the LA102 starts its sweep timing when the FSK sync. tone finishes. The duration of the
sweep will be (f2-f1)×d milliseconds. For 5s sweep segments (OPQR and U), the LA102
timing is as follows:
TIME
0s FSK sync tone ends, sweep begins
0.25s sweep sample 0 taken (allows for settling)
4.74s sweep sample 254 taken (56.75Hz sampling rate)
4.84s sweep sample 255 taken (ignore for user sweeps)
For 20s sweep segments (segment S):
TIME
0s FSK sync tone ends, sweep begins
0.25s sweep sample 0 taken (allows for settling)
20.17s sweep sample 255 taken (12.8Hz sampling rate)
20.67s sweep sample 255 taken (ignore for user sweeps)
For example, to run a 5s sweep from 10kHz to 20kHz at +4dB to be measured on the 0dB
range setting (segment U), send the following commands:
1USU,353,386,140.3,+4 Define user sweep
1DS0,@ Define seq containing seg @
2MC Clear 102 results memory
SQ0 Run seq 0, seg 1, R channel
10kHz is code 354, 20kHz is code 386, 386-354=32 frequency changes in 4.49s, ie
140.3ms per frequency. Therefore d is 140.3. Now the sweep should start lower than
10kHz so that it will be at 10kHz at 250ms. 250/140.3=1, so start frequency code is 354-
1=353. Code 386 will be reached after 33×140.3=4.6299s ready for sample 255, and will
finish at 4.770s. The sweep can optionally be made to run on by adding one or two to the
final frequency code, and this may have some merit if tape speed errors are to be
tolerated. The Lindos sweep segments actually remain on the last frequency of the sweep
for extra time, with the slight advantage that sample 256 (delayed) remains correct over a
range of speed errors.
Read the sweep results from the 102 using the S? command, ignoring the start and finish
frequencies it returns. The LA101 sweep is approximately exponential with time and the
equation given under S? may be used to calculate the frequency of any sample, but for
greater accuracy you may calculate the actual frequency being measured at any time in
the sweep. Note that sample 256 will be invalid with this segment as it is taken late. This
is intended to provide tolerance to speed errors in normal sweep segments, which hold the
finish frequency for some time at the end of the sweep.
154
9. Remote Control
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