Warning: Creating default object from empty value in /homepages/11/d132647312/htdocs/Amfone/mkportal/include/SMF/smf_out.php on line 47
40 meter single-ended 4-FETs




 
The AM Forum
August 15, 2018, 09:25:20 AM *
Welcome, Guest. Please login or register.

Login with username, password and session length
 
   Home   Help Calendar Links Staff List Gallery Login Register  
Pages: [1]   Go Down
  Print  
Author Topic: 40 meter single-ended 4-FETs  (Read 2387 times)
0 Members and 1 Guest are viewing this topic.
ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« on: December 30, 2017, 07:57:17 PM »

Ok, construction has started.  The plan is for 4 parallel FETs in single-ended configuration.  I'll be using a drain choke in the output network.  The picture shows the start of the transmitter.  It'll be mounted on a 1/4" steel plate elevated above the cabinet.  That gives a convenient space for the DDS VFO and the meters.  Inside the cabinet will be the power supply, Heising modulator and audio amp.  The audio section is already done and I just need to mount it.

The goal is 200 watts carrier.  Assuming 90% efficiency, I believe the heat sink is capable of handling the 20 watts of heat.

Jon


* IMG_0007-3.jpg (2156.66 KB, 4032x3024 - viewed 143 times.)

* IMG_0008.jpg (1322.48 KB, 3024x4032 - viewed 123 times.)
Logged

ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #1 on: December 31, 2017, 02:31:08 PM »

Playtime is over for today.  Got most of the inside cabinet done.  I'll start working on the RF deck when I get some more hardware. 

Jon


* IMG_0015.jpg (2051.06 KB, 3024x4032 - viewed 112 times.)
Logged

KD6VXI
Contributing
Member
*
Offline Offline

Posts: 1838


Making AM GREAT Again!


« Reply #2 on: December 31, 2017, 03:53:27 PM »

200 watts carrier at 90 pct is 20 watts.

At 1kw pep, that's a hundred watts.

Heat sink capable of that?  Or is the carrier where the most inefficiency is at?

I never thought about it, all my class E and solid state is fan cooled.....

--Shane
KD6VXI
Logged
ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #3 on: December 31, 2017, 04:06:17 PM »

I知 not sure either. At this point though, I知 just hoping to get a class E waveform on 40 meters with this. I知 going to make the FET and driver section as neat and compact as I can.

I知 not sure my modulator has enough umph for 200 watts carrier, but I値l modulate as much as I can. I can always dial back on carrier.

Jon
Logged

steve_qix
Contributing
Member
*
Offline Offline

Posts: 2357


Bap!


WWW
« Reply #4 on: January 01, 2018, 02:22:50 PM »

If there is any possibility of using the standard single ended push pull design rather than just single ended, it will probably work better.  The harmonic content presented to the output network in a single ended design is extremely high, and I have also found better efficiency with single ended push pull as opposed to just plain single ended.

Along with the drain power dissipation, the heat sink has to be capable of dissipating all of the power consumed in the gates  (which can be a lot), and you need to account for modulation which will increase the heat produced in the drains by 30% to 50% depending on the nature of the modulation.

With analog drive, 100% of the drive power is turned into heat in the gates.  With heat-sink mounted driver ICs and digital drive, 100% of the power fed to the drivers is turned into heat.

Just some suggestions.

Regards,  Steve

Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #5 on: January 01, 2018, 02:57:16 PM »

Last year I attempted to build a push-pull 40 meter transmitter using just a single FET in each phase. I couldn稚 get it to behave at that high frequency, but it worked great on 75 meters with larger tank components. If I couldn稚 get two FETs to work in push-pull, I知 doubting my skill with four FETs.

If sacrificing a little efficiency and having increased harmonics is the trade off for a decent power level 40 meter deck (that works), then I知 game, especially since I use a tuner for 40 meters.

I知 only assuming that single-ended is 兎asier to get working since my first class E transmitter was single-ended, using a single FET for 40 meters. I壇 just be adding 3 FETs in parallel.

As for heat dissipation, I値l be using digital drive. My rough calculation puts that at about 15 watts. My heat sink weighs almost as much as a bowling ball so my confidence interval is high.

Jon
Logged

KD6VXI
Contributing
Member
*
Offline Offline

Posts: 1838


Making AM GREAT Again!


« Reply #6 on: January 01, 2018, 03:07:54 PM »

I'm thinking of a duplexer on the output to deal with harmonics.  Otherwise, that's a ton of energy to have to short to ground.

The solid state amp guys are now moving to duplexes with dummy loads for harmonic energy.  Helps with imd, helps with keeping things cool and helps with efficiency.

