radio frequency circuit design

[akg]

All that the current output is doing (without making any modifications) is giving itself to the resistor. and what I like to know is, other than generating heat, Why would anyone (with experience) want to just connect a grounded resistor to the output, and nothing else?

seems to me that u have not understood the requirement .. :roll:

 

[akg]

..from the transmitting part, the sentence "use a 10k pot to adjust frequency".. is it variable resistor? there is no variable resistor.

the resistor labelled 5600 is actualy a variable resistor .
u have an LC tuned ckt at the receiver . so u need to adjust the transmitting freq to that of the tuned ckt to get the proper o/p

. and.. for the receiving part, how do i know if i get the signal? don't we need to tune at the output??

The LC is the tuned ckt . the o/p is marked in the dia. when the ckt receives a tuned freq , it will give a sq wave o/p .

 

[bananasiong]

..from the transmitting part, the sentence "use a 10k pot to adjust frequency".. is it variable resistor? there is no variable resistor.

the resistor labelled 5600 is actualy a variable resistor .
u have an LC tuned ckt at the receiver . so u need to adjust the transmitting freq to that of the tuned ckt to get the proper o/p

. and.. for the receiving part, how do i know if i get the signal? don't we need to tune at the output??

The LC is the tuned ckt . the o/p is marked in the dia. when the ckt receives a tuned freq , it will give a sq wave o/p .

sorry for disturbing again, the transmitting part. u said that the 5600 is a variable resistor, but is is a VR should have 3 pins? and why there is a sentence "use 10k pot"??

for the receiving part, i only need to get a 27mH inductor? or a variable inductor?

thanks

 

[akg]

sorry for disturbing again, the transmitting part. u said that the 5600 is a variable resistor, but is is a VR should have 3 pins? and why there is a sentence "use 10k pot"??

yes , it may be a VR with a val set to 5.6K. yes a VR has 3 legs , tie the center with a side leg ..u get a VR with 2 legs

for the receiving part, i only need to get a 27mH inductor? or a variable inductor?
thanks

no need of variable inductor.
if ur planning to deploy the above system in a no/very low EMI region ,
then u can construct the receiver ckt as follows.
a receiver coil (not an LC) connected to a high gain amplifier(refer op-amp based amplifiers) + band pass filter (band freq=osc freq of 555).

 

[bananasiong]

the vcc is connected to the +ve terminal of the battery and the ground is connected to the -ve terminal of the battery right? but it doesn't work! i used a cro to measure the output (after the 0.1k resistor), it shows a constant -12v (supply is 12V dc).

how about the receiving part, the pin 7 of the opamp is connected to nothing?? where is the antenna of the receiver??

thanks for helping me..

 

[akg]

the vcc is connected to the +ve terminal of the battery and the ground is connected to the -ve terminal of the battery right? but it doesn't work! i used a cro to measure the output (after the 0.1k resistor), it shows a constant -12v (supply is 12V dc).

the ckt is a normal 55 psc , and it will work .
u have wrongly selected the test point , measure the freq&voltage at the pin3 of 555. the 100R is placed for current limiting at the o/p section of 555.

how about the receiving part, the pin 7 of the opamp is connected to nothing?? where is the antenna of the receiver??
thanks for helping me..

the lm393 contains 2 opamps with open collector transistor , we are not using the second half of the ic , and it is left free.
probably u wont require an antand it should work in ur case) , the coil will pick the freq. and , if u need connect it to pin 2

 

[samteleti]

a simple radio can be made by using LC components im attaching one simple circuit chech out

 

[bananasiong]

the vcc is connected to the +ve terminal of the battery and the ground is connected to the -ve terminal of the battery right? but it doesn't work! i used a cro to measure the output (after the 0.1k resistor), it shows a constant -12v (supply is 12V dc).

the ckt is a normal 55 psc , and it will work .
u have wrongly selected the test point , measure the freq&voltage at the pin3 of 555. the 100R is placed for current limiting at the o/p section of 555.

how about the receiving part, the pin 7 of the opamp is connected to nothing?? where is the antenna of the receiver??
thanks for helping me..

the lm393 contains 2 opamps with open collector transistor , we are not using the second half of the ic , and it is left free.
probably u wont require an antand it should work in ur case) , the coil will pick the freq. and , if u need connect it to pin 2

so.. what i need to do is.. just follow the figure shown by Russlk, right? anything need to be modified? i couldn't get 1100resistor, can i use 1K? or 1K+0.1K??

