Manual
tiny SCR PRESELECTOR
Preselector
Output
Gas Discharge Tube
Antenna
Input
8 bits/256pf variable capacitor
1pf resolution
1.8MHz to 30MHz
Five Band Pass Filters Bank
Ld
Lc
Lb
Le
La
L1
Band B
Band C
Band D
Band E
Band A
Multi-Band-Pass Filter module.
Control Bus
A five bands tuneable Band-Pass Filter bank make up the core of the tiny SCR Preselector.
On SDR applications, where high linearity is needed its passive design keeps a high IP3 factor thanks to an unique large coil wounded on a
T-200 toroidal core, ultra low ESR, C0G (NP0) RF chip capacitors, low RF resistance magnetic shielded relays for tuning and telecom
grade relays for band switching, instead of nonlinear semiconductors that cause distortion in front of strong signals and exhibit
low tolerance to transients.
The tiny SCR Preselector incorporates on antenna input a gas discharge tube as surge suppressor providing safety against static spikes.
The five telecom grade relays are connected to its corresponding section of the coil through the Band Selector control on the program software.
A network of low ESR RF capacitors of 1 pF, 2 pF, 4 pF, 8 pF, 16 pF, 32 pF, 64 pF and 128 pF are connected to the coil in serial fashion emulating
the variable capacitor needed to tune the series resonant circuit formed. Each capacitor is connected to the network by means of its associated
tuning relay. The band-pass filter formed in this way is a classic serial tuned LC circuit, offering narrow bandwidth and low attenuation on the
band-pass segment of frequencies.
The program performs the task of adding or subtracting capacitor values in binary fashion in direct relationship with the tuning control on the
program software. Increments or decrements are done in steps of 1pF.
Available bands are:
• A) 1.8 MHz to 3 MHz • B) 3 MHz to 5.5MHz • C) 5 MHz to 10 MHz • D) 10.5 MHz to 21 MHz E) • 16 MHz to 30 MHz.
A carefully PCB layout design and strong L/C decoupling prevent stages to couple in to each other improving the stop band response
and filtering noise from control lines.
Connection to the control module is done with 16 ways ribbon cable and IDC connectors on both sides, carrying control signals and power supply.
BNC connectors are used for Antenna Input and Preselector Output.
Dimensions are: 153x75mm. (6.02x2.95 inch)
© Heros Technology Ltd 2006. All rights reserved
Z Match
Z Match
