I have long been intrigued by a derelict structure that
appears to be the remains of an unusual radio aerial installation on the lower
slope on the south side of Caerketton Hill at Boghall on the A702 Biggar Road
just south of Edinburgh.1
There are two wooden masts fitted with climbing
rungs. The masts are some 30 metres tall and are about 30 metres
apart. Each mast is formed by two wooden poles cut diagonally at the join
and held together with bolts and metal bands around the mast. The masts lie on
a line running exactly east-west.2
They are guyed by steel cables, with a steel cable running between the mast
tops. The masts support a number of horizontal wires of uninsulated
copper or copper alloy, about 2.3mm in diameter. When I first noticed the
masts in 1971 many of the wires were intact. Only five of these wires now
remain, but it is clear from the residual broken ends of wire attached to the
masts that a pattern of evenly spaced wires extended from just below the top of
the masts downwards to within approximately 2 metres of the ground. The wires
are not insulated from the masts. On the west mast the wires are wrapped
around the mast and secured with staples. On the east mast the wires are
attached with hooks and tension adjusters. At the west mast the wires
have been linked by a wire running downwards which was until some years ago
hanging below the lowest remaining horizontal wire.
In front of the masts, about 10 metres downhill and
equidistant from them, three steel frames are set in concrete into the
ground. This steelwork occupies an area measuring about 4.5m x 2.3m and
looks as if it could have supported a small structure or container.
About 15 years ago I noticed redundant telegraph poles
leading towards the site. I don't recall how many poles I saw then.
The insulators on these poles would have carried at least four circuits using
open copper conductors. Two of these poles remain, and they are now lying
on the ground, a result of decay or possibly demolition if they were in a
dangerous condition. The markings carved on the pole nearest the site are
consistent with markings used by the General Post Office (GPO – later the Post
Office and now British Telecom) to indicate the size of the pole and its year
of production.3 The carving on this pole
indicates the year 1957. The other pole has no carving on the side facing
upwards, and it has not been possible to move it.
The east aerial mast bears a carved marking which is not
very deep and is not easily seen, but it is sufficiently clear for the marks to
be readable. The marks consist of the letters GPO with a number 1908
immediately below, and the letter R below the number. This format differs
from that used on the telegraph pole, but it does suggest a GPO
installation. It occurs to me that the number may be the year of
production, and that the lower section of this mast may be a heavy
telegraph pole recycled from an era when repeater amplifiers were not yet in
use and poles carried numerous circuits on heavy copper wires. If the
lower section of west mast had also been recycled, then its markings could be
at the top end. Another observer has noted that the upper sections of the masts each bear a date carving indicating the year 1957. Punch-hole inspection record plates are fixed to the masts. This type of inspection record appears to have been in use from 1964.3
The nearest buildings to the aerial site are a cottage,
and a brick shed with asbestos roof, standing close together about 150 metres
from the aerial site. The buildings do not resemble any typical building
seen at telecommunication sites. The occupier of the cottage states that
the cottage is some 90 years old, and that the shed is used for shearing
sheep. There is no evidence of any building nearer the aerial masts.
There is no sign of a mains power supply to the
site. In this rural location it is likely that any mains power would be
supplied by overhead line, but there is no trace of any power distribution
poles. Nor is there a trace of anything suggesting a supply from an
underground power cable. A redundant power pole opposite the cottage does have
two disused power line insulators, but these look likely to have supported
overhead power lines to the cottage as the cottage has a rusty metal pole with
two similar unused power insulators. The two fallen telegraph poles do
not have any power line insulators attached, those poles being fitted with only
the spindles for telephone line insulators, a few of the insulators remaining
intact. Might the 50-Volt DC supply from the telephone system have been
used for some low-power equipment on the site?
Some years ago an employee working in the Pentland Hills
Ranger Service office at Boghall advised me that she had been told only that
the masts dated “from the War”. A later item in the Ranger Service
newsletter said that research had revealed the masts were part of a high
frequency aerial for receiving radio signals from South Africa in World War II,
although the source of that information was not stated.4 Recent communication from the author of
the newsletter item suggests that the information came from a former BT
employee who was involved in the maintenance of the masts and former telephone
lines to the old Boghall Farm office, and that the South Africa connection was
also known anecdotally by the farm staff and by the estates team of Edinburgh
University. (The University conducted agricultural research at the farm).
The features of the Boghall masts do not seem consistent
with a typical commercial or government aerial installation for long-distance
high-frequency (HF, otherwise referred to as short-wave) communication.
These sites occupy large areas, with substantial buildings, large high-gain
aerials, and back-up power requiring fuel storage and generators.