 

[akg]

so.. what i need to do is.. just follow the figure shown by Russlk, right? anything need to be modified? i couldn't get 1100resistor, can i use 1K? or 1K+0.1K??

go ahead..use 1k

 

[bananasiong]

so.. what i need to do is.. just follow the figure shown by Russlk, right? anything need to be modified? i couldn't get 1100resistor, can i use 1K? or 1K+0.1K??

go ahead..use 1k

yes!! thanks.. another question, is.. i couldn't find the 27mH inductor.. i only get the 10mH.. do i need to change anything to the transmitting circuit?? can i know the range of this circuit?? thanks for answering..

 

[akg]

yes!! thanks.. another question, is.. i couldn't find the 27mH inductor.. i only get the 10mH.. do i need to change anything to the transmitting circuit?? can i know the range of this circuit?? thanks for answering..

increase the parallel C 2.7 times or , increase the Tx freq 2.7 times .
range depends on the current thru the (ant) loop ., need to check it .

 

[bananasiong]

yes!! thanks.. another question, is.. i couldn't find the 27mH inductor.. i only get the 10mH.. do i need to change anything to the transmitting circuit?? can i know the range of this circuit?? thanks for answering..

increase the parallel C 2.7 times or , increase the Tx freq 2.7 times .
range depends on the current thru the (ant) loop ., need to check it .

1. increase the parallel C? u mean the C which is parallel with the inductor at the receiving part? but i don't think i can get a 0.027uF capacitor..
2. how to increase the Tx frequency?
3. the VR at the Tx, i only need to turn it until i get 5.6K right? or it is a frequency tuner?

 

[akg]

1. increase the parallel C? u mean the C which is parallel with the inductor at the receiving part? but i don't think i can get a 0.027uF capacitor..

u can have a 0.022uF

2. how to increase the Tx frequency?
3. the VR at the Tx, i only need to turn it until i get 5.6K right? or it is a frequency tuner?

adjust the VR , here Ra is 1100, Rb is ur VR (@5600), C is 0.01
now freq of 555 is 1.44/(Ra+2Rb)*C

adjust Rb or C as per ur need.

 

[bananasiong]

1. increase the parallel C? u mean the C which is parallel with the inductor at the receiving part? but i don't think i can get a 0.027uF capacitor..

u can have a 0.022uF

2. how to increase the Tx frequency?
3. the VR at the Tx, i only need to turn it until i get 5.6K right? or it is a frequency tuner?

adjust the VR , here Ra is 1100, Rb is ur VR (@5600), C is 0.01
now freq of 555 is 1.44/(Ra+2Rb)*C

adjust Rb or C as per ur need.

why must use 1.44 to calculate? which c is used to calculate the f? the C is the numerator or denominator?

i've try this circuit, since i cannot get a 0.027uF, i took two 0.056uF in series to get 0.028uF, but the output i get is exactly same as the supplied, nothing to do with RF... why?

 

[akg]

why must use 1.44 to calculate? which c is used to calculate the f? the C is the numerator or denominator?

i've try this circuit, since i cannot get a 0.027uF, i took two 0.056uF in series to get 0.028uF, but the output i get is exactly same as the supplied, nothing to do with RF... why?

pls refer to


also u need "..since i cannot get a 0.027uF, i took two 0.056uF in series to get 0.028uF, but.." such type of adjustments .
use any nearest value u get.

 

[bananasiong]

why must use 1.44 to calculate? which c is used to calculate the f? the C is the numerator or denominator?

i've try this circuit, since i cannot get a 0.027uF, i took two 0.056uF in series to get 0.028uF, but the output i get is exactly same as the supplied, nothing to do with RF... why?

pls refer to


also u need "..since i cannot get a 0.027uF, i took two 0.056uF in series to get 0.028uF, but.." such type of adjustments .
use any nearest value u get.

thanks for the info.. yes.. i have already learned how a 555 timer works.. need some time to try this circuit... thanks ya.. any question i'll ask u again.. thanks

 

[bananasiong]

another question... what is the output at the receiver? is it the same pulse as the 555 timer?

 

[akg]

another question... what is the output at the receiver? is it the same pulse as the 555 timer?

yes it will give u the sq:wave when it receives the tuned freq.

 

[bananasiong]

why must the output of the 555 timer (after the 100R) be connected to the GND (-ve terminal of the battery)? can i connect it to nothing? as an antenna..

 

[Nigel Goodwin]

why must the output of the 555 timer (after the 100R) be connected to the GND (-ve terminal of the battery)? can i connect it to nothing? as an antenna..

It's not connected to ground, it's connected to an 'antenna', a loop of wire which surrounds your area as you required.