Yaesu IC-735 Сервис мануал онлайн [16/149] 209392

Содержание

7 9MHz BAND IF AMPLIFIER AND NOTCH FILTER The receive signal which has passed through the noise gate is amplified by approximately 22dB after being stepped up by L71 FI3 FL 30 is a SSB filter used in both the SSB and CW modes If FL 32 is installed for CW reception of a narrow bandwidth is possible with the NARROW SWITCH If FL 32 is not installed the SSB filter is used The signal does not pass through this filter in the AM and FM modes instead it goes through C155 To ensure full isolation of this filter switch the bias voltage is selected so that all lines are grounded except for the active one IC4 is the 3RD mixer which converts the 9MHz band signals to 455kHz IF signals 8 455kHz IF AMPLIFIER The reception which has been converted to 455kHz first passes through the filter corresponding to the proper mode FI5 is a 15kHz filter for FM FI6 is a 2 4kHz filter for SSB and CW and FI7 is a 6 0kHz filter for the AM mode Ceramic filters are used for all of these Q27 is ON in the narrow AM mode to switch the signal through FI6 2 4kHz Q45 and Q46 provide approximately 50dB of amplification with R349 placed between them for temperature correction This increases the degree of temperature stability IC4 is connected to the output side of the filter with L76 between the two for matching 9 PBT CIRCUIT Local oscillation of Q31 and X2 is injected into IC4 and the BFO circuit causing a relative shift in the frequency of the 455kHz ceramic filter This functions as a PBT X1 and D48 are series resonance notch filters which are switched ON OFF by Q24 The notch frequency is adjusted by varying the bias voltage of varactor diode D48 The amount of attenuation provided by this notch filter is determined by the ratio of the contact point between X1 and L76and series resonance impedance and is stabilized in the range of 32 to 35dB 5V is applied to the anode of D72 for biasing Changing the voltage at the cathode between 0 and 8V provides a variable width for stable frequency adjustment at the center The shift is approx mately 900Hz in the CW mode and an easy to use bandwidth of 1 5kHz 6dB is obtained at the PBT center Detection D88 D91 Configuration of the PBT IC4 9MHz BFO PBT CONTROL Refer to point 10 BFO circuit for the oscillation frequency SSB AM FM Greater than 9 4665 1 8kHz CW Less than 9 4656 900Hz Fig 1 PBT operation of this unit CW CW narrow AM narrow I PBT operation l No change Fig 2 5 2 NOTE Passband tuning does not function when the transceiver is in the AM or FM mode since the maximum shift of the passband system is only 1 8kHz compared with the 6kHz AM filter and the 15kHz FM filter IF shift operation