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Hopefully geting started again




 
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N4LTA
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« on: April 19, 2021, 10:58:17 PM »

I am getting things going again and am working on board with Nigel's PWM power supply and another board with a small 2 FET transmitter based on Nigel's design. I will use two SiC FETs and the transmitter will be for 75 meters. It will be a test transmitter. I have boards designed to duplicate it in 4 and 6 FET designs

The transmitter  has a phase splitter on board and a variable supply for the NCP type Drivers. The phase splitter is based on Rod's design

I have attached a couple of photos.

Pat


* IMG_5992 (1).jpg (176.15 KB, 640x480 - viewed 167 times.)

* IMG_5991.jpg (163.21 KB, 640x480 - viewed 151 times.)
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vk3alk
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« Reply #1 on: April 20, 2021, 05:17:06 AM »

All looks good Pat...

What material are you using for the PWM LPF ?

Actually design the LPF filter last ... see how the TX goes first  Grin

What power level you want and its the current etc:


Wayne
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W9BHI
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« Reply #2 on: April 20, 2021, 11:14:06 AM »

Pat,
I have been trying to contact you, no response back from you.
Everything OK?
Don W9BHI
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M0VRF
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« Reply #3 on: April 20, 2021, 11:48:09 AM »

SUPER SENDUST

Seem to be be rather good.

JB.
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N4LTA
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« Reply #4 on: April 20, 2021, 12:32:23 PM »

Wayne

I will build the transmitter first. I plan to experiment with the PWM filter inductors. I will use high quality polypro caps in the filter and for inductors,  I am not sure.

I have ordered a few low resistance air core inductors for testing. Most all of my cores were destroyed, but I have replaced some and have some 43, 31, and 61 cores .

Looking at something in the 35-40 volt range for carrier, at 2-3 amps. 100 Watts carrier.

I have ordered some large type 61 beads and FETs, and have layed out some PCB material for building the output inductors in your 40 meter transmitter. Hope to give that a try soon.

Don - I got your VFO but it is still packed up. I hope to get it out and play with it soon. The house is still not complete and I have a ton of stuff to do. I am getting there.

JB - Have you tried it yet?  Looks promising if you can find who is selling it in small quantities.

I have t go out of town tomorrow, so it will be a few days before I make much progress.


Pat
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KQ6F
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« Reply #5 on: April 20, 2021, 02:15:23 PM »

When choosing core type for the PWM LPF, an important parameter is permeability stability vs DC current.

Five years ago when I built my PWM rig I compared the various material types from Magnetics, Inc for best permeability stability.  I looked at 60 mu cores in all the families then offered and came up with the C058894A2HT19 core in the High Flux family.

Since then they have added three new families, the Kool Mu, Kool Mu Max, and Kool HF.  I re-ran the numbers and this time included core loss at 100kHz as a second parameter.  Based on these two parameters I would today choose a core from the Kool Mu MAX family.  At an arbitrary DC magnetizing field of 100 Oersteds, the permeability comparison between the High Flux and Kook Mu is 80% vs 77%, almost the same.  But the core loss at 0.1 Tesla is only 570 mw/cm for the Kool Mu vs 1500 for the High Flux.
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M0VRF
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« Reply #6 on: April 21, 2021, 07:46:07 AM »

Just use the type I quoted.

They are however vastly superior to anything else as they are new and modern.

I understand new and modern things aren't the norm on here but may I suggest you try them?

I can push 500W of 150KHz thru' a T106 core without saturation.

I'd contact the manufacturer directly and get some samples. I've never had a problem with that with UK based manufacturers, should be same in US?


I'm in the UK and use PACE Magnetics for all my cores.

Regards.

JB.
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KQ6F
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« Reply #7 on: April 21, 2021, 08:38:03 PM »

Hi M0VRF -

Can you post the manufacturer and part number of the core you refer to?

I'd like to compare its specs against the ones I've investigated.

Thanks
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M0VRF
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« Reply #8 on: April 22, 2021, 02:34:07 AM »

Micrometals are the manufacturer, I'll dig out the part number..

I use the smaller version of these. I guess these are more suited to the higher power you all into over there..

Micrometals Arnold Super MSS Alloy Powder Core: MS-184125-2 (Sendust / Kool MuTM equivalent)

(Equivalent to Magnetics part 77438-A7 and Chang Sung part CS-467125)

Dimensions:
Outside Diameter (OD): 46.74mm

Inside Diameter (ID): 24.13mm

Height (Ht): 18.03mm

Wt: 180g



Magnetic Characteristics:

Permeability: 125

AL Value: 281
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N4LTA
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« Reply #9 on: April 23, 2021, 10:53:59 AM »

I picked up a few 1.4 inch OD Kool Mu toroid forms on Ebay to experiment with. They are 125 Mu. I also have some low resistance air core forms to experiment. I used to have an account at Micrometals - probably expired now.

