600W broadband 1.8-54MHz amplifier using affordable LDMOS devices - Page 1
Forum section: electronics / rf-microwave

author: M0HZH
author_rank: Regular Contributor
timestamp: October 30, 2019, 01:54:03 pm
content: Hi all !Long time reader here, today I decided to join to show off my first big project, a broadband RF power amplifier using a pair of US$35 LDMOS transistors. I've made this design to enter the NXP Homebrew Challenge 2019 and it received a very good response so far from the amateur radio community.See video here (the good stuff starts around 0:45, if you want to skip my ugly mug):https://www.youtube.com/embed/YDm3PJY7yxkFind all the details here:https://qrpblog.com/2019/10/a-600w-broadband-hf-amplifier-using-affordable-ldmos-devices/I am really curious to hear opinions on it as I want to evolve it into a better and more refined design.Thanks,Razvan.

author: TheMG
author_rank: Frequent Contributor
timestamp: November 01, 2019, 01:58:08 am
content: 600W from $35 worth of transistors is pretty good indeed.Would be very interested to see what the two-tone IMD test of this amplifier.That would likely require a spectrum analyzer though, but a "crude" measurement could be made with an SDR if a SA is not available.

author: CJay
author_rank: Super Contributor
timestamp: November 01, 2019, 11:23:19 am
content: Really nice project, those devices are a bit of a game changer.How well do they perform at 54MHz in your design?

author: M0HZH
author_rank: Regular Contributor
timestamp: November 01, 2019, 06:04:33 pm
content: Last measurement had P1dB around 580W at 50MHz, waveform & spectrum looked reasonably clean, gain still over 20dB.I have reworked the output a bit since the article, lost some efficiency and P1dB at 1.8MHz and harmonics look worse now (LPF will solve that) but 3.5 and 7MHz are better and 50MHz is better as well; I expect it to be usable on 70MHz too now.Working on porting the measurement tool to a faster platform (STM32, maybe I can get it to trigger protections fast enough) and then I'm going to have a look at IMD degradation on the Red Pitaya (input vs output).

author: Weston
author_rank: Regular Contributor
timestamp: November 01, 2019, 06:17:59 pm
content: The NXP LDMOS are pretty good devices.I used the MRF101AN for a Class E RF amplifier for a cubesat plasma thruster at 40.68MHz. It fixed some issues I was having in a previous design using a GaN E-HEMT that was not very robust. I ended up submitting that to the NXP RF design challenge.http://superlab.stanford.edu/rfchallenge.html

author: German_EE
author_rank: Super Contributor
timestamp: November 03, 2019, 09:47:45 am
content: Looks good, but the amount of gain from those two devices is terrifying. I would be tempted to include some source degeneration, maybe half an ohm, in each device to bring down the gain and improve the linearity.Your harmonic measurements are good, unwanted products 40 dB down mean a nice clean signal.

author: dk5ya
author_rank: Contributor
timestamp: November 03, 2019, 03:02:19 pm
content: Well done, Razvan. Clean job and a very nice PCB. Would like to see how it works on 70 MHz when input transformers needs to be slightly re-designed causing some loss on 160 and 80mtrs. If so...not sure :-).Let us know about a kit if there will be some (just the PCB would be sufficient).U.

author: M0HZH
author_rank: Regular Contributor
timestamp: November 04, 2019, 03:19:41 pm
content: I've made multiple changes to the design, including a new input transformer. Now the 6m performance is very good, I've seen more than 700W with a beautiful & clean output sinosoid and over 22dB gain. Including 70MHz looks more and more possible, waiting for the transverter to arrive this week.I am preparing to make a small limited run for the kit in the next few weeks. I will post future updates on this page, that also has an email sign-up option:https://qrpblog.com/a600-hf-6m-600w-ldmos-amplifier/Feel free to sign up to get notified when kits will be ready.I need to work a bit more on the IMD measurements setup, the Xiegu X5105 is not the best signal source. As bad as 24dBc on some bands.Cheers,Razvan.

