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How can I build a multiband AM transmitter?

unbuildpain

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How can I build a multiband AM transmitter?

All the DIY transmitters available online are for a fixed frequency, I want to be able change the transmit frequency covering at least 40KHz or more, I want an analog transmitter.
 

wwfeldman

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without being any more obnoxious than is necessary, you can do what i did when i read your post
and a generally decent starting point for almost anything - google it

try this as a start, at least:


in simplest terms, to change the frequency, change the oscillator
 

danadakk

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You have not discussed power levels yet, thats very impactful as to architecture.

Amateur radio handbooks, over the years, show DIY transmitter circuits based on
tubes, bipolar transistors and more recently MOSFET based Class E.


As far as tuning if you want precise tuning DDS chips for the modulator carrier source.
But most equipoment online these days still laregly analog. Good deal of PLL based
as well.

archive.org has a number of ARRL Handbooks to download.


Regards, Dana.
 

biff44

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is it a sign of the times that the questions here are so incomplete that you can not even begin to formulate an answer?

What frequency range?
What transmit power?
What do you mean by "analog" transmitter? Is your input speaking from a microphone.
What MODULATION do you want? AM?
Portable, fixed?
Cost?
 

unbuildpain

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without being any more obnoxious than is necessary, you can do what i did when i read your post
and a generally decent starting point for almost anything - google it

try this as a start, at least:


in simplest terms, to change the frequency, change the oscillator
Before actually asking here, I typed this query and searched on google: "diy multiband am transmitter" and all the results were about frequency locked projects. What search query did you use to find it?

Is there a way to get gerber files from the PCB layout mentioned in that PDF, so that I can build it myself?
You have not discussed power levels yet, thats very impactful as to architecture.

Amateur radio handbooks, over the years, show DIY transmitter circuits based on
tubes, bipolar transistors and more recently MOSFET based Class E.


As far as tuning if you want precise tuning DDS chips for the modulator carrier source.
But most equipoment online these days still laregly analog. Good deal of PLL based
as well.

archive.org has a number of ARRL Handbooks to download.


Regards, Dana.
Thanks for the link and that information about archive.org. I didn't think about power levels because I wanted to build something simple, now that I think about it, something which will transmit within an average sized room of say 10 feet width, 10 feet length and 14 feet height.
is it a sign of the times that the questions here are so incomplete that you can not even begin to formulate an answer?

What frequency range?
What transmit power?
What do you mean by "analog" transmitter? Is your input speaking from a microphone.
What MODULATION do you want? AM?
Portable, fixed?
Cost?

I thought the frequency range would be obvious by mentioning AM.

I haven't thought about transmit power but I think something covers a room size of 10 feet width, 10 feet length and 14 feet height.

My analog transmitter, I mean I don't want to use any digital components in the transmitter.

Again by AM I thought the modulation would be obvious as amplitude modulation

At present anything is okay, portable or fixed whichever has the best power output

I haven't thought about cost because I'm new to this.
 
Last edited:

danadakk

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There is a whole class of mW transmit power activity called QRP in the amateur community. In
fact ARRL has an entire handbook devoted to this.




Regards, Dana.
 

Aussie Susan

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The above answers hint at something very important: do you have an appropriate license to build and use a transmitter?
If you are an amateur radio person then 1) yes you do but only on restricted frequencies, and 2) in passing the exam that would let you build your own kit, you would have covered the principles involved as well as the regulations.
Transmitting, even at low powers, can interfere with (critical) systems used by others which is why it is illegal without an appropriate license.
Susan VK3ANZ
 

BradtheRad

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To transmit within a room seems possible for a waveform generator like mine. I have dialed up the frequency to hundreds of kHz while listening on my AM radio. At the same frequency or a multiple, I hear a sound from the radio, a characteristic buzz. It must be picking up transmissions from the waveform generator.

The signal comes from a XR2206 IC, producing simultaneous sine/ triangle/ square waves to short lengths of wire. The circuit is inside a steel enclosure together with a homemade frequency counter.
 

biff44

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I thought the frequency range would be obvious by mentioning AM.

I haven't thought about transmit power but I think something covers a room size of 10 feet width, 10 feet length and 14 feet height.

My analog transmitter, I mean I don't want to use any digital components in the transmitter.

Again by AM I thought the modulation would be obvious as amplitude modulation

At present anything is okay, portable or fixed whichever has the best power output

I haven't thought about cost because I'm new to this.

