Single FET Class E Rig Idea

[ka1tdq]

I found the picture below on the web and I was wondering what modifications would need to be made to the schematic with a different FET and higher voltage.

I dumpster dove a few weeks ago and came across a nice UPS with a 120 volt transformer in it (I haven't opened it up yet, but I'm hoping there's a center tap). I could rip the rest of the guts out and rack mount it very easily.  Also, from another topic thread, the IXYS DE475-102N21A mosfet could be used (about $60).  This would make for a nice 100 watt-ish carrier rig.

So, specs for a 60 volts carrier at a reasonable current would look like...

Jon
KA1TDQ 

[steve_qix]

Question: do you want to modulate this transmitter or will this be FM (or CW) without modulation?

Since this is AM Fone, I'll assume (bad word!) that you want to modulate the RF amplifier.

Ok, since you're just starting out with class E transmitters, I would suggest the following:

OH, THERE IS NO SHUNT CAPACITOR SHOWN IN THE CIRCUIT!!!  THIS IS VERY BAD!!!!!!

1) Use a 120VDC supply for the total power supply voltage.  Run 45 volts of carrier DC

2) Use a *CHEAP* MOSFET such as the FQA11N90 so if you have trouble, you're not out a lot of money

3) Use 2 FQA11N90 MOSFETs in the RF amplifier for 100 watts of output.

4) Consider single-ended push pull with 2 MOSFETs for greatly reduced harmonic output, better efficiency and a better design in general

5) You need TransZorbs from drain to ground, and gate to ground.

6) You're in 1 land (or have a W1 call).  Where do you live?  There are a lot of folks around the New England area who are well versed in classe E and could offer some assistance/guidance/advise, show and tell, shack visits, etc.  if you build a transmitter and would like a 2nd set of eyes, or help tuning up for the first time.

I built a simple "Valiant replacement" (100 watt output) class E transmitter and it worked exceptionally well.  I still have it if you would like to look it over, and it should still be operational.

It's fun to build this stuff!!

Regards,  Steve

[steve_qix]

Just looked you up on QRZ - definitely not in New England !!!   

[KF1Z]

Just looked you up on QRZ - definitely not in New England !!!   

Nah...

He's about 475 mile South-south East of me.   

[ka1tdq]

Point taken for the push pull and cheaper fets. I'm in a store right now on my phone so will be brief. I'm almost finished with my current amp so I should be on the air in a few weeks.

I will start working on an E transmitter after I'm done and take a short rest. I do want to be in the E club. I checked the Arizona AM website and I dont see anyone here with one here yet. It would be fitting for a 1 lander to build the first one here.

Jon
KA1TDQ

[kb3ouk]

That looks like the schematic that Stu, AB2EZ has on his site of his little 35 watt single FET rig.

[ka1tdq]

I have anywhere from 2 to 15 watts drive available from my crystal controlled transmitter / IRF-510 linear. That could be used in a variation of Stu's circuit, only using both sides of the secondary input transformer to drive the 2 gates (push-pull) with a sine wave.

I'm guessing too that my UPS power supply doesn't have a center tap, so I would have to use the PWM board. The nice thing about this UPS is that it is ready for rack mounting already with most chassis connections already done.

If I build a class E deck, is there floating out there somewhere an already built PWM board that I could throw in?

Jon - cell
KA1TDQ

[WBear2GCR]

Jon,

Dunno where you live, but surely there must be an electronics recycler within driving distance?
That and scrap yards?

I think you need to frequent these places and make some friends...
...lots of *good* stuff gets thrown out. Buy at scrap prices.

No center tap? You want two identical transformers. So you want two scrapped units.

                         _-_-

Not sure you need a CT for a single rail supply though...

[ka1tdq]

Yes, the one supply 120 vdc is what I would be planning.

I just watched a short YouTube video on using the Arduino as a PWM good to about 8 KHz. I'm sure there are a million other ways to do it to get the analog voice signal to the digital gate driver.

