HFU HF Underground
Technical Topics => The RF Workbench => Topic started by: Charlie_Dont_Surf on December 05, 2021, 0519 UTC
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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 (https://app.box.com/v/ty24asdfjAEF00)
Gerber files zip archive is here: https://wetransfer.com/downloads/0415f9221a49b764d95fb207e143c59e20211205050846/d5a62f (https://wetransfer.com/downloads/0415f9221a49b764d95fb207e143c59e20211205050846/d5a62f) (See below for new links)
BOM is here: https://wetransfer.com/downloads/9a9d186b74de847f01f336f0f2ee4b0a20211205050536/9d12ab (https://wetransfer.com/downloads/9a9d186b74de847f01f336f0f2ee4b0a20211205050536/9d12ab) (See below for new links)
(https://i.imgur.com/D9qYHIV.jpg)
(https://i.imgur.com/Q7B8s4z.png)
(https://i.imgur.com/fBRgNWa.jpg)
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interesting
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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
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nice update
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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 (https://we.tl/t-mEexddP14C) See below for updated links
BOM: https://we.tl/t-mJj5yAScly (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.)
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Lulu might.
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Lulu might.
She doesn't get a vote.
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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 (https://app.box.com/v/ty24asdfjAEF00)
Gerber files in a .ZIP archive: https://app.box.com/v/6yw5shwjhnAsygAna29 (https://app.box.com/v/6yw5shwjhnAsygAna29)
BOM in CSV format (can be read by Excel, among others): https://app.box.com/s/q9gj56wmxp8lc4fghy2cukrdyxdu24id (https://app.box.com/s/q9gj56wmxp8lc4fghy2cukrdyxdu24id)
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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.
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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.
(https://i.imgur.com/6k3IDWQ.png)
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.
(https://i.imgur.com/9WrqA2d.png)
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.
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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.
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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?
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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.
(https://upload.wikimedia.org/wikipedia/en/f/fb/Gerber_company_logo.png)
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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.
(https://upload.wikimedia.org/wikipedia/en/f/fb/Gerber_company_logo.png)
LMMFAO
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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.
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Charlie, thats a really professional write up. Thanks for sharing it.
I've always daydreamed of a transmitter system where there's multiple exciters for the different bands and one big amplifier that is broadband.
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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.
Actually, the voltage difference is not all that great. Class E is around 4x Vcc, CMCD is around 3.14x in my experience. There are plenty of good devices in the 600V class now that will work nicely in either architecture. Also, dead time control is nice but not necessary for push-pull operation. I've had PA's running at 80 meters or so with no dead time control circuitry. I even built a 2 mosfet 500W MW PA that is running in commercial service with just a 7486 setup as a phase splitter...no drive loss protection though :-\
For me one of the appeals of CMCD was the elimination of most of the cumbersome ferrite in the output section. I even started using hardline (0.141") coax as a combination tank resonator and output transformer. No ferrite required! Typical PA impedance with respect to Vmod is on the order of 10 ohms or so, assuming the PA is looking into 50 ohms.
+-RH
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Thanks RH. I need to adjust my layout to accommodate a higher Q shunt tank inductor as the current one is the only thing getting warm!
Ok I looked at the peak drain V and noticed it wasn't as high as class E but still, as you say I can see the need for the higher voltage parts so will stick with them.
Single SOIC driver easily drives 3 and would drive 5 devices.
I've taken the little beast to my local university where they'll give it their critique. Will be fun for them I think and make a change from LMBA & Doherty at 40+GHz! There's some learned folk there, one quite well know in amplifier design circles. Hopefully they can help me improve it further.
Oh, just to add, I've never seen the need for any duty cycle adjustment and rather crudely just use a dual inverter at the input, inverting once to drive one driver, then inverting again to drive the other. Using a sine wave at the input adjusting it's level from 3V to 5V give a 40-47% adjustment.
The CMCD design I was given used duty cycle adjustment and I don't see any measurable difference between that more complex design and mine.
Str.
