RF power amplifier questions - Page 1
Forum section: electronics / rf-microwave

author: cdev
author_rank: Super Contributor
timestamp: June 05, 2020, 09:23:19 pm
content: Does it make sense for a beginning ham to buy a QRP-capable SSB/CW capable rig that puts out a couple of watts and then build one's own 200 watt PEP PA for cheap? Are there any good designs?Since I like to experiment with antennas, the idea of having a PA I know how to repair (thats cheap to repair) is very appealing, but does it make sense for a beginner? It seems that its likely by then I will have a VNA, so I suppose that should make it a lot easier. Has anybody done this, and do you have any favorite designs?I dont know how much power I'll end up with to excite it. Not a super lot, probably just a few watts.I'm on a tight budget but I like to build stuff. The idea of having an easily replaceable final is very appealing, so I guess that limits my choices.

author: radiolistener
author_rank: Super Contributor
timestamp: June 06, 2020, 01:29:27 am
content: Building good quality power amplifier is not easy task. I think it's better to buy transceiver with 100W output and reduce output power to 10W in transceiver settings for experiments.With low output power setting it is safe to make short circuit or leave it open. The risk appears when you working on a full power. If there is a problem with antenna the voltage on power amplifier output may be twice higher than normal (due to reflected wave) and it can destroy output transistors.So, just setup low output power mode in transceiver settings if you don't sure that antenna is okay.

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2020, 03:49:45 am
content: Most used rigs I see on ebay even used are still just too pricey for me right now. As I dont know how much I'm going to like the hobby, I may end up not being all that into it, I dont know until I try.The other day I was pointed to a nifty new mostly built kit that costs around $160-200 - a SSB transceiver, that outputs 10w. That looks like a good candidate for the main rig. And then as I already have a lot of the parts (apart from the FETs ) Including a suitable transformer for the DC power supply and some hefty heatsinks that I really want to use in something useful. Otherwise, whats the point of saving this stuff, right?I've seen circuits in the past that looked perfect, that used multiple IRF510 FETs.Here is one example of what I mean, a small cheap ($16) Chinese PA kit which takes a fairly modest amount of power to drive to full output and needs some improvements to really work properly. It uses only two FETs. (too small perhaps, as it looks to be easy to damage trying to run at the higher power)They have a "100w" version for $40. The heatsink on it is larger and likely needs a fan to be safe to use at higher power.As my antenna tuner still has some issues, it seems, (I cant tell- not being able to transmit, but there seems to be some kind of internal intermittent open or something) I want to put a circuit on whatever I end up with to prevent thermal self destruction, either by sensing the SWR or PA current or both.https://dk9jc.de/blog/equipment/142-diy-kits-70w-ssb-linear-hf-power-amplifier-ft-817-kx2-kx3Here is a slightly more expensive "10W" PA ($26) which seems likely to be conservatively rated - that comes with a larger heatsink.http://qrp-labs.com/linear.htmlThis kind of design seems to be the way to go to get on the air for not much $$$ on HF, as so many people have had good things to say about it as far as affordability and easy repair, and the price is right.

author: radiogeek381
author_rank: Regular Contributor
timestamp: June 06, 2020, 04:07:07 pm
content: You may find 10W is more than enough.As for "cheap" PAs. They aren't worth it. Many claim to be linear, but are in fact class C. Other designs are just poorly done and badly executed.The qrplabs amp was a very satisfying build, performed well, and has been reliable. Like all amplifiers, it is a good idea to follow it with a filter, especially if the exciter is prone to harmonics.kb1vc

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2020, 05:27:54 pm
content: Right, of course, I am planning on that.That looks like a nice design! I am also wondering when the transceiver they have been talking about will be available or if it will be available!Quote from: radiogeek381 on June 06, 2020, 04:07:07 pmIs the linearity a function of how the circuit is operated - biasing, or is it determined by the hardware and immutable?

author: geggi1
author_rank: Frequent Contributor
timestamp: June 06, 2020, 07:13:38 pm
content: There are several designes based on IRF type FET. Google a bit on the internet and you can find many designs using this kind of devices. Designs can be found for HF bands and even on 6m. The IRF type are old units and there are more modern devices.

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2020, 09:36:02 pm
content: I have been looking and it seems that there are.If you were building a more modern RF amp and trying to make a robust usable transmitter for a fairly modest cost, what would you use?Quote from: geggi1 on June 06, 2020, 07:13:38 pm

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: June 06, 2020, 09:43:28 pm
content: See something with MRF300, cheap device.Around 300W out from one device, several guys build it, mostly using 2xMRF300.

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2020, 10:01:01 pm
content: 50 volts would be a perfect match to a big medical grade transformer that I scavenged ages ago and have held on to for at least 15 years looking for something to do with it.. Thank you, this looks like a keeper. Will definitely look into it.

author: langwadt
author_rank: Super Contributor
timestamp: June 06, 2020, 10:21:04 pm
content: Quote from: Nuno_pt on June 06, 2020, 09:43:28 pmwith one device it is probably class-c, for a linear push-pull you'll need two and they are ~40€ each

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2020, 10:32:20 pm
content: Thats doable, would that mean I could get 450W or so from two? That seems like a lot of power from two small devices, presumably they need to be very well provided with heat sinking?Yes- looks good!He has an article on qrp blog but I cry foul, this isnt QRP at all..This looks very nice.

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: June 06, 2020, 10:43:59 pm
content: Yes, he's here on the forum also.You need a good heatsink, from 2xMRF300 you should get ~600W for both without distortion, that's what several guys are getting.You need also LPF and some other stuff.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 06, 2020, 10:45:31 pm
content: I was wanting a low power wide band amp for some experiments. I cheated and bought a kit. I only use it at fairly low power or I would have taken the time to make a spreader.https://www.eevblog.com/forum/projects/home-made-pa-and-load/msg635226/#msg635226

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2020, 11:28:49 pm
content: Quote from: Nuno_pt on June 06, 2020, 10:43:59 pmThe arduino based protection circuitry seems like a good idea, to instantly cut power or throttle it way back, would hate to see my very nice 600 watt solid state amp just self destruct itself because of some very short antenna problem.That is a very nice way to go. Lots of gain too, it doesnt need a lot of power to drive it. I would definitely put (powered) fans on the heat sink, blowing sideways or something like that, doesn't have to be a lot of power.

author: cdev
author_rank: Super Contributor
timestamp: June 06, 2020, 11:34:04 pm
content: That looks like a very nice small amp.Is the kit still sold?Quote from: joeqsmith on June 06, 2020, 10:45:31 pm

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: June 06, 2020, 11:35:25 pm
content: See here some already made protection <https://www.w6pql.com/parts_i_can_provide.htm>Also on QRPBlog <https://qrpblog.com/product/b1500-rf-amplifier-backpanel-unit/>

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 12:29:52 am
content: Wow, these links have super useful info, on all sorts of stuff that I am interested in..THANK YOU!Quote from: Nuno_pt on June 06, 2020, 11:35:25 pm

author: OwO
author_rank: Super Contributor
timestamp: June 07, 2020, 04:38:27 am