Need help with a TV transmitter project.

[Dazza]

I really want to make a TV transmitter, I have several uses for it mostly I want it for my arcade machine project.

I have found this project some time ago from POPTRONIX, but there are a few things I am unsure of, firstly whether it will work for me in Australia and secondly (T1) 4.5-MHz 1F-can-style RF transformer , I have a heap of these RF transformers that I have salvaged, but I don't know how to tell if any of them are suitable, would it be possible to make my own? anyone have any idea.  I am a little unsure on what I'm looking for, when searching for an alternative component.


Thanks for any help .

TVTransmitb_3.pdf

 

[audioguru2]

G'day Mate,
Its picture would be upside down, wouldn't it? You would need to drink many Guinness to turn it around!  ;D ;D
The Poptronix project is meant for North America, I don't have a clue about Australia's channel frequencies or whether your TV stations' sound carrier is 4.5MHz from the picture carrier.
Actually, you don't need to know the sound to picture spacing. Just use the sound transformer from a junked TV. Do you know the different look of a sound IF transformer from a picture IF transformer?

 

[Dazza]

Hi audioguru, Thanks for your reply.

So that means every time I use my TV transmitter, I will have to have a Guinness, O well if that's what it takes ;D.

I have a lot of bits and pieces from old video recorders, maybe there's some think in their.

No I don't really know what I'm looking for, but I certainly can get a hold of plenty of old TV's.  Would their be anything else that would need to be modified, that sounds too easy.

Actually I have a little old colour TV that I can take the back off and take a snapshot ;D, or maybe I could even scrap that TV the picture quality isn't very good anyway ;D.

View attachment 36717

View attachment 36718

 

[audioguru2]

Hi Dazza,
Your TVs have a sound IF of 5.5MHz. The transformers look to be the same except for their numbers. You might need a service manual to find the right one. Nothing else needs to be changed but what about channel frequencies? Does the article say anything about RF frequency?

 

[Dazza]

Hi audioguru,

I'll post the entire page, it's from the data section of the Dick Smith catalogue.

It says to use between channel 2 and Channel 6 when attempting to align the transmitter,  I'll do a search to find out what those frequencies are for North America after this post.

Well that's really good news , if that's the only real hassle I will have with this project is T1.  I guess if it comes down to it, I could use trial and error .  Is there any simple way of measuring these transformers?, maybe an AC voltage at the primary, and then measure the voltage at the secondary, this may give a bit of an idea of the ratio between the two windings ???, I don't really know I'm just guessing here ;D.

View attachment 36723

 

[Dazza]

North America TV channels frequencies channel 2 to 6

CH              limits MHz

2                    54-60
3                    60-66
4                    66-72
5                    76-82
6                    82-88

I got this from a calculator I found on the net, hopefully it is accurate.

It looks as though there is only about one channel difference to Australia's channels, so I could align the transmitter to channels between 1 and 5,all of which are free except for Channel 3.

 

[audioguru2]

Hi Dazza,
It looks like Australia's TV channels 3, 4 and 5 are in the FM broadcast band. That's dumb!  ???
Don't the picture carriers make a big noise from an analog-tuned FM radio that tune through them? BUZZZZ!

The Poptronix project should give details about the sound IF transformer, its mfr and part no. or the mfr name and model of the TV set it comes from.
I've never measured one, but maybe all TV sound IF transformers simply have a primary to secondary ratio of one. Then any of them would work fine in your project.  ;D

 

[Alun]

Not if their inductance and parasitic capacitance are critical.

You can also buy ready made low power TV transmitters - you know the ones used in your VCR to connect it to the TV's RF input.

You could just connect an amplifier on the end to boost the signal and if you know the frequency you could go for a class C ampllifier to boost the power even more and increase the eficency too. I'v also managed to transmit the picture from my old master system games console accross my bedroom (about 3 meters) by inserting a 150mm piece of wire in the back of the RF jack.

 

[Dazza]

Hi audioguru, Alun,

Yes that does sound dumb audioguru, but I haven't noticed any interference ???, but what can you expect from people that walk upside down ;D.  Yes the project does give some information about the transformer, including its part number and manufacturer, but I can't find any info about it anywhere on the net ???. I attached the entire project and details PDF, with my first post .


Alun, Thanks for the suggestion, alternative method . When I was very young I had one of those very basic tennis computer games that you played on your TV, I didn't even have to connect it to the TV, it would work from some distance away 8).


Ok, I think I'll just put this thing together, and then report back with an almost working unit ;D.


Thanks for your help, I really appreciate it .

 

[Dazza]

Hi Sasi,

Can you offer me any more info for this component"IFT ?", did you make this project?

Thanks for your reply .

 

[Dazza]

Hi,

Can anyone tell me if those are inductors in the pic posted above, the "blue things" I'm pretty certain that they are ;D.

They have coloured dots on them, can anyone tell me how to workout their value?

 

[audioguru2]

Hi Dazza,
The blue things are probably inductors and should have an "L" number beside them. Their two dots probably indicate their value in uH. The problem is which way is up (or down) so that it might be brown and green which would be 15, or 51.

 

[Dazza]

Hi, audioguru, Sasi,

Yes there is an "L" printed on the PCB, and if I would have taken a closer look, I would of scene that there was a very small inductor symbol :.  There are three dots one large 1 on the side and 2 on top, for example large dot Brown, two small dots on top black then Brown.

Sasi, how well did your TV transmitter perform?  Good quality picture, how good was its range when using a telescopic whip Arial .

I'm going away for a couple of days over Easter, so I should have this project completed by the end of next week.


Have a good Easter everyone, and drive safely if you are going away for the Easter break .

 

[Dazza]

Hi ,

I'm having a problem deciding which capacitor to use for C7 & C9, it says that it is a 2.2 pF in the parts list, but in the schematics it is a 22pF ???

 

[audioguru2]

Hi Dazza,
2.2pF is just about nothing. I use about 22pF in my FM transmitter that operates at the same frequency. Here you have C7 and C9 in series across the coil making 11pF which is about right. 1.1pF across the coil would be half of nothing?  ;D

 

[Dazza]

Thanks audioguru ,

Actually I did go ahead and solder in two 22pF, not because I thought it was the right capacitor, it was because the coin I flipped came up heads ;D.


There is one final thing I am unsure of :-[,  L1  0.15uH miniature inductor?  I don't have a listing for it, any idea on how to wind it myself :-\ .

 

[audioguru2]

Hi Dazza,
For my FM transmitter I made simple coils and used 5pF to 35pF variable trimcaps to tune from about 85Mhz to about 110MHz. You might need more range which is had with a variable inductor like in the project. My trimcaps are very difficult to tune to any certain frequency but an inductor will be multi-turn for better resolution.  ;D

 

[Dazza]

So far so good, project completed and I can see a very bad quality picture on my little portable TV, with no sound and no colour, Channel 5 seems to work best.

Q4, is getting hot I can hold my fingers on it for about two seconds, should it be getting this hot ???  Maybe this is a sign that some think isn't right.

 

[Dazza]

Hi,

I thought I might post an update, on my progress with this project.

Well I'm very glad I've taken on this project, it's been a very good learning experience 8).  Even though I still can't get the bl__dy thing to work properly > ;D.

The picture quality it transmits is now pretty good, and I'm confident I can improve its picture quality and range 8), but the big problem I'm having is getting the sound to come through. I'm determined to do my best to get this thing working without asking for any more help, so I'm going to keep at it until I get it to work , or until I run out of patience and accidentally stand on it a few times or have to ask for help ;D ;D.