©2005 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 11/11/05
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tors. Use only proper, filtered power
supplies of the correct voltage, and
check to make sure any inductive
devices, such as motors or relay
coils, operating from the same power
source have transient absorbing di-
odes connected across them.
Input Voltage Range.
The R139 has an 8 volt regulator
built in. The only circuit which uses
power taken before the regulator is
the audio output ic. These two
branches both may operate with fil-
tered, but not necessarily regulated,
power with a voltage up to 18 Vdc
and having a little ripple. Filtering
circuits in the receiver can eliminate
a little ripple, the type you might get
from an unregulated 12Vdc power
adapter. They can also contend with
some voltage variation with load cur-
rent, which you ordinarily see with
changes in audio output level.
It is normal for the 12Vdc power
adapter to put out about 20Vdc with
no load at all and drop to 12Vdc only
at full load. In the case of the very
conservatively rated adapter we sup-
ply with cabinets, the receiver never
draws enough current to draw the
voltage down to 12V.
Start-up Voltage Checks.
Assuming you have wired up the
9-pin plug to the power adapter or a
12Vdc power supply and have double
checked the polarity, do the follow-
ing.
a. Before plugging in the power
plug, turn off the front panel POWER
switch.
b. Connect the 9-pin plug, and
connect a dc voltmeter from the left-
hand lug of POWER switch S2 on the
pc board. The voltmeter should
show a positive voltage of about
20Vdc if using the 12Vdc power
adapter or about 12Vdc or 13.6Vdc if
using a regulated power supply.
0
Pay special attention to verify-
ing the correct polarity before turn-
ing on the POWER switch. Damage
to the receiver will occur if the polar-
ity is reversed.
c. Turn on POWER switch, and
turn the VOLUME control fully coun-
terclockwise. If you are using the
12Vdc power adapter, the voltage will
drop to about 17-18Vdc. If you are
using a regulated power supply, the
voltage should not change.
d. Connect a speaker and turn
VOLUME control fully clockwise.
With lots of white noise, the supply
voltage should drop to about 15-
16Vdc if using the 12Vdc power
adapter or remain constant if using a
regulated power supply. Turn down
VOLUME when done.
e. Reconnect positive lead of
voltmeter to the lead of ferrite bead
Z1, just above the POWER switch on
the pc board. This carries regulated
voltage to the rest of the receiver; it
should be close to +8Vdc.
f. This completes preliminary
tests. Now it is safe to operate, or in
the case of a kit, to align the receiver.
ALIGNMENT.
Equipment needed for alignment is
an rf signal generator and an fet volt-
meter. (If you have one, analog meters
make it easier to observe tuning.)
Slug tuned coils should be ad-
justed with the proper .062" square
tuning tool to avoid cracking the pow-
dered iron slugs. See A28 Tuning
Tool in catalog.
Variable capacitors should be ad-
justed with a plastic tool with a small
metal bit on the end. See A2 Tuning
Tool in catalog.
a. Connect power and speaker to
J1.
b. Turn on power, and click the
SCAN switch to the left several times
to get to the channel which is about
in the center of the tuning range,
which presumably is channel 3. The
LED's should indicate which channel
is selected
c. Set SQUELCH control R2
fully counterclockwise and VOLUME
control R1 for a comfortable listening
level.
d. Connect dc voltmeter to oscil-
lator test point TP-1, which is the top
lead of R29, just to the right of the
BNC jack. Alternately adjust L4 and
L5 for maximum dc voltage. (Typical
indication is r0.7 to 1.8
Vdc.)
e. Connect stable signal genera-
tor to 10.7 MHz test point TP-2, the
top lead of R17 next to mixer Q3.
Use a coax clip lead and a .01 µf disc
capacitor to block the dc. Connect
coax shield to pcb ground. Set gen-
erator to exactly 10.700 MHz. Use a
frequency counter or synthesized
signal generator. Set the signal gen-
erator level high enough to provide a
full quieting signal. No modulation is
needed.
f. Connect dc voltmeter to test
point TP-4, which is the top of R6
(under i-f amplifier ic U1). Adjust
discriminator coil L8 for +3.3Vdc.
g. Connect signal generator to
BNC jack J2.
Note: The following procedure as-
sumes you are using the five channel
frequencies normally installed in the
R139 Receiver for the US and Rus-
sian weather satellites. If not, use
the appropriate channel frequencies
of your crystals when doing the
alignment procedure which follows.
h. Adjust signal generator to ex-
act channel frequency of your mid
channel. We assume channel 3,
which is 137.500 MHz. Turn output
level up fairly high. Adjust frequency
trimmer capacitor C33 to net the
crystal to channel frequency, indi-
cated by 3.3V at test point TP-4.
i. Repeat this adjustment pro-
cedure for the other 4 channels. Use
the STEP position of the SCAN switch
to change channels. Following is a
list of the capacitors to adjust and
frequencies to set the signal genera-
tor.
Channel
Frequency MHz)
Trimmer
1 137.100 C31
2 137.400 C32
3 137.500 C33
4 137.620 C34
5 137.9125 C35
Note
: To adjust the mixer and
front end, use an fet voltmeter on the
2Vdc range with test point TP-3,
which is the top lead of R9. The
voltage at this point is inversely pro-
portional to the amount of noise de-
tected in the squelch circuit; so it
gives an indication of the quieting of
the receiver. A signal peak is indi-
cated by
maximum
dc voltage.
The reading also varies with the
setting of the SQUELCH control.
Best results are obtained with the
SQUELCH control set just counter-
clockwise enough to open the
squelch. That allows the audio to be
heard and provides a good range of
dc voltage readings with changing rf
signal levels.
With no signal, the test point volt-
age varies from about -1.5Vdc with
the SQUELCH control fully open
(CCW) to about -2.5Vdc with it fully
closed (CW). With the SQUELCH
control adjusted to where the
squelch first opens, the test point
voltage is about -1.5Vdc.
We tell you all this just so you
have a feel for what is happening as
you tune. A voltage from the noise
detector is summed with a voltage
from the SQUELCH control, and the
tuning action will move the test point