author: German_EE
author_rank: Super Contributor
timestamp: November 04, 2019, 04:58:34 pm
content: One thing some of you may have missed, look carefully at the two active devices. They are sold as an A and a B version with the gate and source pins swapped on one device, that way they can be mounted on the PCB as a mirror image.Clever thinking by NXP, or whatever they are calling themselves this week.

author: CJay
author_rank: Super Contributor
timestamp: November 05, 2019, 08:44:34 am
content: Quote from: German_EE on November 04, 2019, 04:58:34 pmPhillips, Mullard, NXP* etc. have been doing that with all sorts of devices for years, there are chip amplifiers that had 'flipped' pins to enable you to design a symmetrical audio amp for instance, it's really neat but a little confusing the first time you bump into them unaware...* And probably many others too, Phillips were just the ones I remember.

author: AF6LJ
author_rank: Unknown
timestamp: November 10, 2019, 10:57:58 pm
content: That was really nice, thanks for sharing.

author: profdc9
author_rank: Frequent Contributor
timestamp: November 16, 2019, 04:13:11 am
content: Congratulations on winning the second place prize in the contest. I think yours was the best, but it is good to be recognized.For a kit, you may want to separate the design into two boards. I did this with my IRF510 projecthttp://www.github.com/profdc9/QRPAmplifierOne board just has the amplifier on it. It has a TX/RX relay and the ability to either key from RF sense or from a line that is grounded due to the transmitter key line. This line may also be used to shut down the amplifier if there is excessive SWR. Also, I have an overcurrent protection that pulls the bias on the transistors low if excessive current occurs due if oscillations start (which can happen if there is a very mismatched load).I use an attenuator on the input and have 3 to 5 watts input so that the input matching is good over the entire 1.8 to 30 MHz band.The second board has three convenient things together on it. It has 6 low pass filters that are relay selectable. Also, it has a tandem match. Finally, it has a sense line to the RF to provide a digital signal for a frequency counter. This way an Arduino (with a 74HC393 clock divider) can sense which band is in use and switch the relay accordingly, as well as provide a measure of forward and reflected power which can be used for SWR shutdown.Some of these features might be useful for making a microcontroller-controlled amplifier.

author: M0HZH
author_rank: Regular Contributor
timestamp: November 18, 2019, 04:36:23 pm
content: Thank you, profdc9.In the mean time, I started offering it as a kit and the first batch sold out in a few hours. Quite happy with it.Your project sounds interesting; I have built a IRF5x0 amplifier before, if you get it right it does a decent job for a small portable PA.I am interested in the Arduino counter / band sense part as well but I haven't seen any successful application yet. My option for now is to use analog / BCD band data from the transceiver or select the band manually. If you find a way to do it with an Arduino reliably, please give me a shout.Cheers,Razvan (M0HZH)

author: dk5ya
author_rank: Contributor
timestamp: January 19, 2020, 09:38:06 pm
content: Finished work on my kit today, well done, Razvan. 580W on 1.8 MHz and even close to 500W on 70MHz with 4W drive.

author: dk5ya
author_rank: Contributor
timestamp: January 19, 2020, 09:39:13 pm
content: With LPF on top of the amp:

author: profdc9
author_rank: Frequent Contributor
timestamp: January 20, 2020, 12:00:58 am
content: That looks impressive. Are you using a 48 VDC switching supply to power it? And if so, which one?

author: dk5ya
author_rank: Contributor
timestamp: January 20, 2020, 10:39:37 am
content: Quote from: profdc9 on January 20, 2020, 12:00:58 amYes I do, its a Lineage Power CP2000AC54TEZ. Quite oversized (2KW) but very silent, no noise whatsoever on HF or VHF. It's the same I use in my 1296MHz 600W amp. Solid like a rock and can be found every now and than at Epay. Bought mine for just 25 bucks.