Tait T800 SL2 25W, Service Manual

Page: 159 / 383

M8SL2-00-002-812
T854 Initial Tuning and Adjustment C3.5
© Copyright Tait Electronics Limited August 2004. All rights reserved.
3.4 Short Tuning Procedure
Use this procedure only if you want to reprogram the T854 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.
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
Connect an RF power meter with suitable attenuation 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.