Urban ham radio operators face a familiar set of challenges — limited space, noise-prone environments, and landlord restrictions. The Multiband City Windom Antennais a well-engineered solution that fits neatly into these constraints. It is an end-fed wire antenna that combines a 26-metre radiating element with a 1:4 impedance transformer and a common-mode choke. Together, these components produce a clean, wideband HF antenna that performs reliably across multiple amateur bands.
City Windom Antenna : Physical Layout
The City Windom is built around five key components: a PL-259 connector at the transceiver, a common-mode choke, a 13-metre length of RG-58 coaxial cable, an LLT 1:4 impedance matching transformer, and a 26-metre copper radiating wire.
The PL-259 connects directly to the transceiver. The feedline — RG-58 at 13 metres — can be of any practical length depending on your station layout. This flexibility makes deployment straightforward whether you are working from a balcony, rooftop, or garden.
Common-Mode Choke
Without a choke at the feedpoint, the feedline becomes part of the antenna. When the antenna system is unbalanced, this causes the feedline to radiate part of transmitted power, and on receive, noise and signal picked up by the feedline couples directly into the antenna.
The choke in the City Windom sits at the transceiver end of the feedline. It suppresses common-mode RF currents from travelling back along the coax shield into the shack — a critical function in city environments where RF noise is already elevated. The result is a cleaner signal, reduced interference to domestic electronics, and better radiation pattern integrity.
LLT 1:4 Impedance Transformer
The feeding point of a multiband end-fed antenna is essentially a wideband impedance transformer. The end-fed wire presents a very high impedance — typically around 2,500 ohms — and the transformer brings this down to the 50 ohms that most transceivers expect.
In the City Windom, the LLT 1:4 transformer sits at the junction between the RG-58 feedline and the 26-metre radiating wire. A 1:4 ratio transforms 50 ohms to 200 ohms, which suits the off-centre feed impedance characteristic of Windom-style antennas. The transformer is wound on a broadband ferrite toroid, ensuring consistent performance across HF frequencies without narrow-band tuning.
26-Metre Radiating Wire
The 26-metre copper radiating wire is the primary radiating element. This length corresponds to a half-wavelength on 40 metres (7 MHz), and resonates as a full wave on 20 metres (14 MHz), a double full wave on 10 metres (28 MHz), and usefully on 15 metres (21 MHz) as well. The advantage of the amateur HF bands is that the frequency roughly doubles at each successive band — 3.5 MHz, 7 MHz, 14 MHz, 21 MHz — which makes it straightforward to create a single wire that resonates on all of them. The far end of the wire terminates at an insulating eyelet, which can be tied to a support point at any height.
The Windom antenna does not require a buried ground system or a radial field. Because the feedpoint is off-centre, RF currents in the two sections of the antenna are unequal, and the coaxial feedline section contributes to the effective radiating structure. The choke controls where this radiation begins and ends, keeping RF out of the operating position.
This architecture makes the City Windom especially practical for flats and terraces — one wire, one transformer, one choke, and you are on the air across multiple HF bands.
The combination of a 26-metre radiating wire, a 1:4 LLT impedance transformer, and a well-placed common-mode choke eliminates most of the practical headaches associated with end-fed wire antennas. If your QTH allows even a single wire run of 26 metres, this antenna deserves serious consideration.
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