DX Engineering donates amplifier to make more QSOs possible.
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Well into its 77th year, the United Nations Amateur Radio Club (UNARC) continues to operate from the UN Headquarters in midtown Manhattan—an employee amenity tucked among far more ordinary facilities like a ping-pong table and a basketball court. Yet behind this modest description lies one of the world’s most distinctive amateur radio stations: 4U1UN.
Remote operation has become the norm in recent years, enabled by the club’s robust network infrastructure. A dedicated fiber link provides stable internet connectivity, allowing UNARC members—including UN operators posted abroad—to run the station from afar. The FlexRadio Flex-6600, loaned to the club by FlexRadio and chosen for its reliability and simple network setup, has performed virtually nonstop for more than five years. Its panadapter has proved indispensable for navigating the dense RF noise endemic to Manhattan and the UN campus.
Complementing the transceiver is an efficiently designed amplifier chain. The ACOM 500S—a lightweight, remotely managed solid-state amplifier donated by DX Engineering, integrates seamlessly with the ACOM eBox and ACOM-06ATtuner/switch. Operators can select any of the three primary antennas without additional switching hardware. This combination has powered thousands of recent QSOs and has enabled increased activity on the low bands, where demand for the 4U1UN DXCC entity remains especially high.
Antennas Above a 500-Foot Icon
Perched atop the UN Headquarters tower, the station’s antennas brave fierce winds, winter storms, and the occasional hurricane. Each maintenance trip requires coordination across multiple UN departments—a natural complication when working in a secure building. Still, regular roof visits keep the equipment and antennas in top shape.
HF & Low-Band Antennas
Alpha Delta DX-LB Trapped Dipole (160/80/40M): This antenna was selected both for its rugged construction and because its compact design fits within the limited rooftop space available at UN Headquarters. A full-size 160M dipole could not be accommodated, so a trapped dipole provided the ideal alternative. The DX-LB is supplied with heavy-duty Alpha Delta End Insulators (ALF-DELTA-CIN) made from UV- and RF-resistant Deltalloy, an essential durability feature given the extreme winds atop a 500-foot building.
The dipole is installed in an inverted-V configuration on a Rohn 9H50 Telescoping Mast, with its uppermost, thinnest section removed. Constructed of galvanized steel for corrosion resistance, the mast collapses into a compact size, making transport to the roof significantly easier. It is guyed with 5mm Mastrant-P Rope (MP05100)—a lightweight, UV-protected, nonconductive synthetic line known for its strength, abrasion resistance, and long service life, with no impact on antenna performance.
The SteppIR BigIR vertical antenna covers 40-6M and uses band-specific tuned radials. Its greatest advantage is multiband capability within the tight footprint available on the UN rooftop. Band changes are controlled remotely through a simple web-browser interface. The BigIR has operated continuously and without failure for the past seven years.
VHF & Beacon Antennas
For 6 meters, a three-element M2 6M3SS Beam was recently added to the station. This antenna was selected for its compact size, light weight, and relatively broad radiation pattern—an important advantage since the current installation cannot accommodate a rotator. A three-element design provides meaningful gain without the narrow beam-width of larger arrays.
The antenna is mounted horizontally on the side of the Rohn mast in a perpendicular configuration, using DX Engineering Genius Clamps (DXE-SSGC-2P). These brackets are simple, durable, and adaptable to many mounting needs, and are made from 1/8-inch-thick 304 stainless steel for long-term corrosion resistance.
The club’s 6-meter capability received a major boost when the M2 beam was installed—a project spearheaded by Metin, K2ECE, the current club president. Nearly 2,000 QSOs across 37 DXCC entities were logged in its first season. With the amplifier now online, even stronger results are expected.
Meanwhile, the Northern California DX Foundation (NCDXF) Beacon continues its mission of contributing to global real-time propagation monitoring.
The Cushcraft MA5VA 5-band antenna has been serving the long-running NCDXF 4U1UN/B beacon. A failed beacon transmitter was recently replaced with an Icom IC-7200 provided by NCDXF. The radio is co-located with the UNARC rack on the 42nd floor.
The Challenges of Operating from the Heart of Manhattan
The most stubborn obstacle at 4U1UN is not paperwork—it’s noise. Urban RF interference regularly sits at S5–S7, easing only slightly on weekends. With countless electronic devices in and around the skyscraper, weak callers often struggle to rise above the noise floor. New AI-based filtering solutions, which have shown promising S/N improvements in early trials, are now being evaluated to help level the playing field for distant stations, especially in Asia.
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- UN Secretariat Building, New York City. The United Nations Headquarters rises nearly 500 feet above Manhattan—home to the 4U1UN Amateur Radio Station. (Image/KO8SCA)
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- 4U1UN Equipment Rack, 42nd Floor, UN Headquarters. The station’s equipment rack sits just below the roof, housing a Flex-6600 SDR, ACOM 500S amplifier, and control gear. (Image/KO8SCA)
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