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0.1 uf electrolytic and 0.1 pf capacitors

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Yes, and a clip from the both of you would shut the both of you up, as we would no longer be working in opinion although I would gladly include mine anyways, but simply show the spectrum involved in the clips captured and lay things to rest. The two of you can argue back and forth till the end of mankind as far as I'm concerned =)

Run a simulation on both audio portions of each circuit...
 
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Run a simulation on both audio portions of each circuit...
Colin's FM transmitters are missing pre-emphasis so their audio frequency response drops -3dB at 3.2kHz, -6db at 6.4kHz and -18dB at 12.8kHz. 15kHz is way down. This is for the European, Australian and New Zealand's 50ms curve.
In Canada and the US (75us curve) it is much worse: -3dB at 2.1kHz, -6db at 4.3khz and -18dB at 12.8kHz. 15kHz is almost zero.
Also, his input coupling capacitor has a value that is so low that there are no bass frequencies.

My FM transmitter has a frequency response that is -3dB at 21Hz and is flat up to 20kHz where it is -1dB.

Here is a graph showing how much pre-emphasis is needed in an FM transmitter. +17dB at 15kHz for North America!
My FM transmitter has it, Colin's doesn't.
 

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You know Mike that never occured to me.
 
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I have never made a frequency response simulation in LT Spice IV before. I tried it with my FM transmitter and I couldn't get the frequency scale marked correctly.
I added the de-emphasis of an FM radio and the frequency response looked very flat.

I didn't simulate Colin's FM transmitter because it doesn't have any low nor high audio frequencies.
 
It's the expense of getting the extra components, such as the regulator, and even the enamelled wire, that put even the original poster off building it. That's why I supply kits for everything I produce.
Of course you can build cheap low-quality projects but what's the point in that? You can buy ready-built crappy stuff for less than how much it would cost to build it.


Alkaline batteries are very expensive and not needed for 30mA circuits.
That's a false economy, alkaline might be more expensive but you eand up replacing the battery far more frequently.

I have compared the output from a radio and from a bug and could not tell the difference and I have a new $15 hearing aid from China, so I can hear it very clearly now.
A hearing aid won't restore your hearing to the same level as someone with good hearing.

Perhaps you should get your hearing aid tested, for a start it's made in China which is never a good thing.

Rather than going on the defensive, why don't you read about pre-emphasis and decide your yourself?

FM broadcasting - Wikipedia, the free encyclopedia
Explanation of Pre & De Emphasis
Preemphasis
Pre-emphasis (FM) explained
WikiAnswers - What is pre-emphasis and de-emphasis in fm

Why not investigate the possibility of designing a premium version of the kit which includes pre-emphasis for better sound quality?
 
You are complaining about the simple FM bug I have designed and suggested the reader construct as a project to show FM transmission.
I have a number of circuits and some of them had pre-emphasis and all sorts of complex additions to the circuit.
Constructors vote with their pocket and vote for simplicity.
I have sold over 100,000 of the simple design without a single complaint. We sold less than 20 of the complex design.
This is only a hobby market I am catering for.
Professional people don't buy kits anyway.
I have never said the performance is "studio quality." And yet all of you are jumping up and down, wanting something professional for someone who wants a project for school.
In the end, the reader didn't build your complex circuit, so all your effort was wasted.
That's why I was so successful.
I catered for a market of “beginners in electronics” and designed hundreds of novelty projects to teach them assembly, soldering, parts identification and hopefully some of the “building blocks” of electronics.
Most of the projects did nothing or very little or flashed a LED or produced a sound, but that is what the readers wanted.
I went the US to help POPTRONICS but it was already dying and the CEO “Larry Steckler” pulled the plug just a I was launching the web version for him.
He could have had a fantastic magazine as I was just at the stage of suggesting he put miniature PC boards on the cover of the magazine using surface mount PIC chips as the basis to a whole range of projects.
But it was obvious the magazine did not pay. The subscription was $18.00 for 12 issues. He paid subscription companies $6.00 leaving $12.00 for 12 issues.
It cost 50 cents to print and 50c to post.
Where is the profit?
The advertising costs were astronomical and this was declining.
In fact the readership was falling too.

So that’s why you have to cater for the beginner. That’s where the monetary return is.
 
When a student is beginning to study electronics and builds a lousy kit that sounds awful and its frequency wanders all over the place, then the student gives up.

Pre-emphasis in my FM transmitter costs just one resistor and one small capacitor.
 
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for 0.1pF i think you should try altering the value of inductance to get the desired frequency response...and try placing two 1pF in series . i.e => 0.5pf
No.
The "0.1pf" capacitor has nothing to do with the tuned circuit.
As was said earlier in this thread, the "0.1pF" capacitor is a supply bypass capacitor and should be 1000pf.
At 100mHz, 1000pf has an impedance of 1.6 ohms.
At 100MHz, 0.1pf has an impedance of 16k ohms so it won't do anything.
 
The only exotic component in audioguru's circuit is the regulator.
fm_transmitter_mod4_pic_schem_212-gif.7058

Luckily it can be omitted at the expense of stability.

You could replace it with an LM78L05 but the battery won't last as long or a simple zener and transistor regulator, again at the cost of stability.
 
An ordinary LM2931A-5.0 low dropout voltage regulator is not exotic.
Most semiconductor manufacturers make a low-dropout 5V small regulator.

My preamp transistor needs a regulated 5V for it to work properly because its DC gain is 21.3.
 
The smallest cap on the capacitor conversion chart is 1pF =.000001uF,So the 0.1pF does not exist.must be a printing error,it's more likly to be 0.01uF (marked 103)
0.1uF (104) & 0.01uF (103) caps are readily available from Maplins,at about 10p each.
cheers Terry
 
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