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Class E Transmitter Progress




 
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ka1tdq
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« Reply #25 on: August 23, 2021, 09:28:06 PM »

That seemed to be the answer in large part. The DC is no longer feeding the IXDD power bus but parasitics still creeped in until I adjusted the duty cycle down more. Applying 13.8 vdc on the drains yielded 12 watts output with class E looking-ish waveforms. Once I raise voltage by testing at 22 volts, things should look proper.

Before that though I'm going to bog down the IXDD inputs like I mentioned before. I want to see if things get less touchy for parasitics by doing so. I've never had an E transmitter as sensitive as this one, so I want to correct the issue before I continue on with voltage levels that will destroy devices.

I made a short video showing this initial testing:

https://www.youtube.com/watch?v=R5_Laqb4RcE 

Jon
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vk3alk
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« Reply #26 on: August 23, 2021, 10:39:01 PM »

Hi Jon...

If I remember correctly ... Steve mentioned the design didn't run all that well at low power levels and needed to be run at say 25-30 watts minimum for the low power tests etc:
Still find it hard to believe you have parasitics though  Shocked

Can you post a picture ?

Run it with slightly more power and test again....


Wayne

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ka1tdq
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« Reply #27 on: August 23, 2021, 10:48:41 PM »

Definitely. Yes, it doesnít run well at low power, as Iíve experienced with every transmitter. I just always do this first test to get settings within the ballpark. Iíll run it at 22 volts, probably this weekend.

The force is telling me that the thin wire from the SMA connectors isnít good.

Jon
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ka1tdq
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« Reply #28 on: September 01, 2021, 11:26:06 PM »

Pulse confirmed.

Here's the first full power test at 300 watts carrier with clean drain waveforms. This was the first tune up. I haven't tweaked duty cycles yet. Also, drain voltage is 53.4 volts at 300 watts, which is way too high.

I also found out that the overcurrent trip circuit works wonderfully! It was trip-tripping away all through the initial tuneup testing (shows you how careful I was this time). Anyway, FETs are safe.

Jon


* Drain 6-FET 300W.jpg (2275.73 KB, 4032x3024 - viewed 91 times.)

* Wattmeter.jpg (2428.04 KB, 4032x3024 - viewed 90 times.)
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WD5JKO
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« Reply #29 on: September 02, 2021, 10:21:05 AM »

drain voltage is 53.4 volts at 300 watts, which is way too high.

In Class E, the nominal peak drain voltage is 3.8 times the DC applied voltage. In your scope plots, if I squint, I see 170v peak, and that would be 170/53.4 or ~ 3.2X

Maybe some output adjustment would help.

Also what is the peak gate drive voltage?  One of the scope plots shows the drain saturation voltage a bit higher than the other. I'd verify the probe compensation first, and try to use the spring ground on the probe instead of a leaded ground clip.

Looks like fun Jon!

Jim
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ka1tdq
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« Reply #30 on: September 02, 2021, 10:47:34 AM »

Thanks!

I need to do a little more welding to it, but pretty soon it should be belching carrier on 3870!

Jon
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ka1tdq
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« Reply #31 on: September 07, 2021, 10:13:41 PM »

Ok, so check this out.

The drain voltage on my power supply is 54.5 volts at full power output of 300 watts. It's way too high for maximum efficiency. As I said before in the previous message that it's hovering around 80%. That's not a completely accurate figure because I'm currently using an analog wattmeter to make my RF power measurement. To make the final bragging rights RF power measurement, I'm going to rectify the RF voltage coming off the antenna jack and used a formula to accurately calculate the power down to the knats ass. This way, the efficiency calculation will be completely accurate as I'm using a digital voltmeter to take that measurement as well as drain currents as measured from a shunt.

So, now we get to the question as to how I'm going to reduce the drain voltage from 54 volts DC down to where it should be around 44 volts DC. That's quite a large step (an 18.5% reduction to be exact). There are many possibilities to do this. I won't drone on about the 100 ways to skin a cat, but rather expound upon the solution that I'm choosing to do this.

Here's my idea:

I'm going to run a toroidal transformer in series with the primary winding of the unregulated power transformer. I'm not going to place a load on the output of the this 'power wasting' transformer but rather just use this series winding as a reactive resistor to AC. As you all know, and I don't even need to say, the low voltage winding on a large current power transformer has negligible DC resistance. However, with AC signals and the iron ferrite in the core gives a reactive resistance which will absorb, if you will, some of the AC voltage and thusly reduce the applied voltage to the primary of the power transformer. The primary voltage still uses the same step-down ratio as before and now, with the primary voltage being lower, the secondary voltage will also be lower.

Voila!!

We are talking class E nirvana!

What do you guys think? Will this work? Has anybody tried anything like this before? Inquiring minds want to know!

Regards, I will wait for your reply...

Jon


* Power waster.jpg (2802.59 KB, 4032x3024 - viewed 108 times.)
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K8DI
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« Reply #32 on: September 08, 2021, 10:11:37 AM »

The idea of reducing the voltage with another transformer is valid/common but doesnít work how you described it. You need to hook the primary to the ac line and the secondary in series with the main transformer. Connected in one direction it will boost the voltage of the main transformers output, the other way it will reduce or buck it, hence the term boost/buck transformer. Thereís plenty of diagrams and links out there, they even sell packaged boost/buck transformers for this.

