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noyb72

Member
Apr 19, 2007
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I gave my introduction in another thread (and have been helped alot THANKS EVERYONE!!) but I still have a problem that I'm hoping someone here can resolve. I am new to linear design and construction and would like to get involved but I don't speak the language. I have figured out what a final is , sort of understand that swing and modulation are not the same, but really can't give a scientific explanation to the use of wound step up transformers and the like. I was wondering if anyone knew of a online resource that could help me out? I'm sure I could get more out of your helpfull responses if I could just understand the jargon but right now, I feel like I'm from another country.

Ron
 

Thanks Bob, I'll definatly keep that one. Can you tell me what the first step down transformer does other than change voltage, or why it's required if your power supply gives you what you need. ( I understand that if the plan had the transformer and called for 20VDC, then you would still need the transformer. I'm just trying to figure out exactly what the transformer does.)

Thanks
Ron
 
Ron,
A transformer has two functions, it can provide isolation between stages (no direct wiring/connection), and it can change voltages up or down. This is only with an alternating current though.
The isolation thingy is good because sometimes a direct connection can transfer 'stuff' that shouldn't be transfered.
The change in voltage is also handy. If the input voltage is 120 volts (fairly standard, sort of) and the circuit calls for 5 volts, then a transformer can certainly 'step' that down easily. One thing about transformers is that if the voltage goes down, then the current goes up and visa-versa. The wattage stays the same (less whatever losses are incurred in the transformer it's self, and there's always some). So, if the input is 120 volts at 3 amps, and the voltage is stepped down to 12 volts (to keep the numbers easy to work with), then the current available at the output end is increased by the same ratio as the voltage was reduced, 30 amps. If the voltage goes up by a factor of 10, then the current goes down by a factor of 10. That's a very simplistic explanation so don't think it's that 'simple' at times. And since it's only a very 'small' part of what a transformer can do, to really understand them requires a lot more typing than I'm willing to do (lazy).
The plain fact is that if you want to learn the 'buzz words', you got to understand what they mean, and that requires time and effort. There really isn't a simple way of doing it. It takes longer, but starting at the 'bottom' and working up is the easiest way. First you build the foundation, then you build the house. Good luck.
- 'Doc
 
Thanks doc.
I understand how transformers work, I just wasn't sure if they had another purpose in amplifiers. I always guessed they assisted in building RF, shows what I know. Great, then if all they are for is to adjust voltage, any voltage regulator should work. I think I'm starting to develope a design. At least I have an idea.

Thanks again

Ron
 
I think you should re-read W5LZ's post. What you saw, and what he said are two different things. The most pertinent part his post as it applies to an input or output transformer in an RF amplifier is the first half of the first line.

Mopar
 
They can also do impedance transformations which also comes in handy. They mainly are concerned with manipulating electrical or magnetic fields (coils, in general). Lots of uses, some sounding sort of contradictory.
- 'Doc
 
mopar2ya
Thanks, I caught that part, I may be making an ass out of myself but by "stuff" I thought he ment "interference," or "damn free redical RF" as my old Bull Nuke (who was a nuklear trained ET,) used to call it. If that's what "stuff" is, then my idea will still work.

Thanks again

Ron
 
The "stuff" is DC and AC. B+ and RF. And, in addition, impedance matching as he pointed out. Makes what might be a Z=4 device work in a Z=50 circuit.

Mopar
 
Mopar

Just read the thread about the amp in the Sony enclosure with the extra thick solder.

Your last post was right on and really cool. You sound like a level headed individual. and Mountaneer is a NUB junior officer it looks like. His piss and vinegar will cool down after getting hir rear chewed off by a master seargent or 5, and hey... it looks like the amp works.

Just wanted to pass the word.

