Trouble shooting circuit

Thread Starter

nerdegutta

Joined Dec 15, 2009
2,676
Hi,

I've tried to make a tv/video transmitter circuit, short range. So I googled around and found a circuit, and modified it a bit/removed the audio part.

See thread:

http://forum.allaboutcircuits.com/showthread.php?t=33002

So now I have this, see attached files.

Problem is... It doesn't work. So far, I found that it's frequency is about 3.1-4.0 MHz. I just don't get it. Guess you guys see the problem in the schematic right away.

In the three open holes, I've put the pot.
 

Attachments

Thread Starter

nerdegutta

Joined Dec 15, 2009
2,676
I'm quite sure I don't have solder bridges. That's one of the first things I check.

But I cannot be to sure enough, I'll check again....
 

thatoneguy

Joined Feb 19, 2009
6,359
Try pulling the inductor apart a bit more and post how much the frequency changes.

Adjusting it's value/length may get enough change in. If it doesn't change much, then something else is wrong.
 

bertus

Joined Apr 5, 2008
20,226
Hello,

The traces are quite long for the intended frequency.
Are you really using a BC547 as transistor?
That is a universal transistor and not a real RF transistor like the BF199 or equal types.

Bertus
 

Thread Starter

nerdegutta

Joined Dec 15, 2009
2,676
Yes, I'm using the BC547. Maybe I should change to another. What do you suggest, I don't think I have the BF199.

So you think the traces are too long... Hmm... Thought I put the components close together.

Is the schematic OK?
 

Thread Starter

nerdegutta

Joined Dec 15, 2009
2,676
Thank you.

I will try to build the one in post #3, changing the NPN's to something similar I got.

Anyway. The schematic I postet, shouldn't it work. In theory?
 

Thread Starter

nerdegutta

Joined Dec 15, 2009
2,676
Just got mail from my local dealer. (Maybe supplier is a better word... :))

I will buy a couple of:

2N2907A
BF199

I saw the long list of transistors in another tread, so I sent him the list. All he had was these... Anyway, looking forward to some quality time at the lab.... :D

Thanks.
 
Top