diy transmitter?

[slidder]

hey all,
i was just curious as to how i would go about making a low powered transmitter, <1 watt, at a frequency of my choice . and also have the ability to change the frequency?

 

[zz0468]

How you would go about it? That's pretty vague. A lot would depend on what the application is for. Is it a ham transmitter? Video? What's the frequency range? Is it operating under Part 15? Depending on what you're doing with it, 1 watt might be considered high power. How you would go about it depends a lot on the answers to those questions, and more.

 

[slidder]

How you would go about it? That's pretty vague. A lot would depend on what the application is for. Is it a ham transmitter? Video? What's the frequency range? Is it operating under Part 15? Depending on what you're doing with it, 1 watt might be considered high power. How you would go about it depends a lot on the answers to those questions, and more.

lets say i want a uhf range, and do not want it to be strong enough to go any further than the area of my house and land(not that large) it would be audios i suppose, but i guess video would be something i could look at later. not operating under anything as the frequency would be "under the radar" sort of speak.
i jsut want to lnow how i can for instance, send out 888.8877 mhz fm and be able to recieve it on the other side of my house with a scanner.. .. REAL basic right now i jsut want to under stand how tranmitting works at very LOW power range .

thanks

 

[JoeyC]

hey all,
i was just curious as to how i would go about making a low powered transmitter, <1 watt, at a frequency of my choice . and also have the ability to change the frequency?

Um, you might consider taking an electronics class. :roll:

 

[SkipSanders]

It works by: 1) you do it 2) you interfere with someone 3) you get a nice $10,000 fine for operating an unlicensed transmitter when they complain.

There are specific frequency ranges where 'unlicensed' (but operating according to the rules) transmitters can be used. Mostly, they'll be limited to 100 milliwatts or so.

The question is, 'What do you actually want to DO?' If it's 'relay audio from something to a scanner elsewhere', you can try using one of the legal low power devices for such things, perhaps a low power FM broadcast band unit, or one of the 902-928 ISM band links.

You can also use wired connection, to get to a specific room, then 'broadcast' to a headset via infrared, for instance.

 

[ImTheWeasel]

Here is a link to a small transmitter i built for myself awhile back.

http://sci-toys.com/scitoys/scitoys/computers/radio/computer_controlled_transmitter.html

Pretty simple design, computer controlled via COM port. Uses a simple program to power the oscillator on and off...

Perhaps this will help you get started.

As stated above however, you need to be sure your within Part 15 rules...

 

[gmclam]

hey all,
i was just curious as to how i would go about making a low powered transmitter, <1 watt, at a frequency of my choice . and also have the ability to change the frequency?

A transmitter typically has two major parts; one is an oscillator which generates the frequency and the other is the modulator. If you just want to emit a "dead carrier", the modulator is not needed. Whether you want AM, FM, ?SB, QAM or some other modulation scheme (and there are dozens) would dictate the modulator you need to design. But a transmitter is more than the sum of its components. There is a skill required to design one from scratch, and another skill to build it. I think the best place to look for starters to understand all of this are some books on ham radio. It will give you the basics. Keep in mind it is just as complicated as designing an internal combustion engine or modern day computer from scratch.

Good luck.

 

[kb2vxa]

Hi Slidder and all,

Your question is far too broad in scope for any definitive answer. Then too you're asking the wrong people, this forum is populated mostly by casual scanner enthusiasts, those who know about transmitters are few and far between. Your best bet is to locate an Amateur Radio club in your area, drop in on a meeting and introduce yourself around when it's over. Likely you'll get coffee and doughnuts out of the deal too. In between bites you can ask your question and let the "experts" whittle it down into something you all can deal with.

I'll bet before they're done you'll have a ham license and know enough basic radio theory to build a simple low power ham transmitter, a "QRP rig" in a breath mints box. That'll get you started and keep you out of trouble 'cuz you'll know what you're doing.

