[amsat-bb] Mount Carmel HS ARC marine buoy deployed and transmitting

Phil Karn karn at ka9q.net
Thu Jul 16 22:44:02 UTC 2020

Over the past year, Randy, KQ6RS and I have mentored the MCHSARC in
designing and constructing a simple marine buoy that was deployed from
the R/V Sally Ride this morning about 700 km off the coast of southern
California. It is up and transmitting WSPR on 20m using the callsign
KQ6RS, and is being received all over the US and into Canada and Brazil.

The electronics is the 20m WSPR version of the WB8ELK "pico tracker"
that has been flown quite a few times (including by us) on long duration
balloons. We removed the solar panels and substituted 21 ordinary
alkaline D-cells wired to supply 4.5V. We estimate battery lifetime will
be 6 months.

The basic design was inspired by Bob, WB4APR, at the US Naval Academy.
Physically, the buoy is just a 5' section of 4" PVC pipe, ballasted at
one end to float vertically in the water. The top is closed by a sewer
pressure test plug I found at Home Depot; it has a bolt in the center
that acts as a convenient feed-through and mounting point for the
antenna, a stainless steel CB whip with a matching network designed,
tested and carefully tuned by Randy. We use the sea as a counterpoise,
but to avoid direct metal/seawater contact we lined the inside of the
pipe with copper tape to form a capacitive connection. We probably spent
too much time on this; Randy even modeled the electrical fields in the
seawater with a professional RF analysis package.

In our first flotation tests in Randy's swimming pool we found that the
ballasted pipe, by itself, was remarkably stable in pitch, roll, sway
and surge but oscillated a lot in heave (up and down). To damp this
Randy added cross arms at the water line to add drag in the vertical
direction. (It wasn't our intent to mimic a religious icon but that's
where the physics went.) Tuning the antenna required sea water, so Randy
did it from a dock on Mission Bay here in San Diego.

We tried to make this thing as rugged as we could. (My favorite saying
to the students was that the sea *always* wins in the end, but we can
delay that long enough to be useful.) Everything inside is held in place
with epoxy or polyurethane foam. Randy reinforced the sewer plug with a
PVC end cap with a hole cut in the center. Although the antenna is
stainless steel, Randy covered it with a type of heatshrink with a
waterproofing compound inside. Activation was by removing an external
magnet placed over a parallel pair of normally closed magnetic reed
switches. (Using two instead of one was my idea.) We even argued how to
guard against the crew forgetting to remove the magnet before
deployment. Randy found some adhesive that would dissolve and let the
magnet fall away; I suggested a big REMOVE BEFORE FLIGHT tag and a float
that would pull it away if it was tossed into the water.

That left the problem of deployment. We couldn't just drop it close to
the coast because it would quickly wash back up on the beach. We needed
a boat ride. We were originally going on a NOAA vessel in April, but
that trip was cancelled due to the pandemic. Randy secured a trip on the
R/V Sally Ride, a research ship operated by Scripps Institute of
Oceanography and home ported here in San Diego.

This map shows the "lawn mowing" pattern they follow to measure and
sample sea water off southern California. We were deployed early this
morning at the most southwestern point shown here:


First report was at 12:52:30 UTC this morning from 29 51.25N, 123
37.50W. That's grid square CL89eu, which I figure is pretty rare for
grid hunters. The current carried us east into CL89fu at 20:32:30. This
is a little surprising since we thought the currents in that area are to
the southwest. But that's why you do science!

You can track us on aprs.fi here:


We also show up on wsprnet.org


Because of the funky way Bill encodes position in WSPR (which was never
designed for this), you'll see some weird-looking callsigns (like
0W7NFU) in addition to KQ6RS.

This was our first buoy, just to get our feet wet (ha ha). Now to think
about what we want to put in our *second* buoy. Two-way links, satellite
tracking, sensors, the works. But remember the "second system" effect...

73, Phil

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