Asymmetrical Charge-Coupled Fm Detector - Carver TX-11b Manual

RFGain +12dB(AM)
Push this switch in to increase the sensitivity for AM stations that are
very weak and/or very far away.
The proper operating position for this switch is pushed in and left that
way, just like the noise reduction button is supposed to be pushed in
and left that way for normal use. On this unit, RF gain plus 12dB button
and the noise reduction button are one in the same and are
automatically switched from AM to FM depending on whether you
listen to AM or FM. For both noise reduction FM and RF gain for AM
you are supposed to leave this button pushed in all the time.
For AM, if you have an overload condition, or hear two stations, one
on top of the other indicating an overload, then release the RF gain
switch and this will always eliminate the offending overload and it will
usually eliminate the two stations on top of one another. If it does not,
then you have to push in the IF wide narrow switch to reduce the IF
response of the AM receiver and this will eliminate this problem of
two stations on top of one.
Noise Limiter (AM)
Push this switch to engage the impulse noise limiter for AM stations.
This circuit will eliminate periodic, low duty cycle interference, such
as that caused by fluorescent lights, thermostats, light dimmers, and
soon.
Pushing this button engages an impulse noise limiter for AM stations.
This switch is very effective for reducing and virtually eliminating
impulse type noises associated with AM reception. It works best on
impulse noises that are locally generated. The normal position for
this button is in the OUT Position. This button does dual duty along
with the multipath reduction on FM, which is also supposed to be in
the OUT position. The normal position for this button is OUT for AM
and FM.
Noise Reduction (FM)
Push this switch to engage the noise reduction part of the
Asymmetrical Charge-Coupled FM Detector™*. Use this switch
gently, pushing it carefully in the center.
Multipath Reduction (FM)
Push this switch to activate the multipath reduction portion of the
Asymmetrical Charge-Coupled FM Detector.
Using the Noise and Multipath Reduction
Switches
The following sections provide information on using the NOISE and
MULTIPATH REDUCTION switches, and the Asymmetrical Charge-
Coupled FM Detector circuit.
The circuit your Carver TX-11 b uses to get you more listenable stereo
than you've ever heard before is the Asymmetrical Charge-Coupled
FM Detector™. The first part of this patented circuit is a charge-
coupled delay line for detecting and reducing phase modulation in
an oncoming signal. This phase distortion is multipath-induced, and
can be compared to the ghosts you see when the TV signals suffer
from it.
The second portion of the circuit is the Leading Edge Detector,
another breakthrough derived from Bob Carver's ear/brain research
(the source of Sonic Holography™, too). He found that all the noise-
polluted L-R part of the FM stereo signal isn't necessary to make your
senses hear stereo. When this part of the Asymmetrical Charge-
Coupled FM Detector is engaged, the TX-11 b uses only enough of
the L-R signal to produce stereo music and programming, rejecting
the rest.
Although the Asymmetrical Charge-Coupled FM Detector can't help
noisy and distorted L+R components of a transmitted FM stereo
signal, it can add up to 23 dB of signal-to-noise ratio (S/N), and make
stereo signals as quiet as stations broadcast in mono. To further
understand how the Asymmetrical Charge-Coupled FM Detector and
various components of the transmitted FM signal interrelate, see
Section 1 of the Appendix.
In FM mode, the lower two of the four switches (on the lower right-
hand side of the TX-11 b) engage the Asymmetrical Charge-Coupled
Detector. The lower left switch engages the noise reduction circuitry;
the lower right, the multipath reduction circuitry. Either one, or both
may be engaged simultaneously.
Pushing just the MULTIPATH REDUCTION switch sets the circuit to
reduce multipath and noise by approximately 15 dB, and optimizes
the circuit for multipath reduction. Pressing the NOISE REDUCTION
switch sets the circuit to reduce noise and multipath by approximately
10 dB. The NOISE REDUCTION switch will optimize the circuit for
reducing noise. If both switches are engaged, there will be
approximately 23 dB of noise and multipath reduction for received
signal strength levels between 1 p,V and 20 (j,V. In other words, very
weak or distant stations.
Which switch you use depends on the problems with reception. Some
stations will sound best if the NOISE REDUCTION is engaged; some
with only the MULTIPATH REDUCTION switched in; some with both.
It's important to remember that most stereo reception problems can
be cleared up by using the MULTIPATH REDUCTION part of the
circuit by itself. At least until you've had a chance to set-up an antenna
system and experiment on a station-by-station basis, we suggest
switching the MULTIPATH REDUCTION in and leave it that way. This
will result in spectacular FM stereo reception in a great many areas,
and for the majority of stations. However, if a station suffers from both
noise and distortion, plus is very weak, use the NOISE REDUCTION,
too.
If your TX-11 b will be used with a commercial cable FM feed, it will
probably be enough to use just the NOISE REDUCTION. Multipath
interference is not really an issue with cable reception. If you're
connected to cable, we suggest the NOISE REDUCTION be simply
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