pa0nhc 73dB 50 Ohm attenuator 20180712.
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Preliminary development data.
The designed PCBs below are yet not available.
This small unit enables you to calibrate the S9 indication of the S-meter of any Short Wave receiver using a 50 Ohms antenna connection. This attenuator must be inserted between a 0dBm signal generator and the antenna input of a Short Wave receiver.
The total package consists of seven little PCBs. The main PCB contains the attenuator circuit. Max. power / Voltage : 250 mW / 3 Vrms. The other six PCBs are for the construction of cheap and nice enclosure.
The attenuator circuit consist or 7 stages which
attenuate 10dB, plus one more stage attenuating 3dB. To achieve accurate resistor values
and results, for one value two
standard value resistors values are connected in parallel.
All stages are of the "T" type, and are connected in series.
To save money and space, the "top of the T" resistors between two stages are combined into one. Resulting in smaller sized, thus cheaper PCBs and housing. Easy soldering is ensured by using axial wired, 2.5x6.5mm 0.25W metal film resistors, and RM8.6 / 1mm PCB holes.
The design of the PCB "ground" path ensures a small parasitic capacitance between each resistor and the "ground" plane. To compensate for the internal self inductance of the used resistors, with the goal to achieve a wider frequency range.
Total dimensions : abt. 2.5 x 3.5 x 9 cm3.