Messages

46

The RF Workbench / C-QUAM stereo on PWM TX

« on: October 29, 2019, 0045 UTC »

Hi,

Redhat, your mention of c-quam with a PWM transmitter got me interested, so I thought I should make a separate thread about it.

As I understand it, you modulate the PWM as you normally would with left and right channels mixed together. Then for the c-quam, you need a device that will offer a phase modulated TTL square wave and you feed that in where you would normally have your crystal oscillator?

Do such devices exist? Could a regular part 15 100mW c-quam transmitter have this extracted from somewhere in the circuit or do I need to build my own device that produces it?




As a side note: It also got me thinking - what would happen if you got two PWMs and fed each side of the amp separately (assuming push-pull design)? would it make an ISB type stereo?

47

The RF Workbench / Re: NCP driver sucks

« on: October 24, 2019, 0833 UTC »

That sounds about right!

Looks like you're on your way...

I must have had mine finished for over 2 years now but stuffing the thing in a commercial available box with the modulator and filter + making it unblowupable has been a challenge.

I think building one of anything is relatively easy. However building 25 and making it easy to do has taken me over 2 years!

I reckon I'll sell 2 a year, so really a complete waste of time one might say but I don't mind, keeps me busy!

I really pleased at the progress you've made.

May I ask about your modulation scheme?

Regards.

Stretchy.

Sure. I'm going to use a Greek PWM board. I have it already, but have not tested it yet. It's a spruced up version of this kit (using bigger FETs): https://www.s9plus.com/puwma%20draft4.pdf

So I've done a bit more experimenting. I made it to 92% @ 6.8 MHz with 12V drive. 
Something is a little weird though. I need exactly 470pf on only one side of the amp. Like I said before, I think I need to change my balun back to the original wire wrapped one I was using. This new one uses coax and it's a bit strange. Could I somehow be fooling the bird meter by using a cap on one side only? If not, then it's got to be my balun. I'm going to put the old one back in tomorrow and see. The new one was actually 1% less efficient or in the noise.

I should never need more capacitance on one side, right? Each side of the amp is exactly the same, so I am guessing it has to be the balun.

48

The RF Workbench / Re: NCP driver sucks

« on: October 21, 2019, 1846 UTC »

Eff will suffer at 10V and FETs wont be fully on and dissipate more heat.

Don't know why you can't just whip off the drivers with a hot air gun, bend the pin and reseat or just lift the pin with a scalpel whilst heating with an iron. I'd always breadboard first.

However you should be ok with the design now. Don't use any grease and just use the greasless insulators (orange ones).

Str.

My PCB company is so fast that it's not worth the effort. The board arrived yesterday and I finished installing everything and tested it.
The inverted inputs work!!!
The efficiency (87%) is not too good, but I know the reason why and I think I can fix it.
The way I connected my balun, I think is a little unbalanced 
I need 270pf on one side and nothing on the other to produce the 87%, so I've got a balance issue. I am going to fix the balun because with the way it connects, the one side is a little longer.
That should help and then I am going to try 12V with some little heatsinks and see if I can get into the nineties.

At 12V 4 of my NCPs draw 430mA (operating at 10V through regulators), but that's along with the crystal oscillator and voltage regulators which get a little warm.

49

The RF Workbench / Re: NCP driver sucks

« on: October 19, 2019, 0534 UTC »

Just fired up my 'Older' design with 4 SiC FETs (I use GaN now) and Yep, 93% efficient.

382W @ 48V 8A55.

Running a 100W carrier at 24V eff is around 96%.

The whole amp is passively cooled and barely gets warm at carrier, so cool in fact I wonder where the power is coming from!

The whole system is calibrated so I know it accurate to a few %, DC and RF wise.

12V I is around 410mA and that's for 4 NCP's and the AD9850 (which gets a bit warm).

So I rekon around 80/90mA per driver?

The drivers do warm up but I can just keep my finger on them (for a while!)

I run the NCP's at 12V and noticed ONLY a 0.3% increase in eff moving to 15V, so 12V is fine.

So not sure why your having the heat problems.

Your layout isn't that different from mine except that I am trying to use the built-in inverted inputs.
It's too hard and kludgy to try and lift those pins, so I just ordered a new board. Waiting for it to arrive now.

