!"
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determine if a minima, or a “dip”, has occurred at this point in the scan. If so, that data point is stored for
later display. The Scan takes approximately 6 seconds at the 1 kHz step rate. At the end of the scan, the
Impedance mode is automatically entered and the SWR and impedance data at the frequency of resonance
is displayed.
c) MODE --
Pressing the MODE pushbutton presents sub-displays representing the four modes available in
the instrument: Impedance, Capacitance, Inductance and VFO. To enter a specific mode, press the dial
pushbutton when that mode name is displayed.
•
Impedance --
This is the main operational mode for the antenna analyzer. Impedance mode is entered
automatically during the power-on sequence, and can be re-entered from any other mode pressing the
dial pushbutton when Impedance is displayed. Upon entry to the Impedance mode, you will see the
following typical display:
SWR 10,345.00
2.1 49 +j 23
•
The top line indicates the frequency
•
The first number on the second line is the SWR. In this case it indicates 2.1:1
•
The middle value is Resistance, the real part of Impedance. In this case it is 49 ohms
•
The rightmost value is the Reactance, or the reactive part of Impedance. In this case it is 23-
ohms inductance. (Capacitive reactance would be indicated as a negative number.)
In the Impedance mode, you have the ability to manual adjust the frequency and see the SWR,
Resistance and Reactance values at whatever frequency is dialed up.
Frequency is changed by adjusting a single digit indicated at the point in the display where the cursor
( _ ) is. Upon power-up of the instrument, the 10 kHz digit is the adjustment point, as shown by the
digit with the cursor in the display above.
To move the cursor to a different digit to be adjusted, press the dial pushbutton while simultaneously
turning the dial. The cursor will move to any of the seven available digits, allowing subsequent
up/down adjustment of that digit with the dial pushbutton is released.
Rotating the dial clockwise will increase the digit value and, correspondingly, the signal generated by
the unit. Counter-clockwise rotation will decrease the digit and the generated signal.
When the digit is incremented past 9, or when it is decremented past 0, the digits above the selected
adjustment point are rolled up or down, respectively.
Using this frequency adjustment scheme, the user can conveniently pick an “increment” digit and
manually scan frequencies with the desired granularity. Rough scans can manually be done by
positioning the cursor under the 100 kHz digit or the 1 MHz digit, giving a wide and course scan of the
frequencies with a quick twist of the dial. The signal frequency can then be set to the area of interest
and the cursor set to a lower granular digit (e.g., 10 kHz or 1 kHz) in order to manually perform a
detailed scan while watching displayed results for SWR, impedance and reactance.
An audio tone may be configured to sound when turning the dial in Impedance mode. When you
approach a resonance (i.e., an SWR "dip"), the tone lowers according to the SWR. Thus the operator
will have an audible indication of when minimum SWR is found. The tones may be enabled or
disabled in the Config menu, and the setting is saved in nonvolatile EEPROM so the selection stays in
the unit when power is turned off.
NOTE: Although the ZM-30 may be adjusted to produce signals as low as 10 Hertz, the practical
lower limit of the unit is about 1 MHz due to the coupling capacitors used in the internal circuitry.
Signal levels will drop to an unusable level with frequency settings below 1 MHz. The upper limit of
the instrument is restricted to 30 MHz, as this is the highest quality signal safely obtainable from a
DDS clocked at 100 MHz.