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Another 4watt Transmitter Question


marvellous
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Im a newB & im Busy Building the http://www.electronics-lab.com/projects/rf/021/index.html and
have a couple of questions? ???

How do I make the Inductors do I use
Enarmelled (insulated)Wire or Do I Just use Bare Wire?
Should My windings be spaced apart or should ther be close together?

Is it possible to substitute 2n2222a for T1

Thanks in advance! :) ;) 8)

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* The inductors is air from wire of coaxial 75W or other 1mm roughly


i believe this should read 75 "ohms' not watts..
so u should just take the center conductor out of a coax cable, and wrap it around a 7mm diameter rod and u are good to go.
i am not sure if u can substitute a 2n2222 for the 2n2219 transistor.
i am sure somone else will know that.
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Im a newB & im Busy Building the http://www.electronics-lab.com/projects/rf/021/index.html and
have a couple of questions? ???

How do I make the Inductors do I use
Enarmelled (insulated)Wire or Do I Just use Bare Wire?
Should My windings be spaced apart or should ther be close together?

Is it possible to substitute 2n2222a for T1

Thanks in advance! :) ;) 8)


Marvel,
I do not know how the author made the original coils, but it is common practice to use the insulated wire and wrap close unless told otherwise.
In regards to the T1 substitution, here is the quick comparison on one page. Looks like mW is lacking on the 2222. You will have to do a little math to make sure it is ok.

MP

post-555-14279141715851_thumb.jpg

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Hi Ante,
The text of that project was corrected in Feb./04, so it should be OK now:
The power output probably depends more on "the tendency of catering" than anything else. I think that means that it will do whatever it wants to do.
The instructions say that the inductors must be made of "air".
It even says that your voice will be transmitted only "as long as you become cleaner" while you are in the shower. So maybe it works better when you are wet and more conductive.
Don't forget to put Q2 in your refrigerator! ;D

Since RF circuits are tuned, then they work in weird and wonderful ways:
Notice that Q2 has no DC bias. It works in Class-C which is very efficient, where it is off most of the time, then it is driven very hard for only part of its output sine-wave. Therefore Q2 dissipates no more than about 1.5W. It has a clip-on heatsink, and might still be cold from being in your refrigerator.
A high current is built-up in L3 and the tuned action of L3 and C4 causes a fairly high full sine-wave voltage across C4. The voltage swing is much higher than the supply voltage.
The tuned action of L4 and C8 causes an even higher voltage across C8, which together with the low output impedance creates the 4W of output.
Since only about 100mW is legal, then the "RF" cops will soon be at your door. 8)

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Hi Marv,
I am sorry that it doesn't work for you. Please don't give-up so soon. We are finished joking about the project's translation and can help you more.
High frequency RF circuits like this one, depend on many wiring tricks. The wiring between components must be very short (on a PCB, not on a breadboard), and the spacing between turns on the inductors is critical.
Maybe the circuit does work, but is transmitting a quiet carrier, on or near the FM band. What did you use for an input audio signal?

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Hi Marv,
Your Walkman is OK and so is the wire for your coils, but L2 should be many turns of fine enamelled wire. Instead, wrap your 0.7mm wire around a 1M, 2W resistor, tightly and one end to the other.

How many volts is your regulated (stabilized) power supply for this project? Can it supply 400mA?
As MP said earlier, "mW" is lacking on the spec's for the 2N2222. Which means that it is too small to get rid of its heat and will burn-out! I figure that a 16V power supply will put about 8.7V across Q1 and about 155mA through it. That is 1350mW. Even the recommended 2N2219 for Q1 will burn-out without a heatsink!
Speaking of heating, with a 16V supply, R3 will have 7.3V across it and 155mA through it. That's 1130mW, and the 1/4W resistor that is recommended will also burn-out! Use a 47 ohm resistor that is rated at 2W.
If you use a 12V power supply, Q1 will dissipate 756mW. Still too much heat for a 2N2222, but near the limit of a 2N2219 without a heatsink.
Didn't you use a heatsinked 2N2219 for Q2? When the circuit works properly, it will get very hot.
You can still use a 2N2222 for Q1 if you use no more than a 15V power supply and change R3 to 120 ohms, 1W. Then the project won't give 4W of output, but probably only 1.5W.

A good test to see if the transistors are working is to feel their heat. Q1 and R3 should always be hot, and Q2 will heat-up only if Q1 is oscillating.

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Thanks for the reply
I got my circuit working (C4 was broken)
I Can transmitt to radio
but none of the transistors get hot ???
(ran it without heatsinks on both transistors)
also the range is short about 5meters

I used a 4.5Ah 12v battery for powersupply!
I used a 2n2222a for t1
I used a 30Cm 1.5mm wire for antenna (soldered onto the Pcb)

Will try your suggestions today for it and keep you posted on it!

can I use 0.2mm insulated wound around a 1Meg resistor
Thanks in advance!

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Hi Marv,
That's great that you got it working. Yeah, broken capacitors don't work very well.
It will transmit much further if you use about 15 turns or more for L2. Use a 1M resistor that is big enough for that amount of your 0.2mm wire.
With your 12V battery it won't have 4W of output, probably only 1W. Therefore leave R3 as a 47 ohm 1/4W resistor, it should be warm but not hot. T1 and T2 should be very warm. Can you measure how much current that the project draws from your battery?
It will be very difficult for you to tune C7 and C8 for maximum output without a signal strength meter, a helper and walkie-talkies. It should transmit a couple of kilometers. Can your helper scream that far?

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My project mesures 134ma from the battery

I have just canged my L2 to 1M 2w and 15turns of 0.2mm(insulated)
also changed R3 to 47e 2W
changed Q1(T1) to 2n2219

changed Battery to powersupply(lm317 based 2A transformer)set @ 15V

now Q2(or T2) is getting verry hot
Q1(or T1) is just warm
Signal is stronger and better quality!

It will be very difficult for you to tune C7 and C8 for maximum output without a signal strength meter, a helper and walkie-talkies. It should transmit a couple of kilometers. Can your helper scream that far?


would Field Strength Meter
http://braincambre500.freeservers.com/field%20strength%20meter.htm
work for tuning?
(We can Use Cellphone for communication)

would the antenna
http://braincambre500.freeservers.com/open%20end%20half%20wave%20dipole%20antenna.htm
work for this project?



Thanks the help I'm getting is appreciated! :) ;) :D8) ;D
(only to think I nearly gave up on this project!)
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Hi Marv,
Perfect, it works well now.
See, don't give-up, we are glad to help.

Did you use a clip-on heatsink and thermal grease for T2 as in the picture?
That Field Strength Meter will be good for tuning but it is designed for 90MHz and may need changes to its tuning parts. You will also need a quiet spot on the FM dial.
Their FM transmitters are very similar to this one, but also for 90MHz.
This transmitter may not work with their 75 ohm antenna.

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