in theory can a RF voltage amplifier with a matched antenna be used to transmit a RF signal?

Thread Starter

genekuli

Joined Oct 21, 2018
103
Could a CATV RF (Coax Distribution) voltage amplifier (eg. one with 20W power consumption, 50dB) with a matched antenna be used to transmit a RF signal (I know this is the opposite of the intended use)? or what would it do if it was used instead of a power amp of the same power consumption (~4W Tx power) in terms of transmitting EMF
 

Delta Prime

Joined Nov 15, 2019
1,147
Hello there :) I think, I have absolutely no idea what you're talking about. You are as intriguing to me, as RF is to you, I mean that in the best possible way! if you can tell me what motivated you to ask this question,like something specific you would like to accomplish.:)
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
Hello there :) I think, I have absolutely no idea what you're talking about. You are as intriguing to me, as RF is to you, I mean that in the best possible way! if you can tell me what motivated you to ask this question,like something specific you would like to accomplish.:)
I was reading up on the differences between a power amp and a voltage amp and I wondered whether a voltage amp would actually transmit from an antenna like a Poweramp does at the right frequencies with the matched antenna
 

Delta Prime

Joined Nov 15, 2019
1,147
I wondered whether a voltage amp would actually transmit from an antenna like a Poweramp does at the right frequencies with the matched antenna
Technically, an amplifier with high voltage gain is a voltage amplifier, but it may or may not have a low current gain. The power gain of an amplifier is also low due to these properties. Transistors, and op amps, given proper biasing and other conditions, act as basic voltage amplifiers. The main application of voltage amplifiers is to strengthen the signal to make it less affected by noise and attenuation. When transmitted signals lose its strength and get deformed, an amplification of the voltage at the transmitter will minimize the effect and receiver will be able to capture and interpret the signal with reasonable accuracy.
Power amplifiers are devices to amplify the input power, if possible with minimal change in the output voltage with respect to the input voltage. That is, power amplifiers have a high power gain, but the output voltage may or may not change. The amplifier efficiency of power amplifiers is always lower than 100%. Therefore, high heat dissipation is observed at power amplification stages. Power amplifiers are used in devices which require a large power across the loads. In multi stage amplifiers, power amplification is made in the final stages of amplification. Audio amplifiers and RF amplifiers use power amplifiers at the final stage to deliver sufficient power the load. Servo motor controllers also use power amplifiers to drive the motors. Power amplifiers are classified into several classes depending on the fraction of the input signal used in amplification. Classes A, B, AB and C are used in analog circuits, while classes D and E are used in switching circuits :)
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
Technically, an amplifier with high voltage gain is a voltage amplifier, but it may or may not have a low current gain. The power gain of an amplifier is also low due to these properties. Transistors, and op amps, given proper biasing and other conditions, act as basic voltage amplifiers. The main application of voltage amplifiers is to strengthen the signal to make it less affected by noise and attenuation. When transmitted signals lose its strength and get deformed, an amplification of the voltage at the transmitter will minimize the effect and receiver will be able to capture and interpret the signal with reasonable accuracy.
Power amplifiers are devices to amplify the input power, if possible with minimal change in the output voltage with respect to the input voltage. That is, power amplifiers have a high power gain, but the output voltage may or may not change. The amplifier efficiency of power amplifiers is always lower than 100%. Therefore, high heat dissipation is observed at power amplification stages. Power amplifiers are used in devices which require a large power across the loads. In multi stage amplifiers, power amplification is made in the final stages of amplification. Audio amplifiers and RF amplifiers use power amplifiers at the final stage to deliver sufficient power the load. Servo motor controllers also use power amplifiers to drive the motors. Power amplifiers are classified into several classes depending on the fraction of the input signal used in amplification. Classes A, B, AB and C are used in analog circuits, while classes D and E are used in switching circuits :)
thank you, so even though it is not designed for it, would a voltage amp transmit EM radiation from a matched antenna if the power consumption of the voltage amp was 20W for example (specifications below)?
  • Output Max Level: 60 dBmV
  • Gain: 50 dB maximum
  • Noise Figure: 7 dB
    Flatness: +/- 2 dB
  • Input Return Loss: >13dB
  • Output Return Loss: >14dB
  • Input/ Output Impedance: 75 ohm
  • Internal AC Fuse: 1 Amp
    Power Consumption: 20W
 
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Externet

Joined Nov 29, 2005
1,654
A cable TV amplifier module connected to an antenna will transmit very well. If a voltage amplifier or power amplifier, a proper impedance matching to the load will make it work. That is what a RF transmitter is: a RF amplifier fed by RF connected to an antenna that radiates RF.

The Motorola RF data book was very good book to have. I only have the pages pertinent to the modules I have.
1617674108185.png
1617674167173.png1617674419489.png
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
A cable TV amplifier module connected to an antenna will transmit very well. If a voltage amplifier or power amplifier, a proper impedance matching to the load will make it work. That is what a RF transmitter is: a RF amplifier fed by RF connected to an antenna that radiates RF.

