U-LULU (Updated LULU) for 48 meters, 20 Watt Class-E AM Transmitter

[Charlie_Dont_Surf]

My first build attempt at the U-LULU, with a board made by JLCPCB using CDS's gerber files.



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. 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
In other parts of the world they seem to be available from Farnell in the UK, Audiophonics in France, AliExpress,  Ebay, Opentip, etc.

[europirate]

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.

[Stretchyman]

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.

[Charlie_Dont_Surf]

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
• It appears you can also buy direct from Sure but the shipping is probably from Taiwan: 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.

[redhat]

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

[Stretchyman]

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.

[europirate]

It appears you can also buy direct from Sure but the shipping is probably from Taiwan: 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!

[Albert H]

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!

[Stretchyman]

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.

[Charlie_Dont_Surf]

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.   

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. 

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)

[Albert H]

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. 

[Charlie_Dont_Surf]

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.