Part Number 74416 Ten-Tec RX400 Manual Revision 0.5
cover 108 to 1650 MHz. The selected filter output is amplified by U2 and lowpass filtered by FIL4 en
route to the RF1 terminal of Mid Band / High Band switch U6.
Position 4 of U3 on the MID/HIGH BAND PRESELECTOR board routes the High Band antenna signals
through one of two highpass/lowpass filter cascades selected by switches U7 and U8. Complimentary
switch positions of U7/U8 are determined by logic line A4. This arrangement creates two half-octave
subbands of 1650-2200 MHz and 2200-3000 MHz. The selected portion of the High Band is further
conditioned by amplifier U9 and highpass filter FIL7 before being presented, along with the Mid Band
subband to switch U6. Based on a logical AND combination of lines A1 and B1, switch U6 routes the
selected subband through amplifier U10 to the MID/HIGH BAND PRESELECTOR board output.
FIRST CONVERTER
The FIRST CONVERTER module contains the first mixer and first IF amplifier for all receive frequencies
above 88 MHz. The first local oscillator, moving in 2 MHz steps from 2528 to 4090 MHz, is highpass
filtered by FIL9, amplified by U7, and applied as high side injection to mixer MX1. On the Mid Band
receive frequencies of 88-1650 MHz, MX1 produces a 2440 MHz first IF which is filtered and amplified
by the cascade comprising FIL6, FIL1, U2, FIL2, U3, and FIL7, selected by switches U1 and U4. This
2440 MHz IF has approximately 80 MHz bandwidth determined by SAW filters FIL1 and FIL2.
On the High Band receive frequencies of 1651-3000 MHz, MX1 produces a 1090 MHz first IF filtered and
amplified by FIL8, FIL3, U5, FIL4, U6, and FIL5, selected by the complimentary positions of U1 and U4.
The 1090 MHz IF has approximately 14 MHz bandwidth determined by dielectric filters FIL3 and FIL4.
Connections E4/E5 pass the Low Band 1st LO output of the FIRST LOCAL OSCILLATOR module
straight through to the SECOND CONVERTER.
SECOND CONVERTER
The SECOND CONVERTER module contains the second mixer for all receive frequencies above 88 MHz.
It also contains the first mixer for receive frequencies below 88 MHz. Each mixer, selected by switch U1,
drives a common 140 MHz IF amplifier. Switches U6 and U7 select an IF filter of either 6 MHz bandwidth
for receive frequencies above 20 MHz, or 2 MHz bandwidth for use below 20 MHz.
The input Mid Band and High Band first IF frequencies of 2440 or 1090 MHz are mixed with fixed Second
LO injection frequencies of 2300 or 950 MHz respectively. Each injection signal is provided by the
SECOND LOCAL OSCILLATOR module, filtered by FIL7, amplified by U3, and applied to the LO port
of mixer MX1.
On Low Band, the LOW BAND PRESELECTOR board supplies the 2-88 MHz RF signal to the RF port of
MX2. The Low Band injection signal is developed in the FIRST LOCAL OSCILLATOR module by
dividing a 2272-3648 MHz VCO by 16 to produce 142-228 MHz in 250 kHz steps. This frequency-
divided first LO is routed through the FIRST CONVERTER module E4/E5 to SECOND CONVERTER
E2/FIL6 and U2, then applied to the LO port of MX2.
The 140 MHz IF output from switch U7 is lowpass/highpass filtered by FIL5 and C50-52, L10-11,
amplified by U8, and routed to the THIRD CONVERTER module via E5.
THIRD CONVERTER
In the THIRD CONVERTER module, MX1 is the third mixer for receive frequencies above 88 MHz
(Mid/High bands) and the second mixer for receive frequencies below 88 MHz (Low Band). The LO
injection signal, developed in the THIRD LOCAL OSCILLATOR module, tunes a 2 MHz range from