The Motorola RF data book was very good book to have. I only have the pages pertinent to the modules I have.
View attachment 234632
View attachment 234633View attachment 234634
so can you Please explain the difference in the EM radiation emitted from a connected antenna between the power amp and the voltage amp, surely there must be some fundamental difference in using the two types of amps in terms of the tx radiation, say for example the two amps both have a 20W power consumption, how will they differ in the tx-ing?
 

Externet

Joined Nov 29, 2005
1,654
antenna between the power amp and the voltage amp
?????
RF is alternating current at a frequency band called RF, 100KHz to GHz
When amplified and fed to an antenna, the electrical alternating current will be emitted as radio waves to space. That is the function of an antenna; it is a transducer from AC to EM waves.
Amplifiers consuming 20W and emitting 4W are wasting 16W as heat. Look at the pictured modules, have big heat sinks for the losses.

Radiofrequency oscillator ----> amplifier ----> antenna ----> electromagnetic waves emission
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
?????
RF is alternating current at a frequency band called RF, 100KHz to GHz
When amplified and fed to an antenna, the electrical alternating current will be emitted as radio waves to space. That is the function of an antenna; it is a transducer from AC to EM waves.
Amplifiers consuming 20W and emitting 4W are wasting 16W as heat. Look at the pictured modules, have big heat sinks for the losses.

Radiofrequency oscillator ----> amplifier ----> antenna ----> electromagnetic waves emission
thanks, sorry i am asking a more fundamental basic question, that is, if the power amp and a voltage amp of the same power consumption are used to transmit a RF EM radiation, surely there is some difference in the two types of amps since one uses higher voltage and the other is higher power? that is the difference in the amperes and voltage of the feed from the amplifiers to the antenna must have an effect right?
 

Externet

Joined Nov 29, 2005
1,654
If I understand you, a voltage amplifier outputting say 100V rms will mate better a 600 ohm impedance antenna than a power amplifier meant for a 50 ohm load. A low impedance antenna will prefer a power amplifier and not a voltage amplifier.
 

Delta Prime

Joined Nov 15, 2019
1,147
A low impedance antenna will prefer a power amplifier and not a voltage amplifier.
Now do you understand how he came to this conclusion?
thanks, sorry i am asking a more fundamental basic question
Do not be sorry and these are not fundamental basic questions
They are questions asked when the foundation of fundamental theory has been laid to build upon. I've noticed you speak in ideals perfect match this perfect match that. You got to get back to basics or it will just confuse you even more and that draws all the fun out of it. :confused:
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
Power is, of course, the voltage squared divided by the load resistance.
That distribution amp outputs 60dBmv, which is 1V into a 75 ohm load or 13mW of power, so that would be the input power into a 75 ohm matched antenna load.
It would broadcast, but not very far.
THANK YOU, precisely what i was meaning to find out, 13mW of power as opposed to a power amp that outputs 4W for the same 20W consumption, right now i can compare the two types of amps in my mind better
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
Power is, of course, the voltage squared divided by the load resistance.
That distribution amp outputs 60dBmv, which is 1V into a 75 ohm load or 13mW of power, so that would be the input power into a 75 ohm matched antenna load.
It would broadcast, but not very far.
thanks, but that 13mW of power for tx, is that with a certain input into the amp? does the input into the amp affect that 13mW of tx power? what would be the maximum that the amp can output tx with maximum input? even a guess from you is much appreciated. i just want to have this basic comparison strait
 

Thread Starter

genekuli

Joined Oct 21, 2018
103
Of course.
If there's no input, how would you expect an output?
Power output it proportional the level of the signal input.
So 13mW out is achieved with an input of 1V output divided by the 50dB of gain or 3.16mV input.
PLEASE tell me what would be the maximum that the amp can output tx (in watts) with maximum input (just before it would burn out)? even a guess from you is much appreciated. i just want to have this comparison basics understood. for eg. in a feedback loop what wattage would it likely reach for its output before damage? (i know this is an abstract question but it helps me to understand the voltage amp)
 
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Thread Starter

genekuli

Joined Oct 21, 2018
103
The maximum is the 13mW of power given in the spec.
If you try to output more, it will likely just saturate and distort the waveform.
It's unlikely that you could burn it out by doing that.
and if the distortion and saturation of the signal was not considered, then what would you estimate to be the highest wattage output tx possible before it would incur structural damage. i just need to know what is the highest possible wattage that could ever possibly come out of it. could it output 4W (or more) even if the signal is clipped/saturated and spans over a broad band range considering it has a 20W power consumption?
 
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BobTPH

Joined Jun 5, 2013
3,655
A maximally clipped waveform is a square wave, and it has twice the power of an unclipped sine wave but...
The extra power is in harmonics. It has no more power at the fundamental frequency than the maximum unclipped sine wave.

You are in the realm of what my wife calls magical thinking if you think you can get useful power out of that signal amplifier.

Bob
 
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