16
filter – reflects a difference in the manufacturers’ approach to design from the antenna to the 1st
mixer.
It is not just the mixer that determines the characteristics of the front end: all of the components
between the antenna terminal and the mixer can have an impact.
Despite the compact design of the TS-480 Series, its RX BPF divides up the 500kHz~60MHz
range into 10 bandwidths. Since several coils are employed in this BPF circuit, small coils have to
be used in a compact transceiver. When discussing front end linearity, attention focuses on
semiconductors such as the PIN diode for switching bands, but in fact the coils used in this BPF
can be “nonlinear” parts, depending on operating conditions. Differences in their characteristics
become more noticeable the smaller they are. In the early stages of developing the TS-480, we
looked at the mutual modulation characteristics of a number of coils, picking only those that
demonstrated the best performance.
With this compact transceiver it was not possible to use a passive tuner equivalent to what is found
in top-end models, but our emphasis on HF performance was such that we selected components
whose advantage cannot even be appreciated from a circuit diagram.
Fig. 9 is a graph demonstrating RX sensitivity. Needless to say, for HF, especially in the low bands,
there is more importance attached to multi-signal characteristics than to sensitivity, but obtaining a
sufficient level of sensitivity can be vital during mobile operations when one cannot expect much in
the way of antenna gain.
As with previous models, sensitivity is set to switch at 21.5MHz with the pre-amp on. However,
there is a difference: previously the pre-amp itself was switched, but in the case of the TS-480 this
is managed by switching the pre-amp’s NFB gain.
Fig. 9: RX sensitivity
To Next Page
Loading...
Need help?
General
