Cheap 100W Power amplifier kit for 1.8Mhz to 250Mhz - Page 1
Forum section: electronics / rf-microwave

author: jujun
author_rank: Regular Contributor
timestamp: July 19, 2019, 05:14:05 pm
content: Hello,I just found this :https://www.nxp.com/products/rf/rf-power/rf-ism-and-broadcast/1-600-mhz-broadcast-and-ism/mrf101an-rf-essentials-kit:MRF101AN-START-KITThe only down side is the quite high voltage needed.J

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 19, 2019, 07:11:51 pm
content: 50V is high? I was expecting 500 to be "high"...Tim

author: edavid
author_rank: Super Contributor
timestamp: July 19, 2019, 08:23:40 pm
content: I don't exactly see the point of this, if you have to pay $50 for it. You still have to design and build the bias and matching networks, which is the hard part.

author: bd139
author_rank: Super Contributor
timestamp: July 19, 2019, 08:46:00 pm
content: Just buy a 48V SMPS moduleThe power FETS look pretty decent. Might build a CW PA here. £20 a go here and actually available and probably won’t leave a crater whenever you blast them into a mismatch.

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 19, 2019, 09:19:31 pm
content: Quote from: edavid on July 19, 2019, 08:23:40 pmThe nice thing about FET PA's is that you can usually use pretty simple transmission line transformers for matching the input and output; the bad thing about FET PA's is that biasing them into stable, linear operation and keeping them there is exceptionally difficult.Then again, the last time I built a linear FET PA from scratch was in the late 90's, back when I knew more about it that I do know... I'd say what it was for, but the FCC might still be trying to solve that particular case

author: bd139
author_rank: Super Contributor
timestamp: July 19, 2019, 09:51:25 pm
content: Sounds like my dual IRF510 PA: 70W out at 3.5Mhz with a free 2W signal at 7MhzThe newer ones are apparently difficult to blow up if you keep them in the SOA. Unlike the older ones which fling bits of encapsulation at you.

author: jujun
author_rank: Regular Contributor
timestamp: July 19, 2019, 11:33:13 pm
content: Quote from: edavid on July 19, 2019, 08:23:40 pmThey provide all the BOM information for several frequencies.https://www.nxp.com/docs/en/data-sheet/MRF101AN.pdf

author: gibbled
author_rank: Regular Contributor
timestamp: July 20, 2019, 12:18:15 am
content: Hmmm... Could build one heck of a metcal power supply with one of those.

author: OwO
author_rank: Super Contributor
timestamp: July 20, 2019, 05:26:19 am
content: The TO220 package is really suboptimal for >10MHz because of the source lead inductance. I still prefer to use refurbished transistors from base stations (occasionally you can find NOS ones too for cheap). These generally cost $5 for a 200W transistor and can operate down to HF.

author: bd139
author_rank: Super Contributor
timestamp: July 20, 2019, 08:15:02 am
content: The tab is source on these packages. You can cut the source lead off as well.

author: Theboel
author_rank: Frequent Contributor
timestamp: July 20, 2019, 08:16:35 am
content: when NXP introduce "plastic package" MRFX1K80N my first thought is who the dummies will build a transmitter with a plastic thing who need on-air 24/7but when I "must" use it for my 10kw FM transmitter and its operate 24/7 even in 40 degree C ambiance I must say I impressed.I do not know yet about MRF101 but I will not underestimate again NXP especially their LDMOS departement

author: rcbuck
author_rank: Frequent Contributor
timestamp: July 20, 2019, 08:34:39 pm
content: QuoteExcept for the schematic. Do they expect you to reverse engineer the board layout to obtain a schematic??

author: Theboel
author_rank: Frequent Contributor
timestamp: July 21, 2019, 07:27:50 am
content: Quote from: rcbuck on July 20, 2019, 08:34:39 pmGood point sometimes NXP made easy thing complicated like there is no online schematic for 27MHz amp for MRF1K50 but when You ask them nicely they will help.And also why they never release 1 to 30MHz linear amp reference ?

author: jujun
author_rank: Regular Contributor
timestamp: July 24, 2019, 12:06:48 pm
content: It seems that the shematic and design files are here :https://www.nxp.com/products/rf/rf-power/rf-ism-and-broadcast/1-600-mhz-broadcast-and-ism/mrf101an-reference-circuits:MRF101AN-REFCirc

author: jujun
author_rank: Regular Contributor
timestamp: July 24, 2019, 12:40:54 pm
content: There is a bigger version of this transistor about 300W in another package.https://www.nxp.com/products/rf/rf-power/rf-ism-and-broadcast/1-600-mhz-broadcast-and-ism/300-w-cw-over-1.8-250-mhz-50-v-wideband-rf-power-ldmos-transistor:MRF300AN

author: sundance
author_rank: Regular Contributor
timestamp: July 24, 2019, 01:05:47 pm
content: Thanks for the additions info.As far as I can see, the packages only contain component placements, Reference circuit overview, compact baseplate and PCB. Unfortunately, no schematic.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 24, 2019, 03:53:49 pm
content: If you need a schematic to work with a linear RF amp, you probably shouldn't be working with one. It's a pair of bias tees...Tim

author: whalphen
author_rank: Regular Contributor
timestamp: July 24, 2019, 04:14:25 pm
content: Very common schematic for a linear amp. Took me 5 minutes to put it in Kicad. If you aren't familiar with this kind of design, I suggest you build one to start learning about it.

author: whalphen
author_rank: Regular Contributor
timestamp: July 24, 2019, 06:21:46 pm
content: How to make one of these using a different transistor or a different frequency? Attached are some notes you can use. It's not very difficult. You just need some familiarity with basic complex number arithmetic -- or use some online calculators. Impedance matching can also be designed using simple, readily available software tools. Give it a try using your own transistors. But don't connect an antenna unless you have a low pass filter and a valid license.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 24, 2019, 07:52:52 pm
content: Yup, not a big deal using different transistors -- you won't get as much bandwidth of course, but the parts cost can be a lot lower.Example:https://www.eevblog.com/forum/rf-microwave/superjunction-mosfets-for-rf/msg2439978/#msg2439978This is an unmatched example (aside from the input transformer, though it's not targetting any particular frequency); expect modest bandwidth (some MHz) for a given matching condition, and better for smaller-die transistors (but watch out for low power dissipation ratings on them).Lower voltage transistors are probably the better deal for RF work, due to the lower impedances being a better match versus junction capacitances -- giving more available bandwidth. This is certainly the pattern with proper RF transistors, though physics (transit time) limits higher voltage parts as well, and all effects (capacitance, gate spreading resistance, transit time, etc.) need to be clear to offer full (GHz range) bandwidth.Tim

author: sundance
author_rank: Regular Contributor
timestamp: July 25, 2019, 05:58:49 am
content: @whalphen:Thanks for the excellent introduction about impedance matching in RF PAs like this - very interesting read. And some nice addition to my "collection" of useful online calculators. And, need it or not, a schematic always comes in handy - thanks for that one, too.Guess it's not going to be rocket science tobuildone of those affordable kits from NXP...

author: AF6LJ
author_rank: Unknown
timestamp: July 25, 2019, 04:55:21 pm
content: Quote from: MagicSmoker on July 19, 2019, 09:19:31 pmThings have changed a bit since then.

author: AF6LJ
author_rank: Unknown
timestamp: July 25, 2019, 05:05:10 pm
content: Quote from: T3sl4co1l on July 24, 2019, 03:53:49 pmI second this.These devices are a bit fragile, and they have a lot of gain at lower frequencies.The designs I have looked at use transmission line transformers as mentioned above.There are a number of Motorola application notes that discuss designing these types of transformers. I know CB hobbyists have tried to use these parts in BJT designs the result was not pretty. (BBI Cough).There are designs you can copy Be careful about selecting parts like output and bypass caps, they have to be rated to handle the currents passing through them.

