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WWV’s 25 MHz Signal is Back on Original Vertical Dipole

08/05/2015

Time and frequency standard station WWV’s resurrected 25 MHz signal — now back on the air for more than a year after going silent in 1977 — is once again transmitting on a vertical dipole from its original antenna and location. The 25 MHz signal came back on the air on an “experimental basis” in April 2014, and it’s been transmitting ever since. The WWV vertical dipole is not something you’d likely find in the average ham radio antenna farm.

“The antenna the 25 MHz [transmitter] is on right now is the original antenna it was on in 1977,” Matt Deutch, N0RGT, WWV’s lead electrical engineer, told ARRL this week. “When the 25 [MHz transmitter] was shut down [that year], the radiating section was removed [and] tossed in the bone yard, and a new longer section put on the tower to make it a 15 MHz stand-by antenna.”

Deutch said that when WWV first reintroduced the 25 MHz broadcast in 2014, it used a broadband monopole. It was later decided to use that antenna for WWV’s 2.5 MHz stand-by transmitter, though. “So, we decided to rebuild the 25 MHz antenna,” he recounted. “A few weeks ago the boys dug the 25 MHz radiating section out of the mud in the bone yard and rebuilt the 25 MHz antenna, so that it looks identical to what it looked like in 1977.”

As Yardley Beers, W0EXS (SK), described in “WWV Moves to Colorado,” in the January and February 1967 issues of QST, “The antennas are center-fed with rigid coaxial cable and are mounted on hinged bases fastened to concrete foundations. The upper one-quarter wavelength section, supported on insulators from the lower one quarter wavelength section, constitutes the upper half of the radiating system. The sleeve consists of nine equally spaced quarter-wave-long wires connected from the center of the tower (one-quarter wavelength above ground) that slope downwards to the ground at an angle of 45 degrees. This sloping skirt, each wire appropriately insulated from ground, not only functions as the lower half of the radiating system, but also serves to guy the antenna.”

Deutch said the 25 MHz WWV vertical dipole now is coupled to its own, dedicated transmitter, radiating 2.5 kW “with near zero watts reflected,” he added, and modeling has showed that the dipole exhibits a lower angle of radiation than the broadband monopole did. “There is no automatic backup transmitter for 25 MHz at this time,” Deutch added. The 25 MHz WWV signal had been operating at about 1 kW for the past 16 months.

Deutch has said that WWV has received reports on the 25 MHz signal from across the Atlantic. The 25 MHz transmission not only provides another option to check your frequency calibration or the exact time, it also can serve to indicate the state of propagation on 12 and 10 meters. 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 signal reports.

 



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