Hy-Gain TH-7DX
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| Frequency | 14 / 21 / 28 MHz - VSWR under 2:1 across all three, including ALL of 10 m (maker's signature claim) |
| Bands | 20m, 15m, 10m |
| TX power | 1500 W (1500 W) |
| Modes | SSB, CW, AM, FM, digital |
| Connector | BN-86 balun and preformed feed straps SUPPLIED (maker copy) |
| feedpoint | dual trapped driven elements via supplied BN-86 balun |
Estimated (unverified): per-band gains (~8.1-8.8 dBd, secondary listings) and weight (~75 lb, retail listings) - the manual's spec table page is unrecoverable from accessible copies
The tribander era's bandwidth champion: dual driven elements buy what no trap recipe alone could - the entire 10-meter band under 2:1 - while the mixed trapped/monoband parasitic deck keeps a real 27 dB front-to-back. Hardware details (diecast clamps, supplied balun, preformed straps) reflect a flagship that was engineered, not just stretched.
Seven trapped-and-mixed elements on 24 feet is serious tower logistics, and the dual-driven system makes assembly less forgiving of improvisation than simpler beams. Three bands only - WARC was the TH-11DX's job - and the brand transition era applies to parts and availability.
The thinking ham's big tribander: where rivals chased decibels, the TH-7DX solved bandwidth - all of 10 m, no tuner, full pattern. If the classic three bands are the mission and the tower is ready, few antennas of its era did the whole job better.
The TH-7DX attacked the tribander problem from an angle its rivals mostly ignored: bandwidth. Trap tribanders traditionally bought their three bands with narrowed sweet spots - fine on 20, tolerable on 15, and painful on 10, where 1.7 MHz of band overwhelmed any single trapped driven element. Hy-Gain's answer - designed in 1981 by Roger Cox, the company's sole design engineer, evolving Howie Pabian's by adding a second driven element fed out of phase,'similar to a log-periodic array cell of 2 elements' in Cox's own account - was the dual-driven system whose headline claim defined the model: under 2:1 VSWR across all of 10 meters, plus full 20 and 15. Behind the driven pair sits a mixed parasitic deck, trapped where bands must share aluminum and monoband where the pattern needs stiffening, with 27 dB front-to-back as the advertised peak over a designed 20 dB band-wide floor.
The hardware reads flagship throughout: seven elements on a 24-foot boom with a 31-foot longest element, diecast aluminum boom-to-mast clamp, the BN-86 balun and preformed feed straps supplied rather than sold separately, and the maker's own rotator guidance naming the T2X and HAM-IV class. It shares its 24-foot boom class with the five-band TH-11DX at roughly 75 pounds to the flagship's 88 - the price of WARC abstinence, paid back in logistics.
The model's standing is unusual enough to be its own credential: the rates a dedicated page in the IEEE's Engineering and Technology History Wiki - which records that it was built to answer the KLM KT-34 series, and that the whole design predates accessible antenna-modeling software, making its bandwidth trick a feat of slide-rule-era RF intuition. Against the classic trapped competition it traded a little gain bragging for bandwidth nobody else had; decades of contest-station rooflines suggest the market understood. Discontinued in the MFJ shutdown and now in ITU-transition limbo, used examples command flagship respect - completeness of the dual-driven hardware being the thing to verify before money changes hands.