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Class E Transmitter Progress




 
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Author Topic: Class E Transmitter Progress  (Read 10531 times)
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ka1tdq
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« on: March 06, 2021, 10:40:22 AM »

Boy, have I been busy! It's been a while but progress does continue with the 8-FET transmitter. I decided to make a series of YouTube videos as I go along. It's not really a tutorial - Steve's website has all the detailed instructions, which I do cite. But, there are literally no YouTube videos out there to sort of chronicle building one of these beasts, so here's my stab.

Video 1: Intro to the project and talk about the phase splitter / duty cycle adjust board

https://youtu.be/j4F0KA-qlE8

Video 2: Demonstration of the phase splitter and talk about next video for crystal oscillator as signal source

https://www.youtube.com/watch?v=SpoEd438Xsg


Jon
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« Reply #1 on: March 06, 2021, 07:18:42 PM »

Nice work, Jon!  Looking forward to the upcoming videos.

73, Tony
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73, Tony K4QE
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« Reply #2 on: March 06, 2021, 07:30:36 PM »

Great idea Jon, to chronicle the build with videos, I enjoyed the videos, looking forward to following along with your build. Good job. Keep up the good work.
Donnie/AG5UM
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wb6kwt
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« Reply #3 on: March 07, 2021, 08:32:37 AM »

Thanks Jon, nicely done. Your camera person is doing a great job also.


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ka1tdq
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« Reply #4 on: March 07, 2021, 11:45:12 AM »

Thanks all! There aren't many builders doing class E stuff in America. I'm guessing 20 people. I enjoy this sort of thing and may be the only current project out there. Sit back and I'll try to keep you entertained.

Kuddos to my wife with camera duties.

Jon
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ka1tdq
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« Reply #5 on: March 07, 2021, 11:45:47 PM »

I am actually almost finished with the oscillator for the 3rd video. It's shown in two pictures attached to the first module. Come to find out, 7740 KHz crystals are common enough on eBay and are twice the frequency for 3870 KHz. I'm waiting on the remaining parts to arrive to finish.

The first picture shows the stand I built for the transmitter itself. I welded up a mount beneath the transmitter that'll hold 4 meters (IXDD bus voltage, drain voltage, Iphase1 and Iphase2). The cabinet on the left will hold the power supply and analog modulator. On top is my antenna tuner with all components mounted at 90 degrees from each other.

Jon


* IMG_0454.jpg (1325.94 KB, 2016x1512 - viewed 326 times.)

* IMG_0452.jpg (1079.79 KB, 2016x1512 - viewed 346 times.)

* IMG_0453.jpg (1029.04 KB, 2016x1512 - viewed 337 times.)
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ka1tdq
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« Reply #6 on: March 11, 2021, 10:31:39 PM »

I finished the oscillator plug-in module and it works correctly with the phase splitter. The first photo shows one of the output square waves along with the clock input. The second picture shows both output square waves.

I'll post video when my wife has a chance to record it.

Jon


* IMG_0462.jpg (1425.95 KB, 2016x1512 - viewed 315 times.)

* IMG_0463.jpg (1368.15 KB, 2016x1512 - viewed 314 times.)
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ka1tdq
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« Reply #7 on: March 13, 2021, 01:17:25 AM »

Here's the third video in the series:

https://youtu.be/iWRlX0hVlrw

Jon
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ka1tdq
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« Reply #8 on: April 03, 2021, 10:32:04 PM »

Here's where things stand now and the 4th video is coming. I've changed the design a little bit on the modulator shelf to also incorporate a negative peak alarm, a negative peak keep-alive circuit, and a pre-modulator overcurrent trip. I was trying to come up with ways to trip on overcurrent but they all weren't very practical. So, I ended up borrowing from Steve's a little bit, but simplifying it for my application. Sorry Steve, but you WAY over complicate things. Aside from the RF deck stuff. That's pretty much how it has to be.

Some parts from DigiKey for the overcurrent trip are on backorder and I want to finish that before I do the video.

Until then, keep busy, partake in some indulgences, and keep the BS below a 7.

Tootles!

Jon


* Modulator and Power Supply.jpg (1740.83 KB, 2015x1511 - viewed 300 times.)

* Overcurrent Trip.jpg (2209.04 KB, 4031x3023 - viewed 367 times.)
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ka1tdq
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« Reply #9 on: April 11, 2021, 10:11:30 AM »

Getting ready to assemble the analog modulator. Here's the layout. My finger is pointing to the simplified overcurrent trip circuit. The power supply is all done.

I'm going to try using epitaxial diodes in the negative peak limiter. They'll be stacked for easy mounting as shown with a TO-220 style resistor on top.

I'll shoot the video after my wife gets back from Vegas this week.