"Keep in mind it is just as complicated as designing...a modern day computer from scratch."

Don't kid yourself, I have designed and built a number of transmitters and even an FM stereo receiver but when it comes to anything more complicated than a binary counter... FO GIT IT! One look in the box and you'll put a Gunn diode to your head and pull the Schmidtt trigger.

 

[slidder]

Keep in mind it is just as complicated as designing an internal combustion engine or modern day computer from scratch.

Good luck.

well, i am sure that once i have understood the basics of how things transmit, i highly doubt it will be as complicated as designing a combustion engine lol it takes years of R&D and teams to make a well efficient engine.. but thanks for the heads up


as for IamTheWeasel. thank you.. pretty simple and straight foward. my question is now, can i buy a variable modulator?? or does it have to be at a specific frequency??

also you say to look at some ham books or online stuff. is there a specific site that anyone would suggest i go to to lear the basics of radio transmitting??

thanks for posts

 

[N_Jay]

. . also you say to look at some ham books or online stuff. is there a specific site that anyone would suggest i go to to lear the basics of radio transmitting??

ARRL.org

 

[gmclam]

All designers are not created equal

"Keep in mind it is just as complicated as designing...a modern day computer from scratch."

Don't kid yourself, I have designed and built a number of transmitters and even an FM stereo receiver but when it comes to anything more complicated than a binary counter... FO GIT IT!

People who are professionals in their trade make their jobs look "easy" to outsiders. If you're trade is mechanical engineer, then designing injection molds may be something easy for you. If you are an electronics engineer, it may be digital, analog or RF circuits. These days people specialize in a sub-field, but that, IMO, is a personal choice. It used to be that digital circuits were "easier" to design than analog. But with clock speeds upwards of 3GHz, digital circuits now have RF and analog properties. So when you say "more complicated than a binary counter", does that include counters at UHF/microwave frequencies? Now isn't that more like RF than digital?

One look in the box and you'll put a Gunn diode to your head and pull the Schmidtt trigger.

LMFAO I dropped my tuning fork when I heard this one.

 

[boatbod]

well, i am sure that once i have understood the basics of how things transmit, i highly doubt it will be as complicated as designing a combustion engine lol it takes years of R&D and teams to make a well efficient engine.. but thanks for the heads up

Actually I'd suggest that designing a useful transmitter is more complicated than an internal combustion engine. Not necessarily more complicated than your car engine, but most certainly more complex than a weed whacker.

The most basic transmitter would be a spark-gap, but then that isn't going to transfer much data along with its broadband interference. After that, you start getting into crystal controlled set (single frequency), which require an oscillator, modulator, one or more multiplier stages and the power amplifier.
At the higher end of the complexity scale, you'll be getting into PLL synthesized tuners, and possibly even very advanced DSP "software" radios.

Most likely it's possible to buy a single chip transmitter requiring the minimum of external components for low power FM operation in specific bands, but again, you still need to know where to start and what you are doing.

Get involved in amateur radio - its fun, the learning curve isn't too bad, and you can purchase off-the-shelf equipment as a starting point.

 

[eorange]

Then too you're asking the wrong people, this forum is populated mostly by casual scanner enthusiasts, those who know about transmitters are few and far between.

Warren nailed it. Too many armchair quarterbacks here are over-complicating the notion of building a basic transmitter. Can we please try not to scare off the new poster?

First, time to set your expectations for an ultra-simple transmitter:
- frequency will be in the ham bands (20-15-10 meters)
- frequency will be crystal controlled
- it will be flea-powered, i.e. 100mW or less.
- no voice, just CW (Morse code)

I just described a transmitter that I built a long time ago, and I'm looking at the schematic right now. 1 transistor, 1 crystal, a handful of resistors and caps, a coil, and a 9V battery.

