Communications Audio Interface for Remote Operations


The technique known as Remote Operations or "Remoting" is a particularly convenient approach for Radio Stations which must be hastily established at temporary locations. It is a scheme which provides a high level of flexibility in the layout of equipment so that a Transceiver, with its power-supply and sundry items, may be installed near to a well-elevated antenna, even if the Operators' position has to be some distance away. The stations which RAYNET establishes, following a User-Service call to an Emergency (or an exercise duty) often encounter physical or organisational constraints which can be accommodated by this flexible approach.

Control stations installed, say, in a User-Service headquarters multi-storey building, benefit most from having the antenna on the roof and only a short feeder to the transceiver installed nearby. This maximizes take-off and minimizes feeder losses, for an optimum transmission (and reception) 'footprint' onto the emergency (or exercise) ground. Remote Operations permit such an arrangement, especially when the actual Operations Room may be as distant as the building's ground floor or basement.

Similarly, Outstations attending a site on the emergency ground may use a similar approach, particularly when being deployed there as a vehicular mobile. The radio equipment can remain secure in the vehicle - and so, still Insured - while the Operator takes up a position inside a tent, caravan, village hall, etc., alongside the personnel for whom the service is being provided.

In both example circumstances the Radio Station is able to meet the primary needs of emergency communications with radio signals that are reasonably optimised, and good overall operational efficiency is maintained.

The required separation is achieved by paying out a length of slender, multi-core signals cable between the transceiver and the remote end, where the operators may use a wide selection of communications Accessories to receive and send messages. By this means they make the best use of the sometimes limited space available for the tasks associated with message handling. The range of Accessories which suit different circumstances, include extension loudspeakers, desk-microphones, 'fist'-microphones, headphones or headsets (being headphones with a microphone attached). These may take a variety of physical forms and be used in a range of appropriate configurations to suit the prevailing circumstances. Furthermore, the scheme also allows a particular operator to design and construct a small selection of bespoke or personal-preference accessories.

The general flexibility of Remote Operations is brought about by employing standardised signals and connectors for all Transceivers and Accessories, so that a set-up may be swiftly plugged together, safe in the knowledge that it will work in all circumstances on every occasion.

When response time is of the essence, excessive set-up delays could be embarrassing.

Fig. 1 Schematic Layout of a 'Remote Operations' Radio Station
KEY: Item operational notes CAIRO items (see later text)
1 Transceiver sited elsewhere to optimise RF take-off Rig-Adaptor signals interface
2 Multi-core signals cable paid out as required "Orange Reel" remoting line
3 Reel of excess cable tucked under desk, on floor
4 Accessory terminal(s) clipped under desk surface Operator Outlet Box connection & control

Having declared that the primary applicability of Remote Operations is for emergency and other hastily established radio stations, the principles and practices which are embodied in CAIRO have been found to be equally applicable in a range of 'every-day' circumstances, e.g. the radio "shack" or vehicle.

RO .1 Clerical Organisation

Radio operations at emergencies (and 'rehearsal' events) invariably involve significant levels of clerical activity and paperwork. At a Control Station the key activities in relation to the radio Net may well include; logging all calls, recording messages sent and received, cross-referring to previous information and message traffic, whilst maintaining duty rotas, activity maps and so forth, to support the entire network of Outstations. This must all be achieved with efficiency, whilst simultaneous liaisons take place with the duty personnel (from the User-Service).

Such intense activity is generally better served by a desk-top organisation which gives priority to the documentation by having face-to-face seating for all personnel. Unlike a conventional radio station - in "the shack" - where equipment typically occupies a bench-like arrangement against the wall, the Remote Station may employ an Operations Desk which occupies a much more centralised and prominent position in the room. This arrangement gives adequate space around the desk for personnel to circulate and deal promptly and efficiently with matters in hand, unhindered by the presence of the radio equipment. (In reality sometimes, the "Operations Desk" may be little more than a portable card- or picnic-table ! )
Also, with the increasing use of desk computers, laptops, etc., for some clerical activities, the additional remote distance reduces any likelihood of RF interference between such computers and the station's Transceiver(s).

RO .2 Simultaneous Operations

More complex activities, where a single Control station must serve many outstations, each delivering significant amounts of message traffic, would not be handled on a single channel without adverse queuing delays. But if two or more radio channels are used to increase message capacity overall, there is every chance that de-sensing between transceivers might occur if they, or their antennas, are too close together. Remote Operations also allow for the radio equipment to be separated properly, whilst keeping all Operators together as a coherent team, either at the same or at adjacent desks in the Control Room. (De-sense avoidance separation is a non-trivial issue; see later 'Chapters'.)

Fig. 2

Multi-Channel Remote Operations

RO .3 CAIRO(Origins)

The forerunner of the full CAIRO scheme was first developed in 1983, by a small team led by Dr. Peter Best, G8CQH. As the idea began to spread (around the UK) the scheme was enhanced, in 1987, into the present Standard by the inclusion of the "phantom-powering" provision for Electret Mikes. Later, in 1990, a user-group augmentation - CAIRO-8 - was incorporated in response to fair-minded feedback. During that development period and since, CAIRO has been validated at numerous emergencies (and training exercises) and also in a selection of non-emergency radio activities, particularly those where multi-operator working is encountered; e.g. contest-group or special-event stations.

Prior to the creation of this Web Site (April, 1997), information was disseminated by way of Magazine articles and then a Manual (see References). It is anticipated that this Web Site will serve existing and future users of CAIRO by offering additional information or clarification pages as these become available.

Within its primary aims for Remote Operations, CAIRO incorporates all the necessary engineering details to support a set of secondary operational enhancements for all radio stations, but particularly those which are temporarily established for emergency communication purposes.

RO .4 The CAIRO Connectors

To avoid the confusion that stems from the wide range of different connectors and signal-to-pin assignments that are found on existing transceivers, CAIRO uses (metallic) DIN connectors throughout. These were adopted because they are widely available, inexpensive and sufficient for the task. Sockets are all of the 7-pin format whilst plugs may be either the 3-pin, 5-pin or 7-pin types.
(The signals have been assigned to the pins to make optimum use of this hierarchical mating.)

Almost without exception, all plugs "look" towards the transceiver whilst multiple, parallel-wired sets of sockets present the (baseband) signals for onward connection towards the remote operators' accessories.
As with any distribution system, chaining, branching and multiple connections are made possible.

RO .5 CAIRO Configurations

The typical CAIRO configuration involves several simple but pre-engineered items. Transceivers require an Adaptor to present their audio and PTT signals onto the 7-pin DIN format. In their most simple form, such adaptors remain external to the Transceiver and do not affect the everyday uses, with the Rig's 'local' or original mike.
Secondly, a length of Line cable is required.
Remote distances of 25m or more are very typical and separations of up to 200m have occurred on fixed channel, VHF or UHF (FM) installations without any noticeable degradation (except that the 'receiver volume' must be increased, slightly). Typically, the Line is scramble-wound onto a drum; e.g. Farnell 147-710, with a single 5-pin DIN plug on the cable's free end and two (sometimes three) DIN sockets set into one of the drum's side plates. The complete item has become known as the 'Orange Reel' being originally constructed from a now-deleted R. S. Components Ltd. blank drum of that colour, but with similar properties and dimensions to the (two-tone grey) item from Farnell .
These drums accommodate about 35m (115ft) of Line Cable (leaving about 15m, from a 50m reel, for wiring-up accessories, etc.).
(The Orange Reel - even when it's grey - is, in effect, the icon of the entire CAIRO scheme !)

Optionally, a remote configuration may also employ one of several styles of Operator Outlet Box.
These permit accessories to be plugged-in, in various combinations, and many of them also provide volume controls so that the listening levels may be adjusted by individual operators, particularly when using the "close-ear coupled" accessories, like headphones or headsets.
The Dual Operator Outlet Box is particularly appropriate when pairs of operators share the duties of a station and use different combinations of accessories according to their personal preferences and given roles. Typically, one person will be the actual Operator at any instant while the other acts as a message Logger. However, their roles may be instantly reversed, by the simple throw of a switch on the Dual Operator Outlet Box.

Finally, the operator(s) will require accessories to terminate the remote line and operate the transceiver in respect of its Speaker, Microphone and PTT circuits. The range of possibilities here is almost endless, but they fall into one of two classes; being either Complete or Partial accessories.

A Complete Accessory houses all three communications functions in a single physical item.
Telephone handsets, modified to include a PTT, or the modern 'speaker-mike' are two examples.

The Partial Accessories include all items which require combination connections at the remote end. Examples here include a desk-mike operated in conjunction with a speaker or headphones, or a headset operated with a separate PTT item. In the latter case, a footswitch is often employed as a very easy to use "Trample-To-Talk" (TTT) control.

These few examples already suggest that partial accessories almost invariably combine in pairs and require the provision of paired sockets at outlet boxes and other distribution panels.