How can I build a multiband AM transmitter?​

you covering the 94 Ghz band?
415 MHz ISM band?
give us a break
 

Aussie Susan

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Sorry @ubuildpain but we certainly did understand that AM means Amplitude Modulation but that does NOT define the frequency range in any way. There is an AM band that is used internationally for radio broadcasts, but that does not stop Amplitude Modulation being used with any carrier frequency.
Whether you use analog or digital components matters little to the signal you transmit. What @BradtheRad and others were outlining is that there are very many ways of generating a signal that can be varied in frequency over a 40kHz range - but whether that range is centred on 1MHz or 1GHz will certainly drive how you generate it.
Also I take @danadakk's point about the FCC regulations but I can't see anything that says you are in the US. Each country has it's own regulations and what can be done in any particular frequency range and power output but I think you can assume that all will have a 'non-interference' clause in there somewhere.
If you need to cover a rom that small then there are many different ways that you can achieve this. You have not said why you want AM (is it because you want to pick up the signal on an AM-band or short-wave radio?) or what information is to be transferred on the carrier?
Also consider the bandwidth that will be involved - you may want to alter the carrier frequency within a 40KHz range but the signal that will modulate the carrier also needs to be taken into account. Telephone quality voice needs about 6-8KHz to properly cover the 300Hz to 3KHz required, and music or data requires even more bandwidth.
@BradtheRad also brings up another good point - the purity of the signal that you are transmitting. You might want to transmit at a particular frequency but great care needs to be taken not to create interference on the harmonic frequencies. Even if you stick to the rules for your country about the fundamental frequency and power, the harmonics could still land you in trouble.
Susan
 

unbuildpain

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How can I build a multiband AM transmitter?​

you covering the 94 Ghz band?
415 MHz ISM band?
give us a break
When I searched for it on the net, all the diy projects were frequency locked projects, so I think mentioning AM transmitter would also give information about the frequency range, that is 530KHz to 1700KHz.
Sorry @ubuildpain but we certainly did understand that AM means Amplitude Modulation but that does NOT define the frequency range in any way. There is an AM band that is used internationally for radio broadcasts, but that does not stop Amplitude Modulation being used with any carrier frequency.
Whether you use analog or digital components matters little to the signal you transmit. What @BradtheRad and others were outlining is that there are very many ways of generating a signal that can be varied in frequency over a 40kHz range - but whether that range is centred on 1MHz or 1GHz will certainly drive how you generate it.
Also I take @danadakk's point about the FCC regulations but I can't see anything that says you are in the US. Each country has it's own regulations and what can be done in any particular frequency range and power output but I think you can assume that all will have a 'non-interference' clause in there somewhere.
If you need to cover a rom that small then there are many different ways that you can achieve this. You have not said why you want AM (is it because you want to pick up the signal on an AM-band or short-wave radio?) or what information is to be transferred on the carrier?
Also consider the bandwidth that will be involved - you may want to alter the carrier frequency within a 40KHz range but the signal that will modulate the carrier also needs to be taken into account. Telephone quality voice needs about 6-8KHz to properly cover the 300Hz to 3KHz required, and music or data requires even more bandwidth.
@BradtheRad also brings up another good point - the purity of the signal that you are transmitting. You might want to transmit at a particular frequency but great care needs to be taken not to create interference on the harmonic frequencies. Even if you stick to the rules for your country about the fundamental frequency and power, the harmonics could still land you in trouble.
Susan
You can go to any shop which sells radios and some radios just mention AM and the frequency range which would be around 530KHz to 1700KHz, the world over that frequency range is referred to as AM band.

Having digital components might require me to program, having analog components wouldn't require any programming. Look at my above comment about AM frequency range.

The reason why I'm looking at AM is because I want to confirm or reject the rumor I heard that people with dental fillings or metal objects in or around skull can hear sounds broadcast with AM.
 

G4BCH

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The reason why I'm looking at AM is because I want to confirm or reject the rumor I heard that people with dental fillings or metal objects in or around skull can hear sounds broadcast with AM.

