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#8
February 2nd 06, 04:38 AM
posted to rec.radio.shortwave
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Hot rodding AA5 radios
craigm wrote: wrote: Most of the mass-produced radios lack the RF coil to properly match the ferrite antenna. As you adjust the oscillator coil you will find a spot where the gain of the circuit is optimum. You are not adjusting the ferrite antenna: you are matching the oscillator to wherever the ferrite is tuned to. This will produce stronger signals. Try it. That would do winders for dial accuracy. ************************************************** ********************************** Actually, this type of radio doesn't have good dial accuracy out of the box, so the tuned version is not much different than the original as long as the tuning device is adjusted. This adjustment is made to have the oscillator 455 khz higher than whatever the ferrite is tuned to. Since there is no easy way to adjust the ferrite, adjust the oscillator coil until it is 455 khz higher than the antenna (ferrite) coil. You will find a spot where the signals are the loudest. This is where the correct difference frequency is 455 khz and the gain is maximum through the IF. For example, if the station you want to receive is at 600 khz, and the antenna is tuned to 610 khz due to manufacturing tolerances, the oscillator must be tuned to 1065 khz to have the correct difference frequency. Since the oscillator is the only thing that can be adjusted, you adjust it. The IF is happy: all it wants is a 455 khz signal. The increase in gain is especially noticeable from 550 to 700. All the radios I have tuned could easily add the new 1600 to 1700 frequencies. The 455 khz IF coils are quite stable: I haven"t run into any that needed adjusting. |
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