LCD RF Frequency Counter
(220-0306)                 Operation                  Faxback Doc. # 38452


TURNING ON/OFF THE COUNTER

To turn on/off the counter, set POWER OFF/ON to the appropriate position.

SETTING THE INPUT IMPEDANCE

To test RF frequencies, set IMPEDANCE to 50-ohm if you connected the
supplied antenna or an optional 50-ohm coaxial cable.

Set IMPEDANCE to HIZ if you connected an optional high-impedance probe,
such as an oscilloscope probe.

Note:  The IMPEDANCE switch is disabled in the logic mode (when RANGE is
       set to 0-10).

SETTING THE FREQUENCY RANGE

To ensure accurate measurements, set RANGE to the proper position for the
frequency you want to measure.

1 - 50    - to measure RF between 1 MHz and 50 MHz.

50 - 1.3G - to measure RF between 50 MHz and 1.3 GHz.

0 - 10    - to measure logic frequencies between 0 Hz and 10 MHz.  (The 
            input must be a TTL/CMOS circuit output.)

Note:  If the measured frequency is outside the counter's set range, the
       reading will be inaccurate.

SETTING THE GATE SPEED

In the RF test mode (with RANGE set to 1 - 50 or 50 - 1.3G), you can choose
between two gate speeds:  64 mS and 640 mS.  The 64 mS gate speed updates
the display every 128 milliseconds, but the resolution is lower than at 
640 mS.  The 640 mS gate speed updates the display only once every 1.28
seconds, but provides the maximum display resolution (the least significant
digit is in units of 100 Hz).

In the logic input mode (with RANGE set to 0-10), you can choose between
two gate speeds:  1 S and 10 S.  The 1 S gate speed updates the display
every 2 seconds, but the resolution is lower than at 10 S.  The 10 S gate
speed updates the display only once every 20 seconds, but provides the
maximum display resolution (the least significant digit is units of 0.1 Hz).

Press GATE SPEED to toggle between the 64 mS and 640 mS gate speed for RF,
or between the 1 S and 10 S gate speed for logic measurements.

USING THE BACKLIGHT

The counter's display has a backlight to help you see the display in low
light conditions.  To turn on the backlight, press LIGHT/HOLD.  The 
backlight stays on for about 5 seconds.

USING HOLD

HOLD freezes the data on the display.

To turn on HOLD, press LIGHT/HOLD to turn the backlight on, then press it
again.  HOLD appears and the data stays on the display until HOLD is
released.

To release HOLD, just press LIGHT/HOLD again.  HOLD disappears.

Note:  You cannot use the backlight without turning off HOLD.

MEASURING FREQUENCIES

Once you have turned on the counter and set the frequency range, input
impedance, and gate speed, do the following to measure frequencies.

If you connected an antenna, fully extend the antenna and be sure
IMPEDANCE is set to 50-ohm.  Then turn on the device whose frequency you
want to measure.

Caution:  Do not let the counter's antenna touch the antenna of the device
          under test.  Doing so might exceed the power or voltage rating of
          the counter and could damage the counter and the device.

For example, to check the frequency of a channel on a CB radio, turn on the
CB, then select a channel and press the CB's talk button.  The counter's
display shows what frequency the CB is transmitting on.

You can measure an RF or a logic frequency using an oscilloscope or other
high-impedance input probe if you have connected the device's cable as
explained in "Preparation," Faxback Doc. # 38451.  Be sure IMPEDANCE on the
counter is set to HIZ, then turn on the device.

Caution:  The RF signal you are measuring should not exceed 1.4V 
          peak-to-peak.  The logic frequency signal you are measuring must
          be a TTL level output.  Measuring signals with a higher voltage
          could damage the counter.

Notes:

The IMPEDANCE switch is only activated in the RF mode when RANGE is set to
1 - 50 or 50 - 1.3G.

In the logic mode with the gate speed set to 10 S, if the measured 
frequency is over range (higher than 9.9999999 MHz), the display shows ---
OF --.-.

When you measure RF, you might see occasional random readings on the 
display.  The counter has special "anti-oscillation" detection routines 
that detect random values and zero the display if the microprocessor 
detects more than four counts, each of which differs more than 50 kHz from
the previous count.  For example:

Count (MHz)             Difference (kHz)             Display (MHz)

19.5500                                              19.5500
18.7800                 770                          18.7800
18.8400                  60                          18.8400
18.7000                 140                          18.7000
20.1500                1450                           0.0000

The counter continues to monitor the input and displays the input frequency
once it finds a stable frequency source.

If you are measuring an unstable frequency source or trying to adjust an
oscillator, this feature will interfere with your adjustment.  You can
disable it by turning off the counter, then turning it back on while you
hold down LIGHT/HOLD.  The display shows all icons.  Once you release
LIGHT/HOLD, the counter resumes normal operation.  However, the special
anti-oscillation detection routines are disabled.  To enable them again,
set POWER to OFF, then back to ON again.

Note:  This feature does not operate in the logic mode.

(km-03/19/1997)

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