CommunicationsAudioInterface for Remote Operations

CAIRO Installations

The mechanical constraints which may sometimes exist on CAIRO-8 active modules and require a loose-tail to be used, are less likely to occur with an item of basic CAIRO hardware. Almost always these items are constructed (or modified) by a user who should arrange for the signals tail to be hard-wired into the item. However, for completeness, the rationale for loose-tails is extended down to CAIRO where 5-way Audio connectors, e.g. Maplin Socket FK25C, Plug FM53H, may be used at the in-feeding end of a CAIRO loose-tail, when required. As before, the pins of this Audio connector are assigned to the CAIRO signal/cores to mimic almost exactly the 5-pin DIN format:

CAIRO Pin Assignment for Audio 5-pin Connectors






Signal :






Colour :






CI .1 CAIRO Loose-Tails

All CAIRO loose-tails should be constructed from the prescribed 4-core, individually screened cable (see CE .1) with 4.8mm sleeving at the cable-clamp. Unlike DIN connectors, with their hierarchical mating that is used to full advantage in CAIRO, the two types of Audio connector do not have an equivalent mating compatability, so there can be no confusion between the two types of loose-tail for CAIRO and CAIRO-8 items.

It follows that any single loose-tail must be prepared to the appropriate specification as a complete lead, transporting all signals as defined by the DIN plug (8 or 5 only) on its 'rig'-end. In particular, the 8-way versions must maintain the 'bus-signals' convention of CAIRO-8, even when a particular module operates with fewer signals. This ensures that loose-tails are never module-specific and become general-purpose items, of their type, in keeping with the principal features of Flexibility and Generality in the overall CAIRO philosophy for Remote Operations.

CI .2 Sturdy Lines

Although CAIRO has been conceived as a scheme for hasty installations at temporary sites, User Services may require semi-permanent facilities in strategic buildings. In multistorey buildings, a 'Rig-Cupboard' on the top floor is a good ploy to allow the feeders, from permanent aerials (or from a permanent mast for temporary aerial fixing), to be kept short. Ideally, the 'cupboard' would be a large, lockable office-type metal cabinet with earth-bonded metal shelves. Each feeder would enter to an appropriate outlet, just above the rear of a shelf. Similarly, each shelf would have an Audio-5 connection plate giving access to an installed CAIRO Line which drops, via service ducting, to the Comms-room where it terminates at a wall-plate pair of DIN-7 sockets (see Fig. 19 A).

In principle, any CAIRO-adapted transceiver may be installed on any shelf, either permanently or as required, according to local practice and ownership. However, as each of the feeders is usually associated with a band-specific aerial, so a particular shelf is thereby made band-specific and may be colour-coded to that effect. If so, then the Comms-room outlet wall-plates may be similarly colour-coded to match the rig-shelf with which they are associated. This will simplify installations and avoid confusions whenever there are several CAIRO 'drops'.

The third provision in the Rig-Cupboard should be that of a common 12V supply to each rig shelf, either from a mains PSU in the base or a high-capacity battery-based UPS. Given that the Rig Cupboard should be at or near the top of the building,Wind and Solar charging methods can be considered within the UPS scheme. (Arguably, if a building is strategic enough to warrant quasi-permanent CAIRO provisions, a UPS scheme would seem to be an equally necessary provision against Mains failure?)

Fig. 19 A Fig. 19 B The Sturdy Line
Typical Permanent CAIRO Installation Sturdy CAIRO Line

For the CAIRO 'drops' themselves, a flat ribbon harness having four individually-screened cores, e.g. Altai's F4CS "liquorice" cable, is preferable for being much more sturdy and of lower core resistivity than the normal CAIRO-Line cable. However, as a cable it is too substantial to be terminated directly in a DIN-5 plug, hence the need for Audio-5 shelf-plates and CAIRO loose-tails. These make for convenient connection to the transceivers, either directly or via (CAIRO-8) augmenting modules which would be set-out on the same shelf. For active service, in the Comms-room, short lengths of standard CAIRO Line are run-out from the wall-plates to the operator outlet boxes at the operations desks, and removed again afterwards.
(All such CAIRO sundries may be stored as spares, in the Rig-Cupboard, when not in use.)

