A1 yes close together
A2 c6 and c13 to 5.2 to 30pf
Lm2931A5.0 to 78Lo5
c12 to 33pf
(and c4 is 100nf
A3 (problem? :roll the current is too unstable to get even an average reading
(but that might be my rubbish multimeter :roll: )

 

Hi Monkeytree,
Your substituted parts should be fine except the 78L05 might operate poorly when the battery voltage drops below 8V. My low-dropout regulator works fine when the battery voltage drops to 5.6V.
Did you build the FM transmitter on a pcb?

__________________
Uncle $crooge

 

i am using 6 AA batteries in a holder giving out 9.75V so that 'should'
be okay?
and yes i did do it on a pcb.

 

As I am very interested in this particular topic - so I tried to simulate the upper (mod 3?) schematic, and I got something like this [see below]... any idea what may be wrong ? Either in ciruct or simulation/simulator (SIMetrix) ?

And what's the purpose of Q3 anyway ?

Frequency : 98.3 with C4 @ 8.2 pF
Interesting obserwation : regardles of V1 the oscillations are attenuated. Either when it gives single pulse (between 10 and 20 us) or works continiously. What's going on ?

Attached Images

audioguru_fmm_sim_1_.jpg (19.9 KB, 548 views)

 

Q3 is an RF amplifier, it produces much greater range, and makes it more stable by giving a degree of isolation between the oscillator and aerial.

I consider simulators a waste of time, particularly for this type of circuit, where it's not likely to even get close.

__________________
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http://www.winpicprog.co.uk

 

Hi Monkeytree,
You can troubleshoot the circuit by measuring DC voltages at its important places like the collectors and emitters. Since it operates at VHF, measure the voltages with a 100k resistor connected in series with the red lead of a working high input resistance (10M) multimeter.

__________________
Uncle $crooge

 

But in order to work (amplify) the transistor must be properly biased, that is it must work in "normal, active" area (if I translate this correctly), and even without simulation, I don't expect Q3 to work like that... unless of course there's something I can't see or understand. What could it be ?

Well, I already know that (and start to agree with You...)
For my bad luck, that's exactly my task - to provide working simulation, but the circuit must also "look like" real.
Not to build an actuall device, or just simulate the spectrum.
Just to make such strange so-called-simulation

 

Q3 is biased by R8 - I don't see your problem?.

An RF amplifer (at least for FM) doesn't need to be linear, and there's no advantage to it being so - in fact there are advantages in it NOT being so!.

This sort of RF amplifier would commonly be used in class C, with no bias at all - I don't know if Audioguru has tried that? (connect R8 to 0V rather than 9V) - but I suspect the 47K is intended to bias the transistor towards class B, as there probably isn't enough drive signal to work in class C?.

__________________
PIC programmer software, and PIC Tutorials at:
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Hi Nigel,
I tried Q3 without bias as a class-C amplifier but it didn't have enough input level to produce much output power. With it biased on, the input signal causes it to amplify very well, and I think it operates in class-B as you say with a very high output voltage swing.
Someone 'scoped one to show its output voltage (35Vp-p) far exceeding the supply voltage due to the high Q of its tuned circuit ringing.

I don't think the sim program knows anything about Q or RF. It just thinks the transistor's collector is shorted to the supply, and displaying the battery's voltage being modulated. :lol:

__________________
Uncle $crooge

 

Indeed. Oscillation around average level of 9 Volts (perpetum mobile ? DC is 9 V, and I get larger voltages in the circuit... ).
... life :evil: Anyway : does anyone have an idea how to prove sim's inability to accurately perform the calculations WITHOUT assebling a circuit ? The more maths, then better.

By the way : please forgive me my strange questions. On holiday I'll take up real electronics.

 

I'll take it for granted, but still i don't see it

__________________
Best Regards, Peter

Soy un hombre muy honrado... :|

 

Try studying the different bias classes, for a simple overview:

Class A (the only one you appear to be considering).

Class B (biased to 'not quite on', how I think Q3 probably is?).

Class C (not biased at all, switched by the signal).

Class D (used purely as a switch, either hard ON or hard OFF).

Class A is usually used in preamps.

Class B is usually used in push/pull ampifiers, but usually modified to class A/B to improve distortion figues.

Class C is usually used in RF power amplifiers, only conducts on positive half cycles, relying on the tuned circuit to 'ring'.

Class D is usually used in 'digital' amplifiers, as it's always either hard ON or hard OFF, it's dissipation is accordingly low.

__________________
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:shock: (sound of hand hitting the forehead ).
Well...newbie is newbie
Thank You very much Nigel, for your patience and advice.

Question for everybody : is there by any chance ready PCB for this circuit ? (mod 3, without IC ). And what the antenna should look like ?

Best Regards,
Peter

__________________
Best Regards, Peter

Soy un hombre muy honrado... :|

 

Hi Antey,
I made mine with Veroboard (with strips of printed copper) and its antenna is just a piece of wire 30 inches long hanging down. I will probably use a telescopic whip antenna from an old RC car transmitter. My Veroboard layout for mod-4 looks like this:

Attached Images

fm_transmitter_mod4_pic_817.jpg (60.3 KB, 464 views)

__________________
Uncle $crooge

 

THANK YOU
But... I'm afraid to ask - do You happen to have a schema for board mod.3 ? Or maybe just suggestions about putting all pieces together - especially about making connections and wiring ? I am not expirenced enough, but I know that there can be some issues regarding additional capacities/inductances...

I'd like to thank everybody once again.

__________________
Best Regards, Peter

Soy un hombre muy honrado... :|