Texas Instruments CC400DK, User Manual, Page: 8 / 22

CC400DK Development kit (rev. 1.5) 2002-09-17 Page 8 of 22
Unfiltered antenna output
The unfiltered antenna output has been made with an option. Two components, L71 and
C71, can be used to match the antenna if the antenna impedance is different from 50
Ω
. To
select this output the zero ohm resistor must be put in R61, and R62 and R63 shall not be
mounted.
LC-filtered antenna output
A LC-filter consisting of L52, C52 and C53 make up a 3dB-equal ripple low-pass filter that
prevents harmonics to be emitted from the transmitter. In receive mode the filter removes
high frequencies in order to prevent distortion and jamming of in the receiver. The filter is
designed for 50
Ω
termination impedance. The LC-filter is selected by placing the zero ohm
resistor in the R62 position. For operation at other frequencies, please use the formulas
below.
⎟
⎠
⎞
⎜
⎝
⎛
−
⋅ ≈
1333 . 0 1
1
RF C
ω ω
,
C
L
ω
6 . 35
=
,
C
C
ω
067 . 0
=
,
where
ω
C
is the cut-off frequency and
ω
RF
is the transmitted RF frequency .
SAW filtered antenna output
To choose this output the zero ohm resistor must be put in the R63 position. The components
around the filter (F2) can be changed to match any SAW filter type. The SAW filter will
introduce additional loss, but will increase the selectivity of the receiver. The 3dB bandwidth
is approximately 200 kHz. The filter can be replaced with another SAW filter with a 3dB
bandwidth of 2 MHz if desirable.
Note: Using the SAW filter, the output power amplifier class should be A or AB and the output
power should not exceed 0 dBm. This will give approximately –5 dBm at the antenna output.
Using power settings above 0 dBm may cause stability problems.