As usual, I found an error or two on the PC boards. I have corrected them and ordered some new ones. At $2 for five boards, it's easier to have them re-made.



Pat
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KQ6F
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« Reply #10 on: April 23, 2021, 01:12:15 PM »

M0VRF -

Don't know what power level you are running but for me both the MS-184125-2 and 77438-A7 cores would be poor choices.  For the number of ampere-turns I'm running the AL (and therefore inductance) would drop to 60.5% at the positive 100% modulation peaks.
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M0VRF
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« Reply #11 on: April 23, 2021, 03:13:31 PM »

Legal limit here is 100W.

I've used the 106 size and they're perfect.

Regards

JB.
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N4LTA
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« Reply #12 on: May 05, 2021, 09:54:34 PM »

Have a prototype two FET transmitter ready for testing. The power supplies are tested and the SMD drivers are tested as far as proper connection. The driver power supply is variable using an LM317 and the HC logic has a 5 volt regulated supply. This is essentially Rod's transmitter with only two MOSFETs and NCP81074A drivers. I used one output transformer instead of two. Looking to get something near 100 watts carrier. I used 1000pf silver mica drain capacitors as  starting point  The bypass capacitors at the transformer center are four 1000pF 1000 volt ceramic chip caps and will serve as the end capacitor in the PWM filter. The phase splitter is based on Rod's circuit also.

The solder jobs looks very messy, but it is not near as bad as the contrasty photo shows.


* transmitter2fet.jpg (88.1 KB, 210x280 - viewed 145 times.)

* draincap.jpg (71.62 KB, 210x280 - viewed 133 times.)

* bypasscaps.jpg (55.98 KB, 210x280 - viewed 132 times.)
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vk3alk
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« Reply #13 on: May 05, 2021, 10:22:39 PM »

Looks good Pat...

Just having lunch and noticed your still online....

Your other photo disappeared  Shocked


Wayne
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N4LTA
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« Reply #14 on: May 06, 2021, 12:18:07 PM »

Wayne - trying to fit them all in 500K

Pat
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N4LTA
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« Reply #15 on: May 12, 2021, 09:59:03 PM »

Put a 50 ohm dummy load on the transmitter and fed the board with a 7.6 MHz square wave at TTL levels. Use an output transformer exactly as Rod used  - 6 turns - 6 turns primary and 11 turns
secondary on a T106-2 core. with 10 volts on the driver, I measure a bit under 5 ohms  resistance at the center tap of the primary winding.
.
I was hoping for a bit more maybe 8-10 ohms. The output waveform with no filter looked close to Rod's .

At 6.3 volts  current was 1.2A
    7.1                            1.35A
    8.02                          1.57A
   9.04                           1.85A
  10.0                            2.02

Didn't have the FETs heatsinked so that was as high as I wanted to go. FETS got slightly warm at about 20 watts

The current and voltage values were measured with the displays on the power supply, so probably accurate enough.

Design goal is  80-100 watts carrier. The divider /phase splitter seems to work fine and  shuts down the driver input properly.

Using a 400 MHz analog scope makes for some interesting unfiltered output waveforms.

I have another board in the works which adds a few things and an onboard filter and room for a larger output transformer.


Pat
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Pat


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vk3alk
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« Reply #16 on: May 12, 2021, 10:23:44 PM »

Really good Pat....

I did change the turns ratio as per the Posting about Rods TX if you wanted a higher loading etc:
When you have the FETs on heatsinks slowly increase the output power.
I feel they should operate well at 150 watts output as long as the efficiency is good etc:

Stopping the pulse train works well....


Wayne
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N4LTA
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« Reply #17 on: May 14, 2021, 11:20:57 AM »

I got the modified boards in. It allows some more space for the output transformer and space for an output filter and a BNC output jack.

I put most all of the SMD components on and the transformer. I also modified the input circuit to an active low input circuit, to match my other devices.

In the design, I used a 2N7002 and found they all  got destroyed in the fire, so I am waiting for one to finish the input and T/R circuit. I lowered the output transformer secondary turns to 8 turns from 11. Will see how the resistance changes. Hopefully close to 6-7 ohms. Also used a larger toroid core . The transformer has #14 AWG primary wire and #16 AWG secondary wire.

Going Marlin fishing this weekend at Hatteras. The 2N7002s are supposed to be here when I get back Monday.

Pat


* transmitter board with filter.jpg (75.92 KB, 640x480 - viewed 133 times.)

