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Help with FM Transmitter

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Here in Canada and in the US a few km's away, there are "educational" and "artsy-fartsy" channels without ads. Occasionally their management come on and beg for donations, sometimes all day and night.
Frequently the same show is on a Canadian channel and an American one at the same time. The Canadian government forces the cable-TV operators to switch the American channel to the Canadian one so viewers are also forced to see Canadian ads over and over and ...... Sometimes they forget and switch too late, or if it is a ball-game on overtime they switch too early. Very frustrating.
My dog and I actually watch and like some ads. Does anyone else watch ads? I want to know about new products and services. I don't like the ads that are the same for years, but my dog does! My trusty remote gets rid of them and the station showing them.

In the UK, how can you watch 4 or 5 shows at the same time like we do? We change channels at each ad, multiplexing the shows. :lol:
 
BTW, Sorry Zach. Of course you are in California. I was confusing you with a similar guy in Australia on another forum. Both of you talk about the same things at the same time. Yes, it is a small world.

My new glasses are so much better than my old ones that now I can see details on women that are very interesting, he, he. The Optometrist lady that presented them to me turned beet-red when I told her what I could see! Yeah, I joke around a lot.

Don't you multiplex TV shows? You don't miss much in the beginning when they are boring, and near the end when they get exciting, the ads come so close together that your brain's sample-and-hold doesn't miss anything.
 
you're probably confusing me with pike :lol:

lol, i knew you must be kidding about those glasses :lol:

of course i multiplex (but i call it channel surfing) during comercials. i dont have enough money to buy half the stuff that comes on, so why should i watch :lol: . Even though i don't watch much TV. . . ive come to realize it is a rather large waste of time.

A couple of times the power has gone out in my neighborhood. It was sort of funny thinking about how many people were forced to do something other than watch tv. People actually came out of their homes and started talking. The dependency that most people have on that box is mind boggling . . . enough philosophy :lol:
 
Hi Zach,
I remember chatting with Pike here, but I confused you with Johnny on another electronics site.

Yeah, my new glasses are crystal clear, to show all their curves and other nice stuff they think is hidden, he, he.

Most TV shows are based on the lowest expected IQ of their viewers. From what I've seen on US shows, many Americans must be reeeealy stupid.
There is an American electrician on another site who wants to add electronics to his electrical projects. But he knows nothing about Amps or Watts! He would wire-up an electric heater and his wiring and connections would get hotter than the heater!
 
do they have reality shows in canada? they are the stupidest things :x .

I doubt you listen to greenday, but one of their lyrics from the song 'american idiot' sums it up: "Don't wanna be an american idiot, one nation controlled by the media" :lol: so true

There are some shows that are just totally mindless. One of which: The Ashlee simpson show. TV cameras follow this new pop star around all day and watch what she does, from eating to putting on makeup to getting her hair done, GAAAHHHWWWWW!!!

He would wire-up an electric heater and his wiring and connections would get hotter than the heater!

ya know whats fun, is to get some steel wire since it doesnt conduct as good as copper, and wire it straight to the mains, making it long enough so there is enough resistance to not pop the circuit breaker right off. If you know how to write in cursive, you can make a very hot and expensive sign that lights up red :lol:
 
Hi Zach,
Do you watch the Jessica Simpson TV show, or The Simpsons?
I like looking at Jessica, she's cute and shapely. I am so busy looking at her that I don't notice what she's doing, he, he.
 
The simpsons is only my favorite show! the only thing worth watching, that , family guy and futurama, good stuff. i like twighlight zone too :lol:
 
Hi Guys,
I built the original preamp circut for the FM transmitter and it sort-of worked! At 9V I expected it to be saturated but it was almost saturated. My lab-workshop is in my basement where it is cool now in wintertime. When I heated the transistor by touching it with my finger, it saturated alright. I measured its hFE at 196, fairly low since 300 is typical on the datasheet. Of course, the preamp transistor would saturate even more and at a lower temp and above if its hFE was typical.
I turned down the supply voltage to simulate a fading battery and its output level dropped until the transistor was cutoff at about 7V. It was very distorted at any supply voltage.

Then I tested my improved preamp. It has very low distortion and good output level with a supply from 6.5V to 9.5V. It had poor bass response so I fixed it here:
 

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Wow guys, you got such a great thing going :)

I actually built an FM transmitter from

**broken link removed**

The strangest thing is: to make it work, I have to connect an oscope probe (without nothing connected to the other end) between the Ground and the Antenna of the circuit (the probe to the antenna and the Common to Ground).

audioguru, what kind of antenna do you use in your circuit, because I think that that's the problem in my case.
I'll try to connect a 12" wire, although my wire was about 8". One of the differences between your circuit and the one I built is a 33 pf cap on the output (between the filter tank and antenna, I'm talking about the buffered _deluxe_ version).


If the circuit works, we should try to tweak it for more output power (range), just for fun ;)


TI|CP
 
Hi TI,
You need an antenna nearly 1m long for the best range.
The 1st tuned circuit has a trimmer cap in parallel with its C2, the 2nd tuned circuit needs the capacitance of your 'scope probe to be the same. Try increasing the value of C6 like this:
 

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Thanks, I'll try that.

Is it right to say that the two tuned circuits should be the same (if the first has a coil, with 12 pF and 22pF variable in parallel, then the second one should be the same). The two variable caps should be connected (i.e. rotated at the same time), to make sure that any frequency provided by the oscillator gets amplified by the buffer (otherwise, it'll get filtered by LC tank of the second stage)?

I'll tell you how that worked out.

TI|CP
 
Hi TI,
The 2nd tuned circuit might not have to be tuned whenever you change your RF frequency. I suspect that the tuned circuits have a fairly low Q, so are fairly wideband. In your case before, it was way off. The oscillator will usually have a frequency at the peak of the tuning, the other one just needs to be in the same neighbourhood. Even so, my transmitter will have the same tuning cap for each coil.
 
While we're on this subject, ive got a question:

I was just tinkering around with another transmitter that i built, and have found that it is not working very well. It worked fine in the summer. The only thing I can think of is that the temperature is affecting it.

How much of a bearing does temperature have on the range of these bugs?
 
Hi Zach,
I can't remember your circuit, please post it again for temperature analysis. If it is anything like the poor design at the beginning of this thread, sure it will be affected by temperature and battery voltage.
 
Its just one of those regular ol' 3v two stage transmitters. I would post a schematic, but its in .pdf form, and it never works when i try to post it. Wuddya think?
 
In Adobe Reader, you have a "snapshot tool" (a little camera in a dotted square, or in menu Tools -> Basic -> Snapshot Tool). Click on it, select your circuit, it will copy it to clipboard. Use MSPaint (or any other imaging software), paste it in there, save as Gif and post it in here.


Good Luck,
TI|CP
 
hey thanx theimperia! ive been wondering how to do that forver :lol:
 

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Hi Zach,
Both transistors in your transmitter have DC negative feedback so should be fairly temperature stable.
The value is very high for the 22K resistor that feeds power to the microphone with a 3V supply, try 4.7K. My electret microphone measured a huge change in current as it "warmed-up" for a few seconds when power was first turned on.
The RF output power and frequency of your transmitter is very dependent on its supply voltage. Maybe its battery needs replacing. I'm going to put a voltage regulator on my transmitter.
 
This seems to be a very well designed circuit :lol:

as for changing the mic resistor, ill leave it because the audio is crystal clear and is very sensitive (you can hear whispering in a small room).

ive thought about putting a voltage regulator on a transmitter, that would be cool.

thanx for the input audio :lol:
 
Hey Zach,
When you post more than 1000 posts, you're just "God-awful", aren't you?
 
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