While it's good to understand the theory behind the transmitter, it ain't necessary when you're following a schematic or kit. What is necessary - and assumed - is a knowledge of good construction (especially RF) techniques, which includes a basic knowledge of circuits, soldering, and components. You get this from a love of hobby electronics.

The fun is finding a schematic, or buying a kit, and just giving it a try. Do some searching for "flea power", "QRP", and/or "CW", and see what you come up with.

Hope this helps. Good luck!

 

[902]

hey all,
i was just curious as to how i would go about making a low powered transmitter, <1 watt, at a frequency of my choice . and also have the ability to change the frequency?

Kits are probably the easiest because they put everything at your fingertips.
Look here: http://www.hamtronics.com
or here: http://www.ramseyelectronics.com/

I used a Ramsey board with an on-board whip antenna to send audio from various radios to an FM radio in another part of the house. I also used a Belkin Tunecast for the same purpose with okay result.

You can hit a number of reference books and build your own, but parts may not be commonly available and substitutions may make your transmitter unstable.

Unless you are transmitting into a dummy antenna, even less than 1 Watt can go well beyond your house. Under the right conditions, very low power can go miles (we have a low power, focused directional pattern link transmitting 26 miles; I used a 100mW service monitor output to talk to someone on a mountain 75 miles away on 902 MHz). You may potentially get yourself in trouble by causing interference. That would usually be to something you never thought you'd interfere with. Be careful. The FCC requires RF emitters to be properly licensed or operating within parameters defined in the respective parts of the Rules. It should be a frequency of THEIR choice (with their power level and antenna).

Oh, and to join the other guys plugging ham radio, that's worth a look at, too.

 

[kb2vxa]

Hi again,

"Warren nailed it. Too many armchair quarterbacks here are over-complicating the notion of building a basic transmitter. Can we please try not to scare off the new poster?
First, time to set your expectations for an ultra-simple transmitter:
- frequency will be in the ham bands (20-15-10 meters)
- frequency will be crystal controlled
- it will be flea-powered, i.e. 100mW or less.
- no voice, just CW (Morse code)"

Actually the low power (QRP) transmitter I had in mind is 5W or less and with a good antenna hams cover long distances with them.

The main thing I had in mind is facing the teacher, we call them elmers, he'll learn faster and easier than stumbling blindly through books. They're valuable teaching aids but no substitute for a teacher! Even if he doesn't want to become a licensed ham he can still learn the basics from one and build toys if that's all he cares about.

Right, don't scare him off with all this pointless out teching the techs nonsense that usually goes on here, this is not the time nor the place to show off what you DON'T know. Go right to the source and ask the horse, he'll give you the answer that you endorse, unless the horse you ask of course is the famous Mister Ed.

Sorry WILLLLLLBURRRRRR, ask your friendly neighborhood Spider Man, er, I mean HAM!

 

[gmclam]

Building transmitters that are CW and operate from a single crystal are so last century. There is no reason that a knowlegable person cannot build a digitally synthesized transmitter with one of several modes of modulation. The key is acquiring the knowledge, and I just don't mean a "canned schematic". I mean understanding what they are doing enough to pass FCC tests, acquire a license, and design/build something that won't get them into trouble.

 

[57Bill]

True. But "last century" was only 7 years ago.

 

[ohiodesperado]

Do a Google search on electronic bug's or listening devices. I am assuming that you are wanting to bug someone and monitor someone.
A simpler way to pull this off is a basic baby monitor. Drop the transmitter in location and either use the receiver, or a scanner to monitor the transmit freq. You are going to be ahead to get one from a garage sale with some age to it or a really cheap one. The newer ones are using 900 Mhz and are spread spectrum digital and not able to be monitored by a scanner.

As far as video, there are several 2.4 Ghz wireless all in one camera's out there that either come with a receiver unit, or are Wifi and can be monitored with a laptop PC with a wireless card. they just require power to operate.

