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Testing AM receiver carrier wave

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Member level 5
May 9, 2010
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I have designed an AM receiver but I initially want to test whether it receives a 27 mhz signal ( this signal is just a carrier wave, I haven't yet included the sound etc within this signal). I have already included the appropriate LC values on the receiver but need to tune it by a varicap. I have got an oscilloscope already an I assume that once I power up the 27mhz oscilator, I should see something i.e a signal on the oscilloscope. Will this happen? will I be able to see a signal on the oscilloscope even if there is still no sound or signal on the carrier wave?

Please help or advise alternative testing method.

Many thanks.

The carrier appears as a DC signal (respectively a DC shift) at the demodulator output. Some receivers are displaying it as a field strength indicator (S-meter).

I tried putting my radio control transmitter (for an airplane) near my oscilloscope. I wanted to see if it would detect any radio signals.

I saw pulses across the screen. As I pushed the stick in different directions, my oscilloscope showed the changing pulse lengths.

The signal was on a 72 MHz carrier. However my oscilloscope is only good up to a megahertz.

To this day I don't understand how I could see those pulses. I guess it was a case of the transmitter putting out a strong enough signal that something just had to show up.

Likewise you may see something. Your carrier wave may come through by itself, if your scope goes up to 27 mHz.

Or, try tuning a shortwave radio to 27 mHz. You may hear audio beeps as your carrier intermodulates with other broadcasts. You may have to hunt around by tuning the radio. Or tune your carrier up and down.

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