thebugger

modified 9 years ago

RF Power Amplifier

630

11:56:15

Okay, I think I made some improvements from the last few schematics I posted. The major difference is that the driver stage works in class A mode, which minimises the need for filtering between stages, and also increases the maximum output power, because less power is spent in transmitting harmonics, which are either way suppressed by the filter, and more power is spent on the fundamental. The other major advantage is that for a power output of 7.7W the input power is only 20mW. This means you can hook a simple cheap car FM transmitter to this amp and still make a pretty professional FM transmitter. One more advantage is the somewhat improved efficiency of the output stage. This is mainly due to the fact that the power amplifier spurs out a very clean signal, which needs minimal filtering and transfers almost the maximum power to the antenna. This improves the Vout/Vcc ratio and thus the efficiency. The amp seems pretty stable, no self-modulating is observable. 
P.S. If you ask me you can probably get by, with a single Pi-Filter, cause the output is clean either eat, but the more filtering the better. This way there are virtually no harmonic emmisions from the amp. 

Some of the specs are: 

- Input Power - 20mW 
- The drawn power for the driver stage is 2.4W 
- The drawn power of the Output Stage is 10.8W
- The Output Power is 7.7W 
- The overall harmonic suppresion is -57dB, and can actually be higher I don't know if I measured it reliably 

published 9 years ago

hurz

9 years ago

So Mr RF, lets start with the basics of RF engoneering and check the input power calculation of 20mW. How have you RF engineer made this 20mW caluclation? BTW its less than 20mW.

thebugger

9 years ago

Yes it's 14.5mW. I change thing over the design constantly and the first thing i usually measure is the input/output ratio. The value must've changed with one of the modifications

Robert_Kidd

9 years ago

So, Mr Offensive plays the same game again!

hurz

9 years ago

No @buggzy, its even much less then 15mW. And “Mr bullshit comments“ walking around without having circuit references. As long you are not interessted in electronic, better shutup.

thebugger

9 years ago

It's around 15mW.

Robert_Kidd

9 years ago

Ah, the cap fits!

hurz

9 years ago

Its 8mW

thebugger

9 years ago

How did you get 8mW? I use the replacement method. Use a second AC source but with a purely resistive load. The best approximate in drawn current was with a load of 20ohms. At 20ohms the power delivered by a 750mV is ~15mW

GingerKing

9 years ago

I get about 14mW for the input. P = Irms*Vrms = (0.037A)*(0.750V)/2 = ~13.9mW assuming a perfect sine wave and all. Thoughts?

hurz

9 years ago

What you guys calculated is the complex power. Just put the input voltage and current on scooe and see the phase shift between both things. You have to use the active power 8mW to compare it with the active output power at 50Ohm which buggzy calculated correct. Just basic knowledge for RF amplifier freaks.

GingerKing

9 years ago

Not trying to hate or anything but, since when did input power rely on the output power? The input is supplying ~14mW to a circuit which happens to be outputting ~7.7W regardless of the phase change. Is this different for RF amplifiers for some reason? I dont understand.

GingerKing

9 years ago

Im book marking this to better understand power equations of RF amplifiers. Please explain if you're not too busy hurz.

thebugger

9 years ago

Can you please elaborate. Is that like measuring reactive power?

hurz

9 years ago

Yes, but give me some time to prepare a good example.

zorgrian

9 years ago

This is a great basis for a film script. Educating his excellency. The film opens with a scene of a spoilt little boy shouting at his teachers, who fear for their lives as they attempt to correct his majesty. As the young byzantine king learns more he uses his acquired knowledge to attack the teachers. Everyone tries to help the young king but further unjust castigation is thrown out upon everyone...

zorgrian

9 years ago

Blind recital and unquestioning repetitive utterance of irrelevant facts are not helpful for anyone. The same can be said for the dogma of refusal to think.

Robert_Kidd

9 years ago

I'd invest in the making of the film. How astute you are!

zorgrian

9 years ago

I suggest we film it on location. We should choose a nice castle in say.... Bulgaria. No need for a casting agency as we can easily do the parts ourselves or use the BBC before they sell the rest of it off to Reuters. Alternatively, the film could be made as a cartoon?

thebugger

9 years ago

Who the fuck asked you for your opinion. A minute wasted of my life reading your stupid scenarios. When you've got nothing to say, just don't ;)

zorgrian

9 years ago

Nasty!!!

Robert_Kidd

9 years ago

I think there was a certain amount of humour intended in zorgian's comments. Perhaps this doesn't carry across as well as it might have.

hurz

9 years ago

@zorgrian, i told you some time ago that i like to help young “engineers“. And im old enough to know they are rarely grateful for this in the moment they know enough. But this is how mankind is, and i dont care. Important for me is to get a little satisfaction while doing knowledge transfer. And im still learning as well. So both sides profit.

thebugger

9 years ago

Favorite Einstein quote. ,,The more I learn, the less I know''

Robert_Kidd

9 years ago

Oh my, @herz you are such a hero! But how does that philosophy of yours allow you, as you frequently do, to put down so many people in the most unpleasant and nasty way? Don't answer - I think everyone knows already.

thebugger

9 years ago

Word!

hurz

9 years ago

Robbi, start with electrical engineering soon. Getting older and wise might help you to understand. But at least start something clever.

Robert_Kidd

9 years ago

Again you judge when you know nothing about me. Tiresome!