author: whalphen
author_rank: Regular Contributor
timestamp: July 26, 2019, 03:48:40 am
content: The first time I built a linear amp, I didn't know what I was doing. It was a kit. I just followed the instructions. But it got me interested in knowing more about how it was designed. I learned quite a bit from the experience. I still have it. It works. The next time I built one, it was also from a kit and included control circuitry and low pass filters. I learned a lot more. And did a lot of reading about RF amplifiers. The next one I designed myself. I've designed several since then. Sometimes you just have to jump in and learn by doing. A $50 kit with all the parts included looks like a pretty good deal for someone who wants to experiment and learn. (Just be aware that you need a license and a filter if you want to connect it to an antenna. And penalties for ignoring the rules can be severe.)

author: edavid
author_rank: Super Contributor
timestamp: July 26, 2019, 04:54:02 am
content: Quote from: whalphen on July 26, 2019, 03:48:40 amThe NXP kit does not have all the parts included, just the FETs, baseplate, PCB, SMA connectors

author: rcbuck
author_rank: Frequent Contributor
timestamp: July 26, 2019, 10:43:58 pm
content: QuoteI didn't say I couldn't reverse engineer and create a schematic from the board layout. I just meant it would have been nice to see the schematic for a quick glance at the circuit.I have a 20 wpm Extra Class license. I have been licensed since 1962. I have built transmitters, receivers, transceivers, tube amps (811, 813), and solid state amps. Last year I built a 50 watt amp for my uBitx. I had to add external bandpass filters between the uBitx and amp since the uBitx has issues with harmonics and spurs. The amplifier was based on the Hardrock 50 design.I can certainly build a HF amp but I don't think I would use a single output device to do it. A push-pull output stage is always better since it significantly reduces even harmonics. Although I must admit I built several transmitters with single 6146 output stages in the 60s and 70s.AB7HE

author: langwadt
author_rank: Super Contributor
timestamp: July 26, 2019, 11:16:27 pm
content: Quote from: rcbuck on July 26, 2019, 10:43:58 pmand since it is available in mirrored pinout it seems made for push-pull

author: rcbuck
author_rank: Frequent Contributor
timestamp: July 27, 2019, 12:05:32 am
content: Yes, and the price is certainly right. Mouser has them for $21.87 each in single lots. A pair of them for $44 gives you the capability of building a 200 W amp.But, do you really "need" more than 100 watts? I guess it would be needed if you are fighting the California kilowattsin a DX pileup.

author: langwadt
author_rank: Super Contributor
timestamp: July 27, 2019, 12:18:02 am
content: Quote from: rcbuck on July 27, 2019, 12:05:32 amor triple the power with MRF300AN, $35.17 in singles from Mouser

author: OwO
author_rank: Super Contributor
timestamp: July 27, 2019, 04:50:58 am
content: MRF6S9125N/MRFE6S9125N is still my go-to transistor for VHF and below. Over 100W and you can get refurbished ones for $4 each from taobao. I've used 5 of these and haven't encountered any duds yet.

author: Lord of nothing
author_rank: Super Contributor
timestamp: August 05, 2019, 10:53:58 pm
content: Quotea guy claim to use a 1kw amp so what do you think?

author: jujun
author_rank: Regular Contributor
timestamp: August 16, 2019, 12:04:27 pm
content: Thank you all for all this interesting readings.There is one thing that I dont understand in the design of a matching network: Ciss and Coss are given a 1Mhz in the datasheet, so how you can know it at the frequency you want to use it ? Is it needed that you measure it yourself ? but how ?Also it seems that Vds have an effet on Ciss and Coss, so to my eyes it seems hard to do it without any mesurements.Maybe because after 20V it's near flat it's not a big problem if you have at least Vds at more than 20V.The complex impedance at 13.5Mhz and at 27 Mhz dosent seems very far. I'am currious to know how they get this data. Simulation ? Measurement ?Any pointer are very apreciated

author: Kalvin
author_rank: Super Contributor
timestamp: August 16, 2019, 12:11:09 pm
content: Quote from: rcbuck on July 27, 2019, 12:05:32 amFor 2m EME you may want to use 1 kW. Probably for HF contesting and pileups 1 kW may be "the thing".

