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

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

On Tue, 21 Sep 2004 09:22:41 GMT, John Steffes
wrote:

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


John,
Thanks for the reply, nice to know I wasn't off-base in my thinking.

Howard

Howard wrote:

On Tue, 21 Sep 2004 09:22:41 GMT, John Steffes
wrote:

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


John,
Thanks for the reply, nice to know I wasn't off-base in my thinking.

Howard

A shortwave preselector can be either active or passive. The former
usually has an amplification stage followed by an impedance matching
output circuit in addition to the tuned circuit(s). The passive type has
only the tuned circuits. Some preselectors can be both active or passive
if the amp' circuit can be turned off (lowered to unity gain) or
completely bypassed. The main advantage of any preselector is it's
bandpass filtering (tuned circuit) which provides a means of removing
signals outside the frequency range (band) that the user wants to hear.
This is particularly useful for receivers (usually portables) that don't
have a good antenna input circuit to accomplish this filtering process
internally.


-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----