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Ok I looked at the peak drain V and noticed it wasn't as high as class E
That's what I see in simulation and in reality too. CMCD peak drain voltage excursion is less than Class E. In my simplistic back-of-the napkin look, CMCD excursion theoretically shouldn't be a lot more than Vdd but in reality I'm seeing something in the range of 2 to 2.5xVdd, depending upon the tank circuit Q, loading and all that jazz.
I've taken the little beast to my local university where they'll give it their critique. Will be fun for them I think and make a change from LMBA & Doherty at 40+GHz! There's some learned folk there, one quite well know in amplifier design circles. Hopefully they can help me improve it further.
I going to make an educated guess that you're referring to Dr. Steve Cripps at Cardiff U. I took a couple short courses from him a very long time ago. He's a world-renown expert in PA design.
https://www.cardiff.ac.uk/people/view/364356-cripps-steve (https://www.cardiff.ac.uk/people/view/364356-cripps-steve)
Oh, just to add, I've never seen the need for any duty cycle adjustment and rather crudely just use a dual inverter at the input, inverting once to drive one driver, then inverting again to drive the other. Using a sine wave at the input adjusting it's level from 3V to 5V give a 40-47% adjustment.
Because CMOS/TTL propagation delay for an inverter is ~3-40 nanoseconds, depending upon the family chosen. A 7 MHz signal has a period of ~140 nanoseconds and a half cycle is ~70 ns. With what you have described, you have probably at least 10 nsec propagation delay on one phase (including the FET driver) and so an additional ~5-15 nsec on the other phase, aside from the 180 degree delay. Ten nsec out of 70 nsec is a significant portion of the waveform and apparently enough for you and the settling time of your CMCD circuit. So in this case, leaving it to chance (which totally doesn't surprise me, coming from you) works, but then you probably haven't looked at the rise and fall times on the gates and drains thoroughly over all conditions, multiple DUTs anyway. I like to have options with the ability to adjust for safety margins and maximize the possible conduction angle, hence a non-overlapping clock generator with some adjustability.
So while your crude circuit isn't adjustable, it's still a dual-phase clock generator at least for some range of frequencies but it definitely doesn't lock out/prevent overlapping.
A non-overlapping clock generator isn' t big deal. At it's simplest level, it's a pair of NOR or NAND gates and an inverter in front.
(https://i.imgur.com/mUyu3CF.png)
(https://i.imgur.com/18hOlUH.png)
Taken from: http://individual.utoronto.ca/schreier/lectures/3-6.pdf (http://individual.utoronto.ca/schreier/lectures/3-6.pdf)
Edit: Ha. Just realized I know the professor at U Toronto that made these slides. So that's two people I (vaguely) know referred to in one post.
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Charlie, thats a really professional write up. Thanks for sharing it.
Thank you. I'm glad that you got something out of it.
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Also, dead time control is nice but not necessary for push-pull operation. I've had PA's running at 80 meters or so with no dead time control circuitry. I even built a 2 mosfet 500W MW PA that is running in commercial service with just a 7486 setup as a phase splitter...no drive loss protection though :-\
Let's put it this way: maybe you are not explicitly controlling it and providing adjustability to it, but one way or another you are probably not cross-conducting much or at all. How that happens - or rather doesn't happen - only you can say. Otherwise, if something - anything - was not there making it not cross-conduct, either by dumb luck or intentionally prevention, you might have somewhat different results.
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:shrug: It doesn't seem to matter much until you get over 4 MHz, then things get hairy, and efficiency tends to nose-dive. My main transmitter has overlap control and drive loss protection, FWIW.
+-RH
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:shrug: It doesn't seem to matter much until you get over 4 MHz, then things get hairy, and efficiency tends to nose-dive.
+-RH
(https://i.imgur.com/RHxBcy6.png)
"Quite curious, Captain."
The behavior above 4 MHz is what I would expect almost everywhere there was actual significant overlap.
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I'm fine upto 15 MHz so far but then devices with a Qg of 2.2nC aren't exactly difficult to drive. Also I'm comparatively QRP in comparison!
Str.
