CD player to radio revisited

[zachtheterrible]

I got to fiddling around with this idea finally.

I sort of got it to work earlier when I tried a 10k for R1 and a 100 ohm for R2. I had to hold the radio very close to the transmitter and I got the sound all over the dial, but it was very fuzzy (i was overloading the front end). If the fuzziness hadn't been there and it was a bit louder, it would have sounded great.

I tried it first that way instead of the schematic, don't ask why :roll:

The schematic version will not make squat.

Is this even plausible?

P.S. I know its not gonna be stereo and i dont care 8)

 

[Nigel Goodwin]

I got to fiddling around with this idea finally.

I sort of got it to work earlier when I tried a 10k for R1 and a 100 ohm for R2. I had to hold the radio very close to the transmitter and I got the sound all over the dial, but it was very fuzzy (i was overloading the front end). If the fuzziness hadn't been there and it was a bit louder, it would have sounded great.

I tried it first that way instead of the schematic, don't ask why :roll:

The schematic version will not make squat.

Is this even plausible?

You need an attenuator on the input from the CD player, it's FAR too large an input for the transmitter. I'd be inclined to add a 10K volume contol on the input of the transmitter, and feed it via a 100K resistor from the CD player.

 

[zachtheterrible]

Thanx Nigel. I hate to imagine how overloaded the thing would have been w/o that 100k because I never got it to work before I put it in.

Im having a small problem. The circuit will only work if either there is no antenna, or there is no input, one or the other. I believe that these two things are creating parasitic capacitance? How would I go about remedying this?

 

[audioguru]

Hi Zach,
Your circuit doesn't have a very important 0.001uF to 0.01uF ceramic disc bypass cap across the battery connection to the circuit board with very short wires. When the 3V is fluctuating at about 100MHz, the transistor doesn't have any gain.

Have you seen my latest FM transmitter? It is very powerful and uses a low-dropout 5V regulator for its preamp and RF oscillator. It has an output RF buffer amp that isolates the oscillator from the antenna. I used lotsa supply bypassing and it works great.
https://www.electro-tech-online.com/threads/low-moisture-content-tester-help-wanted.14899/

 

[zachtheterrible]

Hi audio, that there circuit looks like it would take over my entire neighborhood :lol:
im just experimenting with the 3v design since im so familiar with it, but when im ready to make a final product, i think i just might have to use that circuit for my transmitter. You might remember that I want to use it to not only transmit my CD to my radio, but I also want to be able to crank up the power and take over other people's radios :twisted:

The strange thing is, whenever i add that .001-.01 uf capacitor, i ALWAYS get waaaay less range when it is used in my bug transmitter.

 

[audioguru]

Your transmitter defies logic and reason!

 

[zachtheterrible]

Your transmitter defies logic and reason!

thanx audio, that really helps! like i said, im only building this transmitter to see if it can be done, then ill use a decent transmitter, like yours.

so why do you think that .001uf cap is impeding my performance instead of making things better?

 

[Nigel Goodwin]

Your transmitter defies logic and reason!

thanx audio, that really helps! like i said, im only building this transmitter to see if it can be done, then ill use a decent transmitter, like yours.

so why do you think that .001uf cap is impeding my performance instead of making things better?

I would suspect it's probably making it work correctly, so the frequency may be a LOT different - try altering the coil with the capacitor fitted - it is an ESSENTIAL part of the design, in any circuit really!.

 

[audioguru]

hey Zach,
Nigel is correct, maybe your transmitter needs re-tuning with the 0.001uF cap.

Is it actually a 0.001uF low-inductance ceramic disc, which is 1000pF, or 0.001mF, which is a 1uF electrolytic with a lot of built-in inductance?
Likewise for the cap at the base of the transistor.

 

[zachtheterrible]

Nigel, no wonder they call you an electronics god!! ill have to try that, i bet itll make a lot of difference too!

i was actually getting something over my radio with the .001uf, but very faint, maybe it was harmonics.

yes, the .001uf is a ceramic disc.

 

[Nigel Goodwin]

Nigel, no wonder they call you an electronics god!!

Sixteen more posts and you'll be one as well :lol: