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chinsoon · 22nd January 2007, 10:09 AM

Quote:

Originally Posted by Nigel Goodwin

I suggest you google "superhetrodyne radio", and learn about how a radio works. In the case of a superhet the local oscillator is either above or below the wanted signal, by the amount fo the IF transformer.

of course i have tried.... and read some articles on it. and i know the stages of the superhet receiver... but when comes to circuit level, i cant really find much, especially calculations. at least i know what to expect when i troubleshoot....

Quote:

Originally Posted by Nigel Goodwin

You can't really easily measure the signal around the IF transformer, it will be VERY small - it will be 470KHz or so.

i measured some the voltage... its small like what you mentioned, but the frequency is not 470KHz... (or else i wont have headache..) the datasheet of the ZN414 says that the input range is 0.15MHz to 3MHz and i donno whether is the input within the range or not.

thanks

**Nigel Goodwin** · 22nd January 2007, 10:22 AM

Quote:

Originally Posted by chinsoon

of course i have tried.... and read some articles on it. and i know the stages of the superhet receiver... but when comes to circuit level, i cant really find much, especially calculations. at least i know what to expect when i troubleshoot....

i measured some the voltage... its small like what you mentioned, but the frequency is not 470KHz... (or else i wont have headache..) the datasheet of the ZN414 says that the input range is 0.15MHz to 3MHz and i donno whether is the input within the range or not.

How did you measure it?, and what crystals were you using in both transmitter and receiver?.

chinsoon · 22nd January 2007, 10:35 AM

i used the oscilloscope... and only saw a wave something like that...

even before the NE567... so the input and output of the NE567 i obtain is the same... just differ in magnitude...

**Nigel Goodwin** · 22nd January 2007, 11:03 AM

That looks like bursts of RF, which is what you would expect from a crude AM transmitter. The NE567 needs to be tuned to the modulating frequency.

chinsoon · 22nd January 2007, 11:07 AM

Quote:

Originally Posted by Nigel Goodwin

That looks like bursts of RF, which is what you would expect from a crude AM transmitter. The NE567 needs to be tuned to the modulating frequency.

wow... now these i don really understand...

so how am i suppose to tune the NE567???

by the way, thanks alot for helping

**Nigel Goodwin** · 22nd January 2007, 11:41 AM

Quote:

Originally Posted by chinsoon

wow... now these i don really understand...

so how am i suppose to tune the NE567???

What do you think the 22K pot on pin 5 is for?.

chinsoon · 22nd January 2007, 11:50 AM

well, i tried many ways, including tuning the variable resistor... and the result is still the same...

thanks to Audioguru and RON H who taught me how to modify it, i managed to pull up the output voltage of the NE567 from 1mV to 3mV ( i donno how it happened)... but still not enough to trigger the relay...

**Nigel Goodwin** · 22nd January 2007, 12:57 PM

Quote:

Originally Posted by chinsoon

thanks to Audioguru and RadioRon who taught me how to modify it, i managed to pull up the output voltage of the NE567 from 1mV to 3mV ( i donno how it happened)... but still not enough to trigger the relay...

That's not helping at all - the output should be a switched signal, either 0V or the supply voltage - if you've had your 567's connected as you showed originally, then they are probably both blown?.

chinsoon · 23rd January 2007, 01:00 AM

I have everything connected as shown in the figure. I even changed the NE567 to make sure that the problem is not the IC. but the results remains the same.

That is why i hope to find out there is there any other factors that will affect my output... my problem now is that i can see difference of the output of the NE567 before and after i turning on the transmitter, but the difference just isnt enough to trigger the relay.

Any suggestion how to overcome this? or any idea why is this happening?

audioguru · 23rd January 2007, 02:32 AM

Your first schematic has a missing resistor in series with the base of the BC307 transistor that causes the output transistor of the NE567 to blow up and maybe also the base of the BC307 to blow up.
The output of the NE567 is the collector of an NPN transistor that is trying to go to ground but the base of the BC307 is holding it at 0.7V less than the positive supply with a very high current.
The BC307 is also missing a resistor to turn it off.

The BC307 might not be required since the output of the NE567 can drive a 100mA load (that is connected to the positive supply) directly.

The circuit is missing a diode across the coil of the relay to arrest the inductive voltage spike produced when the relay turns off.

