Hi,

I'm looking for a small, short range TV transmitter. So far I've found this circuit.

But I need only transfer the video, not the audio. Can I skip the parts on the left side of the red line?

 

Seems reasonable to me. Don't leave C3 off though.

 

Hello,

Yes, you are right.
The circuit round Q1 is the audio modulator.
As Bill said do not forget to mount C3.

Greetings,
Bertus

 

Thank you.

So it would be more like this?

 

Hello,

Yes, C3 is needed for decoupling the powersupply.

Greetings,
Bertus

 

Thanks.

I appreciate your time and effort.

Beside studying company economics, this will be my upcoming weekend project.

 

Hello,

Does it also say someting about the coil in the oscillator?
With the current transistors a VHF channel can be used, most preferable channel 2 to 4.
If you want to go on higher channels other transistors should be used.

Greetings,
Bertus

 

Hi,

it's says that it's transmitting somewhere around 50 - 210MHz in the VHF band.

 

Hi,

I found the same circuit on another site. There it said that L1 should be 4 turns, 6mm core turn with 24 swg.

 

Hello,

The frequency will be strongly dependend on the shape of the coil.
The lenght of the coil also counts in the value.
See this page for more info:
http://info.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html

Greetings,
Bertus

 

Hi,

Thank you for the link. I've read the page once before, and I will read it again.

 

You will go nuts trying to keep the Osc. stable, especialy if breadboard.
My advice is to use an old rf mdulator from a throw away V.C.R.
There not hard to spot, or to wire up, old video games , pong ect. would also use such a device, output is selectable on CH. 2 or 3.

 

Hi.

I thought I would breadboard it, and check the frequency with my frequency counter. A DVM13MC2 bought from www.jameco.com and check.

I have a buch of crystals laying in my drawer, can I somehow hook it up to make the Oscillation more stable?

Thanks for the answer.

 

Hello,

Breadboarding a RF circuit is not so good idea.
The stray capacities will give a lot of trouble.

A while ago I posted a link to the "manhatten style prototyping"
http://forum.allaboutcircuits.com/sh...9&postcount=30

This hold a kind of inbetween the breadboard and the dead bug.
Becouse the wiring can be shorter as in the dead bug style, it is fine for RF.

Greetings,
Bertus

 

Hi, Bertus.

Yes I remember that post. Read the page a few times. I think I will take the time to draw and etch a PCB for this, since the oscillation is so important.

Is it possible to use a crystal to make the oscillation more stable?

 

Hello,

Take a look at this page:
http://petlibrary.tripod.com/rfmod.htm
It contains an old schematic from elektor using a 27 Mhz crystal.

Greetings,
Bertus

 

Thanks.

Now I have a lot of reading to do. (Lucky me, I can print the web page to a PDF file, transfer it to my Kindle, and read it in bed, just before i watch NCIS )

Is there any equivalent transistor for the BFR91?