Carver TX-11b Manual page 10

If you scan past the last station on the dial going in one direction, the
tuner will search to the end of the tuning range, then "turn around"
and start scanning in the opposite direction.
NOTE: In order to receive signals below 15 \M (very low power, or
distant stations), it will be necessary to switch the TX-11 b to MANUAL
tuning otherwise these low-strength stations will be cancelled by the
muting circuitry. Tune these stations as we described in the preceding
section on MANUAL TUNING.
Programming
Select AM or FM by depressing the momentary switch for AM or FM
band. An LED above the switch will indicate band selection. Simply
tune to a station or frequency you want to program. Push the
MEMORY button (on the far left side of the 13 progam switches below
the display), then any one of the 13 station preset switches. Any preset
can be programmed for AM or FM.
Once you've pushed the MEMORY button, the red LED above it will
stay lit for about ten seconds, or until you push one of the station
preset switches. The station you selected will be stored in the
memory. Repeat the process for the next station.
Remember that using the manual tuning mode will allow you to
receive more distant stations or weaker signals, because the
threshold circuitry isn't operating during manual tuning. These
stations, weak and/or distant, can still be stored in the TX-11 b's station
preset memories.
Programmed Tuning
Just press one of the station preset switches that has a frequency
programmed into it. Automatic muting will be engaged until the station
is locked in, and the red LED above that preset switch will light up.
Programmed tuning is possible regardless of the MANUAL/AUTO
switch postion.
It might have crossed your mind, but what happens to stations you've
programmed after the TX-11 b is switched off? Programmed stations
remain stored in the memory system, even with the tuner unplugged
for up to three weeks.
We've also included a handy station log to write down the frequencies
and call letters of the stations and program sources (on the last page
of the Appendix). Yes, it's possible to fill up all 13 station presets on
the TX-11 b. Often with stations you've ignored in the past due to
annoying noise or poor quality reception. Since 13 stations can be a
lot for anyone to memorize, just jot the information down in the log
for future reference.
Signal Strength Indicators
The SIGNAL indicators show you the strength of the signal the TX-11 b
is receiving. To the left of the frequency display, the SIGNAL
indicators are arranged in 10 dB steps from 20 dB to 80 dB. The higher
the reading on the indicators, the stronger the signal being received.
Locked Indicator
The LOCKED indicator lights when the tuning circuit has locked
precisely onto the frequency of the station you've tuned.
Stereo Indicator
This indicator lights when the TX-11 b is receiving the 19 kHz pilot of
a stereo multiplexed signal for FM, or the 25 Hz pilot for stereo AM. If
the STEREO indicator does not light, yet the station is positively
locked with a strong signal, it may be the station is mono.
IF Band
This switch controls the IF filter circuit the TX-11b uses. It's useful
when stations are close enough together on the band to start causing
interference. Push in (NARROW) this control to decrease the IF
bandwidth when you're trying to tune a station, and get a nearby sta-
tion causing this type of problem. If crowded airwaves aren't a problem
in your reception area, you should have the control off (WIDE) to get
improved dynamic range. The IF switch works in both AM and FM
bands.
When switching from one IF mode to the other, the TX-11 b's muting
system will be engaged briefly, approximately 1
1
/2 seconds.
AM De-emphasis
This AM stereo tuner is absolutely unique in that it possesses
performance capability that is similar to the performance capability
of an FM tuner. It has bandwidth that extends to 15 kHz and all its
other specifications are very similar to FM specifications. This radio
has the capability of sounding like an FM set. As you may or may not
be aware, FM receivers have a deemphasis curve that is expressed
in microseconds. The emphasis for FM is 75 microseconds. This AM
radio also has a deemphasis curve that allows noise free high fidelity
listening. This switch should be engaged, pushed IN. The reason that
there is a switch on the front panel is that not all AM stations use a
deemphasis curve because AM stereo is fairly new.
However, we have found that every single AM station in the Seattle
area does indeed use a preamphasis curve that requires the use of
a deemphasis curve. The switch should always be in the IN position
for normal use. You'll notice that it comes from the factory taped IN.
We have been unable to find a single case in which the button should
be OUT but we know that theoretically, somewhere in the country,
there is a radio station that probably does not use a preemphasis
curve for broadcasting. If the button is left out while you listen to a radio
station with preemphasis, it will sound much too bright and much too
noisy.
The frequency response of this AM tuner is flat from below 20 Hz to
15 kHz, the same specifications that an FM system has. Using the
deemphasis switch allows approximately a 10dB increase in signal
to noise over the signal to noise that we would obtain without a
deemphasis switch. That's the same reason FM has it, and almost
everything has deemphasis and preamphasis. Cartridges have it -
it's called the RIM curve. FM has it; it's called 75 microsecond, CD
players have it; that is why we have included it - to give the TX-11 b
best possible fidelity.
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