Could you use a line level driver to that gate driver?

[steve_qix]

Have you checked out the PWM schematics at the class e web site?

PWM is not overly complex, but it's not trivial either.  A lot of things will make the audio sound like trash if they are done wrong, but by following a few rules - more or less to the letter - your modulator will sound really good.

For small transmitters such as this one (less than 100 watts), analog modulation might be the way to go.  It is simpler than PWM by quite a bit for low power.  There is a crossover point at about 200 watts, where above that value, PWM has the advantage, and is easier than analog for a variety of reasons.

[ka1tdq]

For simplicity, I am planning on a 2 fet rig so analog would be the way to go. If my big 120 volt transformer doesn't have a center tap to use as a carrier supply voltage, I couldadd in phase a smaller isolation transformer on top for voice peaks. Right? Use the common connection as the point half way in the electrolytic bank and as thecarrier supply.

I'm on my phone and hate to delete all that... that would give me 240 volts.

I could parallel another 120 volt transformer with a center tap and use that to regulate the carrier voltage halfway up the electrolytic bank.

[steve_qix]

You have choices.  If you go strictly class A, then only 1 voltage is needed.  Very inefficient and very simple.  You'll need a lot of heat sink for that one 

Next possibility - class H.  Need 2 supplies as you mentioned.  So, a 120V and a 60V supply (for example) would be required.  Much more efficient but more complex (not too bad, but harder than class A).  I have a number of reasonably straight-forward schematics that I can supply in this area.

Regards,  Steve

[KF1Z]

you might check out the "FAT5" website
http://www.gw8ljj.com/page7.htm

I actually built this a few years ago with the Class A modulator...
Steve probably remembers that.
I never ran it over 25 watts carrier though.


I still have a bunch of parts if you need them.. Likely FQA11N90, and the gate drivers etc...
transorbs..
whatever...  :-)


Maybe even a PWM board I had an extra set, but not
sure if I already passed that along to someone or not.

[ka1tdq]

I just glanced at that website and haven't had a chance to really absorb all the information yet, but it looks like tons of good information/ideas/options.

I opened up my dumpster-diven UPS and, gosh, no transformer.  What's up with that?  Anyway, I will tear it apart and use it as the chassis for the E rig.  I'm going to start gathering parts to see where this project morphs to.  After I finish the RF deck I will put out a call for help with the modulator.

I'm nearly finished with the dual 3-500 amp and the picture is below.  The cat won't be on top during operation.  It will be covered in screen mesh/Plexiglass.

Jon
KA1TDQ

[KF1Z]

I would suggest, for the modulator..

Don't "start small".

Build the full blown PWM, or even the Class-H.

Why?

RF decks are the quick easy part.

The modulator ,,, not so much. and can drive a small RF deck, or quite powerful.
( only very small differences between a PWM modulator/PS that will drive a 100w RF deck, compared to a 500w RF deck... mainly the transformer...)


'Knowing' that once you build a 50-100w RF deck, you will want go build a bigger one,
might just as well 

[DMOD]

You might also take a look at Carlos' website

http://www.lu8jb.com.ar/Amplitud%20Modulada%20.htm


Phil - AC0OB

[ka1tdq]

Good point. I guess I will start gathering parts to cookbook Steve's RF deck and PWM.

In the meantime, I just ordered my 2nd 3-500 for my amp and I should be finished with the wiring by next weekend. My Alinco is still on backorder though. It's awesome because it has outputs for I/Q signals for SDR.

I did a lighting test last night using just the equipment lights and the blue lights on the amp. It is just enough chilling/mood lighting for night chats.

Jon
KA1TDQ

[kb3ouk]

http://www.lu8jb.com.ar/PWM_460_40m_%282%29.htm
This one looks really simple, anyone have any ideas on how well it would work and what would need changed on the RF deck to get it to 75 meters?