* output transformer primary.jpg (49.57 KB, 480x640 - viewed 121 times.)

* output transformer complete.jpg (52.95 KB, 480x640 - viewed 145 times.)
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M0VRF
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« Reply #18 on: May 15, 2021, 08:51:58 AM »

The O/P tran wont work as you've wound both sides in the same direction and need to be opposed.

Been mentioned plenty of times and Nige's pics show it clear enough.

I made the same mistake BTW!

Regards

JohnB.


* OP Tran.jpg (50.6 KB, 379x371 - viewed 108 times.)
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KQ6F
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« Reply #19 on: May 15, 2021, 11:25:20 AM »

Pat's transformer configuration is fine.  It's wound the same as mine.  The two primary halves are wound in opposite directions and the secondary wound all in one direction.  Nigel chose to wind his two primary halves in the same direction with the secondary split into two halves and wound in opposite directions.  The two methods produce identical results.
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KQ6F
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« Reply #20 on: May 15, 2021, 04:55:57 PM »

Put a 50 ohm dummy load on the transmitter and fed the board with a 7.6 MHz square wave at TTL levels. Use an output transformer exactly as Rod used  - 6 turns - 6 turns primary and 11 turns
secondary on a T106-2 core. with 10 volts on the driver, I measure a bit under 5 ohms  resistance at the center tap of the primary winding.
.
I was hoping for a bit more maybe 8-10 ohms. The output waveform with no filter looked close to Rod's .

At 6.3 volts  current was 1.2A
    7.1                            1.35A
    8.02                          1.57A
   9.04                           1.85A
  10.0                            2.02

Didn't have the FETs heatsinked so that was as high as I wanted to go. FETS got slightly warm at about 20 watts

The current and voltage values were measured with the displays on the power supply, so probably accurate enough.

Design goal is  80-100 watts carrier. The divider /phase splitter seems to work fine and  shuts down the driver input properly.

Using a 400 MHz analog scope makes for some interesting unfiltered output waveforms.

I have another board in the works which adds a few things and an onboard filter and room for a larger output transformer.


Pat
N4LTA


Pat -

I think there's something wrong with your setup.  I modeled your circuit with 11-turn secondary on LTSpice and measured 10.4 ohms load resistance.  The 5-ohms you're getting suggests that perhaps the two phases are overlapping to some degree.  I wonder what FETs you're using.  If no overlap and if the drain caps are properly selected, the half sinusoids appearing at the drains should be as shown below.  Their peak values should be 4x the voltage at the primary center-tap.

Rod



* classd_e_002.jpg (206.04 KB, 1000x750 - viewed 117 times.)
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N4LTA
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« Reply #21 on: May 18, 2021, 11:43:53 AM »

I am using the    C3M0350120D device rate 1200 volts at 7.6 amps.

My transformer is wound per Rod's wiring schematic. Might need to rethink the winding since I am only using one transformer? Since this is a 100 watt class transmitter, I only use two of the FETs and half of Rod's circuit. I am using a 560pFpF silver mica 1000 Volt cap from drain to ground. Maybe is should be larger at 75 meters. The signal generator feeding the signal was running  at 7700 KHz,  at a 50:50 duty cycle.

Just got back from fishing, and hope to get a heat sink installed today and more testing dome today. BTW , hook and landed a 450 pound blue marlin and lost another about that size after and hour fight. The one that we caught took over three hours to land. Also caught three nice gaffer Mahi on the meat line. It was rough as hell, about 6-7 feet at 3 seconds.
It whipped my old butt.

Pat
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w9jsw
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« Reply #22 on: June 25, 2021, 10:23:02 AM »

Any progress Pat?

Am looking at Rod's posted schematics. Will you be sharing any of yours? I know that part of yours are variations of Nigels designs for the PWM part. I had some boards done a few years ago on one of his earlier designs. Wondering if they are useful or scrap.

Any testing results?

John
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N4LTA
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« Reply #23 on: June 26, 2021, 12:10:28 PM »

John

I have a transmitter ready for RF testing and a modulator completed. I had ten boards built for the transmitter and you are welcome to one of them. I have Rods phase splitter with a 5 volt regulator and a variable regulator for the SMD drivers as Nigel used. I am using the 1200 volt FETs from CREE. My first try is a two FET transmitter hoping for 100 watts of carrier. I hope to test it this weekend. Work has been very hectic the last month and I have been slow to do anything in the shop.

The  modulator is totally Nigel's design. I have a board for it also with the TR relay on board. I have ten of those also nd you are welcome to have one. At the Chinese prices for PCBs it is crazy not to order 10.

Pat
N4LTA
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