A Brief History of Cave Rescue Telephone Use

Modern use of cave phones

Early use of cave phones

For many years, telephones and wire have been the preferred means of cave rescue communication in North America. Recycled military surplus field telephones are used extensively, along with custom-made devices to a lesser extent. All this equipment has pros and cons so it's good to periodically re-evaluate and try to improve upon what we have. 

EE-8

The old EE-8 is a WWII era phone which has seen cave rescue use in the past. It does OK above ground, but is not particularly well-suited to the cave environment. These phones are not sealed units, the wiring and components are exposed, and the whole package is heavy (10 lbs) and bulky. The military phased these out half a century ago, and now the cave rescue community has too.

TA-312

The popular TA-312/PT phone with the crank handle ringer dates from the 1950's and has been used successfully in cave rescues for many years. The TA-43/PT is an earlier, near-identical version of the same phone which has also been used for cave rescue. These phones have significant range and reasonable clarity. The main drawback is they are heavy (9 lbs) and cumbersome to carry through caves. This can increase fatigue and reduce the efficiency of communication team members, who also have the task of installing and removing comm wire. Also a solid, bulky item like this might inadvertently be handled more roughly than it should, which can contribute to equipment faults.

TA-1

The TA-1/PT sound-powered handset phone is smaller, lighter (3 lbs) and more convenient for carrying through caves. It was also developed in the 1950's, and it has a mechanical visual indicator which works in conjunction with the ringer to show when a call has been missed. Unfortunately, being a sound-powered unit, it has limited talk range and voice is more difficult to hear. This can become critical when more than two phones are connected to the same wire. Other than relatively short range point-to-point, this phone is generally less effective than battery-powered phones for reliable cave rescue use.

TP-6N

More recently, the NATO TP-6N field telephone has been introduced to the cave rescue community as a compatible alternative to older US phones. While this 1970's technology is not exactly new, this rugged phone is substantially smaller, lighter (3 lbs) and the voice clarity is excellent. It offers a ready-made solution which avoids many of the frustrations of earlier cave rescue telephone equipment, and these phones are now popular among cave rescue organizations in the US.

The last analog field telephone used by the US military weighs less than the TA-312/PT but is still rather bulky. More recent units are all digital, and will not work with existing analog field phones. Switching entirely to digital communication for cave rescue would mean adding an unnecessary level of complication. Digital phones often have four terminals, requiring the use of either 4-conductor wire or doubling up on 2-conductor wire. This translates to an increase in weight, cost and complication. None of these later phones are considered practical for cave rescue use.

Piezo transducer 'bubblegum phone'

Not all telephones used in caves are stock standard military equipment. Numerous custom-built designs have been successfully integrated with the military-style field telephone system, although many lack a signal generator to ring other phones. These designs range from a simple piezo transducer elements being used as a rudimentary sound-powered phone, to slightly more elaborate versions like the Cave Rescue Telephone Project, the Cheap Field Telephone and the Pocket Field Telephone. 

Michie Phone

The Michie Phone (pronounced "mickey" - named for the Australian who invented it) is another type of custom-built cave telephone system using only a single wire with a high-impedance earth return. These sealed, compact units are currently used for cave rescue communication in Australia and New Zealand, and a similar Single Wire Telephone system was developed in the United Kingdom. These relatively compact and lightweight systems have been used for caving expeditions around the world. Michie Phones are no longer commercially produced, and these single wire systems will not work with two-wire field telephones.  

HeyPhone

Other types of 'phones' used in caves require no connecting wire. These are earth-current phones and cave radios, which use Very Low Frequency (VLF) electromagnetic induction antenna loops and/or ground stakes to transmit through solid rock. Many versions have been built over the years and used for cave rescue and project caving communication, particularly in the UK and Europe. These include the HeyPhone, the Molefone, and the Nicola System. A Canadian-made version known as the Drummond cave radio has seen occasional rescue use in parts of the US and Canada. 

For non-rescue use such as remote caving expeditions, a pair of cave radios can be very convenient. High Frequency (HF) amateur radio equipment is also being used for voice and data communication in US caves, but this is mostly confined to the dry desert cave environment. Common Citizen Band, Family Radio Service and rescue agency handheld radios can be useful for rescue communication up and down pits and in shallow lava tubes, but the range is severely limited by solid rock. Another option is to program a series of handheld radios to automatically forward data messages back and forth along cave passages using the amateur radio Automatic Packet Reporting System (APRS) or similar methods. 

Cave Radio

VLF cave radios like the example shown above offer significant wireless convenience, but usually at the expense of having to carry and operate bulky, complex and costly equipment susceptible to fickle anomalies. They are best suited to caves where the equipment has been tested and is known to work. While one design may work well in the desert or in lava tubes, it may not be as effective in wet limestone or near sources of electrical interference. 

With a few exceptions, cave radios are not readily available to most cave rescue personnel in the US. Those teams that do use cave radios commonly supplement them with a field telephone system and message runners for redundancy and to communicate with additional locations in the cave. As cave radio technology gradually improves, ultimately smaller, cheaper and more effective units are likely to evolve. However the simplicity of a standardized and robust wired telephone system is a good fit for most cave rescue organizations in North America, and is unlikely to be phased out any time soon.