RO .6 Operator Accessories

By its use of standardised signals and connectors, CAIRO enables the user to prepare a set of accessories to suit their personal style of operating, in a selection of likely circumstances. Headphone or headset operating is a common method at busy stations where the background room noise may be partially, if not totally, suppressed. The lightweight items that are widely available for personal portable music systems are well suited to this role. The assignment of CAIRO signals to the DIN pins allows for the electrical separation of the two earpieces to be retained and used to advantage.

Alternatively, the typical monophone headset (a single earpiece with a mike attached on a boom) is very convenient at desk operations and again when used in conjunction with, say, a hand-held transceiver by a pedestrian outstation. But other forms of accessory may also be prepared, perhaps by modifying or upgrading items available on the second-hand market. Airmed's Airlight headsets (ex Pilots) are often favoured. With personal comfort being of overriding importance in maintaining concentration and morale during a lengthy or demanding session, the convenience of changing quickly to a "fresh" accessory, particularly the head-worn items, is a further beneficial feature of the CAIRO scheme.
In arduous duties, relief operators may be called in and the scheme anticipates that they will be encouraged to bring their own accessories for their sole use. This avoids sharing which might otherwise be to the possible detriment of hygiene. The standardised connector makes all this possible.

Should the need arise, running repairs may be carried out by substituting a suspect item; accessory or transceiver, to deal with it 'off-line' with only a minimum interruption of service.

Lastly, it may be noted here that terminals for non-vocal communications (e.g. "Packet") may be rendered compatible with CAIRO (or CAIRO-8) for use in certain mixed-mode operations.

RO .7 Accessory Combinations

Although the Operator Outlet Boxes are not essential items of CAIRO hardware for individuals to own, they are quite widely constructed and retained as Group equipment. Therefore, the basic functions and typical layout of such boxes should become familiar to all users.

The typical Single Operator Box should have a pair of 7-pin DIN chassis sockets, a volume control, and a short length (1.5m) of Line cable to a 5-pin DIN plug. Optionally, it may also have a small switch (as seen at the rear of this HOIME where its internal body is between the two-sets of DIN-pins and their hook-up wiring). The sockets are wired to the incoming Line signals such that they are a virtually indistinguishable pair which may be used as required. A single complete accessory (e.g. a telephone-like handset) may be plugged into either socket or else two partial accessories (e.g. a headset and TTT footswitch) as a paired termination for the remote Line. The volume control is for immediate adjustment of the received audio, for comfortable listening with "close-ear coupled" accessories; the main level having been previously set at the transceiver.

If present, the small switch is a mute for one of the earpieces of any dual-ear accessory.
In one position, both earpieces will be supplied with the transceiver's received audio signal for the accessory to behave as a monaural item. But in the other position, one feed is removed so that one of the earpieces is silent. This provision is a convenience for operators who use headsets which significantly exclude local sounds but who then need to hear from a support operator from time to time. By the use of this switch, the operator is spared the irritation of lifting an earpiece for local conversation and then readjusting it again afterwards.

Exactly which earpiece is muted depends on which socket of the pair the headset is plugged into since, in this respect, they differ very slightly. Muting occurs at the 'left' earpiece pin of one socket and the 'right' earpiece pin of the other socket. Therefore, by a quick and simple test muting, an operator may first discover which socket leaves his dominant ear un-muted and use this for his headset, to then plug his support accessory (e.g. PTT or TTT) into the remaining socket of the pair.
This simple arrangement makes the electrical orientation of single-ear muting independent of the physical orientation of the accessory on the head, so that "handed" headsets may be worn in their correct orientation and "unhanded" ones in either orientation, for maximum flexibility.

RO. 8 Dual Operator Box

The Dual Operator Box is like a pair of single operator boxes merged into one item. (see Fig.3 below)
It enables two operators to work together (as a "buddy-pair") and provide the on-air and local liaison at a main station. The item may be furnished with drawing-board clips (secured by the lid screws) so that, when the operators sit side-by-side at a shared desk, it may be positioned between them under the desk edge.

The Front panel has a large central switch which toggles sideways, and two volume controls to its left and right. The Side panels each have a pair of DIN sockets and a small mute switch which toggles vertically. Each user plugs his preferred choice of personal accessories into the sockets at the Side nearest to him and, independently of the other user, adjusts the listening level with the volume control which is on his side of the front panel.

