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40 meter push pull RF deck




 
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Author Topic: 40 meter push pull RF deck  (Read 11390 times)
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WD5JKO
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« Reply #25 on: May 15, 2016, 09:37:36 AM »


   Jon,

   Things are looking better on 75m for sure.

That drain waveform is still quite high when the gate drive comes on. I believe the class E guys call this "back porching". The solution is to optimize the output tuning network and/or reduce the pulse width of the gate drive.

Your MHS-5200 is capable of variable PW with the square wave output at these frequencies (< 6 Mhz?). You can also apply a DC offset to make the pulse go from 0 to +5v with the DC offset, and amplitude controls. I also believe the rear terminals have a TTL output as well. If you are using sine wave output still, consider the reduced duty cycle DC offset square wave.

Is that a different scope your using? A 2235 is quite FB.

Off topic, with the MHS-5200A VFO, how do you key it such that it does not block your receiver when not transmitting?

73,
Jim
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ka1tdq
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« Reply #26 on: May 15, 2016, 10:51:10 AM »

Yes, I am using a 2235 for my scope.  I got it at a thrift store for $17.

I reduced the duty cycle down to 35% from 40%.  I also backed off on the loading cap to reduce the back porching.  When I do that, I get a cleaner class E waveform (shown in the picture at 48 volts drain), but my peaks go way up and the efficiency goes to pot (50% ballpark).  

I'm using a 150pf doorknob as a shunt capacitor.  Should I up that value?  Would that help efficiency?  

I've tried changing the value of the inductor (by spreading it out and mooshing it together), as well as the series variable cap, but everything seems to come back and work happier right where they are (inductor at 2.5uh and series capacitor 1/2 mesh).  

In summary, my problem is that I get maximum efficiency when I'm almost unmeshed on the loading capacitor (while back porching), and not where it's properly tuned for class E.

I should also mention that I'm using 50v/div for the drain waveform (on top).  It looks to be 200 volt peaks.

Jon


* IMG_0217.JPG (1870.05 KB, 4032x3024 - viewed 135 times.)
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KD6VXI
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« Reply #27 on: May 15, 2016, 11:31:40 AM »

Jon,

AB2EZ has a spreadsheet for calculating class E amps components.   Maybe grab a copy of it and figure out what values you need and go from there.?

Of course,  there are other software,  etc.   But Stu is local to the forum if you have problems.

I found,  at least at ten meters,  component values got very critical.  Haven't built a low band amp yet.....

--Shane
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ka1tdq
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« Reply #28 on: May 15, 2016, 01:20:42 PM »

I forgot to answer the question from before...

I use this VFO for my CW rig at 2x the frequency, so I don't hear the oscillator. This rig operates on the same frequency though. I will have to hit the "output off" button after each transmission.  I will think of something else though...

And Stu! Are you monitoring this thread? I could use that spreadsheet. But just on gut, I probably have to double the tank values to make 75 meters.

Jon
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WD5JKO
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WD5JKO


« Reply #29 on: May 15, 2016, 04:09:14 PM »


Maybe this will help:

http://tonnesoftware.com/classe.html

Jim
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ka1tdq
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« Reply #30 on: May 16, 2016, 10:50:42 AM »

Awesome program.

My fixed variables are a 150pf doorknob shunt, 48 vdc drain voltage, and maximum tuning range on the series capacitor is 250pf.  The attached picture shows one test example with those parameters giving me 19 watts carrier. 

I wasn't sure about Saturation, Q, and Falltime, so I left those as default.

Does this look about right?

Jon


* Test design 1.JPG (3464.38 KB, 4032x3024 - viewed 152 times.)
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« Reply #31 on: May 16, 2016, 02:05:36 PM »

Here's Stu's spreadsheet.   Turns out I had it on my phone :-)

Jim Tonne's software is great,  too.

--Shane
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* AB2EZmodClassE_PA_design4c.xls (56 KB - downloaded 124 times.)
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ka1tdq
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« Reply #32 on: May 16, 2016, 02:50:20 PM »

Ah, very nice!  (in my best Burat voice)

When you plug a number in that doesn't work, it lets you know.  AND, you can play with the numbers until things turn out nicely.  It sure saves a lot of time experimenting.  I was messing around with stuff for 3 hours last night and couldn't get good efficiency.  Now I see where I have to go.

Thanks!

Jon
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« Reply #33 on: May 16, 2016, 04:40:52 PM »

Not a problem,  Jon.

Having a smartphone has really made me lose a lot of papers,  files,  etc.

Used to be,  it all got dumped to a single repository / drive at home.   Now,  a tablet,  couple laptops,  home computer,  shop computer,  audio processor pc....   Add a cell phone and where is it all a?  Lol

Anyway,  glad it helped.  Maybe Steve can drag the file or the post to another area for future safekeeping?

--Shane
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ka1tdq
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« Reply #34 on: May 16, 2016, 07:02:32 PM »

I ran the following numbers using Stu's spreadsheet, and I'm getting in the ballpark with Idrain and power output.  The waveform looks pretty good too.