Ron
 
oh, i hope i dont put my foot in my mouth with this one.LOL

im no amp tech or anything close, but maybe i can clarify something for noyb.

if its already been said, and im just too dumb to have understood it; i apologize.

my explanation is simple because thats how i understand it, not because i think its all you can handle.
noyb, those things inside RF amps with the wire wrapped through them are called "broadband transformers".
broadband because they work over a wide range of freqs.
transformers because they transform the impedance.

their job is to take the 50 ohms from your radio, and convert it down to about 3-5 ohms that your RF power transistors want to see.
then, after the signal is greatly amplified by the transistors, it is converted back up to the 50 ohms that your antenna wants to see.
the ouput transformer is physically larger because of the greater ammount of current involved. obviously.

thats what i think i know about them, please flame with compassion.LOL
loosecannon
 
loosecannon,
You shouldn't get 'flamed' over that! May not have used all the fancy 'buzz words', but basically describes what happens.
The problem with those broad banded impedance transformers is that they just aren't all that efficient. Convenient, sure! But only if you can't twiddle a knob or two. Being so 'broad banded' also means that they do very little, if any, 'filtering'. (A 'filtering' affect isn't limited only to filters.)
- 'Doc

now sit back and watch the pretty flames...
 
noyb72 said:
Mopar

Just read the thread about the amp in the Sony enclosure with the extra thick solder.

Your last post was right on and really cool. You sound like a level headed individual. and Mountaneer is a NUB junior officer it looks like. His piss and vinegar will cool down after getting hir rear chewed off by a master seargent or 5, and hey... it looks like the amp works.

Just wanted to pass the word.

Ron
Click to expand...

Thanks Ron. Good luck with your projects. There great deal of good folks here with a vast plethora of knowledge that they are willing to share. You and I just have to figure out which ones to follow. I am sure you will do well.

Mopar
 
WOW!!

I just sat down in the USS Seawolf (SSN 21)s radio room and got a crash course in AM radio design from two 20+ year radio chiefs including one who worked in the maintenance facility building and repairing amplifiers for about 6 years! (for those of you who don't know the Seawolf is a submarine.) Basically I was in guys like DTD, Davemade and AM powers' Valhalla. There was more power right next to me than I would ever need. Oh ya, it doesn't hurt that there transmitters typically work with a 5 Hert bandwidth.

So anyways, they showed me the amp that is closest to an amp apropriate for CB/SSB use and it was actually really close to what I've been thinking of. The actual design is of course classified but the points of intrest to me I can talk about and see what you think.

First, they both agreed that 100% modulation is it. There is no more and nothing else.

Second, about design, There transmitter is totally isolated from the amp/s, I mean completly, no exciter or nothing in the same rack. I have been thinking that would be a good way to go. Remove any final stage from the radio and run low impedence line to the amp (probably RCA,) then arrange the amp as a 1x2 only instead of the first transistor acting as an IPA, have it act as the exciter and intruduce the information to the amp in an enviroment completly isolated from the source in order to eliminate RF coming from the source. My power supply will deliver a very narrow band voltage at the best impedance for the amp section.

Oh ya, check this out. They say working on antennae SWR is sort of putting the cart before the horse. They use variable impedence power supplies to tune the amp exactly to the frequency they will transmit on, then they tune for SWR wich is much easier if the amp is set up corectly. I obviously don't have acess to that technology put if you think about it, it shouldn't be all that hard to build an electronically variable impedance matcher that is driven by either a frequency counter or the PLL to adjust for the channel your transmitting on. I won't try that for a while it just looks really really cool, and works great.

Third, some of there amps are just like the new car audio class D mono amps. They drive full power, no modulation. Then the information is introduced after the waveform is built. I have no idea how to do that but they say by not combining the power and information you eliminate distortion. There information amps are class A that are introduced to the class D power. I guess you can imagine how it sounds.

So, absolutly no wraps of wire through broadband transformers ( they don't think to highly of them,. ) I didn't get to see how they impedance match to the antennae, I guess I'll just have to wait untill Monday.

Anyways, thanks for all your help and if you have any comments on my isolation idea I'd love to hear it.

Thanks again

Ron
 

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