preselector4

The Final Version???

Preselector circuit and function
evolution has brought us to this.

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Page 4

These six modules (described in RED)are designed to be mounted in an equipment rack. Also, any one may be used alone or in combination with any other modules.
Preselector Control: is pretty self-explanatory. It allows the entire system to be bypassed for comparison purposes or when not needed. Signal Mode grounds all RF activity and thus provides an RF-Mute. The Antenna module provides various level and functions of static protection utilizing, bleed resistors, Neon bulb discharge, MOV supression and other forms of Transorbs. The Preamp has an attenuator, an input level control to preclude overload/intermod, and an actual gain control. The Transmatch is either a "T" or "Pi" filter which can tame any "wild" antenna impedance -- more for the experimenter than the active listener.

The heart of the system is two modules: The Preselector, discussed on the previous three pages and the optional "null" filter which is great for bandstop functions. In practice, these two units should be of the 12 Ohm or 6 Ohm variety (see previous schematics) since the overlapping skirts of "pass" and "notch/null" should not occur much above the 10 to 20 dB range, IE: when using both, you should be able to achieve significant peaking without the nulling affecting the peak as you "slide" them together in use. Obviously, the sharper the filters are, the closer in frequency, to one another, they may operate effectively. In actual usage, many times it will only be necessary to utilize the "lengthen" or "shorten" functions in order to resonate the antenna system ... and bandpass not necessary.
What is still missing here is a control in the middle of these two units, marked "Bandwidth." It would be a simple matter to take advantage of the internal impedance of the circuit and provide a continuously variable bandwidth control to the "peak" and "notch" functions. I have tried this, but I still haven't convinced myself of the utility or practicaltiy of that function (see the response curves on page 1).

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