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Author Topic: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter  (Read 7450 times)

Offline Charlie_Dont_Surf

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A friend who lives in Europe asked me to design a small transmitter. He has a supply of FT-243 crystals from "the before time" and wants to use them on a small transmitter. I hadn't done much with crystals in years but after doing a bit of looking around, I started looking at the venerable and often used LULU design.

As I looked, there were a number of things that bothered me about them and I could see that there was quite a bit of “low-hanging fruit” that could be easily “picked off the tree” (improved) without a huge effort. In the end, I decided to redo and modernize the LULU for him, making it an updated LULU, i.e., the “U-LULU”. I have added a commercially-available Class-D audio amplifier to make a complete AM transmitter with approximately 20 Watts carrier power output (80 W PEP) in the 48-meter band. This is better than the original LULUs, where output is reported to be in the 10-to-15-Watt range. I decided to publish this design to make it accessible to others.
 
I regard this as an entry-level transmitter, suitable for those with less building and electronics experience. For the SMD haters, I have purposely used a through-hole TO-220 transistor and larger SMD components. Most capacitors are at least Imperial 1206/1210 [Metric 3212/3225] though there are some 0805 [Metric 2012] components.

Complete write-up is here: https://app.box.com/v/ty24asdfjAEF00

Gerber files zip archive is here: https://wetransfer.com/downloads/0415f9221a49b764d95fb207e143c59e20211205050846/d5a62f   (See below for new links)

BOM is here: https://wetransfer.com/downloads/9a9d186b74de847f01f336f0f2ee4b0a20211205050536/9d12ab     (See below for new links)









« Last Edit: August 13, 2022, 2355 UTC by Charlie_Dont_Surf »
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline outhouse radio

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #1 on: December 05, 2021, 2019 UTC »
interesting

Offline Charlie_Dont_Surf

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #2 on: December 10, 2021, 2221 UTC »
interesting

I'm glad that somebody thinks so.

Anyway, there's more to come. I've have become interested in designing small MW/HF transmitters. I can easily improve the gate drive and perhaps get a bit more power output on a smaller board. The end result will make the SMD haters very unhappy but that's the way the cookie crumbles. :D
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline markoramius

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #3 on: December 12, 2021, 1416 UTC »
nice update

Offline Charlie_Dont_Surf

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Apparently the links for the gerber files and the BOM (Excel .CSV format) are dead. Here are new links:

gerbers: https://we.tl/t-mEexddP14C See below for updated links
BOM: https://we.tl/t-mJj5yAScly See below for updated links

The link for the article is still good: https://app.box.com/v/ty24asdfjAEF00

All the links are completely anonymous for both you and me. I have no idea who is downloading any of these nor do I even know how many times they have been downloaded.

If there is interest, I can do a another version with a synthesizer input (in addition to the crystal), a better drive circuit (for higher RF power output) and a single power supply input for the whole transmitter (for simpler installation). It won't be a LULU anymore but I don't think anybody really cares about that detail. (I certainly don't.)
« Last Edit: November 21, 2022, 1833 UTC by Charlie_Dont_Surf »
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Pigmeat

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Lulu might.

Offline Charlie_Dont_Surf

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Lulu might.

She doesn't get a vote.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Charlie_Dont_Surf

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #7 on: November 20, 2022, 2209 UTC »
New Links. I think that these will be available for more than just 6 months or whatever.

Write up in PDF: https://app.box.com/v/ty24asdfjAEF00

Gerber files in a .ZIP archive: https://app.box.com/v/6yw5shwjhnAsygAna29

BOM in CSV format (can be read by Excel, among others): https://app.box.com/s/q9gj56wmxp8lc4fghy2cukrdyxdu24id
« Last Edit: November 21, 2022, 2148 UTC by Charlie_Dont_Surf »
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Stretchyman

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #8 on: November 21, 2022, 1755 UTC »
I've gone ALL GaN now.

Latest devices from GaN Systems in leadless packages, cheap and very easy to drive.

With a Qg of 2nC a single driver can drive 3 devices.

I've decided to use CMCD as it seems to be the simplest and most efficient for a single band design, >90% on a good day. Push pull with 6 devices gives 100W wi 30V@3A7.

Watch this space!  (Actually it will be another thread!!)

Str.
'It's better to give than receive' so why RX when you can TX!

         15W, 60W and 100W models available.

                   Buy one from me, NOW!


                                              ;)

Offline Charlie_Dont_Surf

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #9 on: November 21, 2022, 2147 UTC »
I've gone ALL GaN now.

Well, for you and your business of pre-made boxes, sure. But the average Joe, wanting to build something simple, isn't going to go that far.
And people are doing this. I continue to receive requests to update the links, hence, bumping this post with them.

Latest devices from GaN Systems in leadless packages, cheap and very easy to drive.

With a Qg of 2nC a single driver can drive 3 devices.

I've decided to use CMCD as it seems to be the simplest and most efficient for a single band design, >90% on a good day. Push pull with 6 devices gives 100W wi 30V@3A7.


Yes, and they aren't really something the average Joe are going to try to build because the absolute need for surface-mount techniques, a pre-heater, magnification, and on and on.



The industry is moving toward more and more surface-mount cooling packages such as this, as opposed to a through-hole package which allows for off-PCB cooling. Off-PCB cooling typically takes place on a heatsink, which inherently will have a lower thermal resistance and cool more efficiently than a PCB, at the cost of a chunk of aluminum, or at least metal, and maybe a fan. On-PCB cooling, such as required by these sorts of SMD packages, require a 4 or more layer PCB and extra space on the PCB to obtain best (and probably sufficient) cooling.  If you find that your PCB is insufficient, you can add extra cooling to the SMD-cooling PCB, but it requires ...wait for it... a heatsink and you will have to attach it either by thermal adhesive or push pins, if you have put in arrangements for that. Off-PCB heatsink cooling allows for ad-hoc cooling adjustments, post-PCB fab, and I find to be more flexible overall.

Cooling is not something to be ignored. If the efficiency is 90% and Pout is 100 Watts as you claim, then you are dissipating 10 Watts in the small area of the devices and the immediate area of the devices on the PCB. That is not a trivial consideration, especially in the context of a 30, 60 or 120-minute transmission.

These parts have low breakdown voltages which probably forces you into using a CMCD architecture, as opposed to a Class E architecture, in order to get the RF output power you are claiming, because of the peak drain voltage excursion in Class E. Nothing wrong with CMCD (I'm actually doing some myself) but it does bring a slightly higher complexity, with the need for a non-overlapping clock generator/due diligence to make sure you aren't cross conducting and some sort of output balun, be it a traditional wound one or an LC balun, because at these power levels the typical output impedance is significantly less than 50 Ohms.  On the other hand, if you are intent on using a low BV transistor in Class E, a cascode architecture should work.

The datasheet says an NVG (negative-voltage generator) is not mandatory with these GaN Systems devices but they also say that negative voltages are recommended to suppress gate voltage spikes. I would say the you may have some turn on/turn off issues (due to spiking and other things) if you are not able to source a negative gate drive voltage. This gets to the complexity issue; Qg is low with these, which helps in some ways, but then there are other things that make it complex.

All of this navel gazing is a long way of saying that there is no such thing as a free lunch and tradeoffs are everywhere.

I have other designs in the works for things that someone without a lab full of equipment and a Ph. D. could build. I am at the point where 90% of the things that I put some time into I decide to not pursue further after making the PCB layout or evaluating prototypes. This is about right in light of my professional experience. That percentage will come down in the future.

By the way, you can do similar things to your GaN Systems stuff with plain-old inexpensive MOS, especially when you consider that you are using one MOS transistor to multiple GaN Systems transistors, with the necessary extra  parasitic capacitance that comes from a multi-transistor PCB layout. Also, no need for an NVG.



Watch this space!  (Actually it will be another thread!!)

Nice try at getting around the ban on you advertising your wares here. If you are only publishing pictures with textual descriptions and not the schematics, gerbers and measured results, then you are just advertising.
« Last Edit: November 22, 2022, 0057 UTC by Charlie_Dont_Surf »
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline Pigmeat

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #10 on: December 02, 2022, 2038 UTC »
We used to feed my daughter Gerbers, but her name wasn't Lulu. A Gerbers jar is a handy thing to keep FT-243's in though.

There are a ton of FT-243's lurking in jars and boxes for people to play with. There are various ways of altering the frequency, but it's not usually worth the hassle. I knew a fellow who tried a whetstone and some mineral oil once. The FT-243 quickly went much higher than intended. Oh well, they're fairly cheap.

 

Offline Pigmeat

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #11 on: December 02, 2022, 2124 UTC »
It looks like a nice project for an "experimenter" looking to build a transmitter or exciter. Radio hooligans have been known to do all sorts of things with amps that follow exciters, ask the Russians. Perhaps they were generating the "brown note" earlier today that caused Putin to slip and fall backwards in his high ruble suit.

(Sorry for the minor highjack, but Putin crapping his pants this morning and falling backwards into them is far too good to pass up. It's what made me a pirate.)

BTW, nice design. Are you the guy who came up with the "Franken-Lulu" on the old Homebrew Pirate Group on Yahoo when dinosaurs roamed the Earth?




Offline Charlie_Dont_Surf

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #12 on: December 03, 2022, 0212 UTC »
We used to feed my daughter Gerbers, but her name wasn't Lulu. A Gerbers jar is a handy thing to keep FT-243's in though.

If it makes you feel any better, I can put an image of a baby's face on the next one.



I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

Offline outhouse radio

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #13 on: December 03, 2022, 0246 UTC »
We used to feed my daughter Gerbers, but her name wasn't Lulu. A Gerbers jar is a handy thing to keep FT-243's in though.

If it makes you feel any better, I can put an image of a baby's face on the next one.



LMMFAO

Offline Stretchyman

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Re: U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter
« Reply #14 on: December 03, 2022, 1743 UTC »
Just finished my latest build and sure I'll post up schematic but it's just the same ol' design with more modern devices.

Re soldering them down, piece of cake with a £30 hot air pencil from CH, simpler than soldering and cheaper than a decent iron, it's a technique that's simple to learn and just like we're not hand wiring valve bases anymore it's time to move forward and embrace modern technology, unlike regurgitating the same old designs, plenty of those around, eh!

I'm no spring chicken and knocking on the door of 60, sure I use a X4 magnifier that I hold in my eye socket and enables me to see whilst roasting the little buggers onto the PCB.

BTW I use 650V devices, 3 a side, maybe I'll try the 100V devices at some point.

Just a proof of concept BTW and no intention of selling anything, however I'd be happy to give some PCBs away with SMT parts fitted) so folk could have a play thermselves.

Heat wise, so far I've run the design at 40V and generating 140W @ 91% eff. After 1/2 hr the devices are 45-48C, no fan either, utterly amazing.

The cooling solution is rather simplistic (on purpose) and rather than having a milled slot to access and solder the heatsink to the underside of the devices, I've just used 8 vias under each fet to joint the top and bottom layes and use a 2mm thick copper strip bolted to the underside that then attaches to the heatsink. Crude but effective.

To generate 100W carrier (400W pep) is will need a 70V supply (35V carrier).

The new devices are fantastic and cheap too!

https://imgur.com/a/KAnhgOB

https://imgur.com/f2ZWrDg




Str.
« Last Edit: December 03, 2022, 1754 UTC by Stretchyman »
'It's better to give than receive' so why RX when you can TX!

         15W, 60W and 100W models available.

                   Buy one from me, NOW!


                                              ;)

 


Item image   Troubleshooting Analog Circuits by Robert A. Pease

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