Cave communication for a rescue team

[aricooperdavis]

The field telephones we used at ResCon didn't belong to Mendip, they were brought down by BCRC comms officer from the North Wales team.

My mistake, thanks Estelle! Very good of the North Wales team to bring them down, they were good bits of kit to have a play with

[Stuart France]

Single-wire phones are your cheapest and easiest way forward.  I build a batch of about 30 handsets and 10 base stations for UK rescue teams that ordered them during 2013.  They paid £43 per handset and £64 per base station which represents the parts rather than labour.

These were designed to eliminate all known hassles with the previous generation of caving field phones:
1) stop people from turning them off in the cave (complicated procedure to turn it off once it is on)
2) make them last on three AA cells for over a day's use and step up to a constant 12 volts internally regardless of battery voltage droop
3) turns itself off after many hours of inactivity
4) can send call tones and roger beeps
5) military standard waterproof mic/speaker
6) circuit is potted (not the battery of course) and a single IP68 push button to control everything.

It's written up in the BCA CREJ No.82
http://bcra.org.uk/pub/cregj/index.html?j=82

but you need a login to download the PDF of the article.  That article in Word format and other info about it is in zip file links at:
http://www.linetop.co.uk/cssdata/swt.htm

As to which teams might have spare units they might give away to a good cause:  Gloucester GRG took 10 handsets and SMWCRT took 8.

I may have a few spare PCBs and excess components somewhere, but I've not looked at this since 2013!

[Jopo]

Thought you produced more than that Stuart. Deserved to, fking good sets.
Jopo

[yuvals]

Single-wire phones are your cheapest and easiest way forward.  I build a batch of about 30 handsets and 10 base stations for UK rescue teams that ordered them during 2013.  They paid £43 per handset and £64 per base station which represents the parts rather than labour.

These were designed to eliminate all known hassles with the previous generation of caving field phones:
1) stop people from turning them off in the cave (complicated procedure to turn it off once it is on)
2) make them last on three AA cells for over a day's use and step up to a constant 12 volts internally regardless of battery voltage droop
3) turns itself off after many hours of inactivity
4) can send call tones and roger beeps
5) military standard waterproof mic/speaker
6) circuit is potted (not the battery of course) and a single IP68 push button to control everything.

It's written up in the BCA CREJ No.82
http://bcra.org.uk/pub/cregj/index.html?j=82

but you need a login to download the PDF of the article.  That article in Word format and other info about it is in zip file links at:
http://www.linetop.co.uk/cssdata/swt.htm

As to which teams might have spare units they might give away to a good cause:  Gloucester GRG took 10 handsets and SMWCRT took 8.

I may have a few spare PCBs and excess components somewhere, but I've not looked at this since 2013!

Thanks, that is relay helpful.
Why do you need base station? As far as I understand "Michies" are symmetrical and can be used for both ends of the system.

[Fred]

I'm sure Stuart will reply but having a little knowledge of the Gloucestershire Cave Rescue Group's units I can say there aren't any spare - they are still very much part of their frontline kit.

Regarding the handsets, your right you don't need a specific base station unit. In fact there is a "base station mode" into whcih any unit can be switched - this turns off the auto shut down for example.

The specific base station units have an external speaker and an input for external 12v power - no issue of batteries running out and more appropriate for the control location. The increased price reflects the extra components.

[Stuart France]

Yes Fred is right - you don't actually need a base station.  Any number of handsets can mutually communicate over a single piece of wire (or one laid out in any topology like a Y shape etc) without any base station in the system.

The idea of a base station is the loudspeaker enables everyone in the control room to hear what's going on.  When it's confidential you turn the loudspeaker volume low and the base station operator then listens then via the mil-spec earpiece/mic that in his/her hand since the base station's handset looks just like the underground ones with a PTT push button on the side.

The only 'issue' was that these base stations were designed as 4.5 volts units running from 3xD cells as compared to 3xAA cells in the cave handsets and both designs boost this up to 12 volts internally.  Cave Rescue would not accept primary cells being in a base station and they insisted on having 12 volt lead acid batteries to power the base stations instead.  Goodness knows why as D cells have a shelf life of 5 years and a run time for the base station of 10 days.

Design by committee as ever caused some gremlins, but I think the BCRA CREGJ article shows the original 4.5 volt base station version which is Ok.

[Duncan Price]

Testing of thru-sump cave telephones:

[Stuart France]

OK, the good news is I've had a rummage in my toy box this week and found a few of the now obsolete mil-spec 4T earpieces and some spare circuit boards, already soldered up, for the cave phone handsets.  I've also got a dozen of some "4T-lookalike" earpieces (not military) that I bought cheap on eBay speculatively.  There are none on eBay right now.

The soldered phone circuit boards were made years ago when the BCRC batch of cave phones were manufacturered as spare parts that have never been needed but were funded in price of the delivered handsets, anticipating some hassles I would have to sort out later on.  But I've had no returns of defective cave handsets in 6 years which says something about the design/build or the ability of teams to fix stuff themselves.

So if any bona fide rescue team wants to get in touch with me via a PM then I may be able to sort you out with free PCBs and other parts.  I don't have any left of the metal boxes to house the phones.

[notdavidgilmour]

I believe Cave Link is now out of production 

[Joel Corrigan]

Eh?  What have you heard about Cave Link???

[Fred]

However I've heard from a reliable source within the BCRC that Felix is working on a successor to the current CaveLink. Also support is still available, I know that within the last 6 months he sent out several new keyboards, free of charge, to one of the UK teams with CaveLink.

[Alex]

I believe Cave Link is now out of production 

If that's true, that is quite worrying. I hope they still deal with repairs,  but I guess they could no longer replace them?