Operation - Racal Instruments RA-117 User Manual

6. Operation

1. References to the controls are in capitals and are in accordance with the panel titles
adjacent to them (fig.2).
2. It should be noted that the method of operation of the receiver extremely simple,
depens largerly upon the purpose for which the receiver is being embloyed.
FUNCTION OF CONTROLS.
3. The front panel controls are described in the order in which they could be used for
setting-up prior to use.
POWER
R.F. RANGE MC/S
R.F. ATTENUATOR This control enables the operator to reduce the level of all incoming
MEGACYCLES
SYSTEM
BANDWIDTH
A.F. GAIN
KILOCYCLES
B.F.O.
B.F.O. NOTE KC/S
Makes and breaks the power supply to the mains transformer.
This control enables the selection of one any of five antenna ranges
plus two WIDEBAND positions, one of 75-ohms input impedance
and other a high impedance input of 2000-ohms.
signals when strong unwanted signals are present which cannot be
rejected sufficiently by tuning the antenna.
This control selects the desired Mc/s frequency. The dial should be
checked periodically to ensure that its setting is reasonably central
with respect to the band in use. This is indicated by a reduction
of signal or noise on either side of the correct setting.
This switch provides facilities for STANDBY, MANUAL, A.V.C.,
CALIBRATION and CHECK B.F.O.
The two crystal filters determining the band- width are adjusted
to ensure that their centre frequencies are all within 50 c/s, thus
any bandwidth can be selected without retuning the receiver. Six
bandwidths are provided as follows:-
13 kc/s, 6.5 kc/s, 3 kc/s and 1.2 kc/s (L-C) 300 c/s and 100 c/s
(crystal)
The A.F. GAIN control adjusts the audio output.
This control selects the desired kc/s frequency. The calibration of
this scale may be checked at 100 kc/s intervals by setting the system
switch to the CAL. position and V.F.O. switch set to INT.
The B.F.O. ON/OFF switch makes or breaks H.T. to the beat
frequency oscillator.
The B.F.O. is exatly tuned to a central point on the I.F. ampli-
fier response when B.F.O. NOTE KC/S control is st to zero-beat
with the calibrator. Having standardized the B.F.O. frequency, the
frequency of an incoming signal may be accurately measured by set-
ting the KILOCYCLES control to a zero-beat position; the B.F.O.
should de detuned in order to produce an acceptaple note for c.w.
reception.
[10]