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OLD CAR RADIOS


NOTICE: TO ALL CONCERNED Certain text files and messages contained on this site deal with activities and devices which would be in violation of various Federal, State, and local laws if actually carried out or constructed. The webmasters of this site do not advocate the breaking of any law. Our text files and message bases are for informational purposes only. We recommend that you contact your local law enforcement officials before undertaking any project based upon any information obtained from this or any other web site. We do not guarantee that any of the information contained on this system is correct, workable, or factual. We are not responsible for, nor do we assume any liability for, damages resulting from the use of any information on this site.
OLD CAR RADIOS

You have just purchased an old car radio for a dollar or two at a yard sale.
So, how do you go about hooking up a 12-volt supply and speaker to it, much
less a shortwave converter kit??? What you have in front of you is the bare
metal case of the radio with the on/off switch and tuning knob in front and
either a bunch of colored wires or just a funny-looking connector in back.
So, what's next?

Well, you need the proper tools. Get a couple of assorted screwdrivers, both
regular and Phillips to remove the cover from the radio. Dig out a
voltmeter or VOM, or anything that will measure ohms (if you don't have one,
borrow one from a friend). Fetch your trusty soldering iron and solder and
your needle nose pliers and wire stripper/clipper. These are the basic
tools. If you don't already have them and can't somehow get a hold of them
then you have no business building electronics projects anyhow. A scope
would also help speed up things, but many hobbyists can't afford one. Oh,
yes, you will also need a small 4 - 40 ohm speaker that you salvage from a
broken transistor radio, or some such. Most hobbyists have a half dozen of
these lying around.

You will use the ohmmeter, your power of observation, and a bit of reasoning
and common sense to figure out what the wires or tabs coming out of the car
radio chassis mean. You need to identify the following terminals: the power
- +12 volts and ground, and two speaker terminals (if the radio has wiring
for more than one speaker, which is probable, then you need to find only the
two terminals for any ONE of the speakers).

Finding the ground terminal is easiest. If there are colored wires coming
out of the radio, the BLACK wire is the likeliest suspect. Ok, power up your
ohm meter and clip one lead to the metal chassis of the radio. In turn test
each wire or tab for zero ohms (or just a fraction of an ohm) resistance
from the lead to the chassis. The only one with the zero or near-zero
reading is the culprit - the ground lead. Label it with a small piece of
masking tape.

Locating the +12 volt terminal takes a bit more work. If there is one and
only one red wire coming out of the radio, that is probably it, but do not
take it for granted. Now, open up the chassis by unscrewing one or more of
the sheet metal plates enclosing the works of the radio. You need to get
access to the back of the volume control, which also happens to have an
on/off switch mounted on it. Find the two terminals on the back of the
on/off switch. Twist the volume control so the on/off switch clicks ON. Now,
measure the resistance from either terminal on the back of this switch to
each wire or terminal coming out of the chassis of the radio (paying
particular attention to the RED wire, if there is one). You will read a zero
or near-zero resistance from only one wire or terminal to the on/off switch.
This is +12 volts. Label this wire or tab. Reinstall the metal plates on
the chassis to close it up.

The final step is to find two leads for any one speaker. You will test the
remaining, unlabeled leads or tabs. You will now for the first time power up
the radio. Get your 12 volt regulated power supply (the enclosed file
POWERSUP.TXT gives details on building one if you need to do so), and attach
the +V and GND leads to the terminals on the radio that you have labeled in
the steps above. Carefully apply power. Turn on the on/off switch of the
radio. If the fuse on the power supply has not blown, then you are probably
all right.

Now with your VOM on volts function, read the voltage between the chassis
(ground) and each of the unlabeled terminals. If you read +12 v on any of
them, this is the lead supplying juice to a power antenna accessory, and you
will label it so and leave it alone from now on. Most or all of the leads
should give you a low or no voltage reading to chassis ground. Fine so far.
If you have a scope, the rest is easy. Just connect scope in turn to each
set of two unlabeled terminals. Set the scope time scale to 200 microseconds
per division and the volts/division to about 5. With the power on to the
radio, look for a scope display that looks like an audio signal (scrambled
sine waves of various amplitudes). Sets of two terminals giving this display
are likely suspects of being speaker terminals. Continue with tests below.

If you can't get a scope or do not know how to use one, that is o.k. You
will now use that old minispeaker mentioned above. With the power on to the
radio, clip to the speaker leads (using alligator clip terminated test leads
if you have them, if not, just plain old wires with the ends bared and
crimped as necessary with needle nose pliers) each set of two radio terminals
you want to test. For each test turn the radio volume up and tune the dial a
bit. You will very soon find a set of terminals that works. If you had
happened to hook up one terminal for each of two different speakers, you will
get weird broken up sounds or other strange behavior. Test all the unlabeled
terminals and you will find the pairs that sound best. These sets are
intended to go to the same speaker.

Now, assuming that you have not blown out the speaker (unlikely if you
carefully! followed the instructions above), you can permanently connect the
speaker to the terminals you found, or you can hook up a better speaker that
you have been saving for the purpose, if that is the case.

That all for this stage. Now on to building and installing the shortwave
converter.

CONVERT.TXT

SHORTWAVE CONVERTER

Parts List

C1 Optional capacitor. Use 150pF with 5 Mhz crystal, or 47pF with 8 Mhz
If using crystal ? 10 Mhz omit this capacitor.

C2 33 pF
C3,C5 220 pF
C4 .047 ?F
D1 Zener diode between 5.1v - 6.2v (2N4691 or equivalent)
R1 1K?, ? watt resistor
U1 NE602N Frequency Converter IC
T1 10.7 Mhz miniature IF transformer (green core)
XTAL 5 Mhz or 8 Mhz crystal, or other values (see text file XTAL.TXT)
One for each band you like to listen to

8-pin DIP socket (for U1)

J1,J2 RCA jacks [J2 is optional, see note 3 below]

Motorola plug (optional. If installing converter externally, use for
connecting cable to car radio's antenna jack). Radio Shack parts #274-711

14-pin wire-wrap socket and 14-pin DIP headers for mounting crystals
Optional (see file XTAL.TXT)

Hookup wire


Schematic
=========

????????????????????????????/\/\/\? +12v
? ????? ? ? R1
???C3 ????? xtal ? ?
??? ????? ? ?
? ????? ? ?
J2 (to car radio antenna jack) ? ? ? ?
???? C5 ????????????????????????? ?
? o?????????????????????????????? 7 6 8? ?
???? ?5 ? ?
?gnd ? U1 ? ?
? ? ?
J1 (ant.) ??????????? ? NE602 ? ? ? D1
???? ? 3???????????? ? ???????????????
? o?????????1 ? ? ? Frequency ? ? ? ?
???? ? T1 4??nc ???C1*? Converter ? ? ?
? ? ? ??? ? ? ? ?
??????????2 ? ? ? ? ??? ?
? ? 5???????????? ? ??? C4 ?
? ??????????? ? 3 ? ? ?
? ????????????????????????? ? ?
? ? ? ?
??????????????????????????????????????????????????????????????????????????
?gnd

-----------------------------
Notes:

1) Virtually any construction method (point-to-point wiring, wire wrapping,
etc.) should work, but a printed circuit board is recommended for both
ease and neatness of construction. PC board construction would probably
also help minimize undesirable RF interference from strong local broadcast
stations. See file READ.ME for source of PC board.

2) Connect external antenna to J1 (it works with anything over 2', but better
results are obtained with longer lengths.

3) J2 connects to car radio's antenna jack. If mounting the converter inside
the car radio, omit J2 and run a wire directly from where the center
connector of J2 is indicated to the car radio's antenna jack, otherwise
use coax cable to connect from J2 to car radio antenna jack (see note 3).

4) It is strongly suggested that you install the converter inside the
chassis of the car radio (it simplifies the wiring and reduces noise). If
you do not have room to do so, use a metal case for the converter and a
SHORT length of shielded coax cable for the connection from the converter
to the car radio's antenna jack.

5) Connect +12 volt power input to car radio's on/off switch. That way you
can turn both radio and converter on with that switch.

6) When everything is working, tune in a shortwave station near the middle of
the dial and adjust the slug of T1 for the strongest signal.

7) You may use a signal generator or crystal oscillator to calibrate the
dial, if desired.

XTAL.TXT

CRYSTALS
for your shortwave converter


The original project instructions specify a 5 Mhz and/or 8 Mhz crystal be
installed in the kit at the "xtal" location on the schematic. You would need
to use one of the optional capacitors (150 pF with 5 Mhz, or 47 pF with 8
Mhz) at C1. I have tried crystals of other frequencies with varied success.
A 14.31818 Mhz crystal pulled in more signals than any others I tried (it
gives access to the 19 and 22 meter bands). 11.111 Mhz also works well.
Even a commonly available 3.579 Mhz color burst crystal works o.k. (use a 220
pF cap for C1 with this one). Every different crystal gives you a new band 1
Mhz wide. Experiment.

I strongly suggest mounting a 14 or 16-pin wire-wrap DIP socket where the
crystal would be, instead of hard-wiring in one partical crystal. This way
you can solder each one of your different crystals to a DIP header and plug
them in one at a time for each different band you want to tune. Perhaps you
can come up with an even more convenient method of installing and removing
the various crystals.

There are various sources for cheap crystals. Ham shows and computer flea
markets are best (you can obtain them there for as cheaply as 50c ea., or at
most a dollar or two). Ads in electronics magazines feature them for a
dollar or two each. As a last resort, order them from Jameco or Digikey or
even Radio Shack at $2 - $8 each.

 
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