Note
QST, Apr 1980, p. 4.
QST, Apr 1981, p. 126.
The DenTron DTR-3KA is a manual HF antenna tuner designed for full-power amateur radio stations, it stands out for its robust internal components, versatile matching capabilities, and styling that pairs aesthetically with vintage linear amplifiers like the DenTron DTR-1200L.
Features
The DTR-3KA is designed as a modular addition to any high-power HF communications station, utilizing an optimized manual matching network.
– Dual-In-Line Wattmeter: Features two separate precision meters that simultaneously display forward and reflected/reverse power. The meter system utilizes an external pickup box and includes front-panel switchable ranges for 200W or 2KW/3KW scaling.
– Antenna Switching & Bypassing: The front panel includes a multi-position ceramic antenna selector. Operators can choose between antennas or fully bypass the tuning circuit on Coax 1, or completely bypass the tuner while keeping the downstream antenna matrix active.
Antenna Output Matrix
The tuner provides maximum flexibility by matching a 50-ohm transmitter to a broad multitude of antenna systems:
– Coaxial Lines: Three separate SO-239 coaxial outputs (Coax 1, Coax 2, and Coax 3) rated at a nominal 50 ohms. Coax 2 is specifically designed to handle broad variations ranging from a few ohms up to very high impedances.
– Long Wire: A dedicated high-voltage binding post for high or low-impedance long-wire antenna systems.
Balanced Feed Line: Rear binding posts tied to a heavy-duty internal balun designed to handle balanced feed line impedances from 75 to 600 ohms.
Integrated Dummy Load. A distinct advantage of the DTR-3KA is its built-in dry dummy load.
Cooling System: Requires connection to a 117 VAC rear plug to power an internal cooling fan. The fan control switch on the front panel allows for Continuous running or Auto mode (where it cycles automatically via an internal thermal switch).
Specifications
– Frequency Coverage: 1.8 to 30 MHz continuous tuning.
– Power Handling: 3000 Watts P.E.P. maximum.
– Input Impedance: 50 Ohms resistive.
– Duty Cycle: 50% max operating cycle (strictly limited to 45 seconds on, 45 seconds off).
Important Operating Guidelines
Because of the high circulating currents and voltages present in a 3KW matching network, the Dentron emphasizes strict precautions to protect both the tuner and your radio equipment:
1. Low Power Tune-Up: Never apply more than 100 watts to the DTR-3KA prior to establishing a match. Always tune with low power first, and only increase driver/amplifier gain to maximum output once a minimum reflected SWR is achieved.
2. No Hot-Switching: Never rotate the inductance selector or antenna selector switches while RF power is actively applied to the tuner. Doing so can cause severe arcing across the switch contacts.
3. Dummy Load Limits: Do not apply more than 2KW P.E.P. to the dummy load, and never exceed the 45-second transmission threshold, or the load element may fail and permanently damage your transmitter.
