Eight: IC Shortwave Radio Receiver in Software

Drawer European Article Number 13 in Software Eight: IC Shortwave Radio Receiver

Table 8-3

C16 = 001 C15 C15 C15 C16 = 100 pF C15 C15 C15 T3 Slug In 65 13 MHz 51 79 MHz 43 53 MHz T3 Slug in 84 142 MHz 6 81 MHz 49 63 MHz T3 Slug out 9 183 MHz 71 107 MHz 6 83 MHz T3 Slug out 115 195 MHz 85 11 MHz 67 84 MHz

range you would like your receiver to tune, and then select the values for C15 and C16 from the chart, shown in Table 8-3 A suggested configuration would be C15 = 47 pF and C16 = 100 pF This will give you complete coverage from 6 to 11 MHz by adjusting T3 in or out This is a very active section of the shortwave band and will provide you with hours of listening enjoyment any time of the day Select and install C15 and C16 Finally, you will need to locate an enclosure for the receiver, and then install the circuit board into the enclosure Place the knobs on the potentiometer shafts, locate a 9 volt transistor radio battery and connect it to the receiver battery clips Connect up an antenna and you are ready to test out your new receiver Before turning on your receiver, double-check that you have correctly oriented all three of the ICs, that you have correctly oriented the transistors, that you have installed the diodes correctly, and that you have installed the electrolytic capacitors correctly Finally we will inspect the circuit board for cold solder joints and possible short circuits Pickup the PC board with the foil side of the board facing you and inspect the solder connections You will want to make sure that all of the solder connections look clean, smooth and shiny If any of the solder joints look dull, dirty or blobby then you should un-solder that particular joint and re-solder it over again so that it looks clean, smooth and shiny Next, let s inspect the CP board for any possible short circuits Often stray cut component leads will bridge across between circuit traces and short out a PC trace Another possible source of short circuits is a solder blob which

can bridge across a circuit trace Carefully inspect the PC board for any solder blobs or stray wires before connecting up a 9 volt battery

their frequencies, particularly at sign-on and sign-off times If you like precision, use a frequency counter or calibrated receiver to find the SR2 s strong oscillator signal, remembering that there is a 455 kHz IF difference (above or below) between the local oscillator frequency and the broadcast signal you are hearing

Now, connect up a speaker or headphones, connect up some sort of antenna and install a fresh 9-volt battery and we can begin testing the receiver We have come to the moment-of-truth, go ahead and turn the receiver power switch to the on position After adjusting the volume to a pleasant level, you should hear some shortwave stations by turning the Tune Control, no matter how any of the adjustable coils happen to be set While listening to any kind of station, whether broadcast or Teletype, etc, use a small screwdriver to adjust the slugs in transformers T1 and T2 for the bestsounding reception The Tuning Control covers varying segments of the bands selected by adjustment of oscillator coil T3 Adjustment of T3 anywhere between the full In position to the full Out position will give the user full range between the minimum and maximum frequency coverage set by C15 and C16 Both T1 and T2 must be adjusted with a non-metallic alignment tool such as is used in radio-TV service If you do not have one, a suitable tool can be made by patiently sanding a screwdriver-like blade on the end of a wooden match stick, kebab skewer or small plastic crochet needle Again, please be aware that a metal screwdriver blade will drastically increase the coil inductance and make adjustment quite difficult T1 and T2 are simply adjusted for strongest reception of any signal range that is tuned in If you do not have any sort of testing or frequency reference equipment whatsoever, the easiest way to begin using the receiver, is to set the Tune Control at its midpoint, slowly tune T3 with your alignment tool as though it were a tuning dial Stop when you come into the middle of a group or cluster of foreign broadcast stations Try tuning around these stations with the Tune Control If you like what you hear, readjust both T1 and T2 for best reception Eventually, you will get a clue as to what general frequency band you are hearing, because many stations periodically announce