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C3.6
T881 Initial Tuning & Adjustment
3.4.4
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 narrow bandwidth sets
[ ].
Note 2:
The reference modulation and limiter adjustments are controlled by 256-
step electronic potentiometers (EPOTs), which are adjusted via the "Refer-
ence Modulation" and "Deviation" settings in PGM800Win. This allows the
two point modulation and deviation settings to be adjusted for each chan-
nel.
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 use the "EPOT Fill" option
other channels.
Note 4:
If you are using an RF test set, turn the low pass filter off and set the high
pass filter to 15kHz
1.
Inject an audio signal of 300Hz 1.5V rms (+5dBm) into the CTCSS input (D-range
1 (PL100) pin 8).
Key the transmitter by earthing the Tx-Key line.
2.
Adjust the output from the audio generator to obtain ±3kHz [±1.5kHz] deviation
at 300Hz.
3.
Change the input frequency to 100Hz and, using PGM800Win, adjust the value of
the "Reference Modulation" EPOT setting for the current channel to obtain ±3kHz
[±1.5kHz] deviation (you can use either the mouse or up and down arrow keys).
4.
Change the input frequency back to 300Hz.
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 67 to 260Hz.
1. Use the "EDIT FILL" button on the tool bar or go to "Edit", "Fill", "Epot Settings" on
the menu bar.
10/07/00
1
in PGM800Win to copy the value to the
before
beginning this procedure.
M880-00
Copyright TEL
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