Jon


* IMG_0659.jpg (3105.41 KB, 4032x3024 - viewed 284 times.)
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ka1tdq
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« Reply #10 on: May 24, 2021, 10:56:13 PM »

Here's video #4: Power supply and analog modulator with overcurrent protection

https://youtu.be/MRetD5NT8no

Jon
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ka1tdq
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« Reply #11 on: May 25, 2021, 12:55:12 AM »

For those with attention deficit disorder, this video may be to your liking:

https://www.youtube.com/watch?v=tfZLS6WqKMU

Jon
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ka1tdq
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« Reply #12 on: July 10, 2021, 07:10:25 PM »

I nearly have the RF deck completed, and as usual the plans have changed. I'm now going to use 6 FETs in push-pull for 250 to 300 watts carrier. Last iteration I was going to use 4-FETs only and built the RF deck transformer holder to accommodate only 8 cores. With more power I need more cores (to be on the safe side with no heating), so I had to build the transformer upward rather than outward. Here's the result:

I made it into a 4x4 brick with still only using two cores stacked. I went all fancy and put 1/4" copper tubing in the centers of the cores for the FET windings. I think the brick adds a little style to the look rather than using 16 cores horizontally in a 4x4 arrangement.

Jon


* Xfmr front.jpg (432.1 KB, 1280x959 - viewed 196 times.)

* Xfmr back.jpg (494.02 KB, 1280x960 - viewed 152 times.)

* Deck.jpg (967.12 KB, 2016x1512 - viewed 195 times.)
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ka1tdq
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« Reply #13 on: July 10, 2021, 07:24:52 PM »

Here's everything so far. Modulator and power supply mounted in the cabinet with tuner on top. Raspberry Pi and touchscreen mounted on the side of the cabinet to be the efficiency calculator (programming half done). I learned (learning) to code Python.

Scope to keep track of drain waveforms and I'm also going to mount a couple blue LED strips 1/2" wide behind blue stained glass pieces on the RF deck to add some bling. Above the analog meters is a 20 segment LED bar graph tied to power output. Bling, bling.

Jon



* Transmitter.jpg (3486.32 KB, 4032x3024 - viewed 207 times.)
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vk3alk
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« Reply #14 on: July 10, 2021, 11:30:47 PM »

All looks like its going to work Jon  Smiley


Wayne
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ka1tdq
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« Reply #15 on: July 11, 2021, 12:49:01 AM »

Most importantly the blue LED strips. We just finished a Monet house party (Avon for the 2020's) with a houseful of young women. They're not interested in tank coils and gate capacitance. They like the bright shiny things.

My job for these parties is to be the caged bear in my shack. My wife parades the women up and says, 'This is my husbands office!' They go, ooh and ahh, and I make sure they have something to look at.

I don't verbalize it, but in my head I'm also saying ooh and ahh.  The blind leading the blind.

Jon
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ka1tdq
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« Reply #16 on: July 19, 2021, 11:42:24 PM »

Viva Las Vegas!

The LED power output bar graph below will modulate with blue LED's as well.  Now to actually finish the RF part of it (ha). Everything is mounted, I just need to do all the parts on the heat sink and run the copper on the deck.

Jon

* Vegas-E!.pdf (1571.16 KB - downloaded 117 times.)
* Vegas-E 2!.pdf (2237.53 KB - downloaded 81 times.)
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ka1tdq
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« Reply #17 on: July 26, 2021, 02:03:11 AM »

The heat sink assembly is complete. This rig is getting close to completion and I'll post a video of the testing.

After all that I still have to finish writing the code for the Raspberry Pi efficiency calculator. That'll come in handy for tweaking the last few ounces of efficiency out of this. I'm hoping for the best as I made this tighter than any previous transmitter I built.

Jon

** and yes, 680pf shunts, close enough.


* 6-FET RF Deck 75m.jpg (3518 KB, 4032x3024 - viewed 213 times.)
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ka1tdq
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« Reply #18 on: August 14, 2021, 09:14:08 PM »

Ok, I give, looking for advice. Steve, wake up!  Smiley

So, I'm testing this 6-FET rig and all is well except when I apply power to the drains (a low 13.8 volts in this case, low for initial testing) I hear sizzling bacon. There is RF output but the waveforms are crazy and I don't leave it on long due to the cooking sound.

Here's my setup, all home-brew just for a quick snapshot:


Crystal oscillator ---> Steve's phase splitter duty cycle adjust schematic with IXDD614's on output ---> Short 12 SMA coax going to RF deck ---> Traditional E RF deck


At the gates without drain voltage applied, I am getting the proper 40%-ish duty cycle, 180 degrees out of phase, all that jazz. I apply drain voltage and it sounds like parasitics, but here's what I noticed: With RF coming from the phase splitter/duty cycle adjust module I am getting nearly 12 volts on the IXDD supply rail on the RF deck. When I turn off the crystal oscillator, the voltage goes away.

So, RF from the phase splitter module is getting coupled onto the IXDD supply rail. I've isolated everything and the only possible path is through the 6 IXDD614's on the heat sink assembly itself.

I took a resistance check for each phase of the IXDD's input to the 12 volt supply rail and I'm getting about 7k in one direction and infinite in the other direction. Apparently 7k is enough resistance to couple RF energy in one direction to cause a problem.

