THE HRO RECEIVER
5
Controlr
The main tuning dial is located near the eent,er
of thefront panel and operates the Cgang tuning
condenser.
Full
details of the tuning arrangement
aill be found in the last section of this booklet,
which is reprinted from
an
article originally ap
pearing in
QST.
Starting atthe top right-hand sideof the front
panel, the uppermost knob is the Variable Selec-
tivity Control of the Single-Signal Crystal Filter.
With the crystal filter inuse, minimum selectivity
ill
be found with the pointer nearly vertical.
Rotating the knob in either direction
from
this
point
niU
increase thcselectivity. When the filter
is not in use, the knob should be set atthe point
giving maximum volume and sensitivity.
Immediately below the Selectivity Control is
the Phasing Control and the Crystal Filter
Su-itch. When this control
is
rotated to
0,
the
crystal filter is disconnected. When the control is
atanyothersettingbetwee11
1
and
10,
itacts
as
n
phasing condenser for balancing the crystal
bridge circuit, eliminating heterodyne?, etc. The
action of these two controls is explained in detail
in
Part
2
of the Alignment Section.
The switch below the phasing control is
eon-
nected in the
B+
lead of the receiver and its pur-
pose is
to
shut
off
the receiver
during
periods
of
transmission OR WHEN CHANGING COILS.
This lartfunction is important. Sel.ies connected
ulth the
B+
switch and mounted atthe rear of
the chassis is
a.
pair of oontaots, BSW, intended
forusewith relay control of thereceiver.
The
hottom controlon theright-hand sideis an
R.F. Gaul Control, connected to the second R.F.
tubeand to thetwo I.F.
tubes.
At the bottom left-handside of the front panel
is
located the C.W. Oscillator Switchand Vernier
Tuning Control. Thec.~.oscillator isused to ob-
tain an audible beat note when ~zceiving
O.W.
signals
or
to locate the carrier of
weak
phone and
broadcast stations. After the phone carrier has
been found, the
o.~.
oscillator is, of course,
turned off.
The switch just above the c.w. beat oscillator
dial is far turning the AVC on
or
off.
AVC
ie
dis-
connected with the toggle thrown to the right.
Above this switch is the Audio Gain Control,
which is wired into the output of the diode de-
tector and
swves,
therefore, to control audio
volume xrhen using either headphones
or
speaker.
The S-meter for indicating carrier intensity of
signal strength is in the upper left-hand comer.
Just below it, and to the left, is
a
push-switch
which connects the meter in the circuit.
Operating Instructions
Phone
or
Broadcart Reception
In receiving phone signals, the AVC may
or
may not be used,
as
desired. If it is not used, we
sueeest
onerxt,inr
t,he
audio gain control about
halfway
on
and controlling the sensitivity with
the
R.F.
gain control. If the operator prefers a
"quiet" receiver, the audio control may be op-
erated at
1
or
2.
If
AVC is used (left-hand toggle
thrown to the left), the R.F. gain control may be
turned all the way on;i.e., to
10;
and the volume
controlled by the audio gain control only. The
setting of the turogain controls
is
largely a mat-
ter to be determined by the preference of the
operator and by receiving conditions. If, for in-
stance, local noise
01.
atmospheric static
is
high,
it aill be desirable to retard the R.F. gain con-
trol when using AVC
so
that the sensitivity of
the receiver will be held to
a
definite maximum.
1
If the
C.W.
oscillator is to be used for locating
carriers, as mentioned above, the AVC switch
must be intheoff position (to theright). Turning
on
the e.w. oscillator with the AVC an will block
the reccivei, making reception of anything but
.
extremely strongsignals impossible.
C.W.
Reception
When receiving c.w. signha, the c.w. oscillator
must be turned on and the AVC switch turned
off.Best signal-to-noise ratio will usually be ob-
tained by retarding the audio gain control
considerably and controlling sensitivity with the
R.F. gain control. Turning on the c.w. oscillator
switch will, of course, result in
a
considerable in-
crease in circuit noise. When the control is turned
back and forth, the characteristic pitch of this
noise will change. When the characteristic pitch
is fairly high, the semi-"single-signal" properties
of
the receiver are very pronounced, one side of
theaudio beat note beingseveral times
as
loud
tu;
the other.
Phone Reception Uring the Crystal Filter
The use of the crystal filter in phone reception
is recommended particularly when tho operator
must contend with heavy interference, static,
heterodynes, etc. Since such conditions prevail
at lnost times in the amateur phone bands, the
filter will be found particularly useful to amateur
phone operators. To receive
a
phone signal when
using the crystal filter,the fdter is switched in by
means of the phasing control and the phmhlg
dial set atapproximatsly mid-scalo. The selectiv-
ity control is then adjusted for minimum
selec-
tivity,
ar
indicated by maximum noise
as
the
control is rotated buck and forth. All phone sig-
nals will be greatly reduced in volume, making it
necessary to advance both audio and R.F. gain
rontrols. The signals may then be tuned in in
the usual manner, but it will
bc
found that the
selectivity is very high, with the result that all
audio frequency side bands above a few hundred
cycles are comparatively weak. Normally, thi?
nould result in low intelligibility of the received
signal, but since the background noise, static,
etc. hsve been oorrespondingly reduced, the net
result is usually animprovement.
The principal advantage of the crystal filter,