--Shane
KD6VXI
Logged
ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #7 on: January 01, 2018, 03:32:15 PM »

We池e missing the big picture here... 14 MHz won稚 propagate at night for several years.

Jon
Logged

KD6VXI
Contributing
Member
*
Offline Offline

Posts: 1838


Making AM GREAT Again!


« Reply #8 on: January 01, 2018, 07:03:31 PM »

We池e missing the big picture here... 14 MHz won稚 propagate at night for several years.

Jon

You lost me here.

I was saying, to deal with your increased harmonic content of a single ended amp, use a high pass filter dumping everything above 7 mhz into a dummy load instead of using low pass filters.

The ldmos amps are utilizing this now.

--Shane
KD6VXI
Logged
steve_qix
Contributing
Member
*
Offline Offline

Posts: 2357


Bap!


WWW
« Reply #9 on: January 01, 2018, 07:31:21 PM »

Hmm.. when you say push pull, do you mean "real" push pull (with a single output transformer and both devices connected to it), or single ended push pull like I was talking about?
Logged

High Power, Broadcast Audio and Low Cost?  Check out the class E web site at: http://www.classeradio.org
ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #10 on: January 01, 2018, 09:54:59 PM »

Gosh, Steve, you know... when you're right, you're right.  These rigs are all 'single-ends' fed out of phase and combined in a transformer.  So, right!

Luckily I didn't drill the holes for the heat sink yet.  Let - me - just - move - that - back - and - stick - in - a - transformer ... yeah.

Ok, so 2x2 it is!

Jon


* IMG_0019.jpg (2047.44 KB, 3024x4032 - viewed 97 times.)
Logged

ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #11 on: January 04, 2018, 01:18:04 AM »

I知 just bored and posting pictures, sort of like Facebook.

I did find out that I can login to AmFone.net with facial recognition on my phone.

Jon


* 5DFF1A18-022C-4711-84AE-168F3C744EE9.jpeg (3164.53 KB, 4032x3024 - viewed 133 times.)

* 07B6460D-456B-449E-B682-291820ECCC71.jpeg (2630.6 KB, 4032x3024 - viewed 105 times.)
Logged

KD6VXI
Contributing
Member
*
Offline Offline

Posts: 1838


Making AM GREAT Again!


« Reply #12 on: January 04, 2018, 11:32:57 AM »

I like the coil cradle in the pvc pipe section.  Neat idea!

--Shane
KD6VXI
Logged
ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #13 on: January 05, 2018, 01:17:50 PM »

Getting close!  I'm waiting for a few more parts to arrive and then I can start building the heat sink assembly.  Everything else is done except for the two shunts to measure drain currents.  I'm going to mount an SMA connector for each phase very close to the gate drivers.  That'll help minimize lead length.  And for good measure I'm going to build a ground wall between the two phases using a small strip of copper.  I've planned everything else to minimize other lead lengths as well.

Jon



* IMG_0112.jpg (2219.24 KB, 4032x3024 - viewed 84 times.)

* IMG_0113.jpg (1637.5 KB, 4032x3024 - viewed 83 times.)
Logged

ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #14 on: January 06, 2018, 08:05:43 AM »

Everything is done except for the SMA connectors and resistors. The connectors and the current shunts are coming on the slow boat from China. Once they arrive I can begin testing.

Jon


* EB16A7E9-D639-41F4-8C09-FB138D230987.jpeg (2622.09 KB, 4032x3024 - viewed 115 times.)

* IMG_0120.jpg (2326.82 KB, 4032x3024 - viewed 86 times.)
Logged

ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #15 on: January 13, 2018, 06:46:00 PM »

All done except for the two SMA to BNC short jumper cables. I just need to screw those on and I can begin testing.

Jon


* 7519AACF-DBBA-4D8A-8A33-01ED2A8D96A0.jpeg (3030.52 KB, 4032x3024 - viewed 88 times.)
Logged

ka1tdq
Member

Offline Offline

Posts: 1019


Massachusetts Democrat


« Reply #16 on: January 14, 2018, 05:56:41 PM »

Change of plans.  I'm allowed.

I ordered a BitX transceiver that I want to use for 20 meters SSB.  Output power is 10 watts so this RF deck platform will be great for a single 811A amplifier.  I can use the existing tuning capacitor for the plate capacitor if I put another fixed capacitor in series. 

Large steel plate - baby linear. 

Jon
Logged

Pages: [1]   Go Up
  Print  
 
Jump to:  

AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
 AMfone ゥ 2001-2015
Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Page created in 0.053 seconds with 18 queries.