Fig. 3

Engineering Details of the "DOB" ->

Dual Operator Box


The central switch - the "big switch" - determines which of the two users is currently the active operator, with its toggle arm acting as a simple pointer for this purpose. Electrically, this switch couples the microphone and PTT accessories of the active operator - as pointed to by the toggle arm - onto the Line circuits to the transceiver. At the same time it disconnects the second user's accessories so that s/he can not cause or affect a transmission. (Reception listening is unaffected by this selection switching.) Role reversal, by mutual agreement between the operators, may be instantly achieved simply by throwing this switch, as noted already.

RO .9 Auxiliary Features (DOB)

On the Rear panel where the line-cable enters, as a single 'tail' with a DIN-5 plug on its free end, it is usual to find just ONE extra Auxiliary socket and another volume control. This socket supports additional features for dual-operator working, but, quite intentionally, only one of the following options may be exploited at any time; to avoid electrical conflict and minimise operational uncertainty.

Firstly, an extension speaker may be plugged here and its volume adjusted, independently of the front-panel controls. This would be required when neither operator wishes to use headphones or headsets, but also when both users choose to wear such accessories and yet others in the room still need to monitor incoming radio traffic; perhaps the Duty Controller of the radio team or an Officer from the User-Service organisation.

Secondly, the Line microphone and PTT signals are permanently present at this socket and are unaffected by the front panel selection switch. Thus, if the operators wish to share in the use of a single desk-microphone accessory or a single TTT footswitch, it would be plugged in here instead. Alternatively, various monitoring devices may be attached, like a PTT indicator to show the on-air or standby status, or a suitably interfaced (portable) tape-recorder as a means to log all traffic.

RO .10 "Side-Tone" Enhancement

The final and most subtle feature of this Auxiliary socket is that it enables off-air monitoring; the "side-tone" enhancement, or else supports an operator-operator intercom mode.

The two independent side-panel mute switches each disconnect one earpiece of binaural headsets, as in the single operator outlet box. But, in the mute position, the muted earpiece connection is switched instead to pin-7 of the auxiliary socket where a suitable plug-feeding lead may be used to supply audio from an independent source, when required.

For the "side-tone" enhancement, this audio might be sourced from a CAIRO-adapted hand-held transceiver that is tuned to the main transceiver's (Tx) frequency (or to the 'output' of a Talk-Through Relay, if one is being used), for the operators to hear their outgoing transmissions in one ear - exactly as heard by the Net - whilst listening to the incoming Net traffic, in the other ear.

Alternatively, a simple intercom amplifier might be used so that both operators may hear the active operator's mike, whether s/he is actually on-air or not.

For these purposes the hand-held transceiver or intercom amplifier should be positioned near to the operators, for its own volume control to be used to set a satisfactory listening level.

Usually, the above enhancements will be found to be of particular benefit to the passive operator associated with intensive duties who, for the purposes of accurate logging, is able to note both sides of all radio exchanges, regardless of any distractions occurring around him. Although these options are unlikely to be used in 'low-key' duties, it is strongly recommended that they should only be used, during Emergency and other 'intensive' operations, by operators who have already become familiar with them at practice exercises.

RO .11 A 'Caution'

The general CAIRO configuration, formed from chain-connected lines, distribution panels and outlet boxes, each having multiple-sockets, is intended to be a versatile facility for combining accessories for Remote Operations. Inevitably, this increases the possibility of connecting more than one microphone accessory into sockets which are 'live' to the transceiver's mike input. If this occurs, perhaps inadvertently, transmission audio could be severely degraded, even to the point of being unintelligible on the Air. Therefore, as a matter of routine before commencing operations, operators should always check their remote set-up to avoid this, and should unplug (and set aside) any accessory which is not essential for a particular configuration and operational requirement.

Experience gained in Groups and Teams with a long-standing commitment to CAIRO, suggests that it is of benefit to all members to run practice exercises, from time to time, specifically to test and evaluate their use of CAIRO facilities and their operating techniques within the scheme. Radio support for pre-planned 'fitness' or 'charity' events (Marathons, Charity Walks, etc.) offers a very good setting for this.

RO .12X "KISS" Simplicity

It is the general intention for CAIRO that all items should achieve their purpose as simply as possible; being familiar, to some, as the KISS criteria !
In almost all cases, this should mean that an item will NOT require labels (on switches, controls, etc.) because the purpose should be self-evident to a non-owner, after a few moments inspection and trial use. But from this it follows that designers of items should always ensure that it is never possible for someone else's trial use - their benign "twiddling" - to lead to a malign outcome; e.g. a latched-up PTT (leading to a jammed Net!).

In fact, latching switches for PTTs are generally 'outlawed' in CAIRO, with the notable exception that such a PTT may well be required as part of an in-vehicle "hands-off" arrangement for the user who is both Driver and Operator.






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