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6 . 3 T R O U B L E S H O O T I N G
Troubles may happen sometimes while using a receiver for a long p.rioO. Some troubles
are due to the receiver itself, but some of them may be caused by reasons other than the
receiver.
'Ihus,
even if the receiver is under a trouble conclition, do not conclude that the
trouble is due to the receiver without checking the cause by yourself. Check whether the
trouble is due to the receiver itself or due to the external problems according to the trouble-
shooting befbre contacting with JRC or JRC's sales agent or service station. The inspecting
methods fbr typical troubles are described below.
6.3.1
Decline of the sensitivity
The word "Sensitivity" is used ambiguously among users. In this section, the decline of
sensitivity means not only that the sound volume is not large but also that S/N of the
output signal of the receiver reduces.
Explanation
For some constant high frequency input signal, the sound does not depend on the
performance of the receiver. This depends only on the gain from the input stage to the
AF output stage of the receiver.
For example, "the former receiver could produce the sound loudly enough with
RF GAIN set to 8 graduation and AF GAIN to 2. But the present receiver can't produce
the sound loudly with the same gain settings, unlike the former receiver. This receiver
has very bad sensitivity." This doesn't make sense at all. The effectiveness of RF GAIN
volume and AF GAIN volume for the setting graduation is different among makers.
Even in case of the same model receivers, there are some differences. Also, even though
the distance from the partner station and frequency are the same, the wave strength
varies largely depending on ttre year, season, time, etc. Thus, in order to compare the
sensitivity of the receivers, S/N of the receiver must be compared between receivers
under the following condition: Connect the same antennas to the receivers to be
compared, and receive the same frequency at the same time, by setting the speaker
sound volume to the almost same level.
Checking procedure
( 1) Check whether the receiver is misoperated or not. Check whether ATT is set to ON,
or not. Receive the radio wave in other frequency band. When the sensitivity is very bad
in the special band, receive that radio wave by other receiver, if possible. If the difference
is remarkable between receivers when receiving the same signal in the same time by the
same antenna, it can conclude that the trouble is due to the receiver itself. If that
diff'erence is not remarkable, that is not the trouble of the receiver itself. This difference
depends on variation in receivers.
(2) When the sensitivity reduces even if the frequency band is changed, start the check from
the antentra system. When an antenna multi-coupler or antenna changer is inserted
between the antenna and receiver, connect the antenna directly to the receiver. If the
sensitivity is still bad, connect another antenna to the receiver. If the sensitivity is greatly
improved when connecting the antenna directly to the receiver, check the cable, antenna
multi-coupler and antenna changer successively.
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