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I buy am/fm radio kit but something i dont understand

michael1978

Mar 17, 2012
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Hi,
i buy this kit AM/FM RADIO KIT EL21
I thought they explain something but pfff nothing....
but the problem is that, they dont explain how it works circuit but only how to mount in board transistor resistor etc,
something i dont understand for example the left half circuit side i understand, but the right half circuits i dont understand, let say wat do diode and inductor 800uH and two capacitor 0.0005uF and 0.005uF , and 2.2k capacitor 470p? and 1k8 and 1M and wire earphone. if somebody can help me please this piece of somebody to described with little word thanks

AMFMRECEIVERKOPI.JPG
 
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duke37

Jan 9, 2011
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I do nor know what the input stage does, the 1N60 diode does not have a current source.
The 2k2 resistor and the 1M resistor sets the current through the 2N3904 which is a grounded base amplifier.
The 800μH (not UM) inductor reduces the RF going through to the final stage.
The 1μF capacitor passes the signal through to the final transistor. This is biassed in the same way as the 2N3904 and the 470pF capacitor is there to reduce the high frequency response in case some RF comes through.

P7 and P8 must go somewhere.
 

michael1978

Mar 17, 2012
388
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I do nor know what the input stage does, the 1N60 diode does not have a current source.
The 2k2 resistor and the 1M resistor sets the current through the 2N3904 which is a grounded base amplifier.
The 800μH (not UM) inductor reduces the RF going through to the final stage.
The 1μF capacitor passes the signal through to the final transistor. This is biassed in the same way as the 2N3904 and the 470pF capacitor is there to reduce the high frequency response in case some RF comes through.

P7 and P8 must go somewhere.
i buy last week, this is the manual
:Dexellent thanks so much, so the two transistored are biased in the same way, my i ask why the pick 800uH inductor(how the calculated) also the capacitor(how they calculated 450pf)
and 4.7K
in the left side circuit 5 connect to right side circuit 5, but the 5 right side circuit , i looked the circuit where the components must place(bredboard)
 
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Audioguru

Sep 24, 2016
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The FM tuner is a Mickey Mouse "regenerative" circuit and the AM receiver is a Mickey Mouse "crystal" radio.
A real radio is super heterodyne and is MUCH more complicated with MUCH Better Performance" than this garbage.
 

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(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Audioguru believes that unless something is perfect it has no value.
 

duke37

Jan 9, 2011
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The μ symbol is available up top.

The inductor and capacitor needed will depend on the transistor characteristics. To see the effects, you could do a simulation using LTspice. You want a response up to 5kHz or so.

In #2 I said that the transistor was a common base, it is of course a common emitter.
 

Audioguru

Sep 24, 2016
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Audioguru believes that unless something is perfect it has no value.
When I was about 15 years old, I built a real superheterodyne FM radio kit then later a stereo multiplex adapter kit for it. They worked perfectly. After using them for about 5 years I sold them for more than I paid for them. That was good value. I never ever made a simple Mickey Mouse regenerative tuner or an AM crystal radio that have no value.
 

michael1978

Mar 17, 2012
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The FM tuner is a Mickey Mouse "regenerative" circuit and the AM receiver is a Mickey Mouse "crystal" radio.
A real radio is super heterodyne and is MUCH more complicated with MUCH Better Performance" than this garbage.
Hi AudioiGuru, but i buy, i did not know that is regenerative tuner, , i ask in electronics shop, do you have some educative am/fm radio kit? and he say this is good, when i open i thought they explain how its works but WHAT TO SEE, only how to mount he explain, so first i want to finish this one to understand, after i gonna buy am/fm another educative , but still i dont know wich one to buy, about super heterodyne i sarch on internet but i did not find nothing special to teach you.
 

michael1978

Mar 17, 2012
388
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The μ symbol is available up top.

The inductor and capacitor needed will depend on the transistor characteristics. To see the effects, you could do a simulation using LTspice. You want a response up to 5kHz or so.

In #2 I said that the transistor was a common base, it is of course a common emitter.
The μ symbol is available up top.

The inductor and capacitor needed will depend on the transistor characteristics. To see the effects, you could do a simulation using LTspice. You want a response up to 5kHz or so.

In #2 I said that the transistor was a common base, it is of course a common emitter.
Hi, So if you want select the 800µh and 470p formula only to experiments in ltspice, so is not any formula for exampe if you design for example one like this, how you select the value of inductor and capacitor , if you know the charachtersticks of transistor, is possible to show me one example
i will gonna make it today in ltspice to try, but without formula how to calculate i can learn nothing i think
thanks for advice;)
 

michael1978

Mar 17, 2012
388
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The μ symbol is available up top.

The inductor and capacitor needed will depend on the transistor characteristics. To see the effects, you could do a simulation using LTspice. You want a response up to 5kHz or so.

In #2 I said that the transistor was a common base, it is of course a common emitter.
I did not know,, how to do it , i try to make i did not know, what is his function ? i build all the circuit but i did not find vc and type of transistor and diode, the complete scheme i make it i build i have if you need.
 

duke37

Jan 9, 2011
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800μH
An inductor will have an impedance of 2*pi*f*L, it needs to stop high RF frequencies and pass audio frequencies without too much attenuation. You could assume the input impedance of the following transistor is about 1kΩ. Calculating the frequency at 1kΩ. f=1k/(2*pi*L) = 200kHz so it will pass audio easily but attenuate higher RF frequencies. You should check my calculations and try with different input impedances of the following transistor.

