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.
Located in Fort Collins, Colorado,
WWV is operated by the National Institute of Standards and Technology (NIST).
WWV has invited listeners’ comments and reports on its 25-MHz signal.
