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2. OPERATION
In the interpretation of the cross-talk plotting, it should be kept in mind that
"dips"
will be present at filter switching points in the overall measuring
characteristic, owing to the spectrometer characteristic and to possible fre-
quency deviation on the record. (The "dips" do not exceed 2 to 6 dB if the
synchronous filtering adjustment is correct). See Fig. 2.5.
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Fig. 2.5. Successive plot on the same chart of the left and right channel output
of a high quality pick-up tracing the QR 2009 band
1,
carried out through
the synchronous filtering arrangement. The separatiwt is read directly in dB
as the level difference. The influence of the synchronous
filte'
r ing is clearly
seen since the pick-up response is practically linear up to
7
kHz.
Synchronous Filtering Adjustment.
In order to obtain proper synchronization between the frequency scanning on
the Spectrometer Type 2112 (or the Filter Set
161?.)
and the test signal fre-
quency, it is necessary that the automatic stop position be situated at an equal
distance between two filter switching points.
The
frequency sweep on the
record starts from this position at the frequency of 20 Hz, which corresponds
to a filter center frequency.
Referring to Fig.
1.6
in the Level Recorder Type 2305
manual,
it is seen that
the synchronous filtering switch marked "2112" is actuated from "Drive Shaft
I" in the Recorder, while the "Single
Chart"
automatic stop is actuated by the
"1 : 10"
synchronizing gear. The lat\er may be disengaged by pushing in the
side knob X when the
X 10
pl!tper speed multiplication facility is used. The
relative positioning of the two cam discs considered should therefore be
checked and possibly adjusted befo1e auto:taatic selective cross-talk measure-
ments are made.
This operation which is described in detail in the
following,
need only be
carried out
once,
if the Gear Lever is afterwards kept permanently in its
outer position. This may be made by unscrewing the knob X from the Gear
Lever (normal thread) after the adjustment has been carried out.
No instrument other than the Level Recorder itself is necessary for the adjust-
ment, but in order to obtain a clear indication of the filter switching
moment,
2-2
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