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40 meters - 100 watts




 
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Author Topic: 40 meters - 100 watts  (Read 4542 times)
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ka1tdq
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« on: July 04, 2018, 10:30:20 PM »

I'm starting another class E transmitter.  Here's the picture of progress so far. 

It'll be two FETs in parallel for 100 watts carrier on 40 meters.  I decided to go with an ATC capacitor for the shunt this time.  It makes things more compact.

Jon


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ka1tdq
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« Reply #1 on: July 06, 2018, 11:03:22 PM »

I need to remove the assembly to mount the mica insulators (I can never find those when I need 'em), but this is how the heatsink will look.

Jon


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ka1tdq
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« Reply #2 on: July 07, 2018, 06:55:30 AM »

The heat sink assembly is now all done.  The rest of the work is just brute force chassis assembly. 

Jon


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steve_qix
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« Reply #3 on: July 13, 2018, 02:21:16 PM »

You may be better using one driver per MOSFET and not putting the gates in parallel.  I have had much success with such a design.

Watch out for parasitics.  Resistors in series with the driver inputs will help.

Keep us informed as to your progress!
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ka1tdq
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« Reply #4 on: July 17, 2018, 01:21:45 AM »

I'm waiting on a coworker to finish painting the enclosure. He's much better at painting than I am, with my skills being just a step above graffiti.  He also did the black rack/cabinet in my shack and did an awesome job.  

Each FET does have its own driver. The only resistors I'm using are pull-downs for the driver bus and the wave shaper. The entire FET assembly is pretty tight, in fact the most compact I've ever built, so I'm keeping my fingers crossed that it'll cut the mustard for 40 meters.


Jon
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ka1tdq
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« Reply #5 on: October 13, 2018, 09:13:17 AM »

Maybe waiting can be a good thing. I found a nice piece of stainless steel at the junkyard that will fit all the parts nicely. It'll keep with my current theme of open frame construction.

Jon


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ka1tdq
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« Reply #6 on: October 13, 2018, 01:30:32 PM »

Ok, it's done. Now I just need to test it.

Jon


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« Reply #7 on: October 14, 2018, 04:28:37 PM »

Class E experimentation would be impossible if not for a wide selection of Russian doorknobs. I had to add a second 47pf cap to the series variable and 680pf to the loading cap.

I am getting a class E waveform up to 100 watts. At first I tuned the rig with a 13.8 volts on the drain to find where things should be. I then applied the 48-ish volts to get to the 100 watts. The only problem is that power drifts down as I'm keyed. I'm thinking that my voltage is sagging from my home-brew power supply. I pulled the transformer from an old something at Goodwill. I haven't taken voltage measurements yet because I don't want to blow anything up. I'm going to let things settle and test again when I'm rested.

But, it will put out RF and the scope seems happy.

Jon


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« Reply #8 on: October 15, 2018, 05:32:31 AM »

Hi Jon..

It looks impressive.....

Have never built a single ended Class E but there seems a lot of capacitance there for the loading and series capacitors....
What is the turns ratio on the transformer...
Also do those 2 FB1020-43 cores get hot or very hot ?

Can you post the input gate waveforms .... one without Drain and one with a drain voltage of say 14 volts just to see if all thats OK..

Also too... what is the efficiency ?


Wayne
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ka1tdq
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« Reply #9 on: October 15, 2018, 06:20:26 AM »

The two cores are used just as an RF choke. I'm not sure how many turns I used, but a lot and as many as I could fit. I don't know if it gets hot. I'll have to check the next time I test.

As things sit right now, I have 1600pf on the loading cap and around 110pf on the tuning cap. I aimed at 2.5uh on the coil, but I don't have a meter to measure it. I think that's where I found the sweet stop. There is a possibility that my son played spin the caps since then, and if that's the case then these numbers don't mean anything.

The drain waveforms have a slightly larger duty cycle than I would like, but I had to keep it higher so that they don't freak out under load. I'll post waveforms soon with Vdrain at 14 volts.

Jon
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« Reply #10 on: October 15, 2018, 07:03:30 AM »

Ohhh I see what your doing now...

Will wait for the gate waveforms....
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ka1tdq
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« Reply #11 on: October 15, 2018, 10:13:38 PM »

With 13.8vdc on the drains, I'm getting 13.5 watts output using 1.29 amps. Efficiency is 76%.

I'm having difficulty at the moment transferring scope screenshots to my Mac, so here's a picture.

Jon


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« Reply #12 on: October 15, 2018, 11:33:16 PM »

Its all looks quite good....and in the ball park 76% is very close.....
If you can get 85% I would be happy with that.....

The Gate waveforms are good enough and the Class E waveforms seems fine as well....
What I'm looking at is the Class E waveform is going to 0 volts which indicates that the FET is fully turned ON....

So would put a tick on the driver circuit.....

Your loosing about .6 Watt across the 2 11N90's which brings the efficiency up to appox 80% so you need another appox 6% from somewhere...

What voltage does the Class E waveform goto ?


Wayne





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ka1tdq
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« Reply #13 on: October 16, 2018, 12:54:40 AM »

I didnít tune for maximum efficiency. I just tuned everything really quick for the best waveforms according to my eye. We went out for the evening, but I wanted to post a picture.

This weekend Iíll really dive into it, find a max efficiency point and transfer some real scope pictures (not phone pics).

I also need to try my 48 volt power supply again. If Iím still getting a voltage sag, I can rebuild the power supply with a much heftier transformer that I have on hand.

Jon
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« Reply #14 on: October 16, 2018, 01:28:31 AM »

Thats Ok John just take your time.....

Be good if you could step up the voltage a little more gentle like..... Shocked

Also at low voltage setting you could replace that RFC with a coil appox 10T at 1" in diag over about 1 to 1.5" and see how that goes....
Use 1.5mm to 2mm to make it rigid.....


Wayne
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ka1tdq
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« Reply #15 on: December 13, 2018, 04:16:26 AM »

And alakazaammm! It's now a 75 meter rig. I had another go at it, but it's really touchy at 40 meters. So you know the old saying, "When in doubt... go lower in frequency."

I added some series capacitance and made the coil a little bigg-ah!  You know, all that crap...

I'll test and tweak it during normal business hours. Closing the door on this one will allow me to focus entirely on my Class D build.

Jon

** And Fluffy decided that he wanted to show off.


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« Reply #16 on: December 13, 2018, 09:14:45 PM »

I literally turned it on and the waveform was there. The picture shows 13.8vdc on the drains and I'm getting 5 watts output. I haven't bothered tweaking for maximum efficiency yet, or trying a larger voltage on the drains. I just wanted to see how it behaved on 75 meters, and it's very smooth. It's not touchy and the waveform varies slowly with changes to the caps.

This weekend I'll do the full drain voltage and vary the gate duty cycle for maximum efficiency and see what the real numbers turn out to be.

Jon


* 2 FET 75m 100 watt.jpg (3676.92 KB, 4032x3024 - viewed 147 times.)
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« Reply #17 on: December 15, 2018, 10:53:11 AM »

Hereís the waveform at 100 watts. I just did a quick measurement looking at just the analog meters, and efficiency is at 90%. To squeeze that last few percent out I will need to take digital measurements, but Iím in the ballpark.

Jon


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« Reply #18 on: December 16, 2018, 08:51:15 PM »

The new drain power supply works with both the 2-FET and 8-FET rigs. I'm using Heising modulation, so the voltage sag brings drain voltage down nicely to 48vdc at 300 watts with the big rig, but goes up to 57vdc on the 2-FET version at 100 watts. That's too high. If I want to use the same modulator for the smaller rig, I'll need to put a variac inline.

I haven't tinkered too much with the 2-FET rig, but my efficiency number was too high before using ballpark readings with analog meters. Digitally meters show 80% efficiency. I haven't tried to tweak yet, but it's definitely not there yet. The waveform is clean though, so it will get there eventually.

Jon
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