Assembly Instructions Chapter 4

4-6 kW UHF Translator Chapter 4, Circuit Descriptions
837B, Rev. 0 4-3
RF Signal Path
4.1.1 (A7) 50Ω Filter, DC
Multiplexed, UHF (1035-1204), VHF
L.B. (1035-1902) or VHF H.B.
(2065-1024) or 75Ω, UHF (1035-
1207), VHF L.B. (1035-1903) or
VHF H.B. (2065-1023); Appendix
D)
The RF Input to the Tray, (-61 dBm to -
16 dBm in Level), is fed through J1 for
50Ω to (A7) the input 50Ω Filter, DC
Multiplexed (1035-1204 UHF, 1035-
1902 VHF LB or 2065-1024 VHF HB) or
through J5 for 75Ω to (A7) the 75Ω
input Filter, DC Multiplexed (1035-1207
UHF, 1035-1903 VHF LB or 2065-1023
VHF HB), which is of a double tuned
design that is adjusted to the desired
Input UHF or VHF Channel Frequency.
Note: If the input signal is greater than
-25dBm, an attenuator should be used
to limit the level to -25dBm. +12 VDC,
for use by an (Optional) external
Preamplifier Assembly, connects to the
filter through F1 a 1 Amp Fuse. This
+12 VDC is DC Multiplexed onto the
input signal cable from the
Preamplifier. DS1 a Red LED located
on TB1 in the Tray will be lit if the +12
VDC is present on the input cable. If a
Preamplifier is not used, F1 should be
removed and DS1 should not be lit.
4.1.2 (A8) Dual Stage Amplifier
Assembly (1227-1503) ; Appendix
D)
The signal is next amplified +12 dB to
approximately the -49 to -4 dBm level
by a low noise amplifier located on (A8-
A1) the Dual Stage Amplifier Board
(1227-1501) that is contained in (A8)
the Dual Stage Amplifier Assembly
(1227-1503). The board has
approximately +13 dB or +26 dB of
gain, depending on whether Jumper W1
on J5 is in place. The amplified output
connects out of the board at J2.
4.1.3 (A9) Channel Filter, UHF
(1007-1101), VHF L.B. (1034-
1202) or VHF H.B. (2065-1000) ;
Appendix D)
The signal is then filtered in (A9) a
Channel Filter (1007-1101 UHF, 1034-
1202 VHF LB or 2065-1000 VHF HB)
and then applied back to (A8-A1) the
Dual Stage Board at J3.
More amplification of the signal takes
place on the Dual Stage Board, if
needed. Jumper W1 on J7 should be
removed if the Receiver Input level is
greater than -40dBm.
4.1.4 (A10) Downconverter
Amplifier Assembly, 45.75 MHz.
(1227-1505) ; Appendix D)
The output is connected to (A10) the
Downconverter Amplifier Assembly
(1227-1505) that contains (A10-A1)
the Downconverter Amplifier Board
(1227-1502). The RF, at the -47 dBm
to -2 dBm Level, connects to the "R"
Input Jack of the Mixer Z1 located on
the Downconverter Amplifier Board.
Local Oscillator Signal Path
The Local Oscillator Signal is derived
from a cut to channel crystal mounted
in an oven that is factory set at 45° C.
The Oscillator operates at 1/8 for UHF,
1/4 for VHF High Band or 1/2 for VHF
Low Band of the desired local oscillator
frequency.
4.1.5 (A4) Channel Oscillator
Assembly (1145-1202) ; Appendix
D)
The crystal is mounted on (A4-A1) the
Channel Oscillator Board, Dual Oven
(1145-1201), that is part of the
Channel Oscillator Assembly (1145-
1202). The oscillator circuitry is a
modified Colpitts design operating in a
separate oven set at 50° C. for
improved stability. If the Frequency
Correction Option is purchased, the