470pF
The 470pF is used as a high frequency feedback and will reduce the input impedance of the output stage. Its effect will depend on the gain of the transistor.

It is all rather complicated so that is why I suggested LTspice. The diode has nothing to do with the audio amplifier and as I explained earlier it has no DC path.

It is years since I used LTspice and would need some time to re-learn how to do it. I can just about remember what I had for breakfast. You are obviously starting in the hobby and worth familiarising yourself with a simulation program.

As an exercise, you could calculate the ideal current gain of each transistor assuming the the collector voltage is 5V with a 9V battery supply.
 

michael1978

Mar 17, 2012
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800μH
An inductor will have an impedance of 2*pi*f*L, it needs to stop high RF frequencies and pass audio frequencies without too much attenuation. You could assume the input impedance of the following transistor is about 1kΩ. Calculating the frequency at 1kΩ. f=1k/(2*pi*L) = 200kHz so it will pass audio easily but attenuate higher RF frequencies. You should check my calculations and try with different input impedances of the following transistor.

470pF
The 470pF is used as a high frequency feedback and will reduce the input impedance of the output stage. Its effect will depend on the gain of the transistor.

It is all rather complicated so that is why I suggested LTspice. The diode has nothing to do with the audio amplifier and as I explained earlier it has no DC path.

It is years since I used LTspice and would need some time to re-learn how to do it. I can just about remember what I had for breakfast. You are obviously starting in the hobby and worth familiarising yourself with a simulation program.

As an exercise, you could calculate the ideal current gain of each transistor assuming the the collector voltage is 5V with a 9V battery supply.
thankssssssssssss Duke, yes ideal current is 100mA.... 5v/0.1A = 0.5A, YOU HELP ME A LOT
 

michael1978

Mar 17, 2012
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Duke he help a lot, thank you man very much, but i have one question, 800µ with capacitor is a filter, i leran to filter to stop high frequency, pass low frequency, pass band, is just in my mind
 

duke37

Jan 9, 2011
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thankssssssssssss Duke, yes ideal current is 100mA.... 5v/0.1A = 0.5A, YOU HELP ME A LOT
I was thinking along the lines of what gain the transistor should have.
With 5V on the collector (halfway approx) there is 4V across the 2k2 resistor so the collector current will be 1.82mA.
With 5-0.7V across the 1M resistor, the current will be 4.3μA
The gain of the transistor (beta) to get this condition needs to be 1.82E-3/4.3E-6 = 423. Quite reasonable.
A higher gain transistor will give a lower DC collector voltage and a lower gain transistor a higher DC collector voltage.
I think the 100mA you quote is the maximum which should be demanded of the transistor
 

Audioguru

Sep 24, 2016
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I am not a teacher but I found a real radio kit in Google. It is sold on Amazon and on Walmart online. The kit has the stages of the radios marked and comes with a training course appropriate for high school and university level curricular:
 

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michael1978

Mar 17, 2012
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I am not a teacher but I found a real radio kit in Google. It is sold on Amazon and on Walmart online. The kit has the stages of the radios marked and comes with a training course appropriate for high school and university level curricular:
That i gonna buy next month, i download the manual and i read a little bit is good, but i buy this first i was think he teach me something but nothing.....but thnx to Duke he explain me, but i want to mount this one first , after the next one.,
GoodNight...
 

michael1978

Mar 17, 2012
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I was thinking along the lines of what gain the transistor should have.
With 5V on the collector (halfway approx) there is 4V across the 2k2 resistor so the collector current will be 1.82mA.
With 5-0.7V across the 1M resistor, the current will be 4.3μA
The gain of the transistor (beta) to get this condition needs to be 1.82E-3/4.3E-6 = 423. Quite reasonable.
A higher gain transistor will give a lower DC collector voltage and a lower gain transistor a higher DC collector voltage.
I think the 100mA you quote is the maximum which should be demanded of the transistor
sory i think 10mA, thank you Duke a lot
GoodNight....
 

duke37

Jan 9, 2011
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I have used 5spice to plot the effect of the feedback capacitor across Q2.
Both transistors were simulated as 2N2222.
The red line is 100pF
The top black line is 1000pF.
470pF will come between these two.
The 800μH inductor affects the response at frequencies well above audio.
The advantage of a simulator is that the program deals with all the calculations.

imgMichaelC2002.jpg
 

michael1978

Mar 17, 2012
388
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I have used 5spice to plot the effect of the feedback capacitor across Q2.
Both transistors were simulated as 2N2222.
The red line is 100pF
The top black line is 1000pF.
470pF will come between these two.
The 800μH inductor affects the response at frequencies well above audio.
The advantage of a simulator is that the program deals with all the calculations.

View attachment 41129
GoodMorning Duke,
Sorry for late answer,
But Duke, how did you get those line? now i seee a channges,, do you have maybe stile a file? so i can test
self ?
Have a nice day....
 
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