Ed
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M0VRF
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« Reply #33 on: September 08, 2021, 12:58:10 PM »

Why do you want to run a lower voltage?

Surely just run a higher Z to bring the current down?

Max efficiency is I2R, lots of volts and less I would be better, would it not?

JB.
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vk3alk
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« Reply #34 on: September 08, 2021, 11:39:55 PM »

Hi Jon....

Great to see your TX coming along  Smiley

Since your power supply outputs 55 volts I would probably leave it and run the Transmitter at that level.....
The 11N90s drain to source resistance is appox 1R which is rather high and Steve parallels many together to lower that down so to reduce loss causing heat etc: particularly when he runs his power levels  Wink
I think your using 3 FETs either side which combines to appox .3R generating appox 8 watts of heat at standing carrier and with modulation would increase at lot more.... using 45 volts that would increase to appox 12 watts...
All this adds up but I know you like using big heatsinks !!!
At 55 Volts there is still plenty of headroom available  Smiley Smiley

All this is just resistive loss let alone your efficiency % .....

You do what you reckons best though....


Wayne
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« Reply #35 on: September 09, 2021, 01:23:59 AM »

I agree with Ed. Bucking is an efficient, cheap, and good-regulation way to do what you want.
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ka1tdq
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« Reply #36 on: September 15, 2021, 01:11:59 PM »

Thanks for all the input. I still haven't gotten around to more tweaking yet as I've been busy. It'll go on the air as-is, but as Steve has said before, "Test, test, test!"

Quite honestly though, I'm tickled poop-less that my version of an over-current trip works wonderfully. I only wish I had made a schematic though. I've already forgotten most of it.

Anyway, more to come!

Jon

** I just did the math for adding the second transformer inline (both primary and secondaries), in phase obviously. With 120 volts on the primary and two 35 volt windings in series on the secondary, this will bring me nicely to 44 to 45 volts.

Wham-bam, thank you Ed.
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« Reply #37 on: October 06, 2021, 12:03:18 PM »

Hi Jon,

Hmmmmmmmmmmmm. .  Not knowing exactly what your circuit looks like, I can't be sure, but definitely you should be able to DC couple from the phase splitter to the transmitter.  In fact, this is a good thing.

When the input is not present, are you still getting output from the 2 phase converter ?

Do you have 300 ohm resistors in series with the MOSFET driver's input pins (one for each driver) ?

I assume the driver outputs are NOT paralleled.  If so, that will cause many issues.

Anyway, it sounds as if things are coming along, and that's great !!

Regards,  Steve
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ka1tdq
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« Reply #38 on: October 06, 2021, 01:06:47 PM »

Hey Steve,

I did reconfigure the drain power supply to use just the toroidal transformer only, and quite honestly I'm getting the cleanest class E waveforms I've ever made. I did change the IXDD driver inputs from being parallel to individual feeds via resistors and that may have helped. I'm still getting a carrier drain voltage of about 54 volts and I'll just need to live with that as I'm not using PWM. It's acceptable.

I don't quite understand how the DC coupling to the IXDD's was causing such a problem, but using DC blocking caps fixed the problem.

I had a problem coupling audio to the Heising circuit using an old Radio Shack PA amplifier. The circuit connected directly to the Heising capacitor. I did incorporate a time delay with a large parallel 200 ohm capacitor which allowed the cap to charge to drain voltage before connection to the PA amp. This protects the audio amp from power spikes and has worked well on previous designs.

However, I was not able to push audio onto the RF deck. Not having a schematic of the Radio Shack amp, I'm guessing that maybe it was a class A amp and wasn't able to deal with the voltage on the speaker outputs. Measuring AC voltage on the speaker outputs did show drive, but very little.

To fix this, I decided to go tried-and-true with a class D Crown PA amp. Additionally, I put a large power toroidal transformer in between the PA amp and the Heising circuit for further isolation. This has worked well on previous designs as well. The impedance ratio between the 8 ohm audio output and the modulation impedance was close to 1:1, so I used the 120 volt winding for the PA amp and the 100 volt winding for the modulator deck.

I did this a couple days ago and haven't really had a chance to test it yet at this point. I'll probably get to it this weekend.

Jon
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ka1tdq
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« Reply #39 on: October 13, 2021, 08:52:25 PM »

I know everyone is dying to know, (not!) but I figured out my modulation problem. The 12 volts from the sequencer isn't keying the PA amp cut-in relay. It's a simple wiring issue. I'll test more soon. Very busy, just trying to keep everyone a breast.

Jon
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ka1tdq
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« Reply #40 on: October 24, 2021, 12:44:26 AM »

I'm happy to report that I put it on the air for the first time tonight at 300 watts carrier. It sounds good! I was able to hear myself in the headphones from sampled RF audio.

I stayed under 100% modulation and decided to go a little higher when the overcurrent trip shut down the power supply. I also blew a Transzorb on one phase. No biggie, it's just $2 and everything was protected. I should've implemented this stuff on my E transmitters back in Phoenix.

Anyway, running the drains at 54 volts DC carrier leaves me a little less headroom on voice peaks. I apparently exceeded 540 volts. So next go around I'll run it at 200 watts carrier and maybe just run it at 100% modulation.

Jon
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