User's Manual

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TXRX Systems Inc. Manual 7-9408-1.2 07/25/05 Page 21

61-38-05 UserMan page 21 of 38

assumed that the procedures will be carried out by

a qualified electronics technician observing all

standard safety practices.

Filter Tuning

Filters used in TX RX Systems’ signal boosters are

passive devices of rugged electrical and mechani-

cal design. They are tuned at the factory for the

original design requirements and require no adjust-

ment or maintenance. These devices will stay prop-

erly tuned unless they have been physically

damaged or are tampered with. Filter tuning falls

into two categories; retuning to the original fre-

quency such as when a filter is being repaired or

replaced, or tuning to new frequencies.

A number of points need to be considered before

attempting to tune a signal booster to frequencies

different from the original.

1) The Frequency Range Specification for the 61-

38-05 signal booster family does not mean that

an individual signal booster is field

tunable over

the entire indicated frequency range. This spec-

ification only indicates the frequency range for

which the 61-38-05 components are intended.

Many of the filter assemblies used in a particu-

lar booster maintain reasonable performance

over a range that is within ± 2% of the original

frequency. For greater changes in frequency,

the performance of the filters may degrade

severely. Therefore some filters may need to be

replaced or modified when large frequency

changes are made.

2) In a bidirectional system, will the new inbound

and outbound channels have the same fre-

quency separation from each other as the origi-

nal ones? Frequency separation in bidirectional

designs is one of the prime design criteria. If the

frequency separation decreases from the origi-

nal, the filters will provide less isolation so the

gain may also have to be reduced to prevent the

signal booster from oscillating. Increases in fre-

quency separation are more easily accommo-

dated.

3) If the bandwidth requirement increases, the

bandpass filters may not pass all of the new fre-

quencies. In most cases, the bandwidth of the

bandpass filters cannot be changed by the cus-

tomer.

Sampler

Detector

Electronic

Attenuator

OLC Assembly

Filter

Amp

Control

10 dB Pad

SPECTRUM

ANALYZER

SIGNAL DISTRIBUTION SYSTEM

BOOSTED

RF SIGNAL

Figure 10

: Test equipment interconnection for surveying performance.