AM Transmitter

Thread Starter

MerryGR

Joined Jul 21, 2019
25
Hello engineers, I've been wondering if you would help me with my problem I'm currently facing. I'm student and I want to learn as much electronics as possible. That's why I'm asking for an advice. I'm creating my own AM Transmitter project for my school things. I just wanna know these things:

  1. Where can I get the source of carrier frequency (instead of buying some lab generator). Some integrated chips, or?
  2. Can my audio signal, alongside with carrier frequency (together) enter the transformer to step it up to some higher voltage level than I would obtain from LM386 audio amplifier? I think this would boost the transmission even more, am I mistaken?
  3. Can I use a straight wire antenna of around 2 meters? I don't wanna buy any of those perfectly-made antennas they sell online.
  4. What carrier frequency would you suggest to me? Somewhere around 20MHz?

Thank you for your response.
 

Alec_t

Joined Sep 17, 2013
10,688
What carrier frequency would you suggest to me? Somewhere around 20MHz?
Be aware that most transmissions require a licence. Illegal transmissions could prove expensive! You need to research if there are any licence-free frequency bands in your area, and what transmission powers are legal.
 

Thread Starter

MerryGR

Joined Jul 21, 2019
25
Be aware that most transmissions require a licence. Illegal transmissions could prove expensive! You need to research if there are any licence-free frequency bands in your area, and what transmission powers are legal.
20MHz is allowed frequency for citizens. Also, I think the maximum power listed there is 4W. I just wanna be able to transmit signal over my room. I don't wanna transmit it through the whole city. It's just a project to demostrate its functionality. :D
 

Papabravo

Joined Feb 24, 2006
12,766
20MHz is allowed frequency for citizens. Also, I think the maximum power listed there is 4W. I just wanna be able to transmit signal over my room. I don't wanna transmit it through the whole city. It's just a project to demostrate its functionality. :D
Well, the problem is that a 20 MHz. signal, even at low power, can propagate halfway around the globe. It is unlikely that you could transmit a signal legally at 20 MHz., since by international agreement that frequency belongs to the time standard folks at WWV. Most legal users of the spectrum, take a dim view of dilettantes who just want to mess around. You want to play -- get a license. Also, almost nobody except commercial broadcasters use AM transmission anymore.
 

MrChips

Joined Oct 2, 2009
19,910
Have you checked for legal transmission on 20MHz in your country? It is very unlikely that this is an allowed frequency. It is a time/frequency broadcast standard frequency.

Also 4W is most likely illegal without proper license. For your room try 50mW.
 

Thread Starter

MerryGR

Joined Jul 21, 2019
25
Citizens Band CB-27 includes the frequencies from 26,960 MHz - 27,410 MHz. These stations must not have an antenna gain more than 6dB and shouldn't have directionality on horizontal plane.

Citizens Band channels can be used for scientific, medical and industrial purposes.

According to them, it's a commonly used band if you follow a certain rules.
 

Janis59

Joined Aug 21, 2017
957
3) 300/20MHz=15 meters lambda. Means quarter is 3,75 meters. Or accept, or choose a shortened CLC antenna.
2) Booster cascade
1) Vačkar circuit if adjustable or quatz (Pierce oscillator) if non-adjustable freq
0) RE: Post No.3) 20 MHz and 4W means You may conversate with me straight, 10 000 km afar.
 

Papabravo

Joined Feb 24, 2006
12,766
Citizens Band CB-27 includes the frequencies from 26,960 MHz - 27,410 MHz. These stations must not have an antenna gain more than 6dB and shouldn't have directionality on horizontal plane.

Citizens Band channels can be used for scientific, medical and industrial purposes.

According to them, it's a commonly used band if you follow a certain rules.
AFAIK CB radios do not use AM transmission.
 

Thread Starter

MerryGR

Joined Jul 21, 2019
25
Then I think I shouldn't make the project.. Is there really no chance I could get it done? Besides buying a license...
 

BobTPH

Joined Jun 5, 2013
2,190
If you want to make an AM transmitter, make it for the broadcast band and very low power, less than 100mW.

Use a single transistor oscillator and no RF power stage.

Tune it to a dead spot on the AM band in you area and you will be able to pick it up on a standard AM receiver. The range will be, maybe 10 m.

Bob
 
Then I think I shouldn't make the project.. Is there really no chance I could get it done? Besides buying a license...
Yes there is, as others already pointed out there is the FCC Part 15 AM transmitting rule where one can use a small transmitter, no more than 100mW at the last stage to broadcast in about 30 feet range. Go to FCC site and search for Part 15. There are many DIY schematics on the web.
 

AnalogKid

Joined Aug 1, 2013
8,250
I know that AM is allowed, and I know the original CB radios of the '60s had AM capability, but didn't they mostly switch to SSB by the time of the '73 CB wave.
Not as I recall. SSB was a poor-man's encryption, but the radios were noticeably more expensive.

ak
 

MrAl

Joined Jun 17, 2014
6,935
I know that AM is allowed, and I know the original CB radios of the '60s had AM capability, but didn't they mostly switch to SSB by the time of the '73 CB wave.
Mine and many others were AM only. The SSB users use to annoy us.

As a side note, just dont interfere with anyone else's radio reception and you'll be ok.
 
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