FM transmitter -reallly need help-

[manz]

how to actually determine which is input/output/base for voltage regulator(78L05)

if we see from the 3pins, the flat spot is facing up(sky) and the rounded one facing down(ground) , what is pin most left?middle?and most right?
or is there any other way to determine all those pins?

thanks guys..

 

[Nigel Goodwin]

how to actually determine which is input/output/base for voltage regulator(78L05)

if we see from the 3pins, the flat spot is facing up(sky) and the rounded one facing down(ground) , what is pin most left?middle?and most right?
or is there any other way to determine all those pins?

You just read the datasheet - it has a picture that shows you how to connect it!.

 

[manz]

dear audioguru...

hm i finished doing the mod4 transmitter of yours..

it`s working fine BUT :

1.why can`t i really hear my voice clearly? the voice can be herd but it still got the zzzzsss sound,and it pretty loud (i`m about 2m away from the reciever)..

2. the output transistor gets pretty hot too (can touch just about 4-5sec then it just too hot to be touched).i`m using 100ohm resistor to ground in series with the emitter of the output transistor (like how you ask me to do).

3. about the distance i didn`t test it yet.just trying to make it clear first...

is it because of the inductor? (mine is 10 round of 1mm enamel coated Cu wire,internal diameter is 3mm and i`m using the 78L05 voltage regulator)

really hope you or anybody else could save the day :wink:

thanks a lot guys...

 

[audioguru]

Hi Manz,
I think your radio is overloaded by the transmitter when they are close together and you are tuning to an overload phantom signal. If the transmitter shows up at more than one frequency on the entire FM band then the radio is overloading. My cheap Walkman radio has a local-distance switch that eliminates overload when in local mode so that it can be tuned to my transmitter properly.

I made an RF detector using 10cm of wire as a pickup antenna, a 47pF cap in series with a germanium diode to ground, a 0.001 filter cap across the diode and a shielded cable to my 'scope. That allowed me to tune the output tuned circuit in my transmitter for a peak at its RF frequency. I couldn't use my multimeter because it doesn't have a shielded cable and I had RF all over the place.

The 100 ohm resistor in series with the emitter of the output transistor limits its average current to about 40mA, and so does the high value of its 47k base bias resistor. Therefore 40mA though the 100 ohm resistor produces a voltage drop of 4V, leaving the remainder of the supply voltage across the transistor. If the car battery voltage is very high during charging, it might be 14.3V. Subtracting the 4V across the emitter resistor leaves 10.3V across the transistor. With a current of 40mA, its power dissipation calculates to be 412mW. It is rated for 625mW in a room-temperature ambient so will be hot but fine.

You know what? The 100 ohm emitter resistor needs to have a 0.001uF ceramic disc capacitor in parallel with it for the transistor to produce a much higher output power to the antenna. :lol:

 

[manz]

Dear audioguru...

thanks alot to you and others thats help me building the transmitter..
i`ll work the 0.001uF caps tomorrow.. Hmm that seems to be too important thing to be forgoten :lol:

anyway, after i had wind back once again the inductor i could get crispy clear sound transmitted after that..and it has little frequency drift too (like how it claimed to be :wink: )

i really hope it could get at least about 1km transmitting distance when i test it tomorrow(or is it suppost to be more isn`t it? since i`m using 12v input)..

i`ll say how it goes then...thanks a lot everybody...

(supperb mod4 circuit dude,takes hours to cramped it -for me though :wink: )

 

[audioguru]

Hi Manz,
I'm glad to hear that you got it working well.
When you test its range tomorrow, watch out for the RF cops.

I had mine hanging out of an upstairs window playing my son's alarm clock beeps and I drove my car away while listening for it. If I could see it, it was picked-up fine at about 1km. If anything got in between, even just a tree, it was gone. I measured its range on the same frequency as a low-power (a few thousand watts) station on the other side of my city because my FM band is full.

Put it at the top of a mountain, then listen for it on other mountains. Use Mapquest or the new Google satellite photo maps to determine your range. :lol:

 

[manz]

dear audioguru..

i dont really know whut is happening here.. the signal can be pick up by my Hi-Fi stereo even if it is 8-10 meter. the quality of the voice transmitted is supperb if trough the Hi-Fi stereo. (can also be pick up by walkman)

The problem is why my car receiver can`t pick the signal at all. it is so hard to tune even to just get the sound like it has a transmitter-receiver feedback.(also tested with other cars)i didnt sit in the car nor somewhere near the car, i`m about 5-6m with the car.

with the previous circuit (the simpler one), all of the Hi-Fi, walkman,and also car can get the wave transmitted,but the transmitter is too fragile (can even move them and distance of transmitting is about 200m)

what is actually the inductor (coil) is for? does it to determine the the frequency generated? does it affect the distance of transmitting?

what should i check at the transmitter(caps,transistor,coil ????)

thanks...

 

[manz]

i really want to attach the pic of the circuit of mine..but why cant i posted it.. i`ve read somewhere in the forum about attachment..

but after i pressed the add attachment, then browse...
sellected the file but when i pressed preview, i writen `page cannot be displayed`

been trying it for days..

 

[audioguru]

Hi Manz,
I clicked on Attachment, then Browse, then selected my pic file, then clicked Open, then either Preview and I see my pic then Submit, or just Submit and it works. If your pic file is a BMP, then convert it to a JPG file type in your viewer program before attaching it.

The coil on the left determines the oscillator's frequency by its number of turns, wire size, turns spacing, and diameter of the coil. It resonates with the trimmer capacitor across it plus stray capacitance of the wiring, capacitance of the transistor, feedback capacitor and capacitance to anything nearby.

The coil on the right determines the RF amplifier's frequency the same as above, and should have its trimmer capacitor adjusted for peak output level for maximum range. The tuning of the RF amplifier is very broad and covers about half the entire FM band.

If car radios cause acoustical feedback then the radio is too loud or the transmitter is too close to it. My project has high preamp gain so its microphone can pick-up sounds quite far away. :lol:

 

[manz]

dear audioguru...

if that so, it doesn`t matter wheter what is the size and the number of loops were made isn`t it? as long as it could give the same amount of Henry as the original coiling??is it??

Let say it this way, i tried to make a different sets of coil (4 loops of 1mm enamel coated Cu wire with 10mm diameter) use the 0-27 trimmer caps,and yet, i can still get a very clear sound (as the original coil i used-10 loops of Cu wire on 3mm diam) does this affect anything?? i tried a number of other coiling hoping it could be herd by the receiver in the car..

i`m aware about the sensitivity of the electret mic with this circuit(mod4).. but i just couldn`t understand why it can`t be herd with the car receiver since it could be herd by the Hi-Fi and walkman but the simpler circuit can be herd by all of those..

is it posibble to make it as a simple walkie talkie for used in car while convoying, or i`m just waisting time for thinking of the imposibble? i spent almost 2 weeks for this project already and i`m so close to make it happend that way,but just this very confusing problem keep me and my idea away.but at least i learn so many new things...thanks to you..

Or maybe what i should do is just keep on trying to find the tune by my car receiver since i`ve done it for the hole day already(with a different sets of coil) i`m determine enough but yet not lucky enough- i guess :cry:

do you have any idea or sugestion on what i should do/check/change to make this happen....by the way, my layout i just a few holes wider (about 4-5) than the one you posted,since i used that pic as a guide for my layout (the size and placing).both of the coils also in about the same gap as yours as well. i`ve got the pic from the previous forum you posted it to someonne else but just couldn`t make the layout as small.

hope to hear from you..thanks..

 

[audioguru]

Hi Manz,
There are many combinations of coil sizes and number of turns to make the same inductance. Mine is 8 or 9 turns of 1mm wire close-wound on a 3mm shaft, and the wire spacing at the ends is exactly 0.4".

My trimmer caps go up to 35pF which is a lot more than yours. Therefore your coils will need more turns to match so that they can be tuned to the proper frequency.

Maybe your transmitter is tuned to the image frequency of the radios that pick it up but with poor range. If the radio is set to 100MHz, the image frequency is the IF frequency, 10.7MHz, times two plus 100MHz = 121.4MHz. On some radios the image frequency is 21.4MHz below the tuned frequency so maybe the home radios are one way and the car radios are the other way and therefore don't work. :lol:

 

[zachtheterrible]

if that so, it doesn`t matter wheter what is the size and the number of loops were made isn`t it? as long as it could give the same amount of Henry as the original coiling??is it??

Correct.

i`m aware about the sensitivity of the electret mic with this circuit(mod4).. but i just couldn`t understand why it can`t be herd with the car receiver since it could be herd by the Hi-Fi and walkman but the simpler circuit can be herd by all of those..

Manz, that is very interesting. I thought I was the only one. I made a transmitter similar to audioguru's (but not as high quality :lol: ) and it would give acoustical feedback on my clock radio, but not on my car radio.

Maybe there is some sort of filtering on the car radio that blocks these types of transmitters

 

[manz]

the wire spacing at the ends is exactly 0.4".

what is this phrase means? wire spacing? where is it ? lenght of wire that were put into the hole of the vero board is it?? if yes, we should leave the balance of the wire underneeth un-cut???

 

[audioguru]

Hi Manz,
I made my FM coils like this. Since your trimmer caps have a lower value than mine, maybe make your coils with 10 or 12 turns instead of 8 turns like mine. :lol:

 

[eblc1388]

Beautiful coil image.

Woo, 2nd angle projection. Cool. :lol:

 

[audioguru]

Beautiful coil image.

Woo, 2nd angle projection. Cool. :lol:

Thanks, L. Chung. :lol:
I made the "2nd angle projection" a mirror image on purpose to see if anyone would catch it. You missed it. He, he. :lol: :lol:

 

[manz]

dear audioguru..

I tried as u asked me to,that is to turn more coil (11-12loops )for the inductor..

this is the result:

1. for the Hi-FI - can still pick up the signal..very clear still like previous..

2. for the car receiver - there`s seems like something being transmitted but the sound quality is too bad to understand what did i said (through the car receiver)

should i add more coils to it (13-14 loops maybe) to make it clearer??

or is there any other way to make the previous circuit more stable (that is by pcs-electronics)... what are the things should be added to the previous circuit to lessen the frequency drift..is there any posibble way to do so (incase the crcuit i`m working on it now still can`t work through the car radio)

really hope you can help..