4W FM Transmitter

[spleblem]

hey all readers  (yes you)

im building the 4w fm transmitter and need a bit of help

1st l1 it says it is 4turns 7mm diameter
but 4 turns of what

and the t1,t2
is a 2n2219 but i cant find that at my local electronic shop is there a simalar sort i could use in stead

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[audioguru2]

Hi Spleblem,
Most answers to your questions are explained in the other recent post anout this 4W FM transmitter project here: http://www.electronics-lab.com/forum/index.php?topic=338.0

You are going to need a refrigerator for T2 or a clip-on heatsink and a big high-velocity fan. The circuit must have a proper antenna and be tuned to it or T2 will burn-up.  ;D

 

[spleblem]

ok thanx but what is a proper antena and how do u tune it in right

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[spleblem]

[shadow=red,left]for the transistors would a 2n2222a work becuase thats the closest i can get[/shadow]

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[Alun]

Yes the 2N2222A would be fine.

 

[audioguru2]

Hi Alun,
How are you going to cool the poor little 2N2222A?  ???
It's rated for a maximum of only 1/2W.  :

 

[Alun]

Connect 2 in parallel, and connect a 4.7ohm emitter resistor in series with each of them, and a heatsink would also be a good idea.

The 2N2222A is also rated for 1.8W at <25OC

 

[audioguru2]

Hi Alun,
Philips and a few others rate it at 1/2W. They dont talk about using a heatsink on such a small transistor. I wonder if a heatsink could be soldered to their metal case, not the plastic one though, duh!
That's a good idea to parallel them.

 

[Alun]

Well here it says 1.8W for Tc of <25oC and 0.5W for Tamb <25oC so am I rightly assuming Tc means case temperature?

I don't know about soldering to the case as it would exceed it's storage temperature.

 

[audioguru2]

The project's author would expect you to fasten a refrigerator to it.  ;D
Otherwise operating it at 1.8W would exceed its storage and operating temps.
A big high-velocity fan would do wonders for it!

 

[spleblem]

thanx then is there any other more easier transistor i cant get the right one any where here in australia

 

[audioguru2]

Down Under?
D'day mate! Are you near Oz? How do you like it to be upside down all the time? With kangaroos and wallabees running around all over the place! I have snow when you are sweating.

Go to www.farnell.com and click on your flag. Farnell has nearly everything except refrigerators. Dick Smith has them.
The clip-on heatsink is very important for Q2.  ;D

 

[spleblem]

thanx but that in america and the postage would be heeps to much
i dont got to much money do u think there might be a dirrernt name for the component which might be use in australia

kangaroos are great all ways jumping around on the town roads

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[audioguru2]

Farnell is in at least 23 countries including Australia. I clicked on your flag and went here:
http://au.farnell.com/jsp/home/homepage.jsp
They don't have any 2N2219 transistors because their supplier doesn't make it anymore.
They have thousands here in Canada.
They don't have a 2N3866 transistor either. Sorry.

Try paralleling two 2N2222 transistors as Alun said. Keep the power down with a lower supply voltage. Australia's power limit without a licence is only 10mW.

 

[spleblem]

ok thanx ill try using 2 2n2222 in parallel
thanx a lot

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[Platonas]

Hi,
For both of the initial questions.
T1 can be 2n2222, 2n2222a, 2n2219, 2n2219a, bsx20 maybe 2n3904 and other simillar transistor, slide variations for the C7 capacitor's value to achive oscillation at the desire frequency.
T2 is better to be 2N4427, 2N3866, 2N3924, 2N3553.

For the coils use 1mm or even 0,8mm wire.

 

[audioguru2]

Hi Platonas,
Q1 will dissipate about 750mW in this circuit. Little transistors like BSX20, 2N2222 and 2N3904 can't dissipate so much power without melting.

 

[radiopirate]

Made a heatsink out of a section of thick (3mm) copper tubing lower section fits over T2  6 vertical cuts made from top  20 mm long,    pieces bent 90 degrees to tubing.
small fan from cpu wired to top of heatsink

Using rundown 9v battery for power while tuning
Difficult,  trimmers small even with plastic tuning tool
presence of hand affects tuning.

oscillator var cap replaced  with one from FM radio
Using probe made from 2 diodes 2 capacitors to measure output

Output power drops dramatically at higher frquencies
soldering rather messy,  component placement could be better,
Is this a possible cause of this problem?





             

 

[audioguru2]

Hi Radiopirate,
The case of the transistor is connected to its collector. The stray capacitance of the heatsink to its surroundings kills high frequencies at the transistor's collector.

Can you peak the output with the trimmer capacitors? If they run off the end of their adjustment then their associated coils need their length changed.  ;D

 

[radiopirate]

This problem seems to be with the oscillator
power measured at point between osc and amp
T1 has no heatsink!
Can anything else cause this problem?

can tune roughly