2
2. MAIN FEATURES
2-1. Main receiver
Down conversion format for all amateur bands
A key point in tapping maximum performance from the 1st mixer in actual operation
(say, CW operation) is to prevent the outflow of unnecessary signals, other than the
target signal, from the mixer to the subsequent stage. This is because it can tap the
maximum performance of the digital IF filter using the DSP in the final IF stage. The
TS-990 main reception unit employs a 1st IF frequency 8.248 MHz down-conversion
format. It achieves superior close-in dynamic range unattainable through conventional
up-conversion formats. Even if the interference is a close-in frequency, the receiver
maintains a relatively flat dynamic range, which you can tune without losing your target
signal.
Newly developed mixer
In place of the Double Balanced Mixer, which uses the conventional J-FET, we have
installed the newly developed Double Balanced Grounded Switch Type in the 1st mixer
circuit, which is the heart of the main receiver. The transceiver is also equipped with a
pre-selector function that varies the tuning frequency in tandem with the reception
frequency. It effectively dampens strong interference signals that cannot be minimized
through bandpass filters on dedicated amateur bands. Furthermore, we have achieved
a +40dBm class of third-order intercept points for the signal path of the 1st mixer,
based on selected circuits and components, and by employing large-sized core toroidal
coils for protecting against distortion based on large input signals, as well as using
relays for the signal switching.
Newly developed narrow-band High-IP roofing filter
The transceiver uses a down-conversion method for all amateur band reception, and
features five types of High-IP roofing filter. Narrow bandpass widths selectable are 500
Hz and 270 Hz for CW operation, 2.7kHz for SSB and 6kHz and 15kHz, which are
suitable for AM/FM. These filters are automatically selected in tandem with DSP-based
final bandpass settings. Of course, manual switching is possible as well.
Newly developed VCO frequency division 1st local oscillator
The TS-990 Local Oscillator Circuit is an independent configuration that combines the
main
receiver
and VCO Frequency Division/DDS Direct, the sub-
receiver
and DDS Direct,
and the transmission unit and conventional PLL, with the targeted signal system. The
newly developed VCO frequency division format is used for the 1st local oscillator of
the main
receiver
. The device achieves favourable C/N characteristics that rival the
DDS direct format, and relatively spurious-free local oscillation signals that are
characteristic of the PLL format, by oscillating and dividing the VCO at higher
frequencies than the intended frequency. It is possible to convert it to 1st IF in a pure
state without leaking the target signal as noise by reducing static noise from the local
oscillator and increasing the C/N ratio.
