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SW Converter for AM Radio

Posted by merzaha gulhku Tuesday, July 30, 2013 0 comments
Apart from chucking it in the bin, what can you do with outdated AM automobile radio or clock radio in your junkbox? How about fliping it right into a crystal managed, secure, quick wave radio receiver, for a minimal funding in time and money? Read on. The coronary heart of the circuit shown here is an IC which works by the title NE602, NE612 or SA612. It is a double balanced mixer that features an oscillator that can be crystal-controlled, free working or even pushed externally from a PLL, and many others. It was once in the beginning designed for cellular telephones and is most probably to be had in junked car telephones from the tip. The NE602/612 accommodates a differential input amplifier (called a Gilbert Cell), an oscillator/buffer, a temperature compensated bias community and a energy regulator. Typical frequency response is in far more than 500 MHz for the input and 100 MHz for the oscillator.
Circuit diagram :
SW Converter for AM Radio Circuit Diagram
Supply present is 2.4 mA and the absolute maximum provide voltage is 9 V. Input and output impedances are approx. 1.5 kΩ. As you'll find from the circuit diagram, the enter from the aerial is handed through a ten.7 MHz IF (intermediate frequency) transformer. This offers isolation from the aerial and cut backs the effect of sturdy local AM radio step forward.The transformer may also be salvaged from a dead FM radio or stereo or even the FM component to an previous clock radio. (The AM part is what we want to use anyway so ratting just a little from the FM section keeps cost). A selection of 10.7 MHz IF coils from Toko and other far-Eastern manufacturers may be used, together with the 94AES30465N and 94ANS30466N, but obtaining these as new phases may be more pricey than an entire radio rescued from the tip. There is on a standard basis a small capacitor under the IFT coil, between the pins. If so, do away with it by means of crushing it with a pair of pliers and ripping out the remains. The capacitor will no longer be wanted as we add an exterior one in step with the band wished. The input sign is fed into the balanced input of the IC.
The crystal is hooked up to pin 6. It oscillates at its fundamental frequency and that is mixed with the input signal giving a selection of outputs. The mixer output signal appears on pins four and 5. Here, handiest pin 5 is used for the output. By the way, the enters and outputs are interiorly biased with pull-up resistors, so there's no have to tie the unused pins to ground or energy. The 220 pF capacitor offers isolation to any DC into the AM radio aerial input. Note also that the same circuit can be used to increase the selection of an present short wave radio receiver in precisely the identical method. The AM radio is used as a tuneable intermediate frequency amplifier, with a tuning vary of about 1.6 MHz. You can are attempting different prices for C1 to get resonance on the NE602 input: a hundred and fifty pF for up to 5 MHz, forty seven pF for up to 8 MHz, and no capacitor for as a lot as 10 MHz. In apply however 33 pF will have to do for all ranges. Almost any crystal can be utilized. The creator tried many varieties from FT-243 WW2 surplus ones to 27 MHz, third overtone CB crystals. Every crystal tried worked. TV sub-carrier crystals work well, as do large oven varieties. Several crystals can additionally be linked through a switch, giving a convenient manner of swaping bands. Keep the leads to the swap as short as that that you can think of though to forestall radiation of the crystal oscillator. There are many tips on how to construct the circuit. You could make it right into an external metallic field that can be related to a quantity of radio’s, depending in your location. For instance, if you're a traveller, make it in a small box with an internal 9-volt battery, and leave sufficient wire on the output to wrap a few dozen flips across the clock radio in your Hotel room.

This gives you your quick-wave reception on the go. It can also be imaginable to construct the converter proper into the auto radio. Any form of development method can be used, from a small piece of perforated board that I used, to a extra problematic printed circuit board and even simply lash all of the small components beneath the IC socket. A small swap is additionally used to alter from AM to short-wave. Connect the circuit to the car radio with screened cable to stop or lessen the impact of robust station step forward. To couple the output of the converter to a radio with out an external AM aerial enter, wind several turns of wire round the interior ferrite rod aerial. As steered before, winding a dozen or so turns across the plastic radio case will additionally couple the converter to the radio. This will work at the fee of increased AM sign breakthrough. Connect the positive power lead to the switch on the radio so that it changees the converter on and off as well.

The quick-wave aerial can be 2 to a few meters of wire strung across the room, but better outcomes can be received with a outdoor aerial. The take a look at aerial was about one hundred meters lengthy and 10 meters high. At evening there is a lot of job on the short waves after darkish. Find a weak station round 1 MHz on the AM dial and alter the core of the IFT for minimal extent from the broadcast station. That’s the simplest alterment. SSB alerts can additionally be heard, but as no beat frequency oscillator is fitted, you hear the “duck talk” of the signal. The 10 kHz bandwidth of the radio means that on the ham bands, signals do overlap, however it also makes the broadcast stations sound higher as most of them do broadcast with cheap high quality audio. Digital tuned AM radios are on a regular basis no longer appropriate for the circuit as introduced, because the tuning steps are 9 or 10 kHz apart and we wish a lot smaller steps. The previous manually tuned varieties of automotive radio are what you wish to have. The idea of the circuit is to no lengthyer get too complicated, but to just experience listening on a simple, stable, low cost, brief wave receiver. Experiment and experience!

Author : P. Laughton, VK2XAN – Copyright: Elektor Electronics