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Applying a DC offset of approximately -1V gives suppressed carrier modulation. The DC offset
should first be adjusted to suppress the carrier, and the modulating signal then applied.
Applying a DC offset greater than -1V will invert the MAIN OUT outputs with respect to AUX OUT.
The generator can also be asynchronously gated on and off using the AM facility. Select EXT AM
and apply a suitably offset squarewave to the AM/COUNT IN input. The squarewave V
low
should
be approximately -1V to give carrier suppression and the V
high
should be +3V to +4V to give
normal full output.
External Counter
Selecting EXT COUNT sets the AM/COUNT IN socket to external frequency measurement. The
display changes to show a 6-digit frequency measurement and annunciators EXT and 0·5s show
in the display to indicate external measurement and a 0·5s gate time. Alternate presses of the
GATE TIME button beside the display selects between 0·5s and 5s gate time; measurement
resolution is 7-digit with 5s gate time.
In external counter mode the AM/COUNT IN socket has an impedance of 1M
Ω
in parallel with
25pF. Input frequency range is 5Hz to 20MHz.
Care should be taken when measuring input signals above 350mV rms (the onset of diode
clipping) with poor signal to noise ratios as under these circumstances it is possible for noise to
generate spurious counts. To ensure a correct count, therefore, noisy signals should be
attenuated externally before being presented to the counter. A convenient attenuation factor of 10
can be achieved by the use of a x10 oscilloscope probe.
The function generator continues to perform normally when EXT COUNT is selected with the
exception that frequency locking is disabled while external frequency measurement is in use.
Calibration and Maintenance
Calibration
The frequency meter is provided with a user recalibration facility which is useful for correcting for
crystal ageing. Since the ageing rate decreases exponentially with time it is an advantage to
recalibrate after the first six months.
Recalibration may be carried out by accessing the trimmer through the hole marked CAL beside
the display using a non-metallic trimmer tool. Adjustments can be monitored by using a frequency
standard or standard frequency receiver to provide a high accuracy signal for the counter set to
external frequency measurement.
Maintenance
The Manufacturers or their agents overseas will provide a repair service for any unit developing a
fault. Where owners wish to undertake their own maintenance work, this should only be done by
skilled personnel in conjunction with the service manual which may be purchased directly from
the Manufacturers or their agents overseas.
Cleaning
If the instrument requires cleaning use a cloth that is only lightly dampened with water or a mild
detergent.
WARNING! TO AVOID ELECTRIC SHOCK, OR DAMAGE TO THE INSTRUMENT, NEVER
ALLOW WATER TO GET INSIDE THE CASE. TO AVOID DAMAGE TO THE CASE NEVER
CLEAN WITH SOLVENTS.
Telemeter Electronic GmbH | Joseph-Gaensler-Str. 10 | Phone +49 906 70693-0 | Fax +49 906 70693-50 | www.telemeter.info
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