My efficiency is low though... the best I can get is 62% and power output is 38 watts with Idrain 1.3 amps.  What's nice though is that I've been puttering with this thing key down for a long time and the FET is still cool to the touch.  My drain choke though is definitely running hot, and I think that's where my loss is.  I"m using (4) FB-43-1020 cores stacked 2x2 to make a binocular core.  The transformer is a 1:1 turn ratio. 

My series coil too is pretty cheesy, but it's all I had on short notice.  Attached is the picture.  It's green.

Jon

...and like the Energizer bunny, this thing is still transmitting.


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* IMG_0225.JPG (1006.68 KB, 2016x1512 - viewed 164 times.)
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« Reply #35 on: May 16, 2016, 08:29:32 PM »

You obviously didn't see my original pdm filter coils.

Like a foot long,  THHN  #12 on a 1.5 inch form.

The short one was like a foot long!

--Shane
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WD5JKO
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« Reply #36 on: May 17, 2016, 07:28:32 AM »

My drain choke though is definitely running hot, and I think that's where my loss is.  I"m using (4) FB-43-1020 cores stacked 2x2 to make a binocular core.  The transformer is a 1:1 turn ratio. 

Jon,

   It looks like you are getting there. The waveforms are looking much better. One suggestion on the scope setup. Don't AC couple, and set the DC zero point of the top trace to the middle of the screen, and set the DC zero point of the bottom trace to the bottom of the graticule. This way you can see with just a glance if the FET drain is saturating, and what the ON voltage is. At 50v per division, it is hard to see a FET drain voltage of 2 volts, but when the zero point isn't defined, it is impossible to see the FET on voltage.

   You posted an earlier schematic with a 1t/2t transformer. Is that still in there? Both the Tonne program and the AB2EZ spreadsheet don't use one. The spreadsheet says the drain choke needs to be around 87uh. This will be an RFC, and with only a few amps average drain current, there is no need for big thick wire; 16 awg would be fine, and lots of turns.

Jim
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ka1tdq
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« Reply #37 on: May 17, 2016, 08:21:56 AM »

First of all, thanks everyone for the responses, emails and messages from this last go.  To reduce heating on the transformer, one person suggested to increase from 1 turn to 2 turns on both primary and secondary.  That helped with efficiency rising to 69%, but it wasn't the cure.

Someone else pointed out (as did you Jim) that Stu's numbers are for a capacitively coupled output as opposed to a transformer output.  That's my next try.

So can I get away with just using one FS-43-1020 core for a choke? 

Jon
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w1vtp
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« Reply #38 on: May 17, 2016, 11:45:32 AM »

<SNIP>

My series coil too is pretty cheesy, but it's all I had on short notice.  Attached is the picture.  It's green.

Jon

...and like the Energizer bunny, this thing is still transmitting.

Use a PVC pipe to preserve coil for integrity.  Here's a show of my PWM / PS deck also the inductor for the RF deck. This is for 75 meters

Al


* CLASS E PWM - PS.jpg (419.36 KB, 2560x1920 - viewed 169 times.)

* CLASS E AMPLIFIER (2).jpg (405.88 KB, 2560x1920 - viewed 166 times.)
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ka1tdq
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« Reply #39 on: May 17, 2016, 09:39:30 PM »

I switched to capacitively coupled rather than the transformer coupling, and again, it works but efficiency is low.  51 watts output and 70% efficiency.  This is actually turning into an academic exercise rather than a practical transmitter.  I could modulate it as-is after I buttoned it up, but who's ever heard of a 70% efficient class E transmitter? 

Anyway, the choke I used was my 2x2 stack modified to just a choke with 4 or 5 #12 gauge loops through it. 

The series coil was tightly wound, but I found that by spreading the coils out efficiency went up.  The transmitter tuning was a little more forgiving as well. 

On a positive note, Hillary just won Kentucky. 

Jon


* IMG_0229.JPG (2882.48 KB, 4032x3024 - viewed 147 times.)
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« Reply #40 on: May 19, 2016, 01:06:25 AM »

I found out that my tuning cap value was too low.  I added a couple caps in parallel with it to get me around 420pf.  I then made a new coil to resonate with that. 

I'm getting 40 watts out at 75% now.  It's not perfect, but it'll do.  I'm going to build a Heising modulator for it.  I can't operate 75 meters at my house because of the power line noise, but I can take this mobile.  40 watts is comparable to any rice box and my audio will be much better. 

There's Mt. Lemon down in Tucson that's a mile high and you can drive up it.  It'd be fun to throw up a dipole some evening and put this on the air. 

Jon


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« Reply #41 on: May 28, 2016, 02:20:22 AM »

I threw a DDS VFO on the front and changed the output network back to 40 meters.  I'm running a sine wave output and adjusted the DC offset to get the proper duty cycle.  I'm mounting this transmitter permanently in the shack now, like I had originally intended before.  During receive, I now have convenient access to the VFO's output pot so that I can turn it all the way down and not hear the oscillator (I just have to remember to turn it back up for TX, otherwise no output).