Long-distance HF communication would have been adequately catered for by other
sites established in the UK before the War.5, 6
To provide long-distance HF communication in the event of invasion in World War
II, an emergency long-distance HF transmitting site was established at Saughton
Mains in Edinburgh, associated with a new HF receiving facility at an
existing GPO low-frequency (long wave) receiving site at Kemback near Cupar. 7, 8 The use of a distant site for receiving avoids the risk of breakthrough from the high power transmitter typically used for long-distance commuinication. The existence of a transmitter site in Edinburgh with receiving facility at Cupar would rule out the use of Boghall as a receiving site for the long-distance system.
The copper wires are not insulated from the masts, and therefore would not be suitable as a driven aerial element. They could have acted as a reflector for some driven element
in front. The steelwork in front of the masts could conceivably have
supported a short mast with some element capable of covering the HF spectrum,
although gain would be limited unless a vertical stack of elements was utilised,
which would then require some additional support. Also, the site on a
hillside seems more appropriate for higher frequencies, at VHF and above, where
reliable wave propagation in normal conditions is limited almost to direct line
of sight. The orientation of the masts would suggest a system with maximum
sensitivity to signals from a bearing exactly due south from the site.
South Africa lies on a bearing of about 15 degrees to the east, not a crucial
difference but one which might be significant given that this is clearly a
professional installation.
The GPO did make use of low VHF frequencies for
telecommunication links using rhombic aerials or curtain arrays of
dipoles. In the 1930s telephone circuits to offshore islands were
provided by this method.9 In 1946 an experimental link was
established using rhombic aerials at relay stations, between London and
Castleton in Monmouthshire, and that link was used later to feed television
signals to a local transmitter.10
During World War II the GPO established an
emergency radio scheme to maintain inland telegraph communication in the event of
disruption to land lines. This scheme used medium- and high-frequencies to link fixed stations at major towns and cities with existing coastal maritime radio stations. The Edinburgh station was located at Dr Guthrie's Boys' School at Liberton.8
In addition, it appears that small receiving
sites were installed near the main long-distance HF transmitting stations to permit remote
operation by radio link (presumably at VHF) from a central point in London if line communication
was lost.7 It is not clear just how far these receiving sites were from the associated HF transmitter sites. It seems that this provision applied only to the
HF stations at Rugby and Leafield.8
The masts appear on an Ordnance Survey map that has been dated 1947 (that date is now suspect as the map shows the modern artificial ski-slope at Hillend a short distance to the north). A small rectangular structure also appears on that map, in alignment with the surviving steelwork. 11 In the absence of any sign of another possible need for the telegraph poles, it seems that they did serve the aerial site. However, it does seem unlikely that a telegraph pole installed
during World War II would need replacement as early as 1957, but that does
remain a possibility. If the telegraph lines were associated with the aerial site, then it can be assumed that the site was still in use in 1957. However, the Saughton Mains area is shown on a map dated 1955 already covered with houses (the date of that map must also be treated with caution as it is taken from the same web source as the 1947 map).11 Continued use of the Boghall site in 1957 would exclude the possibility of a connection with the wartime emergency radio scheme, and possibly the long-distance facility at Saughton Mains. Is it possible that the installation was repaired or amended in 1957, or was that the year of construction?
Microwave technology was well-established by 1952, when
the Manchester to Kirk o' Shotts link was operational.10 It seems improbable that in 1957 an older
type of VHF system with limited capacity would be in use when microwave systems
were already available for fixed short-distance links.
All the evidence suggests that the installation was not part of a long-distance HF communication system, and thus that the story about
communication with South Africa is wrong. If this information did
originate with an employee of the Post Office/BT, then did they or someone else
within their organisation provide disinformation to conceal the true purpose of
the installation?
About two miles east of the site, on the path from Bonaly
to Glencorse, an old warning sign indicates that an area further west into the
hills from Boghall was used for mortar and anti-aircraft practice.12 Exactly when that area ceased to be used is not known. The aerial system does not look like
something intended for a simple communications facility on an exercise area.
Radar, navigational aids, electronic countermeasures, and
signals interception facilities used during World War II have been fairly well
documented, but I have been unable to find any information that might explain
the structure at Boghall. It has been pointed out that the GPO, as a department of government, was involved in close cooperation with the armed services.
It may be suggested that the Boghall installation simply
provided mechanical support for some other device. That seems unlikely
since the wires on the masts are copper, which is more expensive and weaker
than steel. The choice of a good conductor like copper suggests at least
some electrical purpose, although not necessarily related to radio.
Historic Environment Scotland have included several radio
sites on their Canmore website, some of them of comparatively recent
construction, but the Boghall masts seem to have escaped attention.13
I would be interested in any information or suggestions
about this very peculiar installation, any recollections of the missing
structure in front of the masts, or any details about similar aerials found
elsewhere.
References:
7. A H Mumford: Long-Distance Point
to Point Communication (1947) Sections 2.1, 2.2, 2.3
8. BT Digital Archives
