©2002 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Printed: 12/14/01
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you may expect that squelch popping
may occur occasionally with squelch
settings at low signal levels due to the
shorter integration period of the noise
detector filter capacitor.
TESTING AND
ADJUSTMENTS.
The first thing to do following in-
stallation is to verify the proper audio
input levels. Connect an oscilloscope
to pin 2 of the ic, and verify (a) that
the audio level is at least 80mV p-p
and (b) that the two tones are at about
equal levels. C1 is a low value capaci-
tor deliberately to equalize the tone
levels counteracting the de -emphasis
in the receiver. If it provides too much
compensation for your particular re-
ceiver, then the high frequency tone
(mark) will be at a higher level than
the space tone. This can be remedied
easily by replacing C1 with a higher
value capacitor. It is only necessary to
have tone balance within about 20%,
and then it is necessary only if you
wish to optimize the receiver for reli-
able reception on weak signals.
The following procedure is used to
set the center frequency of the phase-
locked loop.
a. Temporarily remove the jumper
between E6 and E9 during alignment.
b. Temporarily jumper between
pins E10 and E11.
c. Connect a frequency counter,
via a high impedance 10:1 scope
probe to reduce noise triggering, to
E9.
d. Adjust R3 for a reading of 1700
Hz within a few Hz.
e. Remove test connections and
jumper from E10 to E11.
f. Connect a permanent jumper be-
tween E6 and E9. (This jumper is re-
moved only during alignment.)
To test the unit, simply run it with
and without data input. Check to be
sure that the LED’s indicate when
data is received and distinguishes be-
tween mark and space.
TROUBLESHOOTING.
Finding problems should be rela-
tively easy, since the only circuits
other than the phase -locked loop de-
tector are dc switches. The testing
procedure at the left describes how to
check the detector center frec1uency.
The bandwidth is preset with fixed re-
sistors. You can check for a minimum
of 30 mV p-p audio at E11 to be sure
that sufficient tone level is applied.
Following is a voltage chart indi-
cating proper dc voltages at various
points and under various conditions.
The tests were done with +13.6 Vdc
power supply, b13.6 Vdc is
ideal for operation of the companion
receiver. If you use +12 Vdc or some
other supply voltage, be sure to make
allowances in analyzing your test re-
sults.
Most problems with new kits are
due to construction errors; so be sure
to check all parts and connections if
you have any problem. Seldom is the
problem due to a bad part.
The LEDs can be helpful in check-
ing major functions. DS1 is lit on
space, and DS2 is lit when valid data
(or any tones within the 900 to 2800
approx. bandwidth) are received.
Current drain of the module is 40
mA maximum and depends on data
conditions and load resistance of the
computer equipment.
PARTS LIST.
Ref Desig Value
(marking)
C1
.01µf disc (103)
C2
.033µf mylar (333)
C3
.01µf disc (103)
C4
47µf electrolytic
C5
0.15 µf mylar
C6
.0022µf disc
(2n2K or 2.2nK)
C7
47µf electrolytic
DS1, DS2 Mini red LED
E1-E11
Solder Terminal
Q1
2N3904
Q2-Q3
2N3906
R1
15K
R2
27K
R3
5K, 20-turn pot.
R4
510K
R5
100K
R6
510K
R7
3.9K
R8-R9
1.2K
R10
47K
R11
680
Ω
R12
3.9K
R13
47K
R14
680
Ω
R15
3.9K
R16
10K
U1
XR-2211 PLL detector
TABLE 3. DC TEST VOLTAGES WITH 13.6 VDC POWER.
U1 PIN
1
2
3
4
5
6
7
8
Mark
Space
No Sig
13.6
13.6
13.6
6.8
6.8
6.8
0.2
0.2
0.2
0
0
0
1.5
1.5
13.6
0
0
0
0.15
0.88
*
2.5
7.4
*
U1Cont
9
10
11
12
13
14
Mark
Space
No Sig
6.8
6.8
6.8
6.0
6.0
6.0
3.0
8.8
*
6.0
6.0
6.0
11.2
11.2
11.2
11.2
11.2
11.2
* Undetermined
Xstr Lead
Q1-B
Q1-C
Q2-E
Q2-
B
Q2-C
Mark
Space
0.15
0.88
13.6
1.6
13.6
13.6**
12.9
12.8
-13.6**
+13.6*
*
Xstr Lead
Q3-E
Q3-B
Q3-C
Valid Data
No Tones
13.6**
13.6**
12.8
13.6
+13.6**
-13.6**
** No load voltage; can be much less, depending on load resistance presented by
computer interface unit.
