RF Preselectors
This site is a collection point for information, construction techniques, and theory for
Passive RF Signal Preconditioning.
Type-5 Preselector: Antenna, Signal, and Bypass switches are provided for instant comparison
of raw to processed signal, along with antenna shunting and system shunting.
Selectivity
controls include
Depth and Width with an ultimate rejection of between 48 and 60 dB.
Sensitivity controls provide a signal processing Attenuator and an interstage Gain preamp with
up to +20 dB. The bandwidth of the system is 100KHz to 30+MHz. (2" x 14")
Type-3 Preselector: Antenna, Signal, and Bypass switches are provided for instant comparison
of raw to processed signal, along with antenna shunting and system shunting. Note that each
switch function is indicated with an LED - this was done for use in low light situations.
Selectivity
controls include
Lengthen and Shorten which can be used as Low Pass or High Pass or
together for
Bandpass, with an ultimate rejection of between 48 and 60 dB. Next to the Bandpass
module is a
Band Stop which has the same basic circuitry as the Bandpass, but operates in the
Notch mode. There is a
Tee-section Tuner for matching antenna impedance between 10 ohms
and about 7,000 ohms.
Sensitivity controls provide a signal processing Attenuator and an
interstage
Gain preamp with up to +20 dB. The bandwidth of the system is 100KHz to 30+MHz. (3
1/4" x 19")
Type-4 Preselector: Antenna Signal and Bypass switch is provided for instant comparison of
raw to processed signal. The controls are self explanatory.  
Gain preamp offers up to +20 dB
with the option of using it as an
Attenuator. The bandwidth of the system is 100KHz to 15+MHz.
(9" x x2")
Type-2 Preselector: Antenna Signal and Bypass switch is provided for instant comparison of
raw to processed signal. The controls are self explanatory.  
Gain preamp offers up to +18 dB
with the option of using it as an
Attenuator. The bandwidth of the system is 100KHz to 55+MHz.
(10" x x2 1/2")
Type-1 Preselector System: These 3 (2U) rack panels were the basic prototype building models.
Note that
Antenna Selection and Receiver Selection allows for a combination of 4 of any mix. An
accurate
Attenuator is used for testing and comparisons, and a Pi Tuner provides the
impedance match for any antenna between 20 ohms and 5,000 ohms.
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