Funny thing about efficiency... On the cantenna dummy load I'm getting 70% efficiency.  When I put the transmitter on my 40 meter delta loop, I get 88% efficiency.  The delta loop has an SWR of 1.7:1 in the AM window.  It's resonant and almost 1:1 in the CW portion. 

The waveform looks cleanest and proper at 50 watts carrier, so I'll leave it there.  The Heising modulator that I'm planning to build will drop (as I've calculated) 2 volts at carrier across the choke.  This'll bring drain voltage to a more comfortable level of 46 volts.

Jon


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« Reply #42 on: May 30, 2016, 03:25:58 PM »

I wanted to post a picture of how I'm affixing this to my shack, so here it is. I'm clearly running out of desk space.  After this, I can't build anymore.   Smiley

Everything is all done except for the modulator.  That will sit on the floor under the desk.  The meter for measuring drain current is behind the iambic paddle.  Sequencing is simple, but it requires an extra step.  I need to turn the VFO output on before TX, and off after TX.  Otherwise, it's just a toggle switch TX/RX operation.  

An RF pickup/headphone audio driver is in the aluminum box on the back left corner of the desk.  The headphones are switched in as well during TX so that I can directly monitor my TX audio.

I also mounted the scope on the floor so I can just quickly glance to check out the gate and drain waveforms.  

I still need to buy the parts for the Heising modulator, and they are:

Antek 8KVA 115/50 VAC transformer
124 uF film capacitor
(2) Hammond .1H/5amp chokes

Jon
  


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« Reply #43 on: May 30, 2016, 05:03:05 PM »

Dpdt switch for changeover.

DDS vfo to ground on stby.  Maybe through a xister.

When you lift the switch,  the vfo will come on,  while the switch is transitioning from one state to another....
Assuming the vfo could handle a shorted output (AC coupled).

No??

--Shane
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ka1tdq
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« Reply #44 on: May 30, 2016, 06:59:16 PM »

It probably could handle it fine, but I don't want to risk the FET with no drive with voltage applied to the drains. Worst case right now is that I get no RF output if I have the VFO output at zero. During which case, I won't hear myself in the headphones, realize my brain fart, turn the TX switch back to RX, turn the pot on the VFO back to max, then switch back to TX.

The only way I would risk destroying the FET is by turning the VFO off with drain voltage applied. I doubt I'll do that though.

Jon
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« Reply #45 on: June 02, 2016, 11:46:44 PM »

It seems so much easier to just build a series modulator and don't bother with any kind of modulation that involves iron or parts you don't have....

Hey, on your T/R problem - how about a sequencer?  Here's one I use (pretty simple and all common, easy components).




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« Reply #46 on: June 03, 2016, 06:40:05 AM »

I know, it would make more sense to build a PWM (and probably cheaper too), but I just want to get this on the air simple, quickly, and with what I know works.  Here's a picture of the Heising modulator progress.  I'm repurposing my old single tube transmitter chassis. 

If I get this to work ok, then I'll go full-bore on my next transmitter with sequencing, PWM and a push-pull RF stage.  After all, I've got a 6 foot rack with nothing in it.  I think this rig'll be fine though.  I just did a full 10 minute on-the-air carrier test, and the heat sink and FET got warm (but just barely).  I'm sure it'll handle the modulation just fine.

Keeping the scope permanently connected to the rig I think is a good idea.  I've discovered that the boy likes to come into the shack and rotate my bread slicer repeatedly.  He'll make a good ham!

Jon 


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« Reply #47 on: June 03, 2016, 03:28:49 PM »

Not a pulse width modulator,  a series modulator.

Series modulator can be 3 transistors,  or 1 transistor and a quad op amp.   Quad op amp will give you a couple stages of audio pre amp gain as well.

A series mod can be built up in about 20 minutes,  on perf board.

There are even solid state series mods on this site,  3 mosfet,  that will withstand 1.4 kv.

MUCH easier than a piss weak mod. (pwm)

--Shane
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« Reply #48 on: June 04, 2016, 12:53:31 PM »

Right, I was thinking about a fairly straight-forward analog series modulator.  Can be accomplished with 2 power MOSFETs and an op-amp.

You have a source follower output stage (connected to the RF amplifier DC feed), preceded by a class A voltage amplifier which is fed by an op-amp.  A DC feedback loop runs from the output back to the op-amp (on the non-inverting side) input, with suitable adjustments.  Easy Peazy.

This was the first modulator I used when developing a practical class E transmitter.  Very good for experimentation as long as the power is fairly low (50 to 75 watts -  100 watts tops).  Above this power level, the power dissipation in the modulator becomes excessive, and that's where PWM really works very well because it is SO much more efficient.

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« Reply #49 on: June 15, 2016, 11:31:43 PM »

Here's the modulator progress to date.  All that's left is to buy and install the series chokes.  Hopefully I'll be able to come back with some modulation data in the first week of July. 

In the meantime...

https://www.youtube.com/watch?v=arZdeg_fL-I

Jon


* IMG_0377.JPG (2000.88 KB, 4032x3024 - viewed 121 times.)
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