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Zorch, again on my 8-FET 75 meter transmitter




 
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Author Topic: Zorch, again on my 8-FET 75 meter transmitter  (Read 63078 times)
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ka1tdq
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« Reply #50 on: May 23, 2018, 12:33:57 AM »

I did my first test at 13.8 vdc on the drain and here's the waveforms at around 50 watts carrier.  Side B (the blue trace) looks cleaner than before. 

Jon


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« Reply #51 on: May 23, 2018, 07:09:12 AM »

Jon,
Just a suggestion.  Plug a flash drive into the USB port and then perform a "save to USB" function, the button just left of the trigger level control. Set both traces to the same Zero point and vertical Gain for about 2/3 scale of the traces for best comparison.  Convert file from bitmap to .JPG and post it. Then we can have a critical look at it and make some suggestions.

73s  Nigel
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ka1tdq
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« Reply #52 on: May 23, 2018, 09:19:38 AM »

Thanks, will do!  I guess that would be better than a fuzzy, zoom-in picture. 

I'll be in Vegas for a few days so hopefully I'll get to it on Saturday. 


Jon
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ka1tdq
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« Reply #53 on: May 26, 2018, 12:37:30 PM »

Here's an image of the drains at 13.8 vdc and I had to modify the drive from the VFO to clean it up to look like this.  I think the amplitudes are actually the same height.  I'm using mismatched probes.  I took the channel 2 probe and moved it over to the other side, and it was in fact at the same amplitude.

The other picture is a snippet from my Vegas trip.

Jon


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« Reply #54 on: May 26, 2018, 02:50:03 PM »

don't want to say what I like more, your scope pic or the other one Smiley
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W2PFY
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« Reply #55 on: May 26, 2018, 05:05:19 PM »

https://www.pinterest.com/pin/553590979188484905/

Jon's wireless station Cheesy Cheesy Grin Grin
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Steve - K4HX
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« Reply #56 on: May 26, 2018, 08:33:34 PM »

I though what happened in Vegas stayed in Vegas?
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« Reply #57 on: May 26, 2018, 10:54:42 PM »

The vegas pic has been viewed a lot more than the scope pic Huh Roll Eyes
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ka1tdq
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« Reply #58 on: May 27, 2018, 01:58:13 AM »

I'm just posting the G rated stuff, like this one.  The other stuff stays in Vegas. 

I got new matching probes and the amplitudes are the same.  This shot was taken also at 13.8 vdc on the drains.  I'll do an atmospheric dummy load (75 meters at noon) test sometime soon at full power. 

Jon


* pic_39_1.jpg (99.69 KB, 800x480 - viewed 744 times.)

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VE3ELQ
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« Reply #59 on: May 27, 2018, 07:12:14 AM »

Scope pic quality looks great Jon, much better. Can you post another with the same zero point for better comparison between phases.  They should be identical in width and amplitude and exactly 180 degrees in phase which may take some minor tweaking to achieve. But they look fine to me and should be OK at higher power. Bring it up slowly and watch for abnormalities.  It could be you got some RF into the VFO buffer/driver chain when modulating at high peak levels.  That can cause blown FETs if both phases are driven "ON" simultaneously.

73s  Nigel
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ka1tdq
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« Reply #60 on: May 27, 2018, 08:33:44 AM »

Here are the two phases in comparison to each other.  During my explosions, I didn't have the DDS VFO set correctly at all.  It wasn't even in the ballpark.  After zooming in to look at the phases, I got it to where it is right now.  Maybe a little more tweaking is in order?

Jon


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« Reply #61 on: May 27, 2018, 10:09:17 AM »

Jon,  Looks good to me, should be OK for higher power testing. BUT I have no practical experience with that design so defer further comment to those who do.

73s  Nigel
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ka1tdq
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« Reply #62 on: May 27, 2018, 06:57:31 PM »

Here's 400 watts carrier into the dipole.  It looks a little noisy.  I'm not sure if that the proximity of the scope probes to the RF or the real drain waveforms. 

Jon


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« Reply #63 on: May 27, 2018, 07:25:02 PM »

May be probe ground wire inductance, Try to ground the probe VERY short
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« Reply #64 on: May 27, 2018, 11:33:41 PM »

Hi Jon...

Will throw in my 20 cents if you like...Steve is the best one...
Also noticed Bruce KZ1F is around...he has build many Class E TXs..
Have not seen any Gate Waveforms so will take it there OK and your phasing between modules are 180 degrees apart....
Looking at the waveforms I don't feel your at maximum efficiency as there is overlap...
This is important as Class E was developed because of the horrible FETs at the time to remove the Miller Capacitance which acts against the Gate drive etc:
I would reduce the Power Level to appox half and get all this right before applying operating power....
Again do all your testing at a lower power and also check your efficiency which should be 90% + when tuned correctly....
Remember test test test to get everything right..or it might go bang ...  Shocked
Is your main series output capacitor 500pF...as what Steve has on his WEB site...

