Kenwood KT-1000 manual High Quality AM Section, Independent Power Supply For Local Oscillator

Independent Power Supply For Local Oscillator

One consequence of the relatively high impedance of power supplies is that leakage from the +B line of the power supply unit can feed back to the local oscillator to modulate the local oscillator frequency. This causes tuning inaccuracies by deflecting the tuned frequency above and below its optimum level. Kenwood engineers solved this

problem by eliminating the source itself — the + B line to the oscillator, giving the local oscillator its own independent power supply. With two power supplies, noise due to leak- age is virtually non-existent, even at 100% modulation. In the KT-1000, this is perfectly utilized.

High Quality AM Section

In the past, AM sections of FM/AM stereo tuners have tended to be neglected because of the generally inferior quality of AM broadcasts. Now, Kenwood tuners are fully able to reproduce the upgraded AM broadcast quality, with

AM sections that are as carefully designed as FM sections. In the KT-1000 an IF band selector is provided for the AM section.

Sample-And-Hold MPX Circuit

As with the Pulse Count Detector, Kenwood engineers have taken advantage of the exceptional accuracy of digital pro- cessing with the introduction of the Sample-and-Hold multi- plex decoder. This circuit cleanly extracts the left and right channel signals from the composite FM signal carried by the 38 kHz subcarrier frequency. The wave peaks are con- verted into digital equivalents in the form of pulses. Since only the basic shape of the waves are converted into digital equivalents, transient deflections in the shape of waves

caused by noise or distortion are ignored. This greatly reduces the need for filtering, which vastly improves chan- nel separation, because filtering can obscure important information in the composite signal, interfering with the abili- ty to isolate left and right channel signals. The peak pulses are sampled then held in a capacitor until the next peak ar- rives; thus, the average peak value can be instantly adjusted for precise representation of the original 38 kHz subcarrier. The KT-1000 employs this superior type of MPX decoder.

Quartz Synthesizer Preset Tuning

Kenwood's quartz-PLL tuning circuit uses the ultra-stable oscillating frequency of a quartz crystal to keep the fre- quency generated by the local oscillator locked to the exact tuning frequency. The quartz-PLL circuit can be preset to automatically tune to any one of any combination of as many as eight different FM or AM stations. To preset, the

desired station is manually tuned in, and then the preset button is pressed, after which any one of eight station buttons may be pressed. Whenever that station is desired, pressing the station button previously selected will automatically tune the station. This system is fully utilized in the KT-800.