Fig* 2 Wiring diagram of attenuator with passive attenuator included. The passive attenuator is ait SPDT switch.

Jerry Palmer N3KRX provided Ihe idea to add a passive attenuator to he used in series with the active attenuator—it's jusl a SPDT switch wired as shown in Fig, 2. Il provides 20 to 25 dB of additional loss, which (added to the active attenuator loss) gives 100 to [20 dB of attenuation for getting close to those high power hidden transmitters, [f you feel thai the passive attenuator will complicate your project, leave it out. Remember to u ire the connector J2 directly to the active attenuator in this case.

Active attenuator operation and adjustment

The active attenuator works by mixing an incoming signal with a frequency generated by an oscillator inside the attenuator, to produce an output signal at another frequency. The oscillator frequency of this attenuator is 0+5 MHz. So if a 146.5 MHz signal is incoming, a signal of 147 MH/ (146.5 + 0.5) is produced at the output of the al-lenuator. Since the attenuator is connected to your hand-held radio, this is the frequency that your radio should he >*ei to. The potentiometer controls the signal level that





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