hi, i'm finding a that the amplitude of a doppler shifted signal has a relationship to velocity. would this be a hardware setup/setting that i'm overlooking?
I moved this question about the AD8347 to the RF Components Community. Someone here should be able to assist you.
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Just wanted to clarify - The amplitude of the Doppler shifted signal is different when appraoching the antenna in comparison to the case of departing from the antenna.
A question similar to this was posted a couple of months ago and I've pasted the response below.
The AD8347 only responds to RF & LO signals, and it has no concept of a target. That said, in a typical Doppler application, the 8347's LO would be fed a sample of the LO where the transmitted signal is generated from, and the RF is fed from the received antenna. With a fixed target "in sight", the RF signal is an attenuated and delayed version of the transmitted signal, and the I/Q signals' amplitude and phase will vary with the distance of the target.
Two things are needed for using this signal: the 8347's offset control must be disabled, or the dc outputs that provide the phase info will be nulled out. The intrinsic offsets of the device must also be calibrated out, in order to provide the correct phase info. This intrinsic offset will also vary over part-to-part, temperature, and supply, etc., so be ware.
If the target starts moving, the phase calculated from I & Q outputs will rotate in a direction and frequency corresponding to the direction and speed of movement.
The output amplitude can be maintained using the built-in detectors in AGC mode, and the Gain Control voltage can be used as an indicator of received signal's strength.
Hope this helps to clarify the 8347's expected behavior in your application.
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