DIARY
#29
PROOF OF POWER CALCULATIONS
On February
18th, 2001, Mike Willett and I returned to Puerto Rico to accomplish
several things:
a. Check up on the
performance of the 6 Data Radio system network which has been
operating in El Yunque Rain Forest for 4 months since we completed
the installation service requested by the researchers at the
El Verde Field Station and the National Forest Service's Sabana
Field Station, both parts of the Luquillo LTER.
b. Advise Jess Zimmerman,
Principal Investigator of the LTER on his outline plan to
deploy further radio networks to support new Climate Stations
in the forest - building on the success of our NSF installed
network.
c. Review the three
commercial bids made to the University of Puerto Rico to link
El Verde and the associated Stream House to the Institute
for Ecological Studies in Puerto Rico, 18 miles away, both
by Internet data, and Voice over IP from the University PBX
system, giving El Verde Field Station for the first time full
connectivity to the rest of the world, wirelessly, voice and
data.
d. Visit our Relay Radio
site on the top of El Yunque peak to consider other locations
for which the Forest Service wants us to consider, and to
test how well the solar panel - battery combination has held
up under the incessant rain, occasional hurricanes, and available
sunlight on the cloud-shrouded peak.
Great
View and First Findings
As luck
would have it, when we rendezvoused with Fred Scatena of the
Forest Service and Andrew McFadden, or support tech, at the
Catalina Forest Station inside the Caribbean National Forest
boundaries, it was a gloriously clear, cool day in Puerto Rico.
The usual clouds had not yet moved in to obscure Pico del Yunque
- or the view from the top we would need to evaluate other antenna
locations. We drove to the top in Fred's four wheel RV, which
lost its footing several times on the tortuous, even if paved,
narrow road to the top. Some switchbacks are so severe that
Fred has to back up to get around the corner.
We first
wanted to check the battery status of our Peak Relay Freewave
Radio.
First
Andrew climbed the old rusted pole on which we had mounted the
battery-radio box and small antenna, next to the 75 year old
concrete tower built by the CCC in the 1930s to resemble a 1600's
old Spanish lookout tower. Hanging on the pole with one hand,
he unscrewed the now thoroughly rusted screws holding the cover
on the waterproof box.
With
relief we saw that no standing water poured out of the box,
as it had when we first opened it after two months and a hurricane,
back in November. The inside, in spite of the rubber seals,
still was wet from condensation, and the battery terminals were
corroding from the 100% humidity in the area.
In one
of my previous reports I stated - from what I took to be an
authoritative Puerto Rican government source - the fact that
'100 billion' gallons of water falls on El Yunque annually.
I checked that with Biologist Fred, who confirmed what I suspected.
'Only' 100 million, not billion, gallons fall on the forest
surrounding the peak. Still plenty enough to affect absolutely
every metal structure in the jungle.
After
Andrew completed his tiring task, Mike climbed the pole and
put a voltmeter on the battery. If the constant cloud cover
on the mountain had reduced the current flow to the West Marine
Battery enough over the four months, the battery by this time
would show lower than 12 volt rated voltage. With great relief
and congratulations all around, the battery, after 4 months,
showed 14.6 volts DC while still receiving current from the
solar panel. We didn't want to disconnect that critical link.
Had we done so the voltage would have shown a rated 12 volts
or better. Perfect proof of our original design decisions (for
which Mike gets the primary credit) to use a 45 watt Siemans
solar panel and 33 amp hour West Marine battery to power the
station over months of untended operation in the rain forest.
The working goal I had set, was to insure that a data radio
in the rain forest could operate at least 6 months untended,
reliably.
The only
other thing done was to spray a little 'Battery Terminal Protection
Spray' provided by West Marine of Puerto Rico on the terminals
to prolong their life before closing up the waterproof box.
Mike then sealed the box.
Antenna/Radio Location
In spite
of Fred Scatena's best efforts with his Puerto Rican National
Forest Service colleagues in San Juan, the yearlong 'temporary'
location he secured us for our relay radio on top of Pico de
Yunque, other Forest Service staffers want all the radio apparatus
on the old Spanish observation tower - called on USGS Map Sheets
as the 'El Yunque Tower' - removed so it can revert to a tourist
site. Ours is the most unobtrusive equipment of all.
This
incident underscores the recurring fact - not unique to Puerto
Rico or the National Forest - that installing a wireless system
or network always faces the requirement for very strong commitments,
for long term 'permission' to put up technically required antennae
or relay points on property not under control of the installing
entity. We thought we had such strong commitment from the US
Forest Service, and we were repeatedly reassured there should
be 'no problem.' But there was - and having once sited through
careful and costly site surveys the optimum location for a relay
radio point - it is destructive of a wireless network project
to be faced with arbitrary changes by the owners of key locations
for radios and their associated antennas and power supplies.
This is especially true for long term environmental or biological
study area projects - where operation of the fixed wireless
network is usually needed for 3 to 5 years at least.
Fred
Scatena, on top of El Yunque
So Fred
pointed out the one site which belongs to the Forest Service
which, unlike the Castle Communications radio tower complex
(which can cost on a lease-space basis as much as $1,500 a month)
can be used free of monthly costs since this is a federal government
scientific research project.
Below
is a look from the Spanish Tower roof level, where our current
radio is, down to the US Forest Service buildings and radio
towers. The metal fencing in the foreground is where the Forest
Service would like us to consider.
It only
took a cursory examination of this site to see it would be totally
unsatisfactory. The entire Bisley and Sabena 'sector' - the
Forest Service responsibility portion - or about about one third
of the perimeter would be totally cut out from radio communications.
We then
looked at a possible location just beyond a power pole that
will have to remain in place, and it looked marginally feasible,
reaching all distant data logger sites, but possibly being cut
off from El Verde station, which is much closer to the base
of the highest portion of the Peak, and masked from some of
it.
Only
a return visit, with a systematic test of the relay radio at
the two other proposed locations would prove whether they would
work even to link up the current 4 locations beyond El Verde.
We may have to tell Fred to tell his FS colleagues that, if
the radio is moved, one or another of the major data logging
weather station sites would be lost to wireless communications
- all for aesthetic considerations.
Sabena
Operational Experience
Fred
Scatena brought with him a printed log we had Carlos keep -
the chief data manager for Sabena's field station - each time
he attempted to use the radios to download the Campbell Data
Logger data from Bisley and Pico del Este since the day we first
set it up - October 20th, 2000. Exactly 4 months before.
The
data was very encouraging. In spite of only using a 4db omni
antenna at the Sabena site - covered in other Progress Reports
- Fred reported they use the link 'almost every day' successfully.
And in spite of heavy rains at times that attenuate the signal
- largely because the energy is reflected and dispersed by wet
leaves of the thick jungle foliage the 915Mhz, 1 watt signal,
has to pass through for 4.2 miles, they have found the link
useful. If it were necessary the link could be made more robust
by using a directional Yagi and a small tower near the Sabena
work center. As it was, Andrew replaced the 20 feet of high
loss RF cable between the work building and the antenna, with
LMR400 cable since our last visit, and he reports that there
is more reliable connectivity. The LMR400 should only lose about
1dB of signal strength between the radio and the roof antenna.
So both
the El Verde and Sabena Field Stations have a working set of
digital wireless links to the three Weather Stations at Bisley,
Pico del Este, and El Verde which has operated for 4 months
without failure. We consider that a success, even though further
refinement is possible.
LTER
Plans for Expansion
When
we met with Jess Zimmerman at El Verde Station next day we discussed
the possible expansion of the wireless network. As it turns
out there are 4 additional Climate (weather) stations in the
Mameyes drainage basin that permit elevation differentiation
in reading climate conditions. They all have Campbell Data Loggers
and some have 'short' towers in place. This is basin in which
the Bisley, and up on top, the Pico del Este data loggers and
radios now are installed and operating. (Later there may be
more placed in the Espiritu Santos drainage - which is the slopes
of the mountain where El Verde station is now. We agreed that
on our next visit, when we must test alternative locations for
the El Yunque peak relay radio, we could do a specific site
survey, with radio tests of two of the new sites. We would want
Andrew McFadden and the person Jess mentioned as being a data
collection person to do the actual survey work, under our supervision
- so that they can begin to take over the responsibility, using
separate LTER Funds, for expansion of the network, as well as
maintaining the current 6 radio sites.
Then
Jess could order the radios and equipment necessary from his
NSF LTER supplementary funds, and on a later visit we could
supervise their installation. After which the Luquillo LTER
could be totally responsible for the wireless network, and I
could transfer ownership of all existing radio property from
our project to the LTER.
That
would by the final step of 'technology transfer' from our experimentation
to the LTER's operational uses.
EL VERDE 4 Months Experience
Dr. Jill
Thompson, who has been doing the biweekly data downloads from
the El Verde Tower - previously manually by climbing the tower
and bringing down the data module from the Campbell CR21X -
has now downloaded new data every two weeks by our radio network,
for 4 months.
She reports,
except for a short period in which errors were made that dropped
the battery power to 6 volts, the data was accessible and downloaded
perfectly all 8 times, over the 4 months. In any weather.
Mike
Willett had to do a tutorial for Jill and Andrew to be sure
they knew how to monitor the battery voltage. They had been
doing it from software on the PC in the Lab, but that is simply
not accurate enough. It should be done whenever they suspect
battery problems. She feared an overcharge, with voltage reaching
over 14 volts, would damage the data logger.
This
exercise underscored the continuous need for technical expertise
usually beyond that, or the interests of, the researchers, to
insure the network, over time works properly. I underscored
that need to Jess, and it will be a major Finding of this NSF
Project for all wirelessly networked LTERs.
First
Test of 433Mhz Radios
Mike
Willett brought a pair of Radio Metrics 433Mhz,50mw AM radios
using small, commercial 9 volt batteries that operate at much
lower frequency than the 915Mhz spread spectrum Freewaves 433Mhz.
He had enclosed them in a case with a status light which would
indicate sending and receiving while in test mode.
We wanted
to see just how far out into the Sonadora Plots through the
thick foliage they would operate. Andrew and Mike made several
walking tests - but they failed within 150 meters of the Station.
We
will have to do more work on being able to install progressively
better gain antenna.
18
Miles of Line of Sight
We concluded
this trip to Puerto Rico and the LTER with Mike taking a trip
to the future location of the Institute of Tropical Studies
on the main University of Puerto Rico Campus 18 miles away in
San Juan. While not part of our NSF Project, Jess Zimmmerman
wanted our expert judgment on whether it would be feasible for
him to contract with a communications company to install a wireless
data and voice over IP link from the Institute to El Verde Station.
Andrew
and Mike were able to get to the roof of the new location, which
appears to be more feasible for making an 18 mile Microwave,
line of sight shot to the El Verde Tower than the old location
was.
Only
more examination, with binoculars and perhaps mirror flashing,
will determine if the path is clean.
With
that we concluded our February trip to Puerto Rico.
