M850-00
T855 Initial Tuning & Adjustment
B3.5
Copyright TEL 31/09/98
3.4 Short Tuning Procedure
Use this procedure only if you want to reprogram the receiver to a frequency outside the
5MHz 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).
• 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
5MHz.
3.4.3 Front End Alignment
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:
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 the helical resonators #FL410 & #FL420 to
give best sinad.
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