RF Shorts for Dec. 20, 2012

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.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.