It could be because I put too much thermal paste under the fets and it bulged out and bridged the gate and source. It's not conductive and I've verified that, but it could be a little capacitive. That's my only guess. I'll be careful not to do that when I install the fets on the new board. They do seem to work alright at 10V, so that's what I am going to use. 12V and I can't put my finger on them for more than a second. I may be able to find a type of heatsink like they use on motherboard voltage regulators if I decide to run it at 12V.

50

The RF Workbench / Re: NCP driver sucks

« on: October 15, 2019, 1444 UTC »

I have used the NCP up to 7.290 in the past. Inverting and non-inverting. What keeps them from frying is a few ohms between the driver and the SiC gate.

I thought that was only for protection if the mosfet blows out, so it reduces the current consumption of the driver with no side effect?

51

The RF Workbench / Re: NCP driver sucks

« on: October 15, 2019, 1112 UTC »

On one side only..

Ok, does it work??

Str.

Well, the non-inverted side already works fine (with less than 12V). After reading the truth table again, I don't see why this wouldn't work. Unfortunately, the only way to find out is to send for the PCBs again. I'm just going to go for it. It's only $35 for 6 of them and it's not something I can hack onto my current board because those pins are grounded, so I can't just connect a wire there; I have to get new PCBs. And I shouldn't need pullups or pulldowns because that pin should always be high.

52

The RF Workbench / Re: NCP driver sucks

« on: October 15, 2019, 0016 UTC »

Drive the '-' I/P on both sides but pull up the '+' I/P on one side and down on the other side.

Sounds more complicated than necessary. Do I need to do it that way?
Alright the modification has been made. I just connected the non-inverted input to 5V and drive the inverted input only.

53

The RF Workbench / Re: NCP driver sucks

« on: October 14, 2019, 1548 UTC »

Maybe you have to tie the positive input pins high to get the inverter function to work?

+-RH

Now that I look at it again, yeah, I think you're right.

54

The RF Workbench / Re: NCP driver sucks

« on: October 14, 2019, 1456 UTC »

The design I use uses the AD9850 PCB's on Ebay and they O/P opposite phases already so I've no need to invert.

I'll have a look at your 'problem'....

.................................................

OK, tie the O/P's together, ground the I/P you don't want to use, drive the other.

That should give opposing O/P's.

Str.

Right, that's what I did and none of the inverted ones are working. They are always low. I checked with a scope right on the output of them.

If I fix this, maybe it will work  Even with only one side of the amp firing, I am getting almost exactly 50% efficiency, so I think if I can make the other side work it should be pretty good.
I found that 10V may actually be enough for the drivers. It doesn't seem to lower the output/efficiency until I go to 9V or less.

I don't know if you checked the image of the board, but here it is. You can see the subtle change on the drivers for each side.

Thanks for the help stretchy.

55

The RF Workbench / Re: NCP driver sucks

« on: October 14, 2019, 1147 UTC »

Thanks for the replies!

The NCP's are fine to beyond 14MHz driving GaN.

The issues arrive from driving Qg and the SiC's I use, C3M0280090D have a Qg of 9.5nC. (GaNs have Qg of 6nC)

Power required to drive FET is QgxfxV, so 9.5e-9x7e6x12 = 800mW so they get a bit warm but are fine.

Apart from one op blowing the sh*t out of the whole Tx by powering it with A.C. I've never had one blow.

Are you using the same SiC FETs?

Str.

Yes, that's the one I'm using.

There must be some small difference about my PCB that's making it not work, but it's just too marginal. 800mW in that SOIC-8 seems like a lot. In my situation they are also hand soldered, so the dissipation through the pins is probably not as good as if I had used solder paste.

If I was going to continue this, it wouldn't be hard to make a GaN version of the board because it would just require swapping the drain and source pins. Then the NCPs would run easily with a lot of headroom.

So then the only problem I would have is getting the inverted inputs on them to work.

Stretchy: Have you used the inverting inputs on these? How do you wire it up? I tried connecting the inverted input to the crystal and grounding the non-inverted input, but the output stays low. I have the two OUTH and OUTL tied together, but I think it's wrong. How should it be connected for inverting? Like I said the datasheet is no help and the truth table doesn't make sense. There is no diagram of how to use the inverted input and clearly it's not just a matter of connecting the input to it.

