Sailor RE2100, Technical Manual

Page: 63 / 186

3 SERVICE RE2100
3.6.2.1 CHECK OF SENSITIVITY(RE2100)
The sensitivity of the entire receiver can in J3E mode be calculated from the following equation:
SENS
»
10 log (F
front
+ f
RX
- 1 ) - 7 dB (dB/uV)
G
front
where the following figures shall be taken as typical values:
F
front
= 5.2
»
7.2 dB : Noise factor and figure for Front End
f
RX
= 6.3
»
8.0 dB : Noise factor and figure for Receiver
G
front
= 0.5
»
-3.0 dB : Available power gain for Front End
The equation is only valid when using a single tone SSB test signal, which produces a signal to noise ratio
of 20 dB at the receiver output, and when using a signal generator with an impedance of 50 ohm.
From the figures it can be seen that both the Front End Unit and the Receiver Unit are determining the
sensitivity level.
To exclude the receiver unit, it is necessary to check the sensitivity level of this unit separately, which can
be done by means of the check procedure described in section 3.6.1.1.
The available power gain, G
front
, of the Front End Unit can be controlled by the check procedure given in
the next section (3.6.2.2.).
The check procedure in this section is especially useful to control the insertion loss of the six parallel
coupled bandpass filters, which are used as pre-filters in the Front End Unit. If the sensitivity is poor in
only one band, it is very likely that the corresponding filter or the filter selection circuit has a failure.
The filter selection circuit can be checked by means of the check procedure given in section 3.6.2.3.
1. Connect the generator to the aerial socket through the 50 ohm impedance matching network
shown in chapter 3.3. PROPOSAL FOR NECESSARY TEST EQUIPMENT.
2. Connect the voltmeter to the earpiece output at testpoint TP2-1 for measuring the AC voltage.
3. Turn the RE2100 on.
4. Choose generator frequency f
G
, generator output level V
G
, and Receiver frequency f
RX
as specified
in point 6.
5. Measure the signal to noise ratio SND/N at the earpiece output and check that it is above 20 dB.
(See section 3.5.2.1., point 6 for instructions about how to measure SND/N)
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