CI .3 Spectral Paints

Another CAIRO principle relates closely to the well-known "KISS" criteria and holds that, if an item needs textual labels to identify the functions of its switches, controls, etc., it may well be too complicated (and should be re-thought!). However, colour-coding is always a useful practice, particularly when physically similar items support different services in particular installations. The following colour scheme is based on, but modified from, codes used in PMR and similar circles.

CAIRO Installations Spectral Painting


HF-Low; 160m, 80m, 40m (Red)

HF-High; 20m, 15m, 10m (Orange)

VHF-Low; 6m, 4m (Dark Green)

VHF-High; 2m (light Green)

UHF; 70cms (Blue)

'SHF'; 23cms (Violet)


GREY : 'routine' passive boxes, e.g. Single Operator Box (i.e. unpainted diecast)

BLACK : 'significant' passive boxes, e.g. Dual Op. Box, and 'routine' active modules

BROWN : User-Service primary marker

YELLOW : 'significant' active modules, e.g. TTUs, and RAYNET primary marker

WHITE : Optical, 'BT' or baseband 'data'/digital

When applied, say, to a set of wall-plates in a fixed installation, the plate would be painted overall in the Primary colour, with a vertical band of colour (between the sockets) to signify the RF Band. Thus, a Yellow (overall) plate with a Blue band signifies that it is the remote Raynet 70cms facility, whereas a Brown plate with a (dark) Green band is the User-Service's remote 'low-band' Rig, etc.

CI .4 Portable Sturdy Lines

When the aforementioned quasi-permanent installation is inappropriate, a portable Sturdy Line may be constructed from a heavy-duty blank drum, e.g. Farnell 105-387, which has a capacity for 100m of 'liquorice' cable. To aid rapid installations, the free-end is terminated in a small diecast box with a DIN-7 socket in each of its sides, near the cable entry end of the box. At the other end of the box, a small polythene bag with a 'handful' of lead shot inside (as available to anglers) may be introduced to increase the overall weight as much as possible. Also consider adding a loop of rope (6mm Marlow) through the box, to act as a tie or 'grab'-ring.

All these provisions now enable the Drum to be taken to the top of a building from where its free-end is lowered out of a convenient window to be drawn in again to the Comms Room, several storeys below.. The added weight ensures reasonable stability in high winds and the loop tie is a convenient grab. In the suggested position the sockets are at the 'top' of the box, during lowering, and should not suffer dirt ingress if the end lands on wet ground. Also consider mounting a thick rubber washer (or similar) around the outside of the box, to cushion it against the glass of intermediate windows which it might impact against, when being lowered in high winds.

At the drum, terminate the ribbon cable with a single Audio-5 chassis socket in the side-plate so that a CAIRO loose-tail is used for the final connection to the CAIRO-adapted transceiver, when the drum rotation motion has ceased. (An Anchored Tail would become entangled.) Fig. 19 B

CI .5 Anchored Tails

Experience suggests that the installations, described in this section, account for most of the likely applications of the CAIRO loose-tail and, likewise, the CAIRO-8 loose-tail would only be used on existing 'active' modules, e.g. TNCs, to overcome unavoidable mechanical constraints. Whenever possible an item should otherwise be furnished with an anchored-tail, being a suitable length of appropriate cable terminated in a DIN (5 or 8) plug and passed directly into the item via a grommet and strain-relief anchorage. Not only is it a less expensive way of completing the item, it also eliminates the possibility of that item being rendered useless for the want of a missing tail !






Supplementary Material


Remote Operations

CAIRO Basics

CAIRO-8 Basics

Raynet Packet

CAIRO Installations

CAIRO-8 Relays

CAIRO Relays

Relay Installations

Summary Configuration

Data Card

Handy Hints