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 Makes and breaks the power supply to the
mains transformer.

R.F. RANGE MC/S 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.

R.F. ATTENUATOR This control enables the operator to reduce
the level of all incoming signals when strong
unwanted signals are present which cannot be
rejected sufficiently by tuning the antenna.

MEGACYCLES This cntrol selects the desired Mc/s freq-
uency. The dial should be checked period-
ically to ensure that its setting is reason-
ably 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.

SYSTEM This switch provides facilities for STANDBY,
MANUAL, A.V.C., CALIBRATION and CHECK B.F.O.

BANDWIDTH 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)


A.F. GAIN The A.F. GAIN control adjust the audio output.

KILOCYCLES 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.

B.F.O. The B.F.O. ON/OFF switch makes or breaks h.t.
to the beat frequency oscillator.

B.F.O. NOTE KC/S The b.f.o. is exatly tuned to a central point
on the i.f. amplifier 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 setting 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. reseption.

R.F. TUNE If maximum sensitivity is not required, the
antenna need not be tuned unless strong
unwanted signals are present. It should be
noted that the presence of very strong singnals
anywhere within the spectrum may cause cross-
modulation unless the aerial is tuned. Under
these conditions, CARE MUST BE TAKEN TO AVOID
TUNING THE INPUT TO THE INTERFERING SIGNALS
instead of the signal required. Familiarity
with the tuning controls will facilitate this.

R.F./I.F. GAIN the R.F./I.F. GAIN control is operative both
in the MAN. and the A.V.C. position of the
SYSTEM switch. In the MAN.position of the
SYSTEM switch the setting of the control should
be always at a minimum consistent with satis-
factory a.f. level. The following should be
noted when the SYSTEM switch is in the A.V.C.
position. Reducing the i.f. gain results in a
reduction of a a.v.c. loop gain together with
the a degraded a.v.c. characteristic.
Therefore when in the A.V.C. position, it is
desirable that the R.F./I.F. GAIN control be
set to maximum. A possible execption of this
occurs when receiving interrupted signals in
which the carrier is periodically switched off;
in this case , receiver noise could be trouble-
some during the quiet intervals.

A.V.C. The choice of time-constant depens
conditions. The LONG time-constant (1 second)
should be employed with the choice signals,
the SHORT time-constant may be used with high
speed telegraphy or voice. For hand (low) speed
telegraphy, the MAN. position of the SYSTEM
switch should be used (refer to R.F./I.F. GAIN)

A.F. LEVEL The preset control sets the a.f. level in a
separate a.f. stage for feeding a 600-ohms,
10mW line. It is unaffected by the position
of the main A.F. GAIN control. IT IS MOST
IMPORTANT that the A.F. LEVEL is not turned
towards its maximum position unless the 10mW
600-ohms winding is suitable terminated.

LIMITER When swithced into use, the LIMITER reduces
the effects of noise peaks exceeding the level
of a 30% modulated signal. It does not
introduce noticeable distortion below a 30%
modulation level.

"S" METER With the METER switch in the R.F. LEVEL
position the meter indicates the signal diode
current. In the A.F. LEVEL position, the 10mW,
600-ohms output only is monitored.
A calibration mark is provided at 10mW.

SPEAKER The loudspeaker may be switched ON or OFF as
required. The two telephone jack sockets
remain in circuit in either position of the
SPEAKER switch. The insertion of a telephone
jack disconnects the loudspeaker.

V.F.O. This switch should be set to the EXT. position
when a external 3.6-4.6 Mc/s source is applied.


PRELIMINARY SETTING-UP.

4. The instructions given below are concerned with tuning the receiver
to a signal of known frequency. These instructions (1) to (8) apply
with the V.F.O. switch in either position.

(1) Set the power switch to ON. Allow a few minutes for the
receiver to warm-up.

(2) Set the R.F. RANGE MC/S switch to WIDEBAND.

(3) Set R.F. ATTENUATOR to MIN.

(4) Set A.F. GAIN control to its mid-position.

(5) Set SYSTEM switch to MAN.

(6) Set LIMITER and B.F.O. switch to OFF.

(7) Select bandwidth of 3 or 6.5 kc/s.

(8) Rotate the R.F./I.F. GAIN control to three-quarters of fully
clockwise.


FILM SCALE CALIBRATION

5. (1) Set the SYSTEM switch to CAL.

(2) Select BANWIDTH of 3 kc/s.

(3) Set the KILOCYCLES scale to that 100 kc/s point which is
nearest to the frequency required and adjust the control
accurately until a zero-beat note is obtained. Move the
milled cursor slide on the dial escutheon so that the
pointer coincides exactly with the selected 100 kc/s division.

(4) Restore all other controls to the preliminary setting shown
in para.4. above.


B.F.O. CALIBRATION

6. (1) Set the B.F.O. to on.

(2) Set the SYSTEM switch to CHECK B.F.O.

(3) Adjust the B.F.O. NOTE KC/S control to zero-beat.

(4) Restore all other controls to the preliminary setting shown
in para.4. above.


TUNING

7. (1) Set R.F. RANGE MC/S to the desired frequency band.

(2) Set R.F. ATTENUATOR to MIN.

(3) Set MEGACYCLES dial to the required integer (1 to 29). The
position of maximum receiver noise will indicate the correct
setting.

(4) Set SYSTEM switch to CAL.

(5) Set Bandwidth to 3 kc/s.

(6) Set A.F. GAIN to mid-position.

(7) Adjust KILOCYCLES scale to zero beat at the 100 kc/s point
nearest to the desired frequency.

(8) Adjust the milled cursor slide to coincide with this point.

(9) Switch B.F.O. on.

(10) Set SYSTEM switch to CHECK B.F.O.

(11) Adjust B.F.O. NOTE KC/S control to zero beat.

(12) Rotate the system switch to MAN.

(13) Set KILOCYCLES scale to the required frequency and critically
tune for zero beat in order to centralize the signal within
the i.f. pass-band.

(14) Adjust R.F. TUNE for maximum signal (or noise). For optimum
c.w. reception, "off-tune" the b.f.o. to produce an acceptaple
beat note.

(15) Set the A.F. GAIN to its maximum clockwise position and adjust
the output level with the R.F./I.F. GAIN control.

(16) For m.c.w. or voice reception, switch B.F.O. off.

(17) Set the SYSTEM switch to A.V.C. if required.

(18) Set BANDWIDTH for optimum reception.



"S" METER

8. The "S" meter should be correctly set to zero.

9. With no antenna connected, set the R.F. ATTENUATOR to MAX. Set the
SYSTEM switch to A.V.C. Turn the R.F./I.F. GAIN control to the
maximum clockwise position.

NOTE: Unless the R.F./I.F. GAIN controlis in the maximum position, the
"S" meter calibration is upset.

10. Remove the plated cap below the meter. Adjust the setting of the
balance control (accessible trough the hole in the panel) by means
of a screwdriwer until the meter reads zero.


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