B3.10
T865 Initial Tuning & Adjustment
M860-00-Preliminary
30/06/98
Copyright TEL
3.6
Synthesiser Alignment
•
Ensure that the receiver has been programmed with the required frequencies
using PGM800Win software.
•
Connect a high impedance voltmeter to PL4-1 or the junction of L1 & R1 in the
VCO (this measures the synthesiser loop voltage).
•
Single Channel
Tune VCO trimmer CT for a synthesiser loop voltage of 8V.
Multichannel
Tune VCO trimmer CT for a synthesiser loop voltage of 8V
on the middle channel.
If there is no middle channel, tune CT so that the channels
are symmetrically placed around a loop voltage of 8V.
All channels should lie within the upper and lower limits
of 14V and 3V respectively.
Do not attempt to program channels with a greater fre-
quency separation than the specified switching range of
4MHz.
•
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 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:
Ensure LINKA is bridged and LINKB is not connected if you do not want
the 2dB attenuator (R308, R309 & R310) in circuit. To bring the attenuator
into circuit, remove LINKA and bridge LINKB.
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.
Inject a strong on-channel RF signal with 3kHz deviation (2.4kHz) [1.5kHz] at
1kHz into the antenna socket and adjust front end doublets L410, L420, L460 &
L470 to give best sinad.
Continually decrease the RF level to maintain 12dB sinad.
Roughly tune IF coils L330/L340/L350, CV318 and quad coil L360 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 21.4MHz - you will hear a
beat note.
Trim the synthesiser TCXO (IC700) for zero beat.
Содержание T860 Series II
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