3v transmitter questions

If an extra transistor would only double your output power it's not worth adding!, you should be looking at least ten times the power output (and only 1/10th the battery life) and giving about double the range.

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ten times output power only = double range!?!?! wudup with that?? (thanx nigel)

It takes a lot of power to double the range because your antenna isn't directional (like NASA's very directional dishes) so your signal spreads over a complete half-circle (including upward if the antenna is not exactly vertical).

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very interesting audio. whenever i have my transmitter, the antenna (a flimsy piece of wire) is laying on something horizontal. if i can stick it straight up in the air, or perpendicular to my receiver, i take it that would mean better range??
is there any way of making my transmitter directional without putting dishes and stuff on it? remember, this is a bug, and i am trying to squeeze all of the range out of it without making it huge :lol:

thanx theone, but thats a 9v transmitter, and from what ive heard, it doesn't sound like that would last too long, considering that 9v battery life is very short, and its a class A amplifier. thanx though :lol:

well i guess that ill stick with my design that i have made, and seems to work very well. i'm coming close to 24 hours of the transmitter being on continuously, and the audio is great, and it hasn't drifted a SINGLE bit.

thank you EVERYBODY!! you've made my dream that i've been dreaming for about 2 years become a reality :lol: . i've finally got a little FM transmitter that works!! I can't thank you enough

Hi Zach,
I'm glad to have helped you.
We are all very curious:
1) What or who are you going to bug?
2) Why the long range? Beyond gunshot range?

1. I have no idea what im going to bug :lol: (or if). its just that since i was about 13, ive been interested in electronics, and the idea of mini transmitters reealy fascinated me (and still duz). i started working on it, and when i failed, i just kept on going, i couldn't quit. i gues i just wanted a feeling of accomplishment 8) .

ill probly bug my little sister, just 4 the heck of it :lol: . i was also thinking it would be kind of fun to stick a bug somewhere in my school and listen to it with a little earphone during a really boring class.

2. The reason that i want such good range is because i'm a bit of a perfectionist :lol: . if i build a circuit, i want it to work as best as it possibly can. and besides, the more range i have, the more time i have to run for my life when someone discovers they're being bugged :lol: (i can be a lot farther away)

again, thanx so much :lol:

zachtheterrible said:

ten times output power only = double range!?!?! wudup with that?? (thanx nigel)

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Inverse square law :lol:

Inverse square law :lol:

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ill keep that in mind :lol:

Eh Zac, there's a circuit out now that increases 3 volts to 9 volts so you can throw away those awfull 9 volt batteries, and with nicad's an nimh battery cappacties getting bigger all the time it makes sense to keep using 9 volt circuits but using AA nicads

Hi Zach,
It is true. This Australian project is the same size as a double AA cell battery holder and gives a stepped-up output voltage. It will even give 12V to your transmitter. The article compares the battery life of a 9V battery with the extended life of two AA cells. It has a PCB layout and everything. The project is here:
https://www.siliconchip.com.au/cms/A_100886/article.html

Hey, wow, thats cool!! ill have to use that sometime in one of my projects :lol:

this is very, very, very, very, very embarresing ive gone and done something very very very very stupid

I made my PCB, assemled the whole thing, and it didnt work. I then realize that in my original transmitter (the one assembled on a piece of cardboard) i'd been using a 47 ohm resistor for R5 instead of a 470 ohm resistor( ). It worked great!! thats the weird thing. Now I try a 470 ohm resistor and of course it doesn't work :cry:

Hi Zach,
It should work with 470 ohms for R5. Maybe also change R4 to be 100 times or more the value of R5.
With 47 ohms for R5, Q2's current is high (short battery life) and the range may be farther. Using 470 ohms, the battery will last a long time but the range may be short.

I forgot to ask one thing, just remembered:

will having a 47 ohm resistor in R5 cause me to lose battery power by making the transistor operate in saturation for some of the time? or is this solved by having R4 100 times more than R5?

Hi Zach,
R5 is the only current limiting resistor for the oscillator. The collector coil doesn't have any resistance. So the transistor's current is much higher with only 47 ohms. The high current is stored in the coil's inductance when the transistor conducts, and converted to a high voltage when the transistor becomes cut-off. The high voltage produces a longer range if the antenna's impedance doesn't load it down too much.
The ratio of R4 divided by R5 should be about the same as the transistor's DC current gain.

thanx audio. i'm not sure what you mean by the ratio of R4 divided by R5 should be about the same as the transistors DC current gain. Could you explain a little bit more?

Is there any way of simply calculating the impedance of my antenna so as to get the best range with just a whip antenna? ive been wanting to study up on the subject of impedance matching, but haven't looked for any books or anything on it yet. i'll be geting a book on electronics from my friend who is an electronics engineer, so hopefully it'll go into that subject.

thank you very much!!

P.S. I found out why my transmitter was not working properly, apparently electret mics cannot take much heat from a solder gun :lol:

Hey Zach,
My wifey just brought home one of those scanning FM radios that probably has a Philips IC inside (I didn't break it open yet to see). She got it free for signing up for a credit card.
Its performance is absolute garbage! It is mono, it keeps muting even on strong local stations and its high frequency distortion is so high that I can't stand it. If an announcer utters the letter "S", it sounds like porridge, pudding or mashed potatoes is coming out of their mouth!

Study about transistors and their biasing and current gain.

I don't know the details about antenna impedance, but a certain fractional wavelength of its length is a high impedance and doubling the length is a very low impedance. Frequently the transmitter's coil is tapped to match a certain impedance.

yup, im gonna study those books that i get quite a bit. they're college books. i plan on reading them and then doing all of the math and everything to design a parabolic mic amplifier all by myself. this would teach me quite a bit, and if i am able to do it, my friend thats an engineer said that i would have no problem getting a job as an EE :lol:

Hi Zach,
Just keep studying. The circuits that you are building will help you understand.

An LM386 makes a fairly good amp for a parabolic mic when a cap is added between its pins 1 and 8 to increase its gain to 200. Use an electret mic.

zachtheterrible said:

Hey, wow, thats cool!! ill have to use that sometime in one of my projects :lol:

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Eh Zach,
Heres is the link for the 3v-9v kit available from Jaycar. The prices are in Ozzie $ by usin Yankie $ dey be even cheaper, and at that price it wouldn't pay to make your own circuit board and source the parts. Hope this helps out in your future projects
**broken link removed**

Cheers Bryan1

Edit:- on reading the project in sillychip you can program this kit from 4.5v-20 volts, can support a DC plugpack and also trickle charge Nicad and Nimh batteries

when i make a project that requires 9 volts i am DEFINITELY gonna use that little gadget :lol: thanx bryan