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My 'daily driver' PA has a drive delay and protection circuit onboard, and seems fine up to 10MHz or so. I haven't investigated any higher as I feel there is little merit in doing so, and have no interest in anything above 30 meters. The simple drive circuits consisting of just an xor configured as a phase splitter start having efficiency drop off after 4 Mhz. This makes sense as the drive pulse distortion begins to be a larger fraction of on time with increased frequency Granted this was a PA I built several years ago now and there are other devices and drivers to try.
+-RH
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For me one of the appeals of CMCD was the elimination of most of the cumbersome ferrite in the output section. I even started using hardline (0.141") coax as a combination tank resonator and output transformer. No ferrite required!
I have been unable to find a reference to allow me to design these sorts of things. Even output transformers like TL1 & TL2 & TL3 below, which do use ferrites. Obviously I can copy something somebody already did but I'm looking for some sort of reference on how to design them. Short of having that, I can make some guesses and assumptions as starting points (L and C per foot of the coax, permittivity of the ferrite, etc.) but I'm thinking that there is more to it than that. :D
I dunno, maybe people just start winding and see where they end up and adjust as necessary?
(http://www.w1vd.com/partsplacement.jpg)
(https://i.imgur.com/lgQluNQ.png)
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I used that design as a starting point but ended up just using a single balun on the o/p.
As I'm learning ADS I'll simulate the thing at some point but as it's already working at 93% efficiency I don't see too much to be gained.
I'm interested in any other design that leads to simplification and an increase in efficiency so please post up.
I'm happy to design PCBs and fit the fiddly bits if anyone is interested.
Str.
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I used W1VD's design as the basis of my work. All I did was remove the 1:4 output transformer and directly couple the tank to the balun. This, with a change to modern SiC devices, makes it possible to get kilowatt level carrier power from just two devices. In my current design, the balun has been replaced with a hardline transformer wound into the tank coil, the outer being the primary as well as the tank inductor, the inner being the output winding. The RFC's don't seem to be real critical, just aim for 10x reactance of the nominal line output impedance. Doing these modifications raises the PA modulator impedance to around 10 ohms or so, easing current carrying requirements at high power.
+-RH
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My first build attempt at the U-LULU, with a board made by JLCPCB using CDS's gerber files.
(https://i.ibb.co/nPsGr8Q/2023-03-04-12-24-47lo.jpg) (https://ibb.co/DrDJ4gw)
Learning how to solder all over again with a hot-air rework pencil, great for the chip but how do I stop the tiny caps flying away :)
On a test-jig I'm getting about 15w carrier, still more work to getting the output coil right and finding a suitable modulator. Any ideas on something still available from China in 2023?
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The TPA3116 amplifier boards and their clones seem to work well. Tie the positive outputs together, and add a solder blob to tie the wipers of the pot together. This will ensure that outputs are as close to the same as possible, so one channel doesn't fight the other. Seems to be good to 15W or so.
https://www.ebay.com/itm/284160314693?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=hksnm2-7qz6&sssrc=2047675&ssuid=XS3HxYCuQ6C&widget_ver=artemis&media=COPY (https://www.ebay.com/itm/284160314693?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=hksnm2-7qz6&sssrc=2047675&ssuid=XS3HxYCuQ6C&widget_ver=artemis&media=COPY)
+-RH
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My first build attempt at the U-LULU, with a board made by JLCPCB using CDS's gerber files.
(https://i.ibb.co/nPsGr8Q/2023-03-04-12-24-47lo.jpg) (https://ibb.co/DrDJ4gw)
Learning how to solder all over again with a hot-air rework pencil, great for the chip but how do I stop the tiny caps flying away :)
On a test-jig I'm getting about 15w carrier, still more work to getting the output coil right and finding a suitable modulator. Any ideas on something still available from China in 2023?
Very nice! I feel like a proud papa. :D I saw your DM too and you've obviously figured out posting photos on HFU and you have an additional 5 Watts since that DM so all is good.
As for the power output, it would be good to know if you are trying to do this at 6250 KHz (as I did) or another frequency.
