Horner Down, and King Tor Halt at various towns.

Town	North Hessary Tor	Horner Down	King Tor Halt
Axminster	0.26	0.22	0.19
Barnstaple	0.04	<0.03	0.04
Bideford	0.08	<0.03	0.05
Bodmin	0.37	0.19	0.12
Brixham	0.53	1.50	0.38
Bude	0.33	<0.09	0.08
Camborne	0.20	<0.14	0.08
Dartmouth	0.40	1.30	0.31
Dawlish	0.21	0.17	0.20
Dorchester	0.09	0.13
Exeter	0.40	0.29	0.34
Exmouth	0.93	0.70	0.68
Falmouth	0.37	0.24	0.25
Holsworthy	1.40	<0.06	0.32
Honiton	0.36	0.13	0.37
Launceston	3.10	0.15	0.78
Lyme Regis	0.10	0.12	<0.05
Modbury	1.65	7.80	0.86
Newquay	0.24	<0.17	<0.08
Okehampton	0.04	<0.03	0.06
Padstow	0.33	0.18	0.14
Paignton	0.58	3.70	0.16
Penzance	0.15	<0.15	<0.08
Plymouth	7.30	3.30	4.00
Redruth	0.18	<0.14	<0.08
Seaton	0.09	0.14	<0.10
Sidmouth	0.12	0.19	<0.10
St. Austell	1.40	0.50	0.37
St. Ives	0.43	0.17	0.10
Taunton	0.22	0.05
Teignmouth	0.88	0.82	0.83
Tiverton	0.30	0.08	0.09
Torquay	2.20	2.60	1.10

5. Discussion of Results

5.1 North Hessary Tor Site:
The service area contour map for North Hessary Tor is shown in Figure 1, and the mean field strengths for key towns are listed in Table 1. The results indicate that North Hessary Tor provides excellent coverage for the eastern half of Cornwall. However, the western half of Cornwall would receive a weaker signal, ranging from fair to poor. The town of Plymouth, the largest urban area in the southwest, would receive a good signal with an average strength of 7.3 mV/m. Exeter, on the other hand, would experience a weaker signal at 0.4 mV/m, which is less than ideal.

In North Devon, the boundary for satisfactory service is roughly along a line between Bideford and Dulverton, beyond which a satisfactory signal is already available from the Wenvoe transmitter. It is worth noting that viewers could mitigate any occasional interference from Holme Moss through proper orientation of their receiving aerials.

5.2 Horner Down Site:
Figure 2 shows the service area contour map for Horner Down, and the mean field strengths for principal towns are listed in Table 1. The data reveal that Horner Down would deliver inferior service to most parts of Cornwall when compared to North Hessary Tor. The eastern half of Cornwall, particularly, would be screened by the Dartmoor terrain, leading to signal strengths around 10 dB lower than those from North Hessary Tor. In South Devon, the Horner Down site would provide a stronger signal than North Hessary Tor between Plymouth and Torquay. However, Plymouth itself would only receive 3.3 mV/m from Horner Down compared to 7.3 mV/m from North Hessary Tor.

In North Devon, the signal from Horner Down would be significantly attenuated by Dartmoor, and its coverage would not extend north of the moor. Exeter, for example, would receive a mean signal of just 0.29 mV/m, which is insufficient for proper service. The only town where Horner Down would offer superior service compared to North Hessary Tor is Paignton, which would receive 3.7 mV/m compared to 0.58 mV/m from North Hessary Tor.

5.3 King Tor Halt Site:
The service area contour map for King Tor Halt is shown in Figure 3, and the mean field strengths are again listed in Table 1. The results demonstrate that King Tor Halt would provide weaker signal coverage across Cornwall, with signal strengths generally about 8 dB lower than those from North Hessary Tor. Additionally, King Tor Halt would not deliver better signal strength in any part of Cornwall compared to North Hessary Tor. In Devon, the service from King Tor Halt would be similarly weaker, with Plymouth receiving only 4.8 mV/m and Exeter receiving 0.34 mV/m. The area free from interference from Holme Moss would be limited to a small part of South Devon and East Cornwall.

5.4 General Comparison:
In general, a transmitter located at North Hessary Tor would serve a significantly larger area than one located at either Horner Down or King Tor Halt. The superiority of North Hessary Tor is also illustrated by the population figures in Table 3 (not shown), which indicate that more people would receive satisfactory signal strengths from North Hessary Tor.

6. Conclusion

This report confirms that the North Hessary Tor site is superior to the other two sites for a medium-power television station intended to serve South Devon and Cornwall. North Hessary Tor would provide adequate coverage for most of Cornwall, along with excellent service to Plymouth. While Exeter would not receive optimal coverage from this site, the service would still be better than that provided by Horner Down or King Tor Halt. Based on the results of these tests, the earlier recommendation to build the transmitter at North Hessary Tor is reaffirmed.

NHT Background, Selection and Development

See also:

Source:

South Devon Television Site Tests