The capacitor at the output of the NE567 is not recommended.

bananasiong · 23rd January 2007, 05:42 AM

This device operates at 27 MHz right? What's the purpose of the tank circuit of the transmitter (39 pF and L2)? And is the modulatind signal coming from the 555 timer which is 584 Hz?

chinsoon · 23rd January 2007, 11:03 AM

Quote:

Originally Posted by bananasiong

This device operates at 27 MHz right? What's the purpose of the tank circuit of the transmitter (39 pF and L2)? And is the modulatind signal coming from the 555 timer which is 584 Hz?

actually that was my question as well... still do not understand why is it there... but it seems like its a path for the RF current to radiate...

yes... 27MHz.. and the frequency of the 555 timer is 580HZ...

chinsoon · 23rd January 2007, 11:05 AM

Quote:

Originally Posted by audioguru

Your first schematic has a missing resistor in series with the base of the BC307 transistor that causes the output transistor of the NE567 to blow up and maybe also the base of the BC307 to blow up.
The output of the NE567 is the collector of an NPN transistor that is trying to go to ground but the base of the BC307 is holding it at 0.7V less than the positive supply with a very high current.
The BC307 is also missing a resistor to turn it off.

The BC307 might not be required since the output of the NE567 can drive a 100mA load (that is connected to the positive supply) directly.

The circuit is missing a diode across the coil of the relay to arrest the inductive voltage spike produced when the relay turns off.

The capacitor at the output of the NE567 is not recommended.

Talking about that, i changed the transistors and also the NE567... but i still cant get the output... and i took away the capacitor like what u said, and follow the diagram that you posted that day....

is there any other possibility that cause this?

audioguru · 23rd January 2007, 12:48 PM

When the NE567 has an input signal of 20mV at its input that it is tuned to, then its output will go to ground. It says in the datasheet.

bananasiong · 23rd January 2007, 11:52 PM

Pin 8 og the NE567 is the collector of a NPN transistor, u need to pull up to Vcc via the coil of the relay and with diode protection. When it receives signal, the transistor sill conduct and switch the relay, when there is no signal, pin 8 should be measured as high as Vcc and the relay is not switched.

What I don't understand is the RF part, what is the purpose of they crystal? Then how about the tank?

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22nd January 2007, 11:03 AM	(permalink)
Nigel Goodwin	That looks like bursts of RF, which is what you would expect from a crude AM transmitter. The NE567 needs to be tuned to the modulating frequency. __________________ PIC programmer software, and PIC Tutorials at: http://www.winpicprog.co.uk

22nd January 2007, 11:50 AM	(permalink)
chinsoon	well, i tried many ways, including tuning the variable resistor... and the result is still the same... thanks to Audioguru and RON H who taught me how to modify it, i managed to pull up the output voltage of the NE567 from 1mV to 3mV ( i donno how it happened)... but still not enough to trigger the relay... Last edited by chinsoon; 23rd January 2007 at 01:11 AM.

23rd January 2007, 01:00 AM	(permalink)
chinsoon	I have everything connected as shown in the figure. I even changed the NE567 to make sure that the problem is not the IC. but the results remains the same. That is why i hope to find out there is there any other factors that will affect my output... my problem now is that i can see difference of the output of the NE567 before and after i turning on the transmitter, but the difference just isnt enough to trigger the relay. Any suggestion how to overcome this? or any idea why is this happening?

23rd January 2007, 02:32 AM	(permalink)
audioguru	Your first schematic has a missing resistor in series with the base of the BC307 transistor that causes the output transistor of the NE567 to blow up and maybe also the base of the BC307 to blow up. The output of the NE567 is the collector of an NPN transistor that is trying to go to ground but the base of the BC307 is holding it at 0.7V less than the positive supply with a very high current. The BC307 is also missing a resistor to turn it off. The BC307 might not be required since the output of the NE567 can drive a 100mA load (that is connected to the positive supply) directly. The circuit is missing a diode across the coil of the relay to arrest the inductive voltage spike produced when the relay turns off. The capacitor at the output of the NE567 is not recommended. __________________ Uncle $crooge

23rd January 2007, 05:42 AM	(permalink)
bananasiong	This device operates at 27 MHz right? What's the purpose of the tank circuit of the transmitter (39 pF and L2)? And is the modulatind signal coming from the 555 timer which is 584 Hz? __________________ Superman returns..

23rd January 2007, 12:48 PM	(permalink)
audioguru	When the NE567 has an input signal of 20mV at its input that it is tuned to, then its output will go to ground. It says in the datasheet. __________________ Uncle $crooge

23rd January 2007, 11:52 PM	(permalink)
bananasiong	Pin 8 og the NE567 is the collector of a NPN transistor, u need to pull up to Vcc via the coil of the relay and with diode protection. When it receives signal, the transistor sill conduct and switch the relay, when there is no signal, pin 8 should be measured as high as Vcc and the relay is not switched. What I don't understand is the RF part, what is the purpose of they crystal? Then how about the tank? __________________ Superman returns..