©2005 Hamtronics, Inc.; Hilton NY; USA. All rights reserved. Hamtronics is a registered trademark. Revised: 11/11/05
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is designed to accommodate the volt-
age of the adapter. 12Vdc power
adapters are not regulated, and they
typically put out 18-20Vdc with no
load and drop to 12Vdc only with
their full rated load. (The adapter we
supply is conservatively rated, and
the receiver will never draw the full
rated load current of the adapter.)
The power supply or 12Vdc power
adapter should be connected with its
positive lead on pin 5 and its nega-
tive lead on pin 9. If you are using
the 12Vdc adapter, cut about an
inch off the end of the cable to get to
clean copper never exposed to the
air. Then, separate the two leads
about an inch and strip them 1/8
inch.
BE VERY CAREFUL TO
OBSERVE POLARITY; THE
POSITIVE LEAD HAS A STRIPE
AND THE NEGATIVE LEAD IS
PLAIN.
The lead with the small
grooves molded into it is positive,
and the smoother lead is negative. It
can be a little difficult to tell the dif-
ference, and it is important not to
reverse the polarity and damage the
equipment it is powering.
Wait to actually connect power to
the receiver; there is a procedure
later to test the polarity at first power
up.
0
WARNING: REVERSE POLARITY
WILL DAMAGE THE RECEIVER.
Also, be sure that the power source
does not carry high voltage or reverse
polarity transients on the line, since
semiconductors in the receiver can
be damaged.
Audio Output.
There are 2 sets of audio output
pins so that you can run individual
lines to both a speaker and the line
input on your computer’s sound
card. The two outputs are simply
connected in parallel, and you can
use either or both. Pins 3 and 4 are
the hot leads and pins 7 and 8 can
be used for ground returns. The
output ic in the R139 can provide up
to 1 watt of audio to a load of 8
Ω
or
more. (A lower load impedance
might cause distortion or overheating
at high volume levels.)
Normally, when used to drive a
computer sound card, you will want
to listen on a speaker to hear what
the signal sounds like. This is espe-
cially true during the initial acquisi-
tion period. However, most times,
you probably want the ability to
mute the speaker; so installing a
switch in line with the receiver out-
put to the speaker is handy. The
volume control can be adjusted to
whatever level is comfortable for lis-
tening and proper for the computer’s
sound card.
Tape Recorder Control.
The squelch circuit in the R139
Receiver continually looks for an ac-
tive satellite. If it hears one, it stops
on that channel and turns on a
switching transistor. The transistor
output can be used to activate a tape
recorder, allowing you to play back
the tape into your computer’s sound
card whenever you have time to re-
produce the satellite images on your
computer. The transistor can sink
up to 50 mA of positive current to
ground, with a voltage not to exceed
15Vdc.
Figure 2 illustrates one possible
method of activating a tape recorder.
If your tape deck has a motor circuit
which returns to ground which is
common with the receiver ground
and draws less than 50 mA, you can
use the transistor directly to switch
the motor on and off. If the motor
circuit draws more than 50 mA or if
you are not sure about polarity, cur-
rent, or voltage, then adding a small
external relay wired as shown will
provide a buffer for the output tran-
sistor.
In either case, be sure to connect
a transient protection diode across
the device you are switching with the
transistor. Motors and relays gener-
ate a large reverse transient voltage
when the current path is broken.
Such transients will damage any
transistors or ic's they reach. Provid-
ing a diode, as shown, to conduct
and shunt this reverse polarity cur-
rent will prevent the voltage from
building up to a high enough level to
do any damage.
If you have your tape recorder ptt
switch wired to respond to the tape
recorder control from the receiver,
then you need to somehow disable
this motor control to allow the motor
to operate normally for playback.
You can do this by
unplugging the ca-
ble going to the ptt
jack on the tape
recorder; but a
nicer method
would be to add a
toggle switch to
short the relay
contacts together
when you want to
play back the tape.
Antenna Connections.
The success of reception is very
much dependent on having a good
antenna. The ARRL
Weather Satellite
Handbook
, which we sell, is a good
source of information on building an-
tennas. Good quality, low-loss 50
Ω
coax should be used because the
satellite signals are weak. The coax
should be plugged into the BNC jack
on the rear of the receiver.
If you are using large diameter
coax, it may be necessary to use a
UHF-BNC adapter. Such adapters
are shown in the rear of our catalog.
Another alternative is to use a short
length of smaller diameter, more
flexible, coax between the main cable
and the receiver. That cable can
have a BNC plug on one end and a
UHF plug and double female adapter
on the other.
If you use a preamp, such as our
LNG-137, you can overcome some
cable losses by installing the preamp
right up at the antenna. This estab-
lishes a low noise figure before going
through the loss of the cable.
Note that we do not recommend
trying to feed B+ to power the pre-
amp through the coax as some try to
do. It doesn't pay to try to save the
small cost of light weight hook up
wire and mess up the performance of
the preamp in the process. We have
tested many such methods of feeding
B+ on the coax, and we have not
found a very good way to do it with-
out some compromise in perform-
ance.
INITIAL TESTING AT FIRST
POWER UP.
Following is a safe start-up pro-
cedure, assuming you either built a
kit or are using a power supply setup
the first time. This procedure will
check the voltages and polarity to be
sure that no damage will occur.
0
CAUTION: Reverse polarity or
voltage transients from relays, mo-
tors, etc. can damage semiconduc-
+12 VDC
TO TAPE RECORDER
Figure 2. Circuit To Activate Tape Recorder
R139 RECEIVER
ADDED RELAY
TRANSIENT PROTECTIO N DIODE
XSTR Q1 IN
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