[aprssig] Mammoth Cave APRS Test (quick look).

[Andrew Rich]

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Andrew Rich

On 05/03/2013, at 1:36 AM, Robert Bruninga <bruninga at usna.edu> wrote:

> APRS Cave Test:
> 
> Despite some initial hours of frustration, once the bugs were all found,
> we successfully established a continuous network of 13 digipeaters the 1
> mile length of the Mammoth Cave Cleveland Ave.  (Compare that to the 2000
> mile path we get on our Golden Packet tests in July!).   We demonstrated
> the ability to provide real-time texting and position reporting from
> anywhere along that length to anywhere else along the chain including
> topside.
> 
> It will take time to publish the detail results, but here is what I think
> we learned now:
> 
> 1) VHF range average hop length was 388' with a max of 530
> 2) UHF range average hop length was 439' with a max of 680
> 3) UHF does better.  Even better than the 13% statistics improvement
> suggests.
> 4) Range with a 90 degree passage bend is not drastically different than
> straight
> 5) If waveguide effect exists, it is insignificant.
> 6) Higher power (50W) made little difference to 5W or even less (.5W FRS).
> 7) Typical cave passages were between 30 to 50' wide and 10 to 20' tall
> (big cave)
> 8) More testing needed in smaller passages (though UHF should be good down
> to 2' wide).
> 
> Once everything was configured properly, extending the communications
> system down the cave was as easy as walking until signal was lost, backing
> up 20 to 30' and setting a walkie-talkie(relay) on a rock.  Then
> proceeding.
> 
> Overall conclusion, APRS Radio brings a new range multiplier dimension to
> in-cave communication.  Although the radios are expensive ($500) and need
> a licensed ham radio operator present, the frequency band used is
> identical to the $20 FRS radios available everywhere, making any caver a
> potential contributor to gathering more data on ranges in a much more
> varied environment than the subways of Mammoth.
> 
> Although cavers have used the short range FRS radios in some cases, the
> short range  (a few hundred feet) has not made them a routine part of
> caving.  However, now that APRS has demonstrated how these short ranges
> can be chained together in series up to 14 hops or so, this offers some
> significant opportunities for in-cave communication.  Since anyone can
> test these individual links with just a $20 FRS radio, we would invite any
> cavers to document any FRS radio experience on future caving expeditions
> to gather more data on ranges in a greater variety of passages and to
> document those results.  A paltry 300' radio range in the past has not
> been impressive, but when they can be linked up to 14 times in series, we
> are beginning to see some real potential.  Especially when some of those
> 300' distances may take an hour or more to crawl, communicating at the
> speed of light sure looks handy.
> 
> Results and future info will be maintained as developed on our web page:
> 
> http://aprs.org/cave-link.html
> 
> Bob Bruninga, WB4APR
> US Naval Academy
> 410-293-6417
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