Using a different batch of PCBs (which is inevitable) and using a slightly different winding technique than mine (also inevitable) will introduce possibilities for variation. Your PCB manufacturer will likely have a slightly different material property (called Er, "E sub R" in the spoken lingo) than mine, meaning that you may want to adjust L2, C5 and C6 slightly to compensate. To tune L2, you can push and squeeze the wire of L2 a bit.
One of the decisions I made during the design tuning was to sacrifice bandwidth for maximum power output and this means that the if you are trying to use this transmitter at 50-100 KHz away from 6250 KHz (approximately), you might not get the full output I claim. I think that it may make sense to also offer folks a broader bandwidth output tuning (which I have simulated in the computer but not built in real life) to make it a little less sensitive to my narrowband tuning I specified in 2021. My initial computer simulations suggest that I can get similar power output and broader bandwidth with a completely different set of L and C values. It remains to be seen if this is true in real life but when I verify I will update. I may also add a 43 meter band tuning option too.
For the modulator, perhaps you missed in the text (page 8 ) but I am recommending the Wondom AA-AB31184.
In North America, they are available here: https://www.parts-express.com/WONDOM-AA-AB31184-100W-Mono-Amp-Board-320-3341?quantity=1 (https://www.parts-express.com/WONDOM-AA-AB31184-100W-Mono-Amp-Board-320-3341?quantity=1)
In other parts of the world they seem to be available from Farnell in the UK, Audiophonics in France, AliExpress, Ebay, Opentip, etc.
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Hi
Yes, aiming for the 6.2 - 6.3 range. With 21 turns for L2 it was a little high, peaking in the 6.4 region so I tried 23 turns which brought it down to 5.8, so I've settled on 22 turns for the moment which seems about right with the ability to squeeze or open the coil a little.
I did see that you had used the Wondom board, they seem to be pure unobtainium in the UK, I have accounts with Farnell and their sibling CPC and they don't have them. I'll trawl AliExpress and Banggood to see what they have.
I have tried a clone 100w mono board from eBay also based on the TPA3116 but no joy at all. I'll give it another go this weekend when I have some more time.
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https://www.aliexpress.com/item/1005001350507780.html
Always best to buy directly from the country of origin.
Farnell even sell them so not sure where you're looking but unable to find?
Didn't realise you were in the UK..
Str.
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Yes, aiming for the 6.2 - 6.3 range. With 21 turns for L2 it was a little high, peaking in the 6.4 region so I tried 23 turns which brought it down to 5.8, so I've settled on 22 turns for the moment which seems about right with the ability to squeeze or open the coil a little.
OK.
I did see that you had used the Wondom board, they seem to be pure unobtainium in the UK, I have accounts with Farnell and their sibling CPC and they don't have them.
Forgive me, I was wrong and it appears that Farnell does not carry them nor does AliExpress any longer ("no longer available"). Well that's a bummer. When I started this thing in 2021 they were quite available but of course 2 years is an eternity in this industry, especially with the disruption of COVID-19.
- The price from Audiophonics in France is great and is ~$10US lower than parts-express.com in the US charges. That would pay for the (surely) additional shipping cost from France to me.
- It appears that Sure (Wondom is Sure Electronics) has a "marketplace" store on Digikey (akin to Amazon Marketplace, it appears) and their price is not too bad: https://www.digikey.com/en/products/detail/sure-electronics/MPAB1X100-TPA3116/13982205 (https://www.digikey.com/en/products/detail/sure-electronics/MPAB1X100-TPA3116/13982205)
- It appears you can also buy direct from Sure but the shipping is probably from Taiwan: https://store.sure-electronics.com/product/AA-AB31184 (https://store.sure-electronics.com/product/AA-AB31184)
I'll trawl AliExpress and Banggood to see what they have.
I have tried a clone 100w mono board from eBay also based on the TPA3116 but no joy at all. I'll give it another go this weekend when I have some more time.
