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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 10075 times)
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KD6VXI
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« Reply #75 on: May 31, 2018, 08:19:12 PM »

Sounds like your chicom supply is folding back.

--Shane
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« Reply #76 on: May 31, 2018, 08:31:02 PM »

Hi Jon...

Looks so much better....

The Power Supply regulation to the IXDDs cannot be understated.....it has to be perfect really....
And has to be checked at the Vcc pin of the IXDD not the output from the Power Supply...

So your testing hasn't finished yet .... sorry  Grin

You have 8 drivers and 8 FETs ..... all need checking .... you know waveforms etc: etc:

If one is loafing check it out.......

Also can you tune the output for maximum efficiency .... you have never talked or mentioned about that.....
Steve has a efficiency meter probably made up because some could not find the spot....
Its important too not because it gives more power at less current but cancels out the Miller capacitance that acts against the input waveform causing DC change etc:

Its worth the time to go over Steves WEB site to refresh things etc:

Well hopefully its all OK now...

Ohhh what is the efficiency now ?   are you getting 90% + appox .....


Wayne



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vk3alk
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« Reply #77 on: May 31, 2018, 08:50:57 PM »

I just looked at your gate waveforms again ... the one with the 13.8 volt SMPS....

The volts per division seems at 10 ..... this would mean that you have 20 volts on the gates....

A little high but probably OK being a pulsed wave  .....

12 volts seems to be the way to go.....

Anyway I'm sure your aware of that....


Wayne
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ka1tdq
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« Reply #78 on: May 31, 2018, 09:13:30 PM »

I did mess with the capacitance adjustment on one probe so that's not reading amplitude to spec.  That may be the phase you're looking at.

Anyway, I will do an efficiency measurement.  It's only as accurate as my analog Daiwa wattmeter reading.  Everything else I can measure with a multimeter and is accurate to several digits.  But, it'll be in the ballpark.

But, not tonight... the wife and I are attending a Russian dinner party.  Priorities.

Jon
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steve_qix
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« Reply #79 on: June 01, 2018, 08:42:56 PM »

The drain waveforms look good for a too lightly loaded RF amplifier.  You should have a little "back porch" on the drain waveform ideally.  This usually indicates the best efficiency as well.

In other words, run with the least amount of loading you can get away with before the efficiency starts to drop off.  The loading should "peak" the RF output at proper loading.

This will also help keep the drain waveforms lower.

Otherwise, everything looks quite good !!!

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ka1tdq
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« Reply #80 on: June 01, 2018, 09:24:33 PM »

Thanks!  Running the rig at 300 watts (my intended operational level), I'm getting 90% efficiency.  That's with the loading capacitor fully unmeshed.  I have a fixed amount of capacitance in there with a doorknob, and can't go any lower.

90% is good enough for me, and here's the waveform at that level.  Any more and it's just bragging rights.  Who cares about that?

Jon


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« Reply #81 on: June 01, 2018, 10:45:58 PM »

Hi Jon and Steve...

Yes everything does look quite respectable  Smiley

Been a large total post really ... 4 pages and many viewings.....


Wayne
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« Reply #82 on: June 01, 2018, 11:57:22 PM »

The main reason for the back porch (proper loading) is not just efficiency, but also control of the drain waveform.  A heavier loaded amplifier has a lower amplitude drain waveform, which is always a good thing  Wink
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« Reply #83 on: June 02, 2018, 01:16:19 AM »

Hi Steve..

Actually Jon's waveform is a little high at 200 volts with 48 volts carrier......

What I would do now since your still at this testing stage is make it 100%....or as close to it...
Replace those shunt capacitors and play around with the loading capacitor to obtain the efficiency spot etc:

One day you might miss tune or your antenna could fall off  Shocked and things happen fast at that power level....

Anyway its going better now...


Wayne

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ka1tdq
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« Reply #84 on: June 11, 2018, 01:01:13 AM »

I need more inspiration on what to do next.  I'm heading back to Vegas tomorrow for a few nights. 

Jon
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« Reply #85 on: June 18, 2018, 11:35:17 PM »

Ok, so efficiency does matter.  I'm getting distortion on voice peaks, so I think I need to get them there waveforms a little smaller. 

I was never able to judge where my loading capacitor was set since it didn't have a dial.  Wandering Walmart, I found a compass and tore it apart.  It'll do the job.

So now begins the painstakingly long process of tuning for maximum efficiency.  Nudge the loading capacitor, tune for the power output I want, calculate everything, then redo a bunch of times.  I did this for my single FET 40 meter transmitter.  It too was getting distorted voice peaks.  It wasn't tuned properly, so I did this process and it fixed it.  Now I can blast away into the mic.  How I got both of these transmitters working the first time is beyond me.  I'm learning much more now about operating class E rigs than I did the first time.  Beginner's luck.

Jon


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« Reply #86 on: June 19, 2018, 06:37:53 PM »

Hi Jon...