author: OwO
author_rank: Super Contributor
timestamp: August 16, 2019, 01:32:01 pm
content: The datasheet load/source impedances come from experimental measurements, or "load pulls". Basically the transistor is put in a test jig where the load and source impedances are swept over a range and the "optimal" (usually in terms of efficiency or power output) impedance is recorded. You would not want to design an impedance match based on input/output capacitance at >100MHz because other parasitics (bond wire and lead inductance) also come into play.

author: jujun
author_rank: Regular Contributor
timestamp: August 16, 2019, 01:51:10 pm
content: I don't understand how you avoid to blow the transistor when you sweep the impedance : it must oscillate when the match is very bad ?It would be great if a simulation model of the transistor was avaiable and enable us to do all this measurements in a simulation, but I don't think it exists.Do you mean that the capacitance input and output at 1Mhz (in datasheet) is enough to calculate the matching at for example 7 Mhz ?

author: jujun
author_rank: Regular Contributor
timestamp: August 16, 2019, 02:02:14 pm
content: Wow I just downloaded a MRF101AN s2p file on the NXP website !!EDIT : unfortunately the file start at 30Mhz

author: kafferejsarn
author_rank: Newbie
timestamp: November 12, 2019, 07:21:37 am
content: Quote from: whalphen on July 24, 2019, 06:21:46 pmThere is a short between FET gate and ground in the schematic you provide. I guess C3 is supposed to be connected only to ground and not to the lower side of R1 at all and thus the ground not connected to bottom of R1?This is by the way the first really hands-on description of how to find the input and output impedance of a power transistor! Thank you!

author: profdc9
author_rank: Frequent Contributor
timestamp: November 12, 2019, 08:43:26 pm
content: I have a couple of amplifiers I am working on. One is a copy of the WA2EBY amplifier, and goes up to 40 to 50 watts, the other has six IRF510s (with two more as a preamplifier stage) and should do 200+ watts.https://github.com/profdc9/QRPAmplifierThey also come with a PCB to switch LPF in and out.Dan

author: bd139
author_rank: Super Contributor
timestamp: November 12, 2019, 08:59:10 pm
content: That's pretty cool. Thanks for posting.I was going to attempt a 200W-ish IRF510 based device (I've managed to get two up to 50W without any persistent explosions or instability) but not got around to it yet.

author: K4IDC
author_rank: Newbie
timestamp: January 06, 2025, 02:23:46 am
content: I just found this topic while looking for an amplifier design for a 6m beacon.It seems that the schematic for the PA design shows the gate to be at ground potential.Is there an error in the drawing, or ?

author: RFDx
author_rank: Regular Contributor
timestamp: January 07, 2025, 02:40:42 am
content: Quote from: K4IDC on January 06, 2025, 02:23:46 amYes, that is a drawing error. The gate of the MOSFET should be connected with R1 and L1 and nothing else.

author: mtwieg
author_rank: Frequent Contributor
timestamp: January 07, 2025, 02:49:46 pm
content: I've been eyeing the MRF101 and MRF300 for a while, but they only offer an S2P file (which apparently doesn't even correspond to their reference designs, Idq is x10 higher), nothing else for simulation. Unless one of their reference designs already meets your needs as-is, doesn't seem worth the effort.edit: oops, responded to a necropost...

author: pienari
author_rank: Regular Contributor
timestamp: January 08, 2025, 07:33:36 am
content: Lots of questions..It's much easier to build an rf amplifier with the right rf fet than trying to get something to oscillate properly.I have built a 2018-19 rf amplifier 27-28MHz 2pcs IRF510 fet drive 16pcs IRLZ24.FM dead key tx output is ab. 500w @27.2VIt's great but it has poor efficiency so I don't use it..I later bought a Dx world-e amplifier building kit for 10m range with Ampleon ART1K6 fet.I like that amplifier better.