I have a DROK (or Bangood?) module or two and they are problematic in this application. The audio cuts out intermittently, especially at high output and I assume it to be the over-current protection circuitry doing this. The protection appears to be a bit more over-zealous than a real TPA3116-based module. (The U-LULU is something like a 3-4 Ohm load according to simulation.)
Whatever you end up going with, it needs to drive at least 5 Amps peak at 4 Ohms (100 Watts into 4 Ohms differential = 5 Amps RMS). Of course, we are using the amplifier single-ended with the U-LULU. Four Ohms differential (such as a loudspeaker) is equivalent to 2 x (2 Ohms single-ended to ground). If it can handle a 4-Ohm speaker then it should be good to go. Of course the Bangood and DROK are supposed to drive 3 or 4 Ohms too, so.....
For this weakness and a few other reasons (that I am too lazy to describe right now) I suspect Banggood and DROK modules are built around counterfeit TPA3116 chips that can't drive a 2-Ohm load like the real thing from TI. Caveat emptor.
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The ones I have are DROK or a clone off amazon, and they work fine up to 15-17W carrier and don't cut out until you hit 29VDC input. The PA's I run are around 10 ohms at the DC input. The small boards seem better than the larger ones. I bought one of the larger 100W amps, and upon closer inspection found it had a small IC in it from a LCD TV, which also didn't pass DC. Caveat Emptor indeed.
+-RH
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Shame they keep changing product design or they're simple short lived.
When I started using the TPA3116D2 amps you could get one with heatsink, volume pot with power switch, 1/4" I/p skt and space under the PCB for a voltage reg. I think they redesigned it about 5 times changing the shape and position of the connections every time. Made it a real pita. Ended up buying 200 of the last ones they produced. Less than £10 ea.
Tinytronics in NL did have them a while ago.
SKU:
000250
They may still have some...
Str.
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It appears you can also buy direct from Sure but the shipping is probably from Taiwan: https://store.sure-electronics.com/product/AA-AB31184 (https://store.sure-electronics.com/product/AA-AB31184)
Bought a couple direct from the sure-electronics web site - just a week from order to delivery ... good price too
They are definately a cut above the boards I had from eBay, looks like they have 12v o/p and mute/standby switching as well.
Good call!
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Any ideas on something still available from China in 2023?
I bought a couple of these: HW-576 mono amplifiers from Aliexpress. They cost around £5 each, and are supposed to be "100 W".... With a 24V supply, the positive speaker terminal sits at 12V DC without audio applied, and when I lashed one up to a thrown together "U-LULU" circuit (though using a PLL synthesiser rather than a crystal), I got round 24 Watts carrier and could fully modulate it without anything getting hot! The 3116 IC on the amplifier board has a small heatsink on it, and I expected it to roast, but was pleasantly surprised at how well it survived the abuse!
I added extra filtering to the output of the amplifier, since I really didn't want spurs either side of the carrier - offset by the amplifier switching frequency! My next iteration of the design will continue to use this audio module (I don't think that I could do much better), a programmable oscillator module (one of the really cheap ones programmable with an Arduino), and a PCB that's off at JLC at the moment. The high efficiency and small number of cheap parts required suggest that it might be worth extending this design for higher power, adding some simple audio processing and possibly a little MP3 player board that works with either SD cards or USB sticks. I can see lots of these being shipped to Eastern Europe in the 48m and 41m bands!
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Power wise you just need more volts and a decent SiC or GaN Fet as they're 650V so can run 100V on the drain.
Single ended class E has its limitations so best to go with CMCD, being push pull is easy to get a 50-60W carrier (@24V) and not too much trouble to get 100W (@30V) with the right devices.
As to selling stuff to E EU, noone outside of E US is interested. In the 10 years I've been producing probably sold less than 10 to EU. I think they still like valves!
Str.
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Thanks for the comments.
I bought a couple of these: HW-576 mono amplifiers from Aliexpress. They cost around £5 each, and are supposed to be "100 W".... With a 24V supply, the positive speaker terminal sits at 12V DC without audio applied, and when I lashed one up to a thrown together "U-LULU" circuit (though using a PLL synthesiser rather than a crystal), I got round 24 Watts carrier and could fully modulate it without anything getting hot! The 3116 IC on the amplifier board has a small heatsink on it, and I expected it to roast, but was pleasantly surprised at how well it survived the abuse!
I have recently spent some time trying to squeeze a little more power out the U-LULU. Of course the complexity of dealing with the interaction between the oscillator circuit, the six inverters used as a gate driver and the one inverter used a buffer between them was anticipated but it's still something of a pain in the backside.
You made a good decision to use an external oscillator. When I use an external frequency source, I too can get ~25 Watts without a struggle but using the crystal oscillator as I have configured the circuit will reduce that to probably less than 20W. I had previously assumed that lower power out than 25 W or so was just simply a tuning issue. In fact I have determined the main culprit is the duty cycle of the crystal oscillator, and I am only able to get ~38% duty cycle out of it, despite a lot of tweaking and optimization work. That wouldn't be a problem but that oscillator signal then goes through two inversions in series, the first being the inverter used as a buffer and the second being the six inverters in parallel driving the FET gate. From the standpoint of duty cycle, two inversions in series is equivalent to no inversion, so this leaves the duty cycle of the gate drive only ~38%, as opposed to an external oscillator drive, which is probably ~50% (but if you use a function generator like I did, it can be anything that you want). Lower duty cycle gate drive leads to lower RF power output. This explains the discrepancy in RF output power.
I tried bypassing the buffer and that delivers a higher duty cycle to the FET gate (100-38% = 62%) which is excellent but, because of the interaction between the oscillator, the gate driver inverters and the FET, the output needs to be retuned (big sigh). My first cut without retuning gave me 26 Watts out but the efficiency was terrible, ~50% versus ~90% previously, and this has lead to a thermal issues, SOA (Safe Operation Area) violations and some destroyed FETs as I work on it. :( I'm still getting this sorted out. :D
I'm not excited about dealing with the circuit interactions and I'm really not interested in frittering away my life on a circuit like this but I also want to make this a little better for folks if I can. I will "pull the eject cord" soon enough and work on other things that aren't so fundamentally messy when I've decided I've either had enough of this tomfoolery or I beat this issue into the ground. ;D
I added extra filtering to the output of the amplifier, since I really didn't want spurs either side of the carrier - offset by the amplifier switching frequency! My next iteration of the design will continue to use this audio module (I don't think that I could do much better), a programmable oscillator module (one of the really cheap ones programmable with an Arduino), and a PCB that's off at JLC at the moment. The high efficiency and small number of cheap parts required suggest that it might be worth extending this design for higher power, adding some simple audio processing and possibly a little MP3 player board that works with either SD cards or USB sticks. I can see lots of these being shipped to Eastern Europe in the 48m and 41m bands!
I have already made the schematic and created the PCB layout for a follow-up that is similar to what you describe:
1) frequency source of either a) a selectable crystal oscillator (with a real crystal driver chip that is designed to work at HF) or b) an external oscillator input.*
2) selectable audio preamp circuit for those that want to use laptop computer, mobile phone or MP3 player as the audio source
3) RF filtering on the input of the preamp to keep the amount of RF injection hopefully low enough
3) continue to use a Class-E output, tuned for a lower Q than the U-LULU that should be able to deliver roughly equal power output from 6200-6300 KHz,
4) probably with an output somewhere between 30 to 40 Watts, better than U-LULU, largely due to being able to run the gate drive voltage much higher than 6 Volts.
5) PCB footprint currently equal to the Sure audio module I recommend for U-LULU so that the two PCBs can be stacked one on top of the other.
