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C3.6 T854 Initial Tuning and Adjustment M8SL2-00-002-812

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 mid bandwidth sets ( )

and 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 to 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 to 4 below on the middle chan-

nel and use the “EPOT Fill” option

in PGM800Win to copy the value to the

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

before beginning this procedure.

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 (±2.4kHz) [±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

(±2.4kHz) [±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.

Tait T800 SL2 25W User Manual

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