M850-00
T856/857 Initial Tuning & Adjustment
C3.5
Copyright TEL 31/09/98
3.4 Short Tuning Procedure
Use this procedure only if you want to reprogram the T856/857 to a frequency outside
the 8MHz switching range and do not intend to carry out any other major adjustments
or repairs.
3.4.1 Introduction
Reprogram the operating frequency as described in the PGM800Win program-
ming kit (refer to Section 3.2).
Remove the top cover (nearest the handle).
Set up the test equipment as described in Section 3.3.
Set the links in the audio processor section as required (refer to Section 3.5).
3.4.2 Synthesiser Alignment
• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this meas-
ures the synthesiser loop voltage).
• Key the transmitter by earthing the Tx-Key line.
• Single Channel Tune VCO trimmer C6 for a synthesiser loop voltage of
10V.
Multichannel Tune VCO trimmer C6 for a synthesiser loop voltage of
10V on the middle channel.
If there is no middle channel, tune C6 so that the channels
are symmetrically placed around a loop voltage of 10V.
All channels should lie within the upper and lower limits
of 16V and 3V respectively.
Do not attempt to program channels with a greater fre-
quency separation than the specified switching range of
8MHz.
3.4.3 Output Power Adjustment (T856 Only)
Connect an RF power meter to the output socket and key the transmitter.
Turn RV310 (power control) fully clockwise.
Tune #CV475 (output power trim) for maximum output power and check that this
is >30W.
Adjust RV310 for the required output power (between 5 and 25W).
Readjust #CV475 to reduce the supply current by up to 0.5A.
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