*Or I might just ditch the external oscillator input (though it doesn't take up much PCB space) in lieu of the neat little synthesizers I found (which I mention here https://www.hfunderground.com/board/index.php/topic,115861.0.html (https://www.hfunderground.com/board/index.php/topic,115861.0.html))
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I've done a little more to the U-LULU. I tried a few other FETs with varying degrees of success. I've included my own design of power supply sequencing (based on a bit of simple CMOS logic). With some work, I got efficiency up to around 92% with tuning that's open enough to allow it to go anywhere from 6.25 - 6.45 MHz without much change in power output. The carrier cleanliness is also now up to commercial standards, since I decided to extend the output LPF by an extra section. Just for the sake of amusement (and with a nod towards possible automatic mod depth adjustment) I introduced envelope feedback to the modulator. The audio distortion that I previously had on the unmodified version has completely disappeared (it was previously in the order of 9% at peak mod). Measurements now show the distortion to be well below 0.2%, and I've been able to add some audio response shaping to make it sound a bit "nicer" (according to my wife!).
I also built a couple of these things for MW (1.2 - 1.4 MHz) with really good results. They run virtually cold, provide really good harmonic cleanliness, and have really good sounding modulation.
We've made a few of the early 6.3 MHz versions and they've been snapped up by our Eastern European friends (as predicted). Perhaps the English commercial constructor earlier in this thread has upset potential Eastern European clients, because we've had a lot of expressions of interest from over there - for both versions (SW and MW). The enhanced version - with automatic modulation level control (a three-band audio processor), a built-in MP3 player and a "Universal Input" SMPSU to power it up looks like it should be particularly popular, and I may well make the details available on here for everyone to use. We have also shipped a couple to South America, and received good reports.
It was quite fun to hear one of my hand-built early prototypes - being run in southern Spain - up here at home in the Benelux at New Year! That one produces ~26 W carrier / ~102 W PEP, and uses one of those "ProgRock" synthesiser modules.
We don't intend these to ever be a commercial product, but we're in touch with many clandestine SW operators, and we'll be sure to supply a few of them to interested parties.
In closing, I'd like to thank CDS for his efforts in improving the basic LULU. The original was a pretty clever idea despite its flaws, and the CDS improvements made it into a great little transmitter. There's a whole lot more that can be done to these little beasts, and - when I find the time - I'll be doing some additional design work.
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Albert - Sounds very interesting and thank you for nudging this project along.
I'm very interested to see how you implemented the envelope feedback. I never thought to do something like that because - as far as I could tell - much of the distortion came from the Class-D amplifier. I assumed this because I was operating it at essentially max load on peaks, plus a DC load on top of it (which it was never really built for). The THD dramatically increases from ~10 W to ~100 W (max) output and I just assumed that short of implementing some sort of pre-distortion (which I really was not interested in delving into), that there was probably not much I could do about it, other than use a much bigger Class-D amplifier. Apparently I was wrong.
As for other the use of other transistors, there are a limited supply of TO-220-packaged transistors that could be used and of course it must be said that the TO-220 package is going the way of the dinosaur over the coming years. As far as I know the Nexperia PHP18NQ11T that I used in the U-LULU has not been put on NRND ("not recommended for new designs") or EOL ("end of life") status yet, the former being the precursor to the latter. The Infineon IPP530 is really good in this application too. The TO-220 version is now in EOL but they have a TO-252 version that will likely be available for quite some time. The Toshiba TK11S10N1L should work too, but it only comes in a TO-252.
I have already made the schematic and created the PCB layout for a follow-up that is similar to what you describe:
1) frequency source of either a) a selectable crystal oscillator (with a real crystal driver chip that is designed to work at HF) or b) an external oscillator input.*
2) selectable audio preamp circuit for those that want to use laptop computer, mobile phone or MP3 player as the audio source
3) RF filtering on the input of the preamp to keep the amount of RF injection hopefully low enough
3) continue to use a Class-E output, tuned for a lower Q than the U-LULU that should be able to deliver roughly equal power output from 6200-6300 KHz,
4) probably with an output somewhere between 30 to 40 Watts, better than U-LULU, largely due to being able to run the gate drive voltage much higher than 6 Volts.
5) PCB footprint currently equal to the Sure audio module I recommend for U-LULU so that the two PCBs can be stacked one on top of the other.
Well, I did eventually get the bare PCBs back from fab but I have had to devote a lot of time to activities other than radio in the past 6 months. As a result nothing has been done to test it out.