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B3.10

T855 Initial Tuning & Adjustment

M850-00

31/09/98 Copyright TEL

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.

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.

While maintaining the low level RF input to the receiver, loosely couple into the

second IF an additional high level signal at 455kHz - you will hear a beat note.

Tait T858 User Manual

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