                                 AM RADIO
How to covert an ordinary table model AM radio, or clock radio, or any old 
               transistor radio into a shortwave receiver. 
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Well, you may ask, why should I be limited to converting a car radio into a 
shortwave receiver?  A car radio does have a few non-trivial disadvantages.  
It comes in an unattractive, even clunky metal case, not really suitable for 
display.  You do have to build a separate power supply for it, and even 
though details on doing this without much effort are in the enclosed file 
POWERSUP.TXT, it still does involve extra work and expense, not to mention 
the extra space on your table that the power supply case and external 
speaker hog. 

Say you salvage this nice old clock radio out of your attic. The clock still 
keeps time fine and the radio pulls in local AM stations nicely without too 
much static. Hey, wouldn't it be nice to be able to tune shortwave stations 
on it? 

Yes, it is possible to convert many AM radios to shortwave receivers using 
the converter described in the enclosed CONVERT.TXT file. The disadvantages 
relative to a car radio are that your converted AM radio will be somewhat 
more subject to interference from strong AM broadcasters plus noise and 
static, and it may also be necessary to take extra precautions with the 
"transformerless" power supplies of some older table model and clock radios 
(see below). The main advantages are reduced parts count and lower cost. It 
is quite possible to convert an AM radio for a total cost of $5 or less, 
depending on how many of the needed parts are on hand. 

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                               The procedure:

[Ignore all references in the following section to AC or AC power supply if 
you are working with a battery-powered portable radio.] 

Make certain the AM radio you will be working on is unplugged from the power 
line.  Open the case of the radio by removing the screws that hold it 
together. Save the screws. You may have to disable or outwit spring clips or 
other clever devices in order to get to the circuit board. Disregard the 
warning that there are no "user serviceable parts inside". [Note that if you 
are working on an AC-powered radio and do not know what you are doing, you 
can cause damage to the radio and your test equipment, not to mention 
hurting yourself. Get experienced help if you are new to this, or stay with 
battery-powered radios, where the amount of damage you can do is limited.] 

========================
First, you MUST determine whether the AC-powered radio has an unsafe 
"transformerless" power supply. If the radio has an AC power cord and the 
power cord does not have a "polarized" plug (three-prong or two-prong with 
one prong wider so that it can be plugged in only one orientation), and if 
the radio has no step-down or isolation power transformer, then it has an 
UNSAFE power supply and extra precautions MUST be taken. If you cannot fully 
understand what has just been said, then STOP and do NOT proceed further 
without supervision by a technician or experienced electronics hobbyist. AC 
power can be dangerous! 

If the radio has an unsafe power supply and the power cord does not have a 
polarized plug, this condition must be remedied before proceeding further. 
Replace the unpolarized plug with a polarized one oriented so that the AC 
power "neutral" always connects to the chassis and/or circuit board ground, 
and NEVER the AC "hot". Alternately, you may add an isolation transformer 
that completely isolates the chassis and circuit board from the AC line. 
Doing so requires measuring AC line voltages with a voltmeter, not a 
procedure for beginners, and therefore details of this are deliberately 
omitted. If you do not know how to do this, STOP and get help from a 
technician or experienced electronics hobbyist. Or better yet, work with a 
battery-powered portable radio, and you can avoid this problem completely. 
========================

You will need to locate three points on the circuit board or nearby: the 
circuit ground, the filtered DC voltage, and the point where you will inject 
the output from the SW converter. You will need a DC voltmeter or multi-
tester and your powers of observation. 

Finding the circuit ground is the easiest.  The ground is usually 
identifiable as a large "run" around the etched side of the PC board.  
Another sure bet is the negative terminal of the highest value miniature 
filter capacitor on the circuit board, usually 100 - 500 F. As always, stay 
away from the AC power supply at this stage of the procedure and later. 


The +DC voltage you need is at or near the positive terminal of the above 
mentioned filter capacitor.  Now you will need to power up the radio, 
carefully.  WARNING: KEEP FINGERS AND TOOLS AWAY FROM THE AC POWER SECTION OR 
YOU WILL BE EXTREMELY SORRY!  Put the voltmeter on the 20v DC scale and 
measure the voltage between what you think are the ground and +DC points. 
Your reading should be in the range of about 6 to 15 volts DC. If you have 
an oscilloscope handy, you might wish to confirm your diagnosis by verifying 
that there is no AC ripple between the two points, to make sure you have a 
filtered DC voltage available to power the SW converter. If you do not have 
a scope, you can test by using an ordinary red LED with a series current 
limiting resistor, about 470 . The LED should burn bright and flicker free. 
If you find AC ripple on the AM tuner PC board, this means the radio has an 
UNSAFE power supply, and you MUST remedy this by the procedure given in the 
previous section.

Unplug the radio.  Now you will solder a black wire to the ground point and a 
red one to the +DC power you just found.  These two wires you now attach to 
the ground and +V power points on the SW converter.  You may wish to do this 
using a mini plug and jack combination that will hook to the case you install 
the converter into. Your SW converter will now be conveniently powered by 
the radio and need no external power supply or battery.

The radio is still unplugged. Make certain that there is a wire leading from 
the output of the SW converter. Solder one on if necessary. Connect the 
black and red power leads from the radio PC board to the SW converter. 
Carefully plug in the radio and turn on the power, observing all precautions. 
Put the radio on the AM band if it is not so already.  Turn up the volume and 
twist the tuning knob.  You should hear local AM stations as usual.  If this 
is not the case, shut off the power and check your connections.

Now comes the tricky part.  Your AM radio receives AM stations with the 
converter powered up, but not yet injecting the down-converted shortwave 
signals into the radio's RF stage.  You will need to find, mostly by trial 
and error, the point at which to inject the signals. Attach a long-wire 
antenna (5' or longer) to the antenna input of the SW converter and insert a 
tested crystal into the socket for it on the converter. Now locate the AM 
radio's tuning capacitor, a small plastic square connected by a small shaft 
to the tuning knob on the radio. The tuning capacitor will have 4 - 6 leads 
attaching it to the PC tuner board. Touch the bare end of the wire from the 
output of the SW converter to each of these leads in turn, hold it in 
contact and twist the tuning knob of the radio. At one or more of these 
leads you should hear the bleeps and static and voices speaking in unknown 
languages. There's your culprit. The SW converter output connects to this 
point. Solder a wire there. [Note: this part of the procedure should be done 
at night, when short wave reception is best, and using a crystal for a known 
SW band.] 

Turn off the power to the radio.  You will now consider whether to install 
the SW converter inside the AM radio or to house it in a small case 
externally.  External mounting has the advantage of making it easier to 
change the crystal (and therefore the band of reception).  Internal mounting 
makes everything nice and neat, but you gotta unscrew and open up the radio 
case to switch frequency bands. My personal preference is the external 
mount, with every lead hooked up to plug 'n jack sets.

Reassemble the radio and turn on the power to see if it still works. If not, 
check all leads and joints, and then try again. If you have it working, 
mount everything neatly by the method of your choice. Now you can enjoy the 
pleasures of shortwave listening (SWL) on the cheap. 

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Notes: 

(1)     For adequate reception you will need a "long wire" antenna at least 
        4' long.  A whip antenna may be long enough, depending on your
        location.  Best reception on most SW bands is after nightfall.

(2)     Converting an AM radio to short wave is a relatively simple project
        as such things go.  However, it is emphatically NOT recommended for 
        beginners, especially if working with an AC-powered radio.  Do not 
        hesitate to get help from someone more experienced if you are beyond
        your depth.  Do not under any circumstances take risks with AC power!
