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40 meter push pull RF deck




 
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Author Topic: 40 meter push pull RF deck  (Read 10624 times)
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ka1tdq
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« Reply #50 on: June 28, 2016, 12:02:33 AM »

It works!

I installed my Hammond transformers tonight and put it on the air.  It sounds great!  I directly monitor the output of the transmitter and it's pumped into my headphones.  I'm getting 50 watts carrier with 200 watts peak (more if I hit it hard). 

I watched my waveforms on the scope while I talked and there was variation in the drain amplitude.  I'm a guess'n that's supposed to happen. 

I'll attempt a QSO when I have someone other to talk to than a foreign broadcast station. 

Class E... yeah baby, yeah!

Jon


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« Reply #51 on: June 28, 2016, 07:15:35 PM »

That's pretty cool. What is the TO-220 for?
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ka1tdq
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« Reply #52 on: June 28, 2016, 07:23:34 PM »

That is a 5 volt regulator which supplies the 3 diode keep alive negative peak limiter.
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ka1tdq
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« Reply #53 on: June 28, 2016, 09:21:02 PM »

Well, I was able to give it a little workout today.  I talked with W6TSJ, Tom in CA.  He's in between San Diego and Los Angeles.  He was running 40 watts on a Globe Scout and me on this rig with 50 watts.  We made it despite all the noise and static crashes. 

Anyway, he gave me a really great audio report.  I felt the FET and heat sink after some long transmissions and they do get a little warm, but nothing nearly to be concerned about. 

This is going to make a nice local rig.  If I need high power, I can turn on my other transmitter which is paired to 3-500 triplets. 

Jon
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ka1tdq
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« Reply #54 on: July 02, 2016, 03:16:55 AM »

This rig is awesome and I'm very happy with it.  However, at some point I'm going to want more power and I'll build a larger transmitter.  

For 40 meters, I guess you need to drive each FET (go with an 11N90) with it's own IXDD chip?  Or can you still drive two FETs with a single IXDD, like on 75 meters?

If you do have to go 1 for 1, is it practical to build an 8 FET, push-pull RF deck for 40 meters?  What's the biggest class E transmitter out there for 40 meters that someone's built?  

I just ordered a UDB1308S DDS VFO.  I have a way of getting a variable square wave duty cycle using sine waves with this particular VFO.  Now though, I'll have two outputs and can make a push-pull rig.

Also, there's an industrial metal shop just down the road from me.  They sell copper sheets any size and thickness you want.  This new rig would look pretty cool with a shiny copper base.

Jon
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steve_qix
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« Reply #55 on: July 02, 2016, 08:08:25 PM »

Good work on the existing transmitter !!!!  Maybe we can work sometime when the conditions are favorable.

You definitely need an individual driver for each MOSFET.  I do not know if the IXDD614 will function at 7 mHz.  The IXDD414 definitely worked up there.

The biggest 40 meter class E rig I know of is 1kW (carrier, DC input).  This is with 16 MOSFETs.

Hope this helps!

Regards,  Steve


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ka1tdq
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« Reply #56 on: July 02, 2016, 09:38:03 PM »

I was talking with a guy in CA last night with this rig, and he asked me what the benefit was with class E vs. a tx with a linear combo. I cranked up the microphone gain high so that you could hear a pin drop in the shack, and I said, "Listen, no fans or blowers!" Granted, this rig just does 50 watts, but I'm going to start gathering parts for an 8 FET rig. Now that I know how these things operate and tune, it seems less mysterious.

I'm using a 614 with this transmitter. It seems to do the job.

We've worked at the 300 watt level, but I'm guessing that at 50 watts you would need to get your ESP going to pull me out of the noise.

Anyway, onto bigger and better things!

Jon
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ka1tdq
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« Reply #57 on: July 10, 2016, 06:39:39 PM »

If you have 3 minutes to kill, I made a YouTube video demonstrating this radio.  Here it is:

https://www.youtube.com/watch?v=_2QdiDejfzQ

Jon
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WA2SQQ
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« Reply #58 on: July 18, 2016, 03:33:17 PM »

Nice work - nice video! Thanks for sharing
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ka1bwo
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« Reply #59 on: July 23, 2016, 11:17:59 AM »

Jon,
Very informative video thanks. Great effort to get your transmitter to it's present state congratulations!
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ka1tdq
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« Reply #60 on: July 23, 2016, 11:53:21 AM »

Thanks! 

Here's a picture showing the current state of the new one.  The aluminum knob on the tuning capacitor is temporary.  I'm going to use a non-conductive shaft/knob for that.

I'm going to order all the semiconductors in a little bit, and that's basically the next step.

Jon


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« Reply #61 on: July 28, 2016, 12:15:50 AM »

Some day when the band is open and I'm on 40, it would be great to hear the rig!
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High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
ka1tdq
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« Reply #62 on: July 30, 2016, 08:24:40 PM »

Here's the FET deck so far.  The drain bus is vertical, as you can see, and the gate bus will also be vertical.  I thought afterward about possible RF coupling between the two, but there's space in between to mount a larger 3/4" grounded brass strip vertically the whole length.

There are 10 IXDD chips.  The ones directly center in the two busses are the two driver chips.  The other 8 drive the FETs.  

Soldering now is getting a little tight to finish, so I'm taking a break.

Jon


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