Crystal Filter Circuit; 5A. Single Signal Adjustment; 5B.crystal - Hallicrafters SUPER SKYRIDER SX-28-A Instruction Book

FIG. 2-CRYSTAL FILTER SCHEMATIC
SELECTIVITY SWITCH' POSITIONS
(Sa),
SINGLE SIGNAL ADJUSTMENT
It is extremely simple to attain, single
sig!lal reception with. the SX-28-A. First,
turn on the BFO to the desired Beat Note
and turn the selectivity switch to the
XTAL SHARP position. Pick a good solid
CW
signal, preferably a commercial station
because a commercial is likely to stay on
long enough for you to complete the phas-
ing adjustment for single signal reception.
6SK1
(5) CRYSTAL FILTER
CIRCU~T
In positions 1, 2, 3 the crystal is short circuited. In positioi14 the short
across the crystal is opened and the iron core in the secondary of the:
transformer is ad jus ted for Broad Crystal Action and at this point is
accurately tuned
to
the crystal frequency.·.Due to the. dose coupling
0' £
the secondary to the crystal, the sharply rising resonance curve of
the crystal causes, in contrast, a sharply. falling resonance curve in the
secondary. The combined action of these two characteristics results in
a relati vel y broad resonance curve for the CR YST AL BROAD selectivity
settin~.
In the MEDIUM CRYSTAL No.5 position, C •• is adjusted for
selectlvitv midwaY between the BROAD and CRYSTAL SHARP
settings. (See Fig. 2 and Fig. 4)
In poSItIOn
0,
or CRYSTAL SHARP, the trimmer C
30
is adjusted for
the Sharpes£, crystal action. Under this condition, the Secondaty is
slightly Cletuned from the resonant crystal frequency sufficientlr so
that its resonance curve is not greatly affected by the crystal but still
coupled tightly enough so that it can transfer energy to the cryst'al
circuit. When this point is reached it is indicated by a rise in the output.
Two such points of increased output will normally occur-one for each
adjustment of the secondary on either side of t.he resonant frequency
of the crys tal.
FIG. 3-'-SINGLE SIGNAL OPERATION
You will find on' tuning across this signal
that it has two amplitudes. Tune first to
the weaker of these two amplitQdes. Now,
turn the PHASING control until this
weaker of the two amplitudes is reduced
to a minimum. (If the weaker amplitude
ap~ears
on the right the above procedure
still holds.) Then tune to stronger of the With Selective Switch in XTAL
two amplitudes and adjust the BFO can- Sharp position identify the
trol to a tone most pleasing to you. This weaker amplitude-Tune Re-
adjustment for single signal selectivity will ceiver to the weaker.
-.. djust phasing control carefully
until tliis weaker amplitude is
reduced to a minimum.
Retune Receiver to the
stronger amplitude and then
ad
just pitCI1 control until
you get note most 'pleasing
to copy.
hold with no further adjustment unless you
change the phasing control. (See Fig. 3.)
FIG. 4-CRYST AL SELECTIVITY
..
..
XTAL XTAL
XTAL
..
r-
f-
r-
BIIOAD MEDIUM SHARP
ti.
~
. .
III -
. .
!
•
\
.L
•
. .
/
/
"
I'--'
V
1\
"
\
~V
•
,
lJ
•
I\.
- -
-4
I 1 - 1 " + 1 + 1 + ' + 4 + 1 + '
.........
t'-
r\
-a
-4 -I -I -I 411'" +2 +1 +4 ... "
II
-5 -2 -I 455
+I
+1 . , +4
KILOCYCLES OFF RESONANCE
8. -
,(5b)
CRYSTAL '
The CR YST AL FILTER and
holder are wired directly into the receiver
and do not plug in as heretofore. In this
manner exceptional crystal filter action is
obtained because of the elimination of the
capacity and losses of a sock~t. So .mount-
ing the crystal prevents possible change in
polarity which would occur if the crystal
were improperly inserted in the circuit.
The size of the crystal has been clU"efully
determined to allow the BROAD CR YS-
TAL position to tune as broadly as pos-
sible. The capacity of the crystal holder
has been reduced to. a minimum through
the use of a specially,Jesigned polystyrene
hoider.