Question - RF TX Amplifiers with VARIABLE Output Control

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dapaq2

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Hello Group,

Most every rf tx amplifier that I have seen so far whether it be built into the radio itself or external usually allows the transmitter power to be adjusted, but is usually adjustable only by fixed settings of predefined power outputs, such as for example low=5watts, medium=25watts, high=50watts.

I'd like to know if there are any external RF power amplifiers that offer a VARIABLE (not fixed) TX power output throughout the entire range of the amplifier. When I say 'variable' I mean variable, like as in a potentiometer type of variable. For example if the amplifier is rated for 250 watts, the amplifier could be adjusted VARIABLY (like adjusting the volume control on your radio to turn the music loudness up or down) between 0 and 250 watts throughout the entire range.

I am curious if such a critter exists on the market...

Thank you,
Doug
 

RFI-EMI-GUY

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Linear amplifiers will react linearity over a range of input power levels. No reason a variable attenuator could not be used to adjust the input power.

Some amplifiers like Class C or D can have the output varied by adjusting the supply voltage. In some cases modulation is performed at the final stage.

There is a former of amplification for SSB called Envelope Removal and Restoration that amplifies the frequency component of a SSB carrier and uses the amplitude component to modulate the supply voltage.

So the short answer is yes.

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K7MH

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In general, I'd say there are very few amplifiers genuinely designed for the amateur radio service that do that. Right off, I can't think of any. Most control is done by how much drive is applied to the amplifier by the rig being used. At least HF amps anyway. Pretty much true for V/UHF amps as well.
Perhaps being more specific about just what kind of amp you are interested in may make a difference in the answers you get.

If there was a demand for it, you would find it. It is just some additional cost that has little use or purpose. I have had several amplifiers for HF and VHF over some 45 years and haven't ever felt a need for that designed into an amp.

Some HF rigs but not hardly all of them step down the power level It is very common with V/UHF rigs. Many have for years had variable adjustment. Lower cost and mobile HF rigs are often step style. More full featured and above entry level rigs are variable like the TS-180S in the earlier post.
 
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dapaq2

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This doesn't necessarily have to be for amateur use. I am curious if such an animal even exists. Would be excellent to be able to VARIABLY adjust the transmitter output without having only fixed settings like High/Med/Low or High/Low and each setting having predetermined wattage like 50/20/5 or 50/25...
 

RFI-EMI-GUY

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As mentioned before, a linear amplifier can be driven by a variable power level and that can be accomplished with a variable attenuator. Attenuators can be mechanically or electrically controlled.

The application for such an amplifier would determine the solution . What specifically are you are trying to accomplish?

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SpugEddy

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To answer your question very specifically, YES.
I had a 300 watt amplifier made for me about
10 years ago. It was for 11 meter band and had
a sideband relay. The output was totally adjustable
with a large pot. I could vary my output wattage from
about 25 watts to approx. 300 watts
 

dapaq2

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As mentioned before, a linear amplifier can be driven by a variable power level and that can be accomplished with a variable attenuator. Attenuators can be mechanically or electrically controlled.
Yep I understand what your said the first time, but not sure you understand what I am asking.

What specifically are you are trying to accomplish?
I understand what your saying, its not really about what i am trying to accomplish. Its more of if there are any manufacturers that currently make an amplifier that has a variable output, that i can purchase (if i wanted to) as I would not be looking to build myself. I got to thinking about this and am curious. Thats all...

Thanks much,
Doug
 

RFI-EMI-GUY

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To answer your question very specifically, YES.
I had a 300 watt amplifier made for me about
10 years ago. It was for 11 meter band and had
a sideband relay. The output was totally adjustable
with a large pot. I could vary my output wattage from
about 25 watts to approx. 300 watts
There you go!
 

RFI-EMI-GUY

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Yep I understand what your said the first time, but not sure you understand what I am asking.



I understand what your saying, its not really about what i am trying to accomplish. Its more of if there are any manufacturers that currently make an amplifier that has a variable output, that i can purchase (if i wanted to) as I would not be looking to build myself. I got to thinking about this and am curious. Thats all...

Thanks much,
Doug
This company makes all flavors. This big one is variable 20 dB 160 Watts to 16,000 Watts! Just turn the "go faster" control!

16,000 Watt CW, 10 kHz - 225 MHz RF Power Amplifier

https://www.arworld.us/post/16000A225.pdf
 

dapaq2

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Thank you for the url link. 16,000 watts is just a tad bit much for my needs! :) I see they do offer output values much lower, so if I was going to make a purchase of one of their amplifiers I would most likely choose something in the 100 to 1,000 watt range.

Anyone else have any additional input on this subject and know of any other manufacturers out there other than "AR WORLD" that offers variable output amplifiers?

Doug
 

nd5y

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Anyone else have any additional input on this subject and know of any other manufacturers out there other than "AR WORLD" that offers variable output amplifiers?
Not unless you are looking for expensive lab grade equipment for calibrating wattmeters.
 

dapaq2

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Guys this isn't about what I am looking for to actually use or purchase right now, there is no specific application or use, I am not looking to actually purchase anything, especially anytime soon. I am just looking to see what is out there. This whole subject on variable amplifiers is more about learning and knowing if there are any VARIABLE RF amplifiers out there and who manufacturers and sells them and what products they have to offer in their product line.

Doug
 

K7MH

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Clearly you are not that interested other than curiosity. It has been nearly a year since you started the thread and made your 2nd reply.
It is not that hard to look at the various amplifier makers and see what they have to offer. You MAY find something like that with some CB amplifiers, that wouldn't surprise me. I know of no genuine "amateur radio grade" (so to speak) commercially made HF RF amplifiers that have that function. There is no real need for it and if there were a demand for that kind of function the manufacturers would likely add it.

Since we (as in hams) all most usually have rigs with variable power output which controls the drive to an amplifier it just isn't a necessary function of the amplifier itself.

Those that do not have variable RF output control are often using mobile sized ham rigs or other budget minded ham rigs (or maybe a CB export model) that have set output levels that can be changed in a menu.

If you are looking outside of the manufacturers that make REAL ham radio amplifiers you may find something like that. Having been a ham for almost 50 years and owned several HF amplifiers I have never seen one offered with that function.
If it is going to be for CB, then I would ask about it in a more CB related forum where they would be more familiar with what is offered by manufacturers targeting that audience.
 
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zz0468

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Having been a ham for almost 50 years and owned several HF amplifiers I have never seen one offered with that function.
Tube type amplifiers have some control over power output. Reduced loading would result in reduced plate current, and reduced power out.

But that's certainly not just a "twist the knob" option.
 
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