First Local Oscillator For The Sub Band Receiver; Local Oscillator In The Transmit Block - Kenwood TS-990S In-Depth Manual

First Local Oscillator for the Sub Band Receiver

The first local oscillator for the sub band receiver, which is refined and diverted from the local oscillator circuit of the
TS‑590S, directly feeds output signals to a mixer from a 14‑bit DDS which has superior adjacent C/N characteristics.
During the down‑conversion, the oscillating frequency is lower than that of the up‑conversion method, and the C/N
characteristics for the output signals will be improved further, resulting in fine reciprocal mixing characteristics.
Fig. 47 C/N Characteristics of the First Local Oscillator for the Sub Band Receiver

Local Oscillator in the Transmit Block

In comparison with the first local oscillator using a conventional VCO/PLL system, the first local oscillator using a
DDS system has better characteristics of the adjacent carrier to noise ratio; however, as a transmitter, good C/N
characteristics on distant carrier frequencies are required.
If there is a strong signal present using a distant carrier frequency, and if noise affects the desired signal by poor
characteristics of the distant carrier to noise ratio of the signal, the noise causes interference to reception of the signal.
On a local station or those participating a contest in the multi‑band, interference of reception by noise may occur in
some cases.
Considering the 200 W output power of the TS‑990S and the market demand emphasizing the manner not to disturb
other stations, the TS‑990S employs a VCO/PLL system for the local oscillator circuit in the transmit block, achieving
significant C/N characteristics for distant carrier frequencies.
For its transmission frequency configuration, the up‑conversion method is implemented. The up‑conversion method
employs a high local oscillator frequency, thus a VCO division type local oscillator circuit cannot be implemented. To run
in a wide frequency range, a frequency shift circuit is placed in the VCO oscillator circuit in the VCO/PLL for the local
oscillator of the transmitter. This enables switching to the optimum status by band and fine C/N characteristics can be
implemented.
Sub Band Local Oscillator C/N 14.1 MHz IF: 11 M
Antenna Output C/N
Fig. 48 Transmit Signal C/N Characteristics
LOCAL OSCILLATIOR 05
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