Howard,

The preselectors we have dealt with have been , in general, active. They
have used positive feedback to increase the "Q" of the resonant tank
circuit providing greater selectivity. It is reasonable to accomplish
this using no positive feedback (bandpass design) as you suggested.

John

Howard wrote:
On Tue, 21 Sep 2004 01:15:42 GMT, John Steffes
wrote:


We use an antenna tuner to feed our W8JK antenna for use for shortwave
reception for two reasons:
1. The 8JK has a high impedence input so it is fed with 300 ohm ladder
line; thus the use of the tuner (in this case) acts as a balanced
transformer.
2. The 8JK was "cut" for 20 meters. For use on other frequencies, the
tuner acts (with adjustment) as a conjugate match that provides a 50 ohm
input to the receiver.

Results of the tuner appears to peak signal strength as the impedence of
the receiving antenna is transformed by the matching provided by the tuner.

Tuners are passive in nature; that is, they require no amplifier
electronics and associated power. They may be unbalanced input to
balanced output (or vice versa) or unbalanced to unbalanced
input/output. Preselectors on the other hand are active devices. They
vary in design and may provide matching as well as gain.

The selection of the device you choose will depend on the type on
antenna system you employ.

In any case, good luck!

John


John,
I'm not sure I understand why you feel a preselector is an "active
device"? From everything I've learned, active devices are such things
as transistors, IC's, hybrids etc or a reference to a circuit that
requires power to operate. The preselectors I've seen are 'passive'
in that there are no semiconductors and no power required - excluding
models that also have a built in pre-amp. Rather they are basically a
'tank' circuit that with a combination of inductance and capacitance
create a 'bandpass' so only frequencies in a given range easily pass
through the preselector to the receiver.

Am I missing something in either your explanation or my understanding
of a preselector?

Howard