hi!

still i haven't understood the purpose of the second LC tank...

can you check the modifications i did on the schematic?

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The second LC tank allows the output to swing below ground and above the supply voltage with low harmonics. Your second transistor with its poor biasing might be saturated or might be cutoff (a clipped sine-wave) which produces severe interference harmonics.

I don't know which adjustable regulator you are using.
The output transistor needs to have its own supply bypass capacitor, or remove the choke.
Your audio does not have pre-emphasis so it will sound muffled without treble audio frequencies when played on an FM radio.

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Uncle $crooge

 

can i "play safely" without the second LC tank? if yes show me how...

the regulator is the reg102-A it's an ultra LDO which i had also available.. but at first i didn't wanted to use because for the purpose of my experiments i'm trying to utilize old used spare components and that regulator is new.. i guess it's also too much for that circuit..


btw the ferrite bead is that type "Murata BLM31AJ601SN1L" it's what's left from an old project of mine...are they suitable for my design?!


right now i don't care so much about the audio quality...mostly i'm trying to make it as stable as possible and learn something from it.

 

Simply remove the horrible 83k biasing resistor and replace it with a 47k negative feedback resistor from the transistor's collector to its base. Then a low gain or a high gain transistor will not clip and produce interference harmonics. But the negative feedback will reduce the output level.

Datasheetarchive.com does not know your regulator or its part number is incomplete.

I didn't look for the datasheet of the inductor because it is not needed.

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Uncle $crooge

 

great! thanks!!

ok no prob audioguru.. as i told you this project is done so i can learn a bit of RF and gain some more experience doing my own PCB designs with SMD components so i don't mind about the reduced output level nor the not so great sound quality!!! but i mind it's stability which makes it worthless to play with it.

but i want to know how i can calculate the power output, if you check the last post on the first page you'll see that i tried to calcuate it but JimB stopped me by telling me that it's a "big assumption"... that's why i wanted to know the power output of your transmitter.

 

i did this pcb... based on the schematic on my last post..there are some changes mostly around the regulator that i haven't included to the schematic
any comments most appreciated!

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audioguru i think my regulator oscillates... firstly i tried an adjustable and it was also oscillating now i'm using reg101-33. At the input there is one 100nF and 100uF at the output. i wasn't able to locate the frequency on the radio so i'm getting harmonics and i hear a high pitch sound...the voltage on the regulated rail is 1,65V it's lower than it should, at first i thought it is voltage drop because of the load but you can't hear your voice on the radio... the electret mic doesn't do anything unless you hit it or blow hard on it

i have changed your resistor values on the oscillator from 47k to 22k and 10k to 4,7k so it can be able to work on 3.3V.


help?

 

hi,
Ref your PM.

We need a datasheet for the voltage regulator before we can advise.

At a first look, its the Vreg area thats a problem.

__________________
Eric " Good enough is Perfect "
I will NOT answer PM's requesting technical help, please use the Forum
PIC tutorials: Nigel's www.winpicprog.co.uk/ Bill's: www.blueroomelectronics.com/

 

here it is...

http://focus.ti.com/general/docs/lit...a&fileType=pdf

 

I have never seen the texas Instruments low dropout regulator.
they show it with no output capacitor, 1uF and 10uF. They do not show what happens with a 100uF output capacitor. Try a 1uF output capacitor.

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Uncle $crooge

 

i did it...and the sound pitch gets higher than it is with the 100uF
i have also connected the NR pin with a 10nF capacitor to the ground.

Audioguru i'm thinking to cut the rail at some point before the regulator and add there the murata ferrite bead that i told you on an older post... do you agree?

generaly what do you think about my design? is it bad idea that i have the power input pins near the RF out pin?

 

guys any help?

 

you don't need an inductor in series with the regulator. Instead you need a low dropout regulator that does not oscillate.

In my FM transmitter I kept everything away from the RF parts.

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Uncle $crooge

 

can't we just do something to fix it? i think it's specs are very good to be considered a crappy part...... i was trying to do something by myself my own PCB design with SMDs and now i'm getting a bit dissapointed with all these silly difficulties...



btw yesterday i was reading an old topic of yours...i'm glad we have you back!