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TN-1114-AN
© Tait Electronics Limited 21 December 2005
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Functional Description
Exciter Bypass
The bypass path connects the audio sampled at 25 kHz from the analogue
unbalanced line input directly into the frequency control loop (FCL), which
then modulates the RF hardware. The only digital filtering in the bypass
path is an optional AC filter, which has a cut-off frequency of 0.8Hz. Note
that there is no limiter present in this path.
Receiver Bypass
On the receive audio bypass path, received audio from the FM demodulator
is decimated from 50kHz to 25kHz. It is then directly converted to the
analogue unbalanced line output with no further filtering.
Extended Bypass
There is anti-alias analogue filtering performed on the unbalanced lines, and
also on the FCL outputs. This filtering on the bypass path causes a roll-off
in amplitude as the audio frequency is increased. When extended bypass is
enabled, the analogue filtering on the unbalanced lines is disabled by
hardware, and a digital finite impulse response filter with a constant group
delay is used in both the transmit and receive bypass paths to extend the
frequency response.