If this is more for a learning experience and less a monitoring thing, there are several kits out there that are a single chip FM transmitter. They will require soldering and a bit of electronics knowledge, but are simple enough to build. Video transmission is a whole different animal and you are going to need a strong electronics background to understand how that all works to assemble anything that will broadcast video, then the same for a receiver, it's not as easy as audio.

 

[kb2vxa]

High again,

"Building transmitters that are CW and operate from a single crystal are so last century."

Such a transmitter requires a minimum of parts large enough to be easily worked with and still fit in an Altoids tin you can stick in your pocket. Try making a complex transmitter that small and you'll find yourself working with multi layer PC boards and components the size of a grain of rice. Now which would attract a beginner having a minimum of knowledge and a few ordinary tools? As for "so last century" maybe you never heard "if it ain't broke don't fix it". CW is alive and well and so are simple QRP rigs, you'd be surprised if you actually got into Amateur Radio and discovered what it's all about.

"There is no reason that a knowledgeable person cannot build a digitally synthesized transmitter with one of several modes of modulation."

There are two, the knowledge must be on the engineering level which means holding a BSEE, GROL or Amateur Extra (not having aced the test mind you) AND having a shop equipped with some very specialized tools and test equipment.

"I mean understanding what they are doing enough to pass FCC tests..."

Memorizing questions and answers on an Amateur exam is "so easy a caveman can do it", passing a VE test these days is simply acing. It's nothing like the old days when you had to actually learn something and sit for the exam at an FCC office actually doing calculations and drawing schematics.

Clam, welcome to the real world. Now go play with your iPhone and let the beginners begin at the beginning. If you think I'm being sarcastic I am but for cause. I've worked in the electronics industry for years and envy the laboratory conditions, maybe that's why I'd work on my pet projects at my test bench when the plant was closed for the weekend. There's no way I could ever have such a setup, I couldn't begin to afford ONE piece of their test equipment. I'd love a Wayne-Kerr digital LCR analyzer but $40,000 I have not.

Anyway the poor guy got scared away so the point is rather moot.

 

[gmclam]

Such a transmitter requires a minimum of parts large enough to be easily worked with and still fit in an Altoids tin you can stick in your pocket. Try making a complex transmitter that small and you'll find yourself working with multi layer PC boards and components the size of a grain of rice....

All components are not soic surface mount, but even so you needn't look any further than inside your scanner for a good digital frequency synthesizer. That same circuit could be used as part of a transmitter.

CW is alive and well and so are simple QRP rigs, you'd be surprised if you actually got into Amateur Radio and discovered what it's all about.

I've been on amateur bands but not for some time. Never did CW.

There are two, the knowledge must be on the engineering level which means holding a BSEE, GROL or Amateur Extra (not having aced the test mind you) AND having a shop equipped with some very specialized tools and test equipment.

I hold none of those degrees and have designed such circuits (and they have passed FCC testing....).

It's nothing like the old days when you had to actually learn something and sit for the exam at an FCC office actually doing calculations and drawing schematics.

I do hold an FCC license, which I had to travel to the field office of the FCC in San Francisco to take. The test was hardly "memorization" and did have lots of tube theory in it. I was allowed to use a calculator, but of course only to do the math. Yup, drew schematics as well.

Clam, welcome to the real world. Now go play with your iPhone

Don't have one, never will.

I've worked in the electronics industry for years and envy the laboratory conditions, maybe that's why I'd work on my pet projects at my test bench when the plant was closed for the weekend. There's no way I could ever have such a setup, I couldn't begin to afford ONE piece of their test equipment. I'd love a Wayne-Kerr digital LCR analyzer but $40,000 I have not.

I too have worked in the electronics and broadcast industries for over 30 years. I've actually held two simultaneous professions; one designing and building devices and another operating them.

Anyway the poor guy got scared away so the point is rather moot.

It certainly didn't help that several of the original posts in this thread were people scaring him, telling him the legalities and reasons not to do it. I actually started with some advice about his original question.

Good day to you too!