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Circuit Description
Low Current Base Tech 3.5
LOW CURRENT IMPROVEMENTS
In order to improve standby current consumption the Receiver Unit, Transmitter Unit, Analog Logic Unit and
Front Panel Unit have been modified from the original Base Tech III configuration. These improvements will
start to be incorporated into all Base Tech III radios manufactured in 2012. Earlier versions of Receiver Unit,
Transmitter Unit and Analog Logic boards should not be mixed. RF Power Amplifiers remain unchanged. A
label marked
“Low Current Variant”
will be affixed to all receiver, transmitter, analog logic and front panel
units for easy identification. The Front Panel Unit may be used with either standard or Low Current models.
RECEIVER UNIT
1) RF
Section
An incoming signal is fed to the pre-selector bandpass filter and amplified by Q861. It is then fed to the
post-selector bandpass filter. The balanced mixer, consisting of IC811, produces the first IF (VHF =
48.5 MHz/ UHF = 73.35 MHz) by injection from the 1
st
local oscillator generated by RX VCO.
2) IF
Section
The first IF signal is fed to crystal filter, XF801, then amplified by Q810. Again, this signal is fed to the
4-pole crystal filters and amplified by Q001. Following amplification, the signal is fed to the 2
nd
IF
processor (IC001). The 2
nd
local oscillator (crystal) signal is directed to IC001 to produce the 2
nd
local IF
signal (455 kHz). IC001 amplifies the 2
nd
local IF signal, which then becomes an audio baseband signal
through a detector circuit internal to IC001. This audio signal is then directed to the low pass filter
inclusive within IC002, after which it is sent to audio processor, IC3.
3) VCO
section
The oscillator circuit produces the 1
st
local oscillator signal
(VHF = RX fre 48.5 MHz / UHF = RX frequency – 73.35MHz).
The 1
st
local oscillator signal is amplified by buffer Q302, then amplified by pre-amplifier IC301 and
post-amplifier Q303. The amplified signal is fed to the first balanced mixer. The VCC for the VCO has
been changed from 7 volt s to 5 volts.
4) PLL
Section
The PLL IC, IC806, with integrated pre-scaler compares the phase between the VCO frequency and
reference oscillator frequency (12.00 MHz) by method of dividing the frequency, and produces VCO
control signal. Then, this control signal is fed to the charge pump and fed to the low-pass-filter. The
supply voltage of charge pump is multiplied by IC807 (to approx. 13 V) to achieve greater S/N ratio.
5) Low
Current
Improvements
An additional 5.5 volt dc source has replaced the 12 V dc source for main on board power. An additional
12 volt line has been added for the 7 V dc regulator. This significantly reduces current consumption
losses to heat.
13
© 2012 Midland Radio Corporation
Содержание 91-1060-91-1110
Страница 22: ...Circuit Description Low Current Base Tech 3 5 Notes 2012 Midland Radio Corporation 18 ...
Страница 23: ...Block Diagram VHF 60 Watt Low Current Base Tech 3 5 19 2012 Midland Radio Corporation ...
Страница 24: ...Block Diagram VHF 110 Watt Low Current Base Tech 3 5 2012 Midland Radio Corporation 20 ...
Страница 25: ...Block Diagram UHF 50 Watt Low Current Base Tech 3 5 21 2012 Midland Radio Corporation ...
Страница 26: ...Block Diagram UHF 100 Watt Low Current Base Tech 3 5 2012 Midland Radio Corporation 22 ...
Страница 27: ...Front Panel Unit Schematic Low Current Base Tech 3 5 23 2012 Midland Radio Corporation ...
Страница 28: ...Analog Logic Unit Schematic Low Current Base Tech 3 5 2012 Midland Radio Corporation 24 ...
Страница 29: ...VHF RX Main Unit Schematic Low Current Base Tech 3 5 25 2012 Midland Radio Corporation ...
Страница 30: ...VHF RX VCO Unit Schematic Low Current Base Tech 3 5 2012 Midland Radio Corporation 26 ...
Страница 31: ...VHF TX Main Unit Schematic Low Current Base Tech 3 5 27 2012 Midland Radio Corporation ...
Страница 32: ...UHF RX Main Unit Schematic Low Current Base Tech 3 5 2012 Midland Radio Corporation 28 ...
Страница 33: ...UHF RX VCO Unit Schematic Low Current Base Tech 3 5 29 2012 Midland Radio Corporation ...
Страница 34: ...UHF TX Main Unit Schematic Low Current Base Tech 3 5 2012 Midland Radio Corporation 30 ...
Страница 35: ...Front Panel Unit Layouts Low Current Base Tech 3 5 31 2012 Midland Radio Corporation ...
Страница 36: ...Analog Logic Unit Layouts Low Current Base Tech 3 5 2012 Midland Radio Corporation 32 ...
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Страница 43: ...Palm Microphone Schematic Low Current Base Tech 3 5 39 2012 Midland Radio Corporation ...
Страница 62: ...5900 PARRETTA DRIVE KANSAS CITY MISSOURI 64120 PHONE 816 241 8500 FAX 816 241 5713 www midlandradio com ...