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Analog modulating a 1000 watt carrier class E rig




 
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Author Topic: Analog modulating a 1000 watt carrier class E rig  (Read 8302 times)
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steve_qix
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« Reply #50 on: August 05, 2019, 08:19:39 AM »

Wow !

Well, bring it up slowly; monitor the drains for parasitics on modulation peaks and let us know  Cheesy
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ka1tdq
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« Reply #51 on: August 05, 2019, 05:12:47 PM »

Slowly is key with these things. It's like a moon shot. Everything has to go right for it to work.

I was finishing up the heat sink assembly and testing drive to all the gates when I discovered that gate drive would come and go. It turns out that the coax cables connecting my VFO to the heat sink assembly were intermittent.  That would've been bad under load!  I tried a different cable and everything was fine.

Jon


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« Reply #52 on: August 10, 2019, 10:30:52 AM »

Things are looking better now. The 90 degree SMA elbows were giving intermittent connection as well. I had just finger tightened them, but I don't want that weak spot in there so I got rid of them.

And I got new cables from HRO (they're in town).

Jon


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steve_qix
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« Reply #53 on: August 10, 2019, 10:52:08 PM »

The gate waveforms look pretty good.

Do you have duty cycle control?  The on time is a little long for standard MOSFETs, and there may be a slight amount of on-time overlap in the waveforms.  If you superimpose the two traces, one over the other, with the same zero-point, that will reveal any overlap.

It's definitely coming along !!
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ka1tdq
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« Reply #54 on: August 11, 2019, 08:55:57 AM »

I've remounted the heat sink assembly and just need to do the wiring between it and the rest of the transmitter.

Duty cycle is adjusted by changing the amplitude of the sine wave going to the master IXDD, which drives the slave IXDD's.  I'll kick it back a few notches and shoot for about 43% duty cycle. 

Jon


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« Reply #55 on: August 11, 2019, 03:02:43 PM »

Here's gate drive for each phase with the heat sink assembly mounted. I'm drawing about 8.3 amps at 12 vdc for total IXDD current (not under load; no drain current yet).

Jon


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« Reply #56 on: August 11, 2019, 06:33:05 PM »

It's all done!

I'll apply drain voltage next weekend when I have time.

Jon


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« Reply #57 on: August 11, 2019, 11:00:34 PM »

Before I go too far, this is what I've got on my initial try:

112 watts output for 11.3vdc on the drains at about 15.2 amps total drain current. Efficiency at this point is about 65% and the picture shows the drain waveforms for two of the drains (I'm using the top and bottom drain bus on the scope.

I have the drain power supply on a variac and can bring everything up slowly.

What are your suggestions?

Jon


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« Reply #58 on: August 12, 2019, 07:18:07 PM »

I have found that a drain voltage under about 20VDC does not yield good results.

At 20V things usually start to come together.  Also, the design impedance of the RF amplifier should be more or less used.  So if designed for 45V @ 26A (as an example), the impedance of 1.7 ohms should be reasonably maintained (within 30%) for best results.

For 20V, the total current would be around 11A.
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ka1tdq
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« Reply #59 on: August 12, 2019, 08:41:18 PM »

I haven't found the sweet spot yet, but I'm getting closer!

Here's the waveforms at 300 watts.  I'm running 28.6 Vdrain at around 13.6 amps. That puts me at 78% efficiency.  The current measurement isn't exact since I'm just measuring one drain current and multiplying it by 4.

The dummy load gets warm rather quickly too.

I had to lower the value of one of the fixed doorknob capacitors in the loading circuit because I was getting fully unmeshed.

Jon


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« Reply #60 on: August 13, 2019, 03:30:29 AM »

Here's 400 watts on the dipole and 89% efficiency.

I keep having to back power down as drain voltage isn't up all the way yet. I'm at 35.4 Vdc at around 12.6 amps.

The next step is to remove the variac.  I'll back drain current down for that and then readjust.

My goal was for 400 watts carrier.  I'm there... I just need to ease off this friggin' Ferrari!

Jon


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« Reply #61 on: August 13, 2019, 04:57:19 AM »

Well done Jon.... Grin

Should I mention the word PWM next........ Lips sealed

I have one of Steves Overload shutdown kits .... you can have if you want .....
No payment ... can just post to you  Smiley
Maybe some incentive for the next build....


Wayne
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ka1tdq
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« Reply #62 on: August 13, 2019, 07:52:23 AM »

Hey Wayne!

I do have PWM on the back of my mind. I came across this helium compressor enclosure some time ago that would fit everything nicely beneath the desk. If and when I decide to go that route, I'll just order the whole enchilada from Steve. I appreciate the offer, but I don't want to waste it either. Time will tell.

In the meantime...

https://www.youtube.com/watch?v=RvV3nn_de2k

Jon


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« Reply #63 on: August 14, 2019, 06:44:54 PM »

Wow, you don't need anything NEARLY as big as that box !

Here is a PWM modulator I built which will handle a 24 FET rig no problem.





The power transformer is external, and sits behind the transmitter.  I am NOT a fan of mounting anything heavy on a chassis.  Best to have it on its own.
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« Reply #64 on: August 14, 2019, 06:46:07 PM »

Oh, that is in a 7 inch high rack enclosure.  So, it is not very big at all, considering the power.
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« Reply #65 on: August 14, 2019, 07:02:03 PM »

I like the front panel appearance. Timeless and unique.
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« Reply #66 on: August 14, 2019, 07:42:56 PM »

45 volts at 250 amps eh?

For 24 fets?  Lol


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« Reply #67 on: August 16, 2019, 01:48:23 PM »

I was testing it on the air this morning when something went wrong with my drain power supply. I think the transformer might've blown. I'll need to unrack it and see.

For the testing I was able to do, the audio ranges from crystal clear to very distorted depending on tuning. I sample the audio coming off the transmitter and send it to my headphones.

The last step I had done was to pull the variac out of the input and plug the drain power supply directly into the wall. It worked for a few seconds and then something went wrong.

Jon
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« Reply #68 on: August 16, 2019, 08:45:09 PM »

I'm amazed it worked as well as it did. My rectifier PVC cap assembly had all loose hardware and the common ground stud was loose (all not good when drawing lots of current).

I'm going to completely redo the power supply and get rid of the clip leads and bungee cable holding the volt meter.

Jon


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« Reply #69 on: August 17, 2019, 08:14:17 AM »

I'd be surprised if the transformer is the issue.  Most likely a rectifier.

The rectifiers for this type of duty will get *HOT* and MUST be heat sunk.  Otherwise they will melt down internally.

I use various bridges ranging from 50A bridges to 200A bridges.  High voltage is not a requirement - in fact, lower voltage is better (less loss).

Heat sinking of the rectifiers is mandatory.  The heat sink I use with the 50A bridge rectifier for my 24 FET rig gets fairly warm after a long transmission.

I attached a picture.  You can see the rectifier heat sink near the bottom of the picture, near the power transformer and filter capacitors (48000uF total).

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« Reply #70 on: August 17, 2019, 06:39:17 PM »

Thanks for the tips!

Here's a block that DigiKey has in stock that is 60A at 600V:

https://www.digikey.com/product-detail/en/vishay-semiconductor-diodes-division/VS-UFH60BA65/VS-UFH60BA65GI-ND/9477549

I can bolt the connections to the rectifier with this model.

Also, I was using my current transformer in a voltage doubling circuit (half the current available). I'm going to upgrade to an Antek version that will use a full wave bridge.  

Jon


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« Reply #71 on: August 17, 2019, 08:44:01 PM »

Those will definitely work.

If you want to spend less money, I use these:

https://www.mouser.com/ProductDetail/Comchip-Technology/GBPC5006-G?qs=sGAEpiMZZMtQ8nqTKtFS%2FAgQizVVuOFlTMPKXRfKYJU%3D

and these:

https://www.mouser.com/ProductDetail/GeneSiC-Semiconductor/KBPC5006T?qs=sGAEpiMZZMtQ8nqTKtFS%2FKGlmTW84eZIGDm4lDGEeghFuiQYvB%252BPRA%3D%3D
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« Reply #72 on: August 25, 2019, 11:01:05 PM »

I don't have anything done on the inside yet, but this is how it'll look.

I'm just waiting on the heat sink to arrive and to order the transformer.

Jon


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« Reply #73 on: August 26, 2019, 02:04:26 PM »

Nice. the color's right! reminds me of a garage shop battery charger!
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« Reply #74 on: September 02, 2019, 03:49:26 PM »

Ouchy.

Drill bit broke and went into the palm of my hand. Iím ok though. Itís the simple power supplies that get you.

Jon


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