User's Manual
1 1 7 B 2 0 W at t V H F H igh Band Transla t or UHF/ VHF Re ceive r Tr a y,
w / ( Opt) Freque ncy Cor r e ct ion
Circuit Descript ion
- Page 1 of 3 -
The UHF/ VHF Receiver Tray w/ ( Opt ional) Frequency Correct ion select s the desired UHF or VHF On
Channel I nput Signal and convert s it t o a Com bined I F Signal of 45.75 MHz Visual + 41.25 MHz
Aural. The Tray also has provisions for a Frequency Correct ion Opt ion t hat consist s of a VCXO
Channel Oscillator Assem bly wit h a PLL Circuit which m aint ains an exact I F Out put Frequency, over
the capture range of the PLL circuit , even if t he I nput UHF or VHF Frequency m ay vary.
RF I nput Signal Path
The RF I nput t o the Tray, ( - 61 dBm t o - 16 dBm in Level), is fed t hrough J1 for 50Ω to ( A7) t he
input 50Ω Filt er, DC Mult iplexed (1035-1204 UHF, 1035- 1902 VHF LB or 2065- 1024 VHF HB) or
through J5 for 75Ω to ( A7) t he 75Ω input Filter, DC Mult iplexed ( 1035- 1207 UHF, 1035- 1903 VHF
LB or 2065- 1023 VHF HB) , which is of a double tuned design t hat is adj ust ed to the desired I nput
UHF or VHF Channel Frequency. Not e: I f t he input signal is great er t hen - 25dBm , an att enuat or
should be used t o lim it t he level t o - 25dBm . + 12 VDC, for use by an (Opt ional) external
Pream plifier Assem bly, connect s t o the filter through F1 a 1 Am p Fuse. This + 12 VDC is DC
Mult iplexed onto t he input signal cable from t he Pream plifier. DS1 a Red LED located on TB1 in t he
Tray will be lit if the + 12 VDC is present on the input cable. I f a Pream plifier is not used, F1 should
be rem oved and DS1 should not be lit .
The signal is next am plified + 12 dB t o approxim at ely t he - 49 t o - 4 dBm level by a low noise
am plifier locat ed on ( A8-A1) t he Dual St age Am plifier Board ( 1227-1501) that is cont ained in ( A8)
the Dual Stage Am plifier Assem bly ( 1227-1503). The board has approxim at ely + 13 dB or + 26 dB of
gain, depending on w hether Jum per W1 on J5 is in place. 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 t o
( A8- A1) the Dual St age Board where t he sam e am plification t akes place. Jum per W1 on J7,
located on the Dual St age Board, should be rem oved if t he Receiver I nput level is great er than -
40dBm . The out put is connect ed to ( A10) t he Downconvert er Am plifier Assem bly ( 1227-1505) t hat
cont ains ( A10- A1) the Downconvert er Am plifier Board ( 1227- 1502) . The RF, at the -47 dBm to - 2
dBm Level, connect s t o t he "R" I nput Jack of the Mixer Z1 located on the Downconvert er Am plifier
Board.
Local Oscillator Signal Path
The Local Oscillat or Signal is derived from a cut t o channel cryst al m ounted in an oven t hat is
fact ory set at 45° C. The Oscillat or operat es at 1/ 8 for UHF, 1/ 4 for VHF High Band or 1/ 2 for VHF
Low Band of the desired local oscillator frequency. The cryst al is m ount ed on ( A4-A1) t he Channel
Oscillat or Board, Dual Oven ( 1145-1201), t hat is part of the Channel Oscillator Assem bly ( 1145-
1202). The oscillator circuit ry is a m odified Colpitt s design operating in a separat e oven set at 50°
C. for im proved st abilit y. I f the Frequency Correct ion Opt ion is purchased, t he VCXO Channel
Oscillat or Assem bly ( 1145- 1206) , which cont ains the VCXO Channel Oscillat or Board (1145- 1204) ,
is used in place of t he st andard Channel Oscillat or Assem bly, and an AFC voltage from the PLL
circuit m aint ains t he frequency of the VCXO.
The out put of the Channel Oscillator is connect ed to t he ( A5- A1) the x8 Mult iplier Board
( 1227- 1002) for UHF, the x4 Multiplier Board (1227- 1525) for VHF HB or t he x2 Mult iplier Board
( 1227- 1524) for VHF LB, which is located in ( A5) t he Mult iplier Enclosure ( 1265-1125). The proper
m ult iplier board takes the out put of the Channel Oscillator ( + 3 dBm ) and m ult iplies it eight , four or
two tim es by a series of three, two or one x2 Broadband Doublers ( 2x2x2 = x8), which produces
the L.O. signal on t he desired frequency needed for t he upconversion process. The signal is t hen
am plified t o t he + 16 dBm level. A sam ple of the m ult iplied L.O. Signal is fed t o a det ect or circuit
which lights t he Green LED DS1 that indicates t hat the L.O. is present at the Out put Jack J2 of the
Mult iplier Board. This Green LED is seen through a hole the lid of t he Mult iplier Assem bly and is an
indication, when lit , that there is a signal present at t he out put of the Mult iplier Board. The L.O.
signal is filt ered in (A6) a L.O. Filt er 1007-1101 UHF, 2065- 1000 VHF HB or 1034-1211 VHF LB) and
then sent ( + 15 dBm ) t o J2 on (A10-A1) t he Downconvert er Am plifier Board. The L.O. I nput to the
Downconvert er Am plifier Board is connect ed thru a 3 dB m atching pad t o t he "L" I nput of the Mixer
( Z1) at a + 12 dBm level.