problem wth remote control circuit design

[richmon74]

HI All
i'm trying a student project on remote control circuit. (i don't know much about rf designs). the transmitter circuit i've attached here has some errors which i want someone to correct for me.

I guess the major error is in the antenna matching sub-section of the circuit.

 

[richmon74]

plz I still need this correction very well

 

[Borber]

What kind of transformer is T1 and what is your problem? Schematics looks OK at first look. Has oscillator enough output signal to drive Q2? You can check operation with suitable oscilloskop.

 

[richmon74]

What kind of transformer is T1 and what is your problem? Schematics looks OK at first look. Has oscillator enough output signal to drive Q2? You can check operation with suitable oscilloskop.

the major problem is that there is no out put at the antenna point. from my observation the junctions of C7 & CV2 and C8 & CV3 are grounded and i don't see how there could be an output in such a situation
the circuit was brought to me for correction and construction and i'm not an rf designer so plz help

 

[Borber]

Yes you are right. There is a shortcut in output circuit. I was negliglent at first look. Instead of shorts you can plase suitable capacitor. If you give me more details on bandwidth of the filter I can try to calculate it. For the first you can place two 56pF capacitors. But it is too much experimental approach.

 

[richmon74]

the capacitor values r already there but i think it just needs some alterations on the drawings - there might be some missing links

 

[Borber]

What is value of emitter resistor of Q3. It looks like 2.2k. It should be about 220ohm or even smaller, I think, with bypass capacitor about 1nF. What is supply voltage? Picture is barely readable. Output filter needs tuning to acheive max output power.

 

[richmon74]

i've attached the protel version of the cct (protel99se) it is more readable.
I guess the emitter resistor of Q3 is 100 and VCC is +9V. I don't know which bypass capasitor u r talking about.

I'm more particularly interested in the output filter circuit 'cos that's where i'm most stucked

the corrected cct is attached in the post below

 

[Borber]

I checked your circuit. If the crystal frequency is 1MHz then the output filter is wrong. Please check the crystal frequency and let me know the right one so I can give you filter details. Next thing I don't understand what is 555 chip doing. Is it some kind of oscillator? Check it's output waveform. It seems that C1 must be connected only between pin 3 of 555 and primary of T1 (not to pin 2 and pin 6).
I think there is missing decoupling capacitor between L2 and secondary of T1 to the ground.

 

[richmon74]

It seems that C1 must be connected only between pin 3 of 555 and primary of T1 (not to pin 2 and pin 6).

That's very correct.

I'll take time to correct the circuit to what i have wth me here and post it in a moment

 

[richmon74]

The 555 timer is a tone generator (the whole project is a monotone remote control light switch. i have the receiver section which i'm still editting and i'll put up that soon). I don't know about the decopling capacitor b/w d points u mentioned. maybe it should have been there.

Here is the corrected circuit.`

 

[Borber]

Corrections on filter and bypass capacitor can be as follows: