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100 watt transmitter new version




 
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Author Topic: 100 watt transmitter new version  (Read 1432 times)
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N4LTA
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« on: July 19, 2021, 06:02:00 PM »

Just got some new boards. The old transmitter had the MOSFETS standing up. It worked  but had some problems getting short leads and that bothered me.

I layed out a new board with the MOSFETs laying flat. I also layed out a board for GaN MOSFETS that is due in a few days. While ordering, with the price of the Chinese boards so cheap, I made some boards for a one turn ferrite form like Wayne used in his 40 meter transmitter. I have hand made these in the past but it is a pain. These were about $1 each. One board makes two ends.
Just built the board this afternoon and will put the MOSFETs in tonight. The board takes a 2X CMOS or TTL 5 volt square wave  and splits the phase  and the signal to the drivers is enabled woth a low signal at the enable input. In tests it is very effective  and might be usable for CW.. Have not tested that.

I plan to use the same type 3 Cree MOSFETs that I used in the last version. More later

Pat N4LTA


* board.jpg (126.59 KB, 640x480 - viewed 162 times.)

* board close.jpg (169.31 KB, 640x480 - viewed 161 times.)

* one turn.jpg (34.13 KB, 480x640 - viewed 138 times.)
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N4LTA
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« Reply #1 on: July 20, 2021, 09:09:47 PM »

Partially test the new board and all was well except for a bad 78L05. Replaced it and everything is playing well.

Fed it a 7500 KHz signal and the phase splitter and enable circuits are working well. All seems stable and cool. I have not installed the MOSFETS or the Silver Mica caps.

Plan to let it run all night enabled with drivers working but into an open circuit. If all is well, I'll put in the MOSFETS and the output transformer and start testing with some power.

The photo is the output of the drivers at no load.

Pat
N4LTA


* output to gate - no fet.jpg (126.84 KB, 640x480 - viewed 130 times.)
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vk3alk
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« Reply #2 on: July 21, 2021, 01:08:23 AM »

Hi Pat...

Wasn't going to reply but those waveforms played on my mind....
Hopefully your CRO probes are aligned correctly  Cheesy but they are not what I would expect...
Haven't used those drivers before only the IXDDs but if the input to them are nice and square the output without load should be very similar you would think...
Not saying they are bad  Roll Eyes but well maybe not good...
Have attached some very old pictures but have others somewhere but cannot find them....
One is for 80M and the other is 40M....
The rise and fall times for the 40M are longer as you would expect but they are sharper etc:
Are you sure those CRO probes are aligned ?

I have some of those ( Chinese junky things )

Will wait for your reply...

If it was my TX would not connect the FETs as yet but check things out first...


Wayne


* 40MIXDD_noload.JPG (470.35 KB, 1600x1200 - viewed 131 times.)

* 80M IXDD output.JPG (335.58 KB, 1600x1200 - viewed 131 times.)
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N4LTA
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« Reply #3 on: July 21, 2021, 09:37:49 AM »

Wayne

I suspect the probes.  They are a $40 set of Chinese probes. One of the tips of my HP 500MHz probes was missing so I grabbed these.

I'll check it out . I also have some HP 100 MHz probes.

Pat
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M0VRF
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« Reply #4 on: July 21, 2021, 05:44:49 PM »

It's the probes, have you calibrated them?

I use the same drivers and they're Very square..

J.
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N4LTA
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« Reply #5 on: July 21, 2021, 10:43:10 PM »

It was the probes.

They would not calibrate at 500 nSec scale. I calibrated them as best I could. The wave is now reasonably square. The scope is a 500 Mhz scope and it shows some ringing.

I think I am OK and will install the MOSFETS tomorrow and test.

Pat
N4LTA


* IMG_6245.jpg (119.3 KB, 640x480 - viewed 119 times.)
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vk3alk
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« Reply #6 on: July 21, 2021, 10:56:57 PM »

Hi Pat....

Everything is Ok now .....
It always was but best to be sure  Smiley

The ringing is just part of life using CRO Probes....
Its all good fun really..... Cheesy


Wayne
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