Tait T860 Series II, Service Manual

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C3.6 T867 Initial Tuning & Adjustment
M860-00-Preliminary
30/06/98 Copyright TEL
3.4.3 Two Point Modulation Adjustment
Note 1: In this and following sections deviation settings are given first for wide
bandwidth sets, followed by settings in brackets for mid bandwidth sets ( )
and narrow bandwidth sets [ ].
Note 2: Reference modulation and limiter adjustment are controlled by
PGM800Win. Electronic potentiometers (256 step) are used to allow chan-
nel-by-channel adjustment of deviation and two point modulation.
Note 3: To optimise the modulation response across the switching range, repeat
steps 1-4 below for each channel that will be used (usually needed only for
data applications). In applications where the modulation response is less
critical (e.g. voice use only), carry out steps 1-4 below on the middle channel
and cut and paste the value to all other channels.
1. Inject an audio signal of 500Hz 1.5V rms (+5dBm) into the CTCSS input (D-range
1 (PL100) pin 8).
Key the exciter by earthing the Tx Key line.
2. Adjust the output from the audio generator to obtain ±3kHz (±2.4kHz) [±1.5kHz]
deviation at 500Hz.
3. Change the input frequency to 50Hz and adjust “reference modulation” via
PGM800Win to obtain ±3kHz (±2.4kHz) [±1.5kHz] deviation (you can use either
the mouse or up and down arrow keys).
4. Change the input frequency back to 500Hz.
Repeat steps 2 and 3 above until the deviations achieved at the two input frequen-
cies are within 0.2dB of each other. You will need to do this at least four times.
5. Sweep the audio between 50 and 300Hz for peaks.
Note: A peak between 50 and 300Hz will indicate a fault condition, i.e:
- incorrect set-up
or - modulation circuitry fault.
The specification window is ±1dB relative to 150Hz from 65 to 260Hz.
3.4.4 FM Deviation (Limiter) Adjustment
Note: If the T867 will be used over the whole 8MHz switching range, you must set
the deviation for each channel. However, if the module will be used on fre-
quencies that cover only a 1MHz (or less) switching range, you can set the
deviation on the middle channel and use this value for all other channels
with the “fill” option in PGM800Win.
Inject 1kHz at -10dBm into the line input (D-range 1 (PL100) pins 1 & 4; pins 2 & 3
shorted; refer to Section 2.2 of Part F).