Is the audio OK now or do you still have a problem....
Finding the efficiency point is sort of similar to learning to drive a manual car....getting the clutch and accelerator working together nice and smoothly....
If you don't get it right its called kangaroo hopping over here....but that's another story...

When you figure it out you always seem to remember how its done... Grin

Not sure if not being at the efficiency point of your transmitter would effect the audio though  Undecided

Wayne

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ka1tdq
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« Reply #87 on: June 19, 2018, 09:38:02 PM »

Iíll find the efficiency sweet spot this weekend using my antenna and the 75 meter dummy load (the noontime sun). I just stopped at Sears and picked up an additional two digital multimeters for the process. Two will measure phase current and the third will measure drain supply. Itíll just make things go faster.

I also ordered an audio compressor to limit high excursions. My son gets excited and wants to scream into the microphone, so I need to minimize the shock to my FETs.

After all is said and done, Iíll do an audio check. Hopefully my kangaroo hopping is gone. We donít have any nifty saying over here like that, other than itís AFU.

Jon
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« Reply #88 on: June 19, 2018, 11:40:40 PM »

Hi Jon...

Our whole language is full of " nifty sayings "
We call it Australian Slang or Lingo ......come to think of it those words themselves would not be in the dictionary.... Shocked
As an example...I would never say " I am going to drive the car now "
I would say " I'm gunna hit the road now " .... make sense of that....
Don't know where it all started from but for me from birth.. Grin

Back to AM stuff I suppose.....

FETs live happily as long as they operate within their specifications...although they can tolerate excess current to a point....
If your little son there screams into the microphone your TX should still be happy unless something exceeds things....
My guess would be your modulator ........ and would be worth running some checks....
You could get your son to scream into the mic again and set your DSO to trigger at some high voltage point as an example.....just a bit of mucking around really....

The thing with PWMs is if you set your Mark Space ratio to 60:40 you can never exceed 150% modulation peaks...so now you can calculate things....
But like what Steve said about that efficiency point too reduces or keeps under control the Class E waveform.....if it goes too high and with peaky modulation applied could exceed the 900 volt rating of the 11N90.....
Just guessing thats all......hope what I said makes sense.. Smiley

Maybe purchasing Steves PWM kit would fix all this up .....


Wayne
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KB2WIG
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« Reply #89 on: June 20, 2018, 11:55:44 AM »



Wowsers..I didn't know that Ray Charles was an Aussie.


KLC
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Steve - K4HX
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« Reply #90 on: June 20, 2018, 09:02:04 PM »

What about "Stone the flaming' crows!"   Grin
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« Reply #91 on: June 20, 2018, 10:51:25 PM »

or "boiling the billy"
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« Reply #92 on: June 21, 2018, 12:22:22 AM »

Thanks for all the comments everyone...

Was a bit worried I said the wrong thing.. Smiley

Ray Charles did have a song " hit the road again" ... I'm sure...no it was "on the road again"


Wayne

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ka1tdq
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« Reply #93 on: June 21, 2018, 12:33:45 AM »

My analog meter board has convenient sampling points for the digital meters.  

I wish there were an easier way to calculate efficiency.  

Jon


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« Reply #94 on: June 21, 2018, 05:16:50 AM »

Hi Jon...

Hopefully your output circuit is the same as Steves....that is the large coil / 500pF tuning cap and the loading cap of 3000pF......
I have never used all the meters that you have installed trying to calculate etc:

What I did by experimenting a while ago now was to use a low power level like 100 Watts....

So tune up for power output of 100 watts  ...... the tuning cap was just off maximum capacitance and the loading cap was nearly fully meshed.....

Then I looked at the power meter reading say the 100 watts and the current meter.....
By decreasing the tuning 500pF capacitor and decreasing the loading capacitor was able to giggle around until I noticed that the power output remained at 100 watts but the current dropped...

I won't carry on any more it might confuse things more for you.....

What I was trying to achieve was same power out with less current..

Steve does have an efficiency meter but have never used it......

If you keep giggling ... for me anyway it just happened and never forgot  Grin

I am sure he will pop up at some stage and add some comments that might shred more light on things....

Give it a try.......if successful increase your power level and repeat again....


Wayne

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ka1tdq
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« Reply #95 on: June 24, 2018, 08:06:05 PM »

I bought an audio compressor and did a more accurate efficiency reading.  I'm getting 93.7% efficiency.  I don't have a digital wattmeter, but the Daiwa CN-801 is a pretty good meter.  I made my adjustments with the dial right on the 200 watt mark. 

I still had audio distortion and a little hum though.  Long story short, it was from the audio amp that I use to drive my Heising modulator.  Side A has distortion, but side B is crystal clear.  I'm guessing that something in the audio amp took a hit during one of my explosions.  Anyway, I'll just use side B and run everything very conservatively at 200 watts. 

Clean waveforms, crystal clear audio... 4 pages later and I'm calling this one good. 

As a parting note, this picture was taken at the wax museum in Vegas over the weekend.  It's a little cleaner than my other pictures, just like my audio!

Jon


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