Cave Radio Design

[Rob Gill]

The following letter from Ron Taylor appeared in the CREG Journal and I’m sure that members of this Forum would like to contribute to the discussion:
“
I have been developing the SubPhone, a DSP-based cave radio design which has performed well over a number of trips to Matienzo. [An introductory article appeared in the September 2018 CREG Journal.]

Those involved with the development of cave radios are few, but between us we have an opportunity to make a real difference to cave exploration and safety. Historically, developers have used their own preferences to determine key parameters such as operating frequency and mode with the result that many systems are incompatible.
I suggest that we shape the next generation of cave radios by producing a set of recommendations describing preferred modes, frequencies, beacon centre frequencies etc., to bring about compatibility of future radio systems to support inter-operability for rescues, expeditions and general use.

Perhaps the CREG Forum might be a suitable starting point from which to establish a discussion to exchange ideas and lay down draft specifications.
I'm open to suggestions and would be most willing to contribute.
Ron Taylor
”

[IACooper]

...Historically, developers have used their own preferences to determine key parameters such as operating frequency and mode with the result that many systems are incompatible.
I suggest that we shape the next generation of cave radios by producing a set of recommendations describing preferred modes, frequencies, beacon centre frequencies etc., to bring about compatibility of future radio systems to support inter-operability for rescues, expeditions and general use....

Whilst it's a bit of a pain, 87kHz seems to have been a fairly standard frequency for a good few decades. It was the choice for molephone, and for backwards compatibility was adopted by HeyPhone. Nicola1, Nicola2 and Nicola3 are slightly off 87k, but are close enough to allow compatible operation with only a very slight shift in pitch. A search online shows a few other homemade radios based around the HeyPhone design have adopted frequencies that are basically compatible with 87kHz as well. In a similar way it seems upper side band has become the default standard, even though in practice testing suggests lower sideband offers slightly better Loran-C rejection. I think there's at least one rescue team which skipped HeyPhone and still have Molephone for voice comms. If the aim is to settle on a standard frequency and mode for interoperability, then for backwards compatibility with a lot of radios already in existence, I'd suggest 87kHz USB needs to at least be a fall-back option, even if something else is chosen as a preferred channel when compatibility with others isn't required.

Ian.

[John Rabson]

A general set of desiderata would be a good idea. May I point out a couple of ergonomic aspects which are sometimes overlooked? Members of cave rescue organisation will no doubt wish to comment on these.

Working in a cave rescue situation can be extremely fraught. It was pointed out at the meeting at The Chapel (at the end of which what is now known as the Heyphone was adopted as the design) that the number of controls which could be set by the user should be minimised. For example, some people did not care for a volume control because it could in the heat of the moment be turned down without anybody noticing. John Hey dealt with that by including a stepped attenuator to ensure that the volume could never be set down to zero except when the set was switched off.

Similarly, care needs to be taken with such facilities as setting frequency and sideband.

John Rabson