Discussion in 'Homework Help' started by vead, Dec 24, 2011.

Nov 24, 2011
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hi everyone,i am trying to design single stage tuned transistor transmitter for short distance to learn the basic calculations of transmitter i know i need following part
amplifier circuit-the NPN single stage amplifier which amplify the signals
oscillator circuit- tuned circuit which use to create carrier siganls
audio source-to convert audio signal in to voltage signals
antenna-to transmit Rf signal

i know only 20hz audio frequency
transmitter distance 30m
power supply 12v
operating frequency 500khz
am modulations
(i am not sure that my transmitter operate this range i have no idea i only guess above value if i wrong please correct me )
i don't care bad quality of transmitter

i just wanna know how to design amplifier circuit ,what is gain for this transmitter what frequency generate throw tuned circuit for this transmitter
i am new so i have many basic broblms please give me information how i can design single stage tuned transmitter what parameter i need

thanks to all

Last edited: Dec 24, 2011
2. ### thatoneguy AAC Fanatic!

Feb 19, 2009
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Have you learned/seen in your class materials how to make a 500kHz/0.5Mhz Oscillator with one transistor?

Get to that part, and show what you came up with.

What is the modulation supposed to be: AM or FM? (500kHz is below the typical AM range, so this is an unknown)

Nov 24, 2011
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no i have no more idea is it possible 500khz oscillator with one transistor if no so what is maximum range of oscillator with one transistor

4. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
Can you show a schematic of an oscillator?

All that is needed is something that resonates and an amplifier

So, a crystal and a transistor would be a good way to give feedback to the crystal to keep oscillating at around 500kHz.

Or, an LC "tank" circuit that is periodically bumped by the amplifier to keep oscillating?

Here's a couple ideas, I expect you can do better:

Higher Frequency Transmitter

This would be outright cheating

If you use either of those, please describe the principle of operation in a post here as a "Thanks". That way we know you learned something from it. I usually never give answers out, but hey, it's Christmas!

Dec 26, 2010
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You can probably find details of how to build a simple transmitter, possibly some of the links that you have been given will help, and there is certainly a lot more information to be found on the internet. Understanding the theory behind it, so that you can design your own is another matter. For this, it would be better to work up from much more basic ideas. To start with, a few things may be worth noting about what you have asked.

NPN bipolar transistors are the most common type, but there are other devices which could be used, not necessarily even solid-state.

The term "oscillator circuit" in physics may describe just the resonator wiich defines the working frequency, but more usually in electronics includes the amplifier which sustains the oscillations.
Audio frequencies extend between limits usually taken to be between 20Hz and 20kHz, although not everyone can hear all of the range. 20Hz is a very low bass frequency, too low for many loudspeakers to reproduce properly.

This frequency is just below the usual AM Medium Wave broadcast band. Not many commercial radios will tune it.
In Europe the MW band ranges from 526.5 kHz to 1606.5 kHz[ and in North America it goes from 535 kHz to 1705 kHz.

A 500kHz oscillator using one transistor is possible. The range will be dependent on how effective an aerial is used, and on the details of the design.

A small transistor of the sort you might use may produce only a milliwatt or so into a short inefficient aerial, ans so won't get far. In principle however an RF power transistor could be used to generate many watts of RF, and with a long aerial and a good earth system could go for miles.

Note however that in most regions a licence is required to operate a transmitter. Depending on local regulations, it is sometimes permitted to operate at very low powers at certain frequencies, but high power transmitters are generally illegal without a licence.

Nov 24, 2011
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thanks dear this idea is vary helpful for me
i want to ask some questions

if i know part
transmitter operating frequency
transmitter distance range
transmitter output power
low level modulations with linear amplifier
power supply
antenna height

now my question is how to start to make simple transmitter circuit
ok first i select audio amplifier how we know what amplifier is need what is gain of amplifier
i want first build audio amplifier circuit and next stage power amplifier and next stage tuned circuit
i have few knowledge about amplifier, oscillator
what i do to understand the concept

thanks for help

Feb 19, 2009
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8. ### Audioguru New Member

Dec 20, 2007
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Another student with a lazy teacher who teaches nothing.
<snip>

Last edited by a moderator: Dec 28, 2011

Nov 24, 2011
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have you any problems from Indian student ?
everybody know me i am Indain

Last edited: Dec 28, 2011
10. ### amilton542 Active Member

Nov 13, 2010
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Don't under estimate India. As far as Power Systems are concerned they are best-of-breed.

11. ### Audioguru New Member

Dec 20, 2007
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My excellent eye surgeon is from India. But he was educated here in Canada.

Maybe the Indian who is trying to design a simple AM transmitter is doing it without a teacher. He should learn the basics of electronics and of radio circuits first, in his own language on a website in India.

Apr 5, 2008
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13. ### hobbyist Distinguished Member

Aug 10, 2008
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India, has some EXCELLENT colleges, for teaching electronics, mechanical engineering, ect...
These can be found on there 'youtube' channels, these teachers are extremely educated, they know there stuff, and they know how to teach these courses with great accuracy.
Most of our own American educators would do well to learn how to teach these subjects, to help our young students get a true education in the science fields, rather than trying to teach nonscientific fairy tales like evolution, and all that boloney.

14. ### Wendy Moderator

Mar 24, 2008
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Overall we have had students from everywhere who have covered the spectrum from excellent to lazy.

This site is international, that is not going to change. If you can not handle a thread just move on. Personally I have the highest reguard for people trying to learn a complex subject that is not in their mother tongue.

When I was a teen I was self taught, and full of misconceptions. The electronics classes clashed with my college bound courses. Since this is a learning site we're going to have to cut people slack. Personally I like helping beginners. It can be frustrating, but it is also rewarding.

Dec 26, 2010
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From what I have seen of questions asked by students from different regions, it seems that some teachers concentrate on the rote learning of lists of facts and theories, without helping the students to understand and use of what they have learned. While this may apply to students from many regions, it may be more associated with certain countries.

Although the best education available in such places is clearly excellent, as witness the many eminent people who have their origins there, many individuals may have poorer opportunities. In particular, I suspect that a system of cramming schools designed to help less successful students pass examinations may have a role in the poor understanding of some material.

It is unhelpful to make negative statements about people simply because of their nationality or ethnicity, but it may be well to realise that the opportunities available to people in other regions may differ, as may their cultural and moral background.

Whatever their situation, I feel that students would do better to realise that stocking up on facts at a crammer, or obtaining model answers to plagiarise, is no way to master a subject. It seems though that in some regions cheating is very prevalent, perhaps against a background where desperate individuals care more about getting a vital piece of paper than learning anything in particular.

While I cannot condone such behaviour myself, I'm not sure that we can expect to apply the same moral standards to people living in different societies as we might to our own people. That does not mean we should ever want to help them cheat on their assignments.