For the record, all these parts are spec'd to 2 MHz...that is all.  In the early days of using power conversion parts, I quickly found that the DIP package parts smoke driving anything over 1 MHz.  I switched to tabbed devices and all my problems went away...sortof.  It did take a bit of fiddling with different parts until I settled on the '614's.  in most applications, you can use the TO-263 version up to about 9 MHz or so, depending on what you are trying to drive.  My fets are about 1000pf each and the 614's will happily drive them to about that, maybe more with decreased performance and more heat.  I'm not sure if there is much of a performance difference between the 4452's and the '614's but the heatsink tab on the latter is tied internally to VSS, which makes layout and thermal management easier.

Fall is here, and 4 MHz historically has worked much better for me than 6 MHz when the leaves start to fall 

+-RH

Eventually some day when I have more time, it's clear to me that the 614s combined with GaN are probably the best, most durable and fool proof way. I love how the tabs are grounded on the 614s and the transphorm GaN. All fets should be that way.

56

The RF Workbench / NCP driver sucks

« on: October 13, 2019, 1749 UTC »

I'm on my 4th revision of my PCB and the first one was the best. On the first one, I used TC4452 because I didn't know about the IXDD614 at that point. After that I found out about the NCP and thought it would be better than the 614 and so I built my last three PCBs based on it. It was a big mistake and I wasted so much time on it and now if I want to use the 614s, I have to basically start over at square one. So I am giving up for at least a year. It pisses me off because I'm not the type to be able to put something like this down, but it's not worth it to get angry over something like this.

BTW: The waves going in and out of them are square as can be (as square as the crystal source which is connected with very short straight traces).

So what's wrong with them?
1. They get dangerously hot at 12V and above - they may do 15V with a heatsink on top, but they were emitting a smell like they were about to pop (and I did pop several).
2. The datasheet (especially the truth table) is either just really confusing or the design is just wrong. Based on the truth table, there is no way to use the inverting input as the output will always be low. I found this to be the case in practice also.

So yeah, I think it will work with GaN cause they only need about 8V, but if you got it working with SiC at higher voltages, then you must have magical powers.

So for now, I'm just going to use my original design board that works good below 5 MHz. I guess I won't be on the 'fun' band any time soon lol 

EDIT:

Here's the datasheet: https://www.onsemi.com/pub/Collateral/NCP81074-D.PDF

Truth table page 5.

57

The RF Workbench / Re: IXYS-RF better than GaN?

« on: October 07, 2019, 2356 UTC »

That was my suspicion, thanks!

Right now I use C3M0280090D which has 280 mOhm and 150pf

I am looking at GaN:
41mOhm and 1500pf
https://www.transphormusa.com/document/datasheet-tp65h035ws-650v-gan-fet/

60mOhm and 1000pf
https://www.transphormusa.com/document/datasheet-tp65h050ws-650v-gan-fet/

So they have lower RDS on, but much higher capacitance. So what is more important RDS on or capacitance? Would they be better?

Thanks

58

The RF Workbench / IXYS-RF better than GaN?

« on: October 07, 2019, 2256 UTC »

I just came across these mosfets that are designed specifically for class D or E amplifiers. I knew about SiC and GaN being good options, but I didn't know they made fets for this specific purpose. Do you think they would be better than GaN? The RDS on doesn't look as good as the Gan, but what do you think? Maybe it's just older technology being advertised for this purpose?

IXZR16N60
IXZR08N120

http://ixapps.ixys.com/DataSheet/IXZR08N120-120A-120B.pdf
http://ixapps.ixys.com/DataSheet/IXZR16N60-60A-60B.pdf

They're kind of expensive, but I might try them at some point.

59

The RF Workbench / Re: Stretchyman 40w GaN TX is sick

« on: October 07, 2019, 1041 UTC »

I have a cheap-o PS I got from amazon. Its really stable and has its own variable fan. Says it can do up to 15A.

I don't understand why so many people buy those unbranded Chinese power supplies. I've seen many of those malfunction.
I could understand if the price was significantly cheaper, but IT IS NOT.

You can get a good quality meanwell of that power level for $30
$19 vs $30 bucks isn't a big deal.

https://www.trcelectronics.com/View/Mean-Well/LRS-350-24.shtml

Once you get into the higher wattages, then it makes sense. For those higher powers, eltek flatpacks, and Chinese Velikas are good.
https://www.aliexpress.com/item/32835899833.html

Sorry to get off topic. I'm done.

60

General Radio Discussion / Are there no radio laws in Greece?

« on: October 06, 2019, 2041 UTC »

There are so many pirate rig builders in Greece. Specifically AM, but I see a lot of HF and FM stuff also.
Does anyone know the details of this?