Re: AE7EU Top Level PCB Mod
Diver Martin <diver.martin@...>
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The mixer is used as an attenuator. As you bias/turn on the diodes, the more they go into conduction (e.g. not an attenuator). Balance the circuit, and it becomes an isolator, roughly to the tune of 50dB per the datasheet. This is why I have a negative gain opamp on the output of the log amp. As audio level goes up, the output of the log amp goes up. Invert this, so that maximum audio output = low voltage on the mixer (attenuator), increases attenuation and decreases overall RF reception, and thus the feedback loop.
The attenuator is switched in only on RX; obviously you don't want to TX 10W through this attenuator at any attenuation level.
On Fri, Jan 12, 2018 at 11:37 AM, Mike Woods <mhwoods@...> wrote: