Buffer AM signal (5W)

Thread Starter

MrsssSu

Joined Sep 28, 2021
266
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Dear all, may I ask how to buffer an AM Signal so that it contains more power, maybe 5W for my Remote Control RC?

I have buffered the AM signal using op-amp but the power output is just not enough. I have tried using this push-pull transistor pair, but the waveform seems to be unbuffered.

I would appreciate any help I can get and my LT Spice file is below for download.

Thank you for reading and have a nice day :)
 

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Papabravo

Joined Feb 24, 2006
21,258
Are you licensed to transmit that kind of power?

What you are looking for is an RF power amplifier. What is the carrier frequency?
It appears to be 160 kHz. and a Class C amplifier for that frequency will be a challenge to find components for.
 
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DickCappels

Joined Aug 21, 2008
10,226
Not a very good looking transmitter design. Is this for the 180 kHz band? You might find that a magnetic antenna will work better, especially if the device you controlling my remote control is a moving device of some sort. I know that in some parts the world the maximum input power to the final stage of a transmitter at that frequency is 1.0 watt.

What carrier frequency do you intend to use, what modulation mode do you intend to use, and what is the maximum transmitter input power and the antenna limitation for the country in which you intend to use this?
 

MisterBill2

Joined Jan 23, 2018
18,941
I am trying to imagine what sort of RC application would use 160 KHz.
Not only will a resonant output circuit be relatively massive, but any effective antenna will be very large.
Many if the audio amplifier modules will function at that frequency and be able to deliver fairly low distortion.
BUT certainly there will be legal issues if power is radiated in that part of the spectrum.
In addition I do not see that amplifier as producing anything close to an undistorted output.
 

DickCappels

Joined Aug 21, 2008
10,226
In the United States that part of the spectrum for Industrial, Scientific,and Medical use, and has been used by unlicensed radio amateurs for as long as I can remember. It is allowed by FCC rules & regulations part 15 of the Code of Federal Regulations.
 

MisterBill2

Joined Jan 23, 2018
18,941
In the United States that part of the spectrum for Industrial, Scientific,and Medical use, and has been used by unlicensed radio amateurs for as long as I can remember. It is allowed by FCC rules & regulations part 15 of the Code of Federal Regulations.
Certainly correct, BUT the power allowed is typically 100 MILLIwatts. And there are some extreme antenna length rules as well.
And still, that is not a suitable frequency for remote control, both because of the antenna considerations and because of the high ambient noise level.
 

Danko

Joined Nov 22, 2017
1,841
"160/190 kHz
This is a Part 15 unlicensed chunk of spectrum from 160 to 190 kHz for anyone to use. Maximum power of 1 watt and short antennas limit the range. There are no known applications, and it is used mainly for experimentation."
https://www.mwrf.com/community/article/21848974/how-low-in-frequency-can-you-go

"§ 15.217 Operation in the band 160-190 kHz.
(a) The total input power to the final radio frequency stage (exclusive of filament or heater power) shall not exceed one watt.
(b) The total length of the transmission line, antenna, and ground lead (if used) shall not exceed 15 meters.
(c) All emissions below 160 kHz or above 190 kHz shall be attenuated at least 20 dB below the level of the unmodulated carrier. Determination of compliance with the 20 dB attenuation specification may be based on measurements at the intentional radiator's antenna output terminal unless the intentional radiator uses a permanently attached antenna, in which case compliance shall be demonstrated by measuring the radiated emissions."
https://www.ecfr.gov/current/title-...5/subpart-C/subject-group-ECFR2f2e5828339709e
 

DickCappels

Joined Aug 21, 2008
10,226
Certainly correct, BUT the power allowed is typically 100 MILLIwatts. And there are some extreme antenna length rules as well.
And still, that is not a suitable frequency for remote control, both because of the antenna considerations and because of the high ambient noise level.
You are 100% entitled to your opinion. Coding methods can greatly reduce interference from noise sources. In some places that band is fairly quiet. In the United States the 100 milliwatts input power applies to 11 meter and AM bands. Some other license-free bands have different limitations like the field strength at a certain distance. 160 kHz transmitters and receivers have their mobile uses if magnetic antennas are used.

Let's see what the thread starter is thinking about before we get mired in discussing details that might be irrelevant with respect to the purpose of this thread.
 

DickCappels

Joined Aug 21, 2008
10,226
Yes, and we do not know where he plans to use the transmitter nor the allowable power (or field strength) in that region. Let's wait and see whether the thread starter is even interested in continuing.
 
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