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WWV 25 MHz Signal Swapped to Circular Polarization, Reports Invited:

from The ARRL Letter on July 13, 2017
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WWV 25 MHz Signal Swapped to Circular Polarization, Reception Reports Invited:

The resurrected 25 MHz signal of time and frequency standard station WWV http://www.nist.gov/pml/div688/grp40/wwv.cfm is now emanating from a circularly polarized turnstile antenna. WWV had used a vertically polarized antenna on 25 MHz in the 1970s. Silent since 1977, the 25 MHz signal returned to the air on an "experimental basis" in April 2014, and it's been transmitting ever since -- initially on a broadband discone until August 2015, when it switched back to a vertical, which it used until the July 7 switch to circular polarization.

"[W]e are broadcasting with 2 kW from a circularly polarized turnstile antenna," WWV lead electrical engineer Matt Deutch, N0RGT, told ARRL this week. "It is just your standard plain-vanilla turnstile -- two horizontal orthogonal dipoles with a quarter-wave phase-shifting coax linking them."

When the 25 MHz transmitter was shut down in 1977, the antenna's radiating element was "tossed in the bone yard, and a new, longer section put on the tower to make it a 15 MHz standby antenna," Deutch has recounted. When WWV first reintroduced the 25 MHz broadcast some 37 years later in response to requests, it used a broadband monopole. But, it was later decided to use that antenna for WWV's 2.5 MHz standby transmitter and to rebuild the 25-MHz antenna. The old radiating section was retrieved, and the antenna rebuilt so that it looked like what was being used in 1977.

Deutch said it's hoped that the latest antenna change to circular polarization might be helpful to anyone studying propagation during next month's total solar eclipse, which will be visible across the US. "My effort right now is focused on getting the word out, just to make people aware that [the 25 MHz signal] is available, if it can be useful to them."

Located in Fort Collins, Colorado, WWV is operated by the National Institute of Standards and Technology (NIST http://www.nist.gov/). WWV has invited wwv@nist.gov listeners' comments and reports on its 25 MHz signal.

Source:

The ARRL Letter

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