TMB-1 Tri-Mode Buffer Amplifier Box

Posted on Feb 5, 2014

The TMB-1 is an RF amplifier unit / receiving accessory that can be used with a low-impedance broadband loop, a high-impedance terminated loop (such as a Pennant, Flag, or Kaz Delta), and whip (telescoping rod) antennas. This particular design is optimized for 0. 5 to 2. 0 MHz operation (medium wave broadcast and 160-m amateur). Sensitivity is sligh

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tly less, though still usable, in the 150-500 kHz and 2-6 MHz ranges for longwave, tropical band, and 80-m amateur operation. Circuit changes, mostly with regards to the RF transformers, would be necessary for better performance on other frequency ranges. The accompanying schematic drawing shows the TMB-1 circuit. The buffer amplifier is considered as a generic building-block assembly having an input, an output, DC power, and ground. The schematic of this amplifier card follows the main TMB-1 drawing. A table of suitable integrated circuit buffers is also presented. The antenna element (loop or whip) and TMB-1 box are often situated somewhere other than at the receiving position. Typical sites include the roof of a building or vehicle, the top of a mast, or out in a field. Sometimes two or more antennas are deployed a considerable distance (over 30 m) apart to form a phased array. DC power is transferred to, and RF output from, connector J9 of the TMB-1 through the 50-ohm coaxial cable. At the receiving position, DC is split off through an inductor and RF through a capacitor (the classic bias tee arrangement). This would normally be built into the phasing unit or preselector ahead of the receiver. A few receivers may themselves have a built-in DC-biased RF port. If the TMB-1 is used close to the receiving position, you can supply DC power (+12 V to +15 V typically) to J7 and take DC-blocked RF out to the receiver (or...

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