scales. One covers the full fre-
quency range with graduations in
third-octaves with centre frequen-
cies from 2 Hz to 160 kHz. The
other range covers third-octave cen-
tre frequencies between 2 Hz and
40 kHz, and includes A-, B-, C-, 0-
weighting, and a Linear position.
Both models have a "Linear" mode
available on the Range switch,
which permits a Linear output to be
obtained at any point in a scan,
without moving the Manual Filter
Selector.
The centre frequency of the se-
lected Filter band is indicated on a
half-inch digital display that also
shows whether the Filter is function-
ing as a third-octave or as an oc-
tave filter, or whether a weighting
network has been selected.
Filter Scanning
In addition to its control of the Fil-
ter switching as directed by the
Manual Filter Selector, the Digital
Controller can operate the Filter
scan on the commands of an exter-
nal source. Control by a Level Recor-
der Type 2306, Type 2307 or Type
2309 is possible with both Band
Pass Filters. On the Type 1617 con-
trol can also be exercised via the
built-in IEC Interface, or an X-Y Re-
corder such as Type 2308 can be
operated in synchronism with Filter
scanning (possible with Type 2607
Measuring Amplifier or equivalent).
Selection of manual or recorder
control is made by the Filter Control
Mode Manual/Recorder switch,
while the Stop/Run switch enables
the Recorder in use to be controlled
from the Band Pass Filter. This con-
trol facility is blocked when "Man-
ual" is selected, or when the Type
1617 is being controlled via the In-
terface.
When operating in any remote
control mode, the progress of the
scan can be followed on the Digital
Display, as the Manual Filter Selec-
tor does not rotate during an auto-
matic scan. The Filter frequency
sweep always starts from the band
in which the Manual Filter Selector
is standing, it sweeps through the
selected range, and being internally
actuated, it returns instantly to its
starting point. This saves analysis
time when low frequencies (with
correspondingly long averaging
times) will not be required while
operating the Type 1617 with an X-
Y Recorder, or under digital control
via the Interface bus. Similarly,
when recording sound on a Level
Recorder, unwanted low frequency
bands can be excluded from the
trace to yield a clear audio fre-
quency spectrogram.
1618
oil
Oro. .00.." *0,4 3 23.13.- • 30*.
Connections for synchronisation
with a Level Recorder Type 2307 is
made via a 7-pin DIN socket on the
rear panel (see Fig.6). Connection
to a Level Recorder Type 2306 is
achieved via an 8-pin DIN socket,
which with the Type 1617 is also
used for X-Y recording.
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Fig.6. Rear panels of the Band Pass Filters
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Fig.7. Conditions where longer averaging times are required for high frequency signals. The
lower curve was made with too short averaging time, while for the upper curve, averag•
ing was correct
5
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