I notice too that your still using door knobs for your shunts capacitors....don't think there quite suitable for the task .....

I will hang back for them to comment...


Wayne
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ka1tdq
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« Reply #65 on: May 28, 2018, 05:07:13 AM »

Hey Wayne!  Good to hear from you.

You're right, and I haven't looked at the gates under drive.  There could be an issue there.  The waveforms look absolutely clean at 150 watts.  Around 200 watts and above they start to get dirty.  Also, at 400 watts my home security system starts to freak out.  It's very loud and every few seconds will alarm while I'm transmitting.  I think that's due to the system being in close proximity to the antenna though.  We'll see...

I'm hoping that the drain bus isn't coupling to the drive bus at high power levels.  I put a ground bus in between to prevent that.  It worked the last time.  It's a similar concept as a grounded grid linear... no neutralization required!  Looking at both a drain and gate waveform at the same time should tell me as I increase power.

I will test more at lower power levels and see.

Jon
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« Reply #66 on: May 28, 2018, 06:45:00 PM »

Hi Jon...

Looks like Vegas is the place to go to clear the brain and have a cuppa  Tongue

OK Class E TX....

Could you post a photo of your Gate Waveforms without any voltage on the drains of the FETs....both phases one on ch 1 and the other ch 2...
You need to check the waveforms on all FETs...they all should be similar....
Have attached a photo of one of mine some time ago...

The DC should be appox 43% at the 10 volt mark to ground as per the picture...
The waveforms should be similar to mine...nice and clean..

Also the 12 volt supply to the IXDD drivers....what type of supply are you using .... analog / SMPS ?
They need to be bypassed with a say 10uF and a good quality .1uF right at the Vcc pins of the IXDDs......


Wayne


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vk3alk
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« Reply #67 on: May 28, 2018, 07:29:10 PM »

Also too check that the IXDD are working as a team  Smiley

Place your thumb hard down on each IC feeling the temperatures are all the same.....
None warmer or colder then the others....all the same....


Wayne
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ka1tdq
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« Reply #68 on: May 31, 2018, 09:57:36 AM »

Here's the gate drives (for two FETs) with no drain voltage applied.  The duty cycle looks acceptable, but the noise is present here as well.  I do have some commercial 80m low pass filters that I can throw inline with the DDS VFO output to the transmitter.  Maybe that'll clean it up a bit?

Jon


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« Reply #69 on: May 31, 2018, 01:00:02 PM »

Try again with a VERY short ground lead of the scope probe. May be resonance in the scope leads. I use fuse clips a lot directly soldered to GND where the ground of the scope probe fits in, so no ground lead at all.
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KB2WIG
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« Reply #70 on: May 31, 2018, 02:56:53 PM »



Here is a nice vid,    Oscilloscope Probe Ground lead length affects on signal quality

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

klc
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vk3alk
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« Reply #71 on: May 31, 2018, 06:31:35 PM »

Hi Jon...

The DC is different on both.....one quite low maybe just under 40%....

What type of power supply are you using to the IXDD...
Can you place a probe right at the input pin to them and take a photo and post...

There is often high frequency switching ripple a bit like a sawtooth waveform present..
If the ripple exceeds 1 volt PEP thats too high and has to be filtered better...

Steve uses LM2576 IC quite close to the IXDD....there good regulators....

For testing purposes a small motorbike or car battery will remove that ripple and give you a better idea as to what it should be....


Wayne
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ka1tdq
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« Reply #72 on: May 31, 2018, 07:06:02 PM »

I'm using a cheap, Chinese regulated 12 volt power supply that you get off of eBay.  I never thought, but that could be an issue. 

Here's another screenshot of the gates.  I put the 20MHz band limit on the scope and it cleaned up a little nicer.

Jon


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ka1tdq
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« Reply #73 on: May 31, 2018, 07:22:49 PM »

...and actually, here's the gates again using a 20 amp Radio Shack switching 13.8 vdc power supply.  It seems to look even better with this than the Chinese power supply. 

I did notice that the Chinese power supply dropped from 12 to 10 volts under load whereas my Radio Shack power supply is rock solid.

Jon


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ka1tdq
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« Reply #74 on: May 31, 2018, 07:53:27 PM »

...and here's the drains at 400 watts carrier.  Thanks Wayne!

Jon

https://www.youtube.com/watch?v=L09qnRfZY-k


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