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Transceiver Circuit

Ty Ban

Aug 27, 2017
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A potentiometer is a resistor with a slider (the arrow) that you can slide along the resistance. You can move the slider anywhere from one end to the other end of the resistance or anywhere in between.
Take a potentiometer apart to see the resistance and the slider.
What would the potentiometer do to the circuit during transmit mode?
 
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Ty Ban

Aug 27, 2017
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Does the transmit part of this really connected to the other received part?
 

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kellys_eye

Jun 25, 2010
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That circled part of the schematic only changes the operation of Q1 from an 'accurate' crystal-controlled oscillator (during transmit) and a 'looser' oscillator used for the mixer circuit that Q1 operates as during receive.
 

Ty Ban

Aug 27, 2017
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That circled part of the schematic only changes the operation of Q1 from an 'accurate' crystal-controlled oscillator (during transmit) and a 'looser' oscillator used for the mixer circuit that Q1 operates as during receive.
So it really is connected? The circled one
 

kellys_eye

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If the walkie-talkie is in 'receive' then ALL the switches will have the wiper (the arrow) connected to the points marked 'R'.

Equally if the walkie-talkie button was pressed (transmit) then ALL the wipers (arrows) will be connected to the points marked 'T'.

At no point are the wipers (arrows) ever NOT connected to anything. They are ALWAYS on either 'R' or 'T'.

The schematic only shows them 'disconnected' because they don't presume to know what condition the circuitry is going to be in at any one time.
 

CDRIVE

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May 8, 2012
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The schematic only shows them 'disconnected' because they don't presume to know what condition the circuitry is going to be in at any one time.

As a personal preference I would rather see the PTT switch shown in the RX position. A simple note "Switch shown in RX position" will suffice. Shown as is it can be interpreted as a center off switch.

Chris
 

kellys_eye

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So would I.... but we can't really expect a professional schematic for such a cheap'n'cheerful device. It serves the purpose - to those that have the basic concepts of schematic reading...
 

Audioguru

Sep 24, 2016
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The potentiometer adjusts the level of your voice when you transmit.
The RF transistor is a crystal oscillator during transmit and is a super-regen circuit (not a mixer) during receive. A simple super-regen circuit is used as the radio receiver in children's radio controlled toys.
The very simple transceiver is a child's toy.
 

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Ty Ban

Aug 27, 2017
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The potentiometer adjusts the level of your voice when you transmit.
The RF transistor is a crystal oscillator during transmit and is a super-regen circuit (not a mixer) during receive. A simple super-regen circuit is used as the radio receiver in children's radio controlled toys.
The very simple transceiver is a child's toy.
Oh ok thanks for the info.
 

Ty Ban

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So I made the actual PCB layout, solder the components and when I test the circuit, there was no noise coming out of the speaker, but I can hear the " snap sound " inside the speaker whenever I turn on the main switch meaning there is a voltage flowing. I cant transmit and receive in either the walkie talkie (cause I made 2). In the picture below, can you tell me where among the 12 pins of the push switch should I connect each T,R, COMMON(arrow)? cause I think there is where I made a mistake. Please help, thanks.
 

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Audioguru

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The switch is simple to see what connects to which of its pins.

The RF transformer connects to the antenna and the transformer has a tuneable ferrite core.
Does your RF transformer have a ferrite core?
Have you tried to tune the transformer?

Maybe you should buy a pair of cheap walkie talkies to see the parts they have.

Here is the switch wiring:
 

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Ty Ban

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Is the RF transformer your talking about is the inductor slug? (Cause you can tune it)
 

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Ty Ban

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That is what my actual pcb is, the one with the circle is the inductor slug.
 

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