I've never had this problem with other E decks and I don't have a spare IXDD 614 to experiment with. Any suggestions as to what would cause this?

Jon
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ka1tdq
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« Reply #19 on: August 14, 2021, 11:08:48 PM »

** Ok, my bad. I posted incorrect information. The problem of the induced voltage is still there without applied RF and with the oscillator off. I simply apply power to the phase splitter/duty cycle adjust board and the problem shows up.

I'm going to drive the RF deck with a completely isolated DDS VFO and see if the parasitic problem is there or not. It may be and I'll need to figure that out, but at least I'll be able to rule out this weird applied DC issue. One thing I did not do is put a 'grid snubbing resistor' inline with the to the IXDD inputs. We've talked about this extensively years ago but I didn't see the benefit and thought it was just a joke. However the way I've built this one, I could easily just add one to each phase without a problem to give it a try.

And actually, I used a morphed version of Steve's VFO. The duty cycle adjust portion is verbatim but I'm driving it with a JK flip-flop that is always enabled. I didn't incorporate a switched enable like his but rather switch DC on and off completely to the whole module during TX/RX transitions. Also, since the JK is always enabled, one of the Q outputs will always be 'high.' I'm not sure how this would all work out in the end with the logic on the duty cycle adjust portion. It probably wouldn't matter but to think through all that logic will make my brain blow up.

Not to mention I'm surrounded by mosquitoes.  Roll Eyes

Anyway, I've got it. I'll putter some more and get it.

Jon
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ka1tdq
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« Reply #20 on: August 15, 2021, 03:02:36 AM »

So, yeah... after thinking about the problem it is entirely a parasitic.

I've attached a photo showing the how I currently have the IXDD drive from a common bus fed from an SMA connector and how I will modify it. Steve's method of parasitic suppression allows the full drive voltage to be applied to the input of the IXDD. My 150 ohm resistors are too buried to dig out so I'll need to leave them in place. I'll get rid of the common bus and feed each input via its own 150 ohm resistor. To bring total impedance down to 50 ohms I'll need to add a 100 ohm resistor at the SMA connector.

This method will cut the applied drive voltage in half as it is seen at the input, but with about 14 volts peak it won't be a problem. In fact, keeping the original 150 ohm resistors in place and bogging down the system even more may help to bury the parasitic.

The other photo shows you how I have it currently. You can barely see the SMA connector and it has a small gauge wire coming from it and is attached to the common drive bus wire. That thin wire was probably the recipe for disaster.

I'll let you know how it works out.

Jon

* New driver inputs.pdf (2849.85 KB - downloaded 68 times.)
* SMA and common input bus.pdf (1520.55 KB - downloaded 84 times.)
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« Reply #21 on: August 15, 2021, 10:37:03 PM »

Hi Jon....

Ok on the parasitics and stuff.....
Have never had any parasitics before that I know of anyway .... maybe I'm just lucky  Smiley

Your output stage is made really well and looks great...
Couldn't see any RF bypass capacitors there on the IXDDs but sure that you have them soldered in...
With only 14 volts applied to the drains you would think all would be good at that power level....

Have attached a photo of how I run tests on things...
I have anything attached to a sheet of Aluminium acting as my chassis ground for want of a word...
If you look at the photo you will see my test oscillator and Steves Duty Cycle control board .....
Not sure how well you have everything bonded together or whether your relying on your coax for common grounding etc:
On your Duty Cycle adj board are those blue capacitors disk cermanics acting as low impedance to ground ?

Maybe I'm barking up the wrong tree but I am careful with my grounding....
I probably would not have those yellow wires as links too on the DC board and are not sure how good the gnd is on the underneath side etc:

Just some thoughts  Grin
If I was close by would drop over and have a look etc:

Wayne


* 40M Nigel testing.JPG (468.58 KB, 1600x1200 - viewed 127 times.)
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ka1tdq
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« Reply #22 on: August 15, 2021, 11:29:34 PM »

Hey Wayne,

Could also be grounding.

I have those same blue capacitors, 6 in total, on the 12 volt IXDD bus.

Iíve never had a parasitic issue either and Iíve built 4-ish E rigs.

Itís something simple. Iíll figure it out without killing it, I hope.

Jon
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ka1tdq
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« Reply #23 on: August 16, 2021, 11:17:03 AM »

The fact remains however that when I apply DC power to the phase splitter module, it also 'turns on' the rail voltage for all the IXDD614's (which is not good). Very likely that could be the cause of the parasitic since, as you stated, I did build my heat sink assembly very well.  Wink

Anyway, as a quick check, I'll do the DDS VFO drive thing to see if the problem goes away. If it does I could just put .47uF's in the line going between the phase splitter module and the coax leading to the heat sink assembly. I'd just need to readjust the duty cycle, probably.

But first, M-F 9 to 5, then meet my-main-man-Dennis in ye ole' Arizona, then test.

Jon
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« Reply #24 on: August 16, 2021, 06:18:41 PM »

Yes put capacitors in line as DC blocking .....  Smiley



Wayne
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