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Author Topic: Question about stretchy 350W SiC deck  (Read 262 times)

Offline OgreVorbis

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Question about stretchy 350W SiC deck
« on: December 02, 2019, 0203 UTC »
Hey stretchy,

I am back at the shortwave transmitter again. I've had it working great below 4 MHz, but now I am back to trying to make it work higher again. I thought I had it at 87% efficiency, but I looked on a spectrum analyzer and it's terrible. When I run it next to the filter, then it's great, but only 76% efficiency @ 6.8 MHz. I am almost 100% sure it has to do with my broadband output match.

Anyway, I'm thinking about buying your SiC RF deck. The 350W one with 4 fets I believe. How much would that cost?

I know you use those T200-2s. What else do you have to match the output beside the transformer?
Yours is not wideband, right? you have to tune it to the band?
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Offline Stretchyman

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Re: Question about stretchy 350W SiC deck
« Reply #1 on: December 02, 2019, 0716 UTC »
Funny you should ask as have just sold one last week (just the generator), PM me for prices!

I no longer use the SiC FETs and have gone GaN as they're much easier to drive.

I'll have a root around as I'm sure I've got an older quad SiC somewhere, let me know what 16 freqs you want so I can program and test it for you. (6-7MHz ONLY)

The T200 tran is just 1:1 and sets the impedance of the O/P stage, more turns = less I and Higher Z.

You conjugate match whatever Z using series L and parallel C, very simple.

Mine's set for 5R as I'm using 48V 10A (4R8!), a higher Z would be much better (using a higher voltage of course) and efficiency would also improve because of less I2R loss.

I had tried different matching methods but the one I use is the simplest, most compact and most efficient design I tried.

It's class E so not wideband but it's kinda D/E and can get 1 MHZ B/W at 40m which is plenty, it's a single band design after all and have no intention of switching in seperate LPF's etc..

Changing band wise you'd have to use different material on the T200's if you went lower as you'd need more turns (no room left!) to keep the Z, maybe use thinner wire but the PTFE silver plated stuff I use is fairly thick and already getting warm!

Fine if you want to go higher (GaN ONLY) and have one working at 14MHz.

So thinking aloud here.............. I have a Quad SiC cased up for testing (can't check as I'm away from home, back Friday) somwhere I think.......................Will need a HS bolting to the case tis all...

Let me know.

Prob best to ask questions via PM

No Worries.

Get in touch.

Regards

Stretchy.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

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Offline OgreVorbis

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Re: Question about stretchy 350W SiC deck
« Reply #2 on: December 02, 2019, 0833 UTC »
OK, I'll send a PM...

I see, so the match is a lot like this, but with only one core for the transformer:



Interesting they say to omit the L for 40m.

Wonder if it would work at all if you just omit both and just use a 4:1 transformer. Probably not as well, but I'm kinda curious. I will try on mine and see what happens.

I ordered a T200A-2 core for my design. I'll try the match as you suggested and if I still have trouble, then I will order yours.
« Last Edit: December 02, 2019, 0838 UTC by OgreVorbis »
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Offline Stretchyman

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Re: Question about stretchy 350W SiC deck
« Reply #3 on: December 02, 2019, 0942 UTC »
I need a 3T L on a T157-2 and 1n5 to match to 50R.

YMMV!

You can use 2 toroids as per the 'older' design or use a single toroid which MUST HAVE opposed windings..

Str.
'It's better to give than receive' so why RX when you can TX!

                            Buy one from me, NOW!

Great discounts on ALL my transmitters if purchased via HFUnderground


                                              ;)