The resurrected 25-MHz signal of time and frequency standard station WWV 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.”
Deutch has explained that 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 stand-by antenna,” Deutch 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 stand-by 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 are aware that [the 25-MHz signal] is available, if it can be useful to them.”
Before the change, Deutch said WWV had received reports on the 25 MHz signal from across the Atlantic. The 25 MHz broadcast includes the same information transmitted on all other WWV frequencies and at the same level of accuracy.
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