Reports of such phenomena seem to occur in areas of high field strength, i.e. close to broadcast station antenna. You are not to be able to generate such field strengths outside a screened room without causing significant interference to other users.
I don't dismiss that these effects do occur but they do seem to be very rare. All I can say is that in the course of my career I have been exposed, for short periods, to high field strengths from amplitude modulated transmitters from LF to microwaves and have never experienced any auditory effects; only some thermal effects on my skin. I have heard of some people hearing the buzz when in the main beam of a radar transmitter.
 

unbuildpain

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Reports of such phenomena seem to occur in areas of high field strength, i.e. close to broadcast station antenna. You are not to be able to generate such field strengths outside a screened room without causing significant interference to other users.
I don't dismiss that these effects do occur but they do seem to be very rare. All I can say is that in the course of my career I have been exposed, for short periods, to high field strengths from amplitude modulated transmitters from LF to microwaves and have never experienced any auditory effects; only some thermal effects on my skin. I have heard of some people hearing the buzz when in the main beam of a radar transmitter.
Maybe it is because you didn't have any metal fillings in your teeth or in or around your skull, maybe it was just radiation without any modulation, had it been amplitude modulation, you might have heard some sounds.

Here is a link of AM sounds being heard through weed burning up near an AM transmitter:
 

G4BCH

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I have had metallic fillings in my teeth for over 60 years, and it certainly was modulated AM broadcast, Analogue TV and radar with transmitter powers to the antenna to greater than 1MW.
The effects demonstrated in the video have been known about for over 100 years, ever since spark transmitters were invented. The people in the video in my opinion were acting with crass stupidity. The burning felt in their hands was RF heating, That can cause long lasting damage deep in the tissue. The power level involved there would have been far higher than you can generate at home, in the tens of kW. I would not recommend that you or anyone else try an experiment like that. Exposure to the RF field strength at the base of that antenna would have been hazardous enough let alone coupling into it through the weed, had he not been wearing thick gloves he would have been seriously burned and not just on his hands, the result may have been fatal.
I have seen the effects of high RF fields. Do not play with high power RF unless you know what you are doing, not just think that you know what you are doing. The consequences can be very serious and not show immediately.
Treat RF power with the same respect that you would high voltage.
 

unbuildpain

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I have had metallic fillings in my teeth for over 60 years, and it certainly was modulated AM broadcast, Analogue TV and radar with transmitter powers to the antenna to greater than 1MW.
The effects demonstrated in the video have been known about for over 100 years, ever since spark transmitters were invented. The people in the video in my opinion were acting with crass stupidity. The burning felt in their hands was RF heating, That can cause long lasting damage deep in the tissue. The power level involved there would have been far higher than you can generate at home, in the tens of kW. I would not recommend that you or anyone else try an experiment like that. Exposure to the RF field strength at the base of that antenna would have been hazardous enough let alone coupling into it through the weed, had he not been wearing thick gloves he would have been seriously burned and not just on his hands, the result may have been fatal.
I have seen the effects of high RF fields. Do not play with high power RF unless you know what you are doing, not just think that you know what you are doing. The consequences can be very serious and not show immediately.
Treat RF power with the same respect that you would high voltage.

Maybe your metal fillings aren't amalgam or silver, Lucille Ball apparently had amalgam fillings and it was reported she heard AM radio and Japanese spies transmitting.

Do you think a transmitter which covers small room be able to generate enough signal strength to make metal fragments vibrate? Like dental fillings or metal frangments in skull region.
 

G4BCH

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My fillings are amalgam, and I've never experienced any effects., and am very sceptical of any sensationalist claims made by any celebrities.
I don't think you will be able to safely or legally generate enough power to produce any effect. See Aussie Susan's reply #7 above.
All professional tests at high field strengths are a conducted in a screened room to prevent interference to other spectrum users.
If the effects you are investigating are common then radio amateurs, who are regularly exposed to much higher field strengths than the average person would have by now reported their teeth chattering while transmitting. I've never seen any reports and have never experienced anything when using any of the transmitters at my station.

Personally I would not make what amounts to a diathermy machine and get my head anywhere near it to see if I can hear the modulation whether through my teeth or anything else.
A few milliwatts should be safe, probably won't have any effect but will still potentially be able to cause interference over a considerable distance. to give you some idea, a neighbour of mine had an electricity meter with a microprocessor whose clock oscillator caused significant interference to everyone over a several hundred metres radius. As n experiment I found I could still hear it 15km away!

as I said before only do this if you know what you are doing, not just think that you know what you are doing.
I think the others on the thread would probably concur.
 

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