Doug Lung / 12.20.2012 04:10PM
RF Shorts for Dec. 20, 2012
A review of RF-related news during the past week
HF Radar Used to Observe Ocean Currents
Last year in another RF
Shorts story I wrote about tracking
ocean currents by radar. This week I found Notes
from the field: Observing the ocean from dry land by Dr.
Martini that explains exactly how it works in practice, with photos.
“While the scenery was amazing; we did in fact
have a mission,” said Martini. “And that was to take down the six antennas (three
at each site) that make up a HF Radar array. The HF Radar is land-based
instrument that oceanographers use to measure surface currents. It does this by
transmitting electromagnetic radio waves out over the ocean, where they are
reflected back from waves at the surface. The reflected waves are then measured
by a receive antenna, also onshore. By figuring out how the transmitted waves
change after reflection, we can determine the speed of water at the surface.
And there are some pretty rad physics that make measuring ocean currents from
land possible.”
The article includes graphs
and charts showing the results of the measurements.
“HF radar systems give us a
lot of data,” said Martini. “They give us large scale maps of coastal surface
currents and illustrate how these currents change in time. By comparing the HF
radar data to wind data or even tidal models, we can figure out which dynamics
drive these currents. In terms of biology, knowing which way the surface
currents are moving gives us information on where nutrients are going, or where
they are not.And even more importantly,
the real-time data can be used to respond to man-made disasters such as oil
spills or waste dumps. Figuring out where pollutants may go is key to figuring
out how to contain them.”
I was surprised at his
comment, “if you live near the coast in the “Lower 48,” there is probably an HF
Radar system measuring your currents—right now!”
To prove his point, he
provided this link: http://hfradar.ndbc.noaa.gov/.
PC Board Log-Periodic Antennas
Once again I've come across
another excellent article from “Test and Measurement World” on affordable RF
test equipment. This time it’s PC
board log periodic antennas by Kenneth Wyatt. He writes,
“Always on the lookout for low-cost and small broadband antennas that I can
pack into my EMC troubleshooting kit; and having seen a few displayed at the
EMC symposia, I thought I'd look into PC board designs. It wasn't long before
one antenna designer rose to the surface in my research - Kent Britain
(WA5VJB). Now, I'd known of Kent from past amateur radio microwave symposia and
other VHF+ radio activities, but I'd forgotten he also specialized--and sells--
a number of off-the-shelf and custom PC board antenna designs. I decided to order
three types of log periodic (LP) antennas designed for the frequency range, 400
MHz to 11 GHz. Together, they cost me all of $53. He also sells an interesting
Vivaldi ultra-wideband (UWB) antenna covering 5 to 18 GHz for just $6.”
It sounds like these could be
just the thing for tracking down third-harmonic radiation from UHF TV
transmitters and identifying local interference on UHF through microwave
frequencies.
Polish Government Mandates Outdoor TV Antennas
Last week Andrew Katolo at
Screendigest.com, reported New
Polish building regulations specify TV reception equipment. He
writes, “All new blocks of flats built in Poland from next year will be
required to include infrastructure for receiving digital TV and Wi-Fi,
according to regulations from the Polish Ministry of Transport and
Construction. The new regulations will come into force in March 2013. Every new
block of flats will have to be equipped with collective digital terrestrial
antenna, a collective satellite dish of at least 1.2-meters in diameter set to
receive signals from at least two satellites, as well as fiber and cable infrastructure,
including switches to the public network and connections to every dwelling.”
He continued, “Regarding TV
services, the new regulations do not favor any platform. Inhabitants will be
able to choose any provider present in their area depending on their offering.
Cable TV players will be able to save on network roll-out and invest more
elsewhere. The DTT platform, currently offering 15 free-to-air channels, will
become even more attractive without the need to buy the antenna typically
required in urban areas. Nonetheless, satellite TV seems to benefit most from
the regulations, with dishes being pre-installed.”
Here in the United States many
apartment houses used to provide an over-the-air antenna connection. As cable
TV became more popular, the antennas were neglected or disconnected and
residents had no choice but to subscribe to the cable or satellite service the
landlord allowed into the building. I like the Polish plan that gives tenants a
choice.
Comments and RF related news
items are welcome. Email me at dlung@transmitter.com.