User's Manual

16
Atmel AVR2092
8427A-AVR-10/11
Figure 5-7. Board layout – transceiver RF tuning.
During tuning, the best compromise in between RX and TX performance has to be
found. Tuning should be done for the receiver first.
First step should be to verify the 50 matching at U1, pin 5. After that, the capacitor
position and value can be slightly varied. The reception performance should be
measured using a packet error test. Typical tuning capacitor values are 1pF ±0.5pF.
To simplify the tuning, the receiver input power should be adjusted to a value where a
PER of ~1% can be measured. For the measurement 5000 to 10.000 Frames should
be used to get a clear PER value. After a board tuning change the PER should be
measured with the same environment as before. Now the new sensitivity can be
evaluated based on a simple rule of thumb. A PER change by one decimal power
(from 1% up to 10%, or down to 0.1%) corresponds in average with a 1dB change in
sensitivity. The tuning measurements have to take the whole frequency band into
account.
The matching point for best sensitivity can, but may not be identical with the best S11
matching point. The matching point for the lowest noise figure will be different from
the best S11 matching point that can be measured.
When satisfying reception sensitivity was achieved, the transmitter performance
should be tested. Main parameters are transmitting power, EVM, spurious emissions
and performance flatness over the whole frequency band.
5.7 Ceramic antenna
5.7.1 Antenna design study
Part of the diversity board development was the evaluation of the antenna setup. A
dedicated board was designed to determine the key design parameters for a diversity
antenna configuration.