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Chapter 14: SLR 8000 Radio Frequency Distribution System (RFDS) Equipment
173
14.3.1.4
Tuning the Preselector (Alternate Method)
While less precise than the preferred method previously described, this method allows retuning the
preselector without removing the station’s cover nor removing the station from its mounting in a cabinet
or rack. While less accurate, this method still allows minimum specified performance to be achieved.
preselector without removing the station’s cover nor removing the station from its mounting in a cabinet
or rack. While less accurate, this method still allows minimum specified performance to be achieved.
When and where to use:
Once the Network Analyzer (NWA) is properly calibrated, perform the following procedures to tune the
preselector.
Once the Network Analyzer (NWA) is properly calibrated, perform the following procedures to tune the
preselector.
Procedure:
1 Set up the connections by performing the following actions:
a Remove the protective plug of the probe cavity from the rear of the preselector.
b Connect the 350–470 MHz band preselector to the NWA through the adaptors and cables
shown in the following figure.
Figure 128: Connecting Preselector to the NWA
Table 70: Callout Legend
Label
Description
1
To Port 1 of NWA
2
Tuning Screw 1
3
Tuning Screw 2
4
Tuning Screw 3
5
Tuning Probe to Port 2 of NWA
2 Unit Tuning:
a This procedure is identical to that described in
Method) on page 168
. The exception is that one will not be able to see the absolute insertion
loss of the preselector assembly. The approximate insertion loss using the tuning probe in
the alternate method is as follows:
the alternate method is as follows:
• VHF 50 dB +/- 10 dB
• UHF 30 dB +/- 10 dB
As such, insertion loss is relative, with a return loss still yielding an absolute measurement.
With this method, tune for a return loss greater than 18 dB across the
4 MHz passband of interest.
With this method, tune for a return loss greater than 18 dB across the
4 MHz passband of interest.
b Reinstall the preselector's protective plug of the probe cavity.
1
3
2
4
5