ATT-20 Variable Attenuator
useable frequency range: 0,1 - 1000 MHz
attenuation: 0 to 20dB continuously variable
control: 3 turns of the knob for the range 0 to -20dB
insertion loss at 0dB stop: less than 0,2dB
no intermodulation - passive
input connector: BNC/f
output connector: BNC/m
input/output impedance: 75 Ohms
size: 18,5 x 34 x 70 mm
weight: 35 g

This device provides a variable fine control attenuation in a very wide frequency range. It utilizes a quality Piher attenuator with the range from 0 to 20dB. Zero attenuation corresponds to the clock-wise stop and maximum attenuation to the anti-clock-wise stop of the control knob.

This attenuator can effectively reduce or eliminate intermodulation resulting from strong signals at the input of a receiver/scanner. Compared to the internal attenuators in the receivers/scanners which are fixed 10 or 20dB, this allows the user to precisely set just the minimum necessary attenuation that will eliminate the intermodulation (this can only be several dBs) while not sacrifising the receiver's sensitivity.

It is a useful accessory for all hand held and table top scanners (Yupiteru, Alinco, AOR, ICOM, YAESU, Uniden-Bearcat etc.). Its BNC coax connectors simply fit onto the antenna input connector and the antenna is connected to the BNC connector of the attenuator. The filter finds its use at places with strong broadcast signals from LW, MW and SW bands and especially from VHF FM band. These signals very often cause overloading of the receiver front end and hence significant deterioration of sensitivity.

The input and output impedance of 75 ohms remains constant over the whole frequency range and attenuation range and for reception purposes present neglieable SWR of 1,5 with 50 ohm systems. The input and output are galvanically isolated.