2ctiby

9 years ago

Robert sums up the attitude of Hurz. Hurz continues to tell others to stick to electronics if they make personal comments, but he spues out lies and insults permanently. Anyone who makes interesting electronic efforts is put down by him in a disparaging way in an effort to deter them from continuing. There are many of us who continually have to suffer his unkindness and unfairness and the EC community needs to be aware of this when viewing his 'help'. If you dare to question any of his points you will face being insulted by him. He has no understaning of academic reason and debate. Bear in mind that he is a self taught hobbyist with no qualifications in electronics. His knowledge is good in some areas but he intimidates and deceives in his delusional belief that he is the ultimate in all areas.

Robert_Kidd

9 years ago

@thebugger, I'm sorry this thread has gone in this direction. Hopefully quite soon @hurz will provide the 'example' he mentioned a while back.

2ctiby

9 years ago

@thebuggar, I'm sorry too. You have had to take permanent insults from Hurz but many of us are backing you. Hurz never changes in his bad attitude unfortunately. We are, like Robert says, waiting on that earlier promised example too. Nothing wrong with being a hobbyist like myself, but Hurz has a delusional idea of acting like a qualified authority.

hurz

9 years ago

Im am what?? But you are waiting for me? LOL

Robert_Kidd

9 years ago

I'm trying to persuade you to get back to the point of @thebugger's original topic, please! I am not especially interested in it but do have a passing interest.

hurz

9 years ago

2cent and robbi-kiddi, instead of being a paire of trolls you should noticed that a real engineer and/or interessed EC user in electronic does sit down try to understand what I was talking about. BTW, buggzy and maybe others already did. Sure you trolls haven't noticed, cuz you anyway have absolut no idea what I was talking about "active power". But others with some electronic intusiasmus do feel I'm right or wrong and try to verify that (check buggzys latest circuit). But you both trolls are so "sorry" LOL. I m sorry that you are here on EC and allowed to post comments. But Im just sorry (only a little) and ignore that. Keep on trolling!

Robert_Kidd

9 years ago

Oh we understand perfectly well what you say yet you presume we do not because @herzer always knows better than anyone. Meanwhile we await the example you promise. What's the problem - can't you deliver the 'good example' to back up your argument?

hurz

9 years ago

Right, troll.

Robert_Kidd

9 years ago

You have a troll fixation.

Robert_Kidd

9 years ago

Have you considered therapy?

hurz

9 years ago

Yes

Robert_Kidd

9 years ago

Ha, you DO have a sense of humour!

thebugger

9 years ago

Actually @hurz you're trolling. We have no reason to troll. We post our circuits and everything and you start trolling on them. And when you're wrong, god forbid, you just vanish from the comments, never to be found again on the same schematic. And yes we know about active power and reactive power, but most of us have worked on low frequency schematics, and I for instance never on motors on such, so we've had no reason to measure the reactive power of something

hurz

9 years ago

Power is power. And you do measure 20mWatt power, right? Or do you measure 20 trolls?

thebugger

9 years ago

The difference is so miniscule that only you would be grumpy enough to grasp on it. Whether it's 14mW or 8mW no one really cares you know? And trust me when I speak for all of us, there's not a greater troll than you here in EC! And P.S. When someone else is wrong you're always very eager to step in and bestow your judgement (which no one asked for), but when you're wrong you just mysteriously vanish from the comments, never to be seen again on that post again.

thebugger

9 years ago

Actually I stand corrected, there's this other guy that makes @Hurz look like morning sunshine when it comes to irritability and trolling, @Zogrian or zorigian or something, he's just extremely captious and also extremely unhelpful. At least with hurz with all the irritability comes a lot of knowledge too, that other guy's all about poking in your eye, and nothing else significant.

hurz

9 years ago

Your description says 20mW and not 14mW. Then follow the comments, its getting lower and lower. The lowest so far is 8mW. 20/8 -'To be not to pedantic its the factor of 2. And you got the idea to mention the input power AND output power. So what is closer to think about a ratio you like to demonstrate. And why not, thats ok to do? Why are you so pist off? You've been not aware of active and reactive difference power? No problem for a simulator, but maybe in reality if you want to build real RF amplifier in the near future. Keep up learning.

thebugger

9 years ago

Yes I'm building a real FM transmitter right now and a difference of 6mW will make absolutely no difference at all. As I said I rarely correct stuff in the description, although I work on the circuits constantly. P.S. I'm not pissed at you. You're an ok guy actually, once you get used to it, but that guy Zorigian is really a pain in the bum

hurz

9 years ago

This is fine. But the power matters a lot! And as always I look pedantic. But you mentioned it yourself sometimes in a different circuit (keyword oscillator pulling) but you probably forgot it cuz you just took that info from google and havn't had that as real expirience? You are really stubborn again and in other thread I just gaveup. Here my last words for this thread. Input power for the power amp stage matters a lot, cuz the connected oscillator stage (which is here naive ideal) must match perfectly to it!!!! Ignoring a factor of 2 in power will endup in a bad design. You went to far in an area you have no knowledge and this is what zogrian makes how he is.... So do get some expirience in making what you simulate, and please dont be a fraud.

thebugger

9 years ago

14mW or 8mW doesn't matter at all. Most oscillators can supply 10 times that power. They're usually kept low in power, but not too low, certainly more than 10mW

thebugger

9 years ago

Just check my veronica FM transmitter example

hurz

9 years ago

Yes, and Im afraid you messed up the well tuned impedance machting interface with your additional stage.

thebugger

9 years ago

Yeah this is a very early prototype. This is a more refurbished version http://everycircuit.com/circuit/5212662341828608

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