I have to build a project with a AM transmitter and receiver. The idea is that I will speak something which will be transmitted and received to the receiver. The Transmitter and the receiver assembly will be located very close (within couple of feet). My question is that for the receiver circuit, do i still need a tuner even though it is receiving only one signal from the transmitter?
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3 Answers
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My question is that for the receiver circuit, do i still need a tuner even though it is receiving only one signal from the transmitter?
Radio receivers use "tuning" so they can discriminate against those radio frequencies that they DO NOT want to receive thus, only allowing through the frequency of carrier wave that they DO want to receive.
You also need a demodulator to convert the modulated carrier back to audio/speech.
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\$\begingroup\$ I don't have variable inductor or capacitor. Is there a way I can have a tuner without variable inductor or capacitor. If the answer is no, I have to make by myself. Please suggest how I will be able to build by myself \$\endgroup\$ Commented Jun 13, 2017 at 4:05
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\$\begingroup\$ If you haven't got an inductor and capacitor then you need to buy them. You can make an inductor quite easily of course but, without knowing your skillset or operating frequency then I cannot advise. Do some googling on crystal radios maybe. \$\endgroup\$– Andy akaCommented Jun 13, 2017 at 6:29
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\$\begingroup\$ Inductance is just a coil. I should be able to make it. For the transmitter can you please me what carrier frequency I should use to modulate the signal in my situation. The distance between the transmitter and the receiver does not matter. I can place them pretty close. Does the transmitter length has to be lambda/4, which is pretty long. \$\endgroup\$ Commented Jun 13, 2017 at 14:14
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\$\begingroup\$ I have both inductor and capacitor of fixed rates. I don't have the variable ones \$\endgroup\$ Commented Jun 13, 2017 at 14:16
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\$\begingroup\$ That is a start but the values needed depend on the carrier frequency and what type of antenna you have connected. I cannot advise you on carrier frequency because this will be governed by legislation in your part of the world. For a very short distance between transmitter and receiver try looking for circuits on google that suggest they are AM modulators (about 1 MHz) and then you can use an off-the-shelf radio for receiving. \$\endgroup\$– Andy akaCommented Jun 13, 2017 at 18:05
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The receiver must be tuned to the same frequency as the transmitter, so it does need some form of tuner.
answered Jun 11, 2017 at 22:23
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\$\begingroup\$ Please give me idea about the demodulator and the resonant circuit. There are so many in the internet and I don't have an idea about which one to use. \$\endgroup\$ Commented Jun 13, 2017 at 14:23
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You can use dipoles, but at 1MHz for 1/2 wavelength you need 1/2 of 300 meters.
I suggest you use resonant flat (pancake coil) inductors with air-capacitors. For Q of 100 at 1MHz (giving you +-5KHz bandwidth -3dB), with 1 ohm loss assumed, the ZL and ZC is J100. That requires 16 uH inductor, loop or pancake style. Cap is ---- 1uF at 1MHz is -j0.16 ohm; you need 1uF/600 = 1,600pF. Either the Tx or Rx antenna needs some mica trimmers or air-gap trimming.
answered Jun 11, 2017 at 22:37
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\$\begingroup\$ Um, the question was "do i still need a tuner". \$\endgroup\$ Commented Jun 12, 2017 at 7:45
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\$\begingroup\$ A half wave dipole is a bit of an overkill to transmit over 'a couple of feet'. I think the OP is about tuning the frequency of TX/RX, not antenna tuning. \$\endgroup\$– ChuCommented Jun 12, 2017 at 12:33
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\$\begingroup\$ Can you guys please tell me about the demodulator and tuner circuit. I can't use a germiniun diode. \$\endgroup\$ Commented Jun 13, 2017 at 14:20
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\$\begingroup\$ Can you guys please tell me about the demodulator and tuner circuit. I can't use a germiniun diode. I am confused about all these that you guys are dying. I am supposed to pick a diagram from the internet. I want to make sure I pick the right one (not the one where I need a long Antenna \$\endgroup\$ Commented Jun 13, 2017 at 14:37