Will this work?

[daviddoria]

so they are the exact same circuit minus the LED??

wouldn't one have to make the oscillation and the other one "undo" it by doing everything in reverse?

just seems odd that they are exactly the same...

 

[daviddoria]

**broken link removed**

that is a great page for anyone (like me) who is looking into this sort of thing.

Turns out what we're making is an Armstrong series fed oscillator, correct?

ok, so one more time through this...

transmitter:
current is applied to the tank circuit (to determine the freqency). From the tank circuit we apply the current to the collector of the transistor. The secondary coil collects the feedback and runs to the base of the transistor. This action turns the transistor on, allowing the whole process to start again.

is that correct?

If so, I will try to explain the receiver... in which i probably won't have as much success hehe

 

[john1]

Well i also put the 330 ohm in the supply line, but only so as
the emitter can go to ground, that is just traditional.
That circuit should work ok.
If it wont oscillate, reverse one of the coils, not both.

so they are the exact same circuit minus the LED??

Not really, one has to oscillate, the other has to respond.
The transmitter oscillates, the receiver responds.
Lets get the transmitter (oscillator) running first, ok

The receiver doesn't have to 'undo' things, picking up a signal
is not like de-coding a message.

 

[daviddoria]

haha the only reason i'm trying to get both working is how am i supposed to tell if the transmitter is working with out a receiver?? haha

i will build this in about 2/3 hours (and i'll try it in a room with a tv like you said), once that is done, i'll let you know if i can tell if its working, otherwise we need to work on the receiver so we can tell if its working hehehe

i'll get back to you tonight.

 

[john1]

You will know because the current draw will be low if it is
oscillating, and higher if it is not oscillating also if its
oscillating you will see the effect on the TV picture.

I had a look through that page, but not for long because that
logo bottom right was so annoying. Yes it is a good explanation
and i think you're right about the circuit being a series
Armstrong tickler type. Though ive never spent much time giving
them names. That page also mentions feed-back, and shows a
drawing of a spark where feed-back occurs. It also shows a
separate winding for the output, but i think you will be ok
with just the radiation from the oscillator.

transmitter:
current is applied to the tank circuit (to determine the frequency).
From the tank circuit we apply the current to the collector of the
transistor. The secondary coil collects the feedback and runs to
the base of the transistor. This action turns the transistor on,
allowing the whole process to start again.

Well sort of, but not quite.
You are right about the the 'pick-up' coil controlling the transistor
current, so you have clearly realised its relevance in this circuit,
you also realise that the action is cyclic and repetitive.

The 'pick-up' (tickler) coil only picks up changes in the collector
coil, and in this case passes those signals to the base, to increase
them.

Thats about as brief as it gets.

If the collector current is falling, the signal says: reduce more.
If the collector current is rising, the signal says: increase more.

At first sight it might seem that the transistor would simply open
or close, and that would be that.

But as i said the tickler coil only picks up changes.
So when the transistor current stops moving, at top or bottom, the
tickler coil stops pushing and the collector current changes.

So the current rises and falls continuously.

The frequency is determined by the L & C pair, called a tank.

Don't worry about the receiver, i think you will find that easy.

John

 

[daviddoria]

hmmm

well i built it...

http://www.bandtank.com/david/t1.JPG
http://www.bandtank.com/david/t2.JPG
http://www.bandtank.com/david/t3.JPG

but it doesn't affect my tv...
does that 100% mean its not working? shall we work on recevier theory so i can try them out?

are the coils in line enough?

what is a good next step?

 

[john1]

looking at pics

 

[john1]

Better pics please.
Are the tracks the short way?
Show underside too please.
Try to get more light on the board please.

Have you tried reversing one coil,
that doesnt mean unsolder it,
turn it through 180,
re-insert,
resolder.

Thats no good because then its still the same way round.

The turns have to go the other way,
or the connections can be swapped with the coil still.

 

[john1]

Could you tell me what equipment you have, roughly ?
voltmeter ?
current meter ?
scope ?
etc ... etc ?

Making a reciever wont help.
Yes it should affect the picture.
The construction is a bit spread out,
but it should work.
the jumpers are too big but it should still work.

What is the transistor ?

 

[daviddoria]

2N3904

i have a multimeter w/ voltmeter, ammeter etc.

i get about 8v across the 330 resistor, then almost 0 across the 1.5k... is that wrong?
what would cause that?

also, i don't know if these even help, but here are more pics (this time with the coil hooked up backwards)

http://www.bandtank.com/david/t4.jpg
http://www.bandtank.com/david/t5.jpg
http://www.bandtank.com/david/t6.jpg
http://www.bandtank.com/david/t7.jpg

thanks for all the help

 

[john1]

Yes, thanks.
those pictures are much better.
the coil actually looks the same way round to me.

Its the turns that have to be reversed,
moving the coil through 180 will not do,
cos then its back the same.

Will study these pics some more,
still uncertain that the circuit is right,
have to go to bed now.

I also will try to do one,
and try to show pics.
i have no camera,
will try to borrow.

 

[daviddoria]

what i did was keep the coil where it was but switch sides of the things it was connected to .... if the left side was + and the right side (-) i put the left side (-) and the right side +.

wow if you built one and took pics and stuff that would be amazing!

before you use your time to do that... we might troubleshoot this a little more. still dont see how there can be 0v across a resistor..