Tait T800 SL2 25W, Service Manual

Page: 54 / 383

B3.10 T855 Initial Tuning and Adjustment
M8SL2-00-002-812
© Copyright Tait Electronics Limited August 2004. All rights reserved.
3.6 Synthesiser Alignment
• Ensure that the receiver has been programmed with the required frequencies
using the PGM800Win software.
• Connect a high impedance voltmeter to the long lead of L1 in the VCO (this meas-
ures the synthesiser loop voltage).
• 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 programme channels with a greater fre-
quency separation than the specified switching range of
5MHz.
• The TCXO =(IC700) output frequency should be trimmed when the IF is tuned.
Refer to Section 3.7.
3.7 Alignment Of Receiver Front End And IF
Note: 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 [ ].
Align the synthesiser as instructed in Section 3.6. For multichannel operation align
the receiver on a frequency in the middle of the required band.
Set RV230 (front panel gating sensitivity) fully clockwise.
Inject a strong on-channel RF signal with ±3kHz deviation (±2.4kHz) [±1.5kHz] at
1kHz into the antenna socket and adjust the helicals (#FL410 and #FL420) to give
the best sinad.
Continually decrease the RF level to maintain 12dB sinad.
Roughly tune IF coils L310, L320, L330, L340, L350, L360, L370, L380, L385 and
L390 for best sinad.
While maintaining a low level unmodulated RF input to the receiver, loosely cou-
ple into the first IF an additional high level signal at 45MHz, you will hear a beat
note.
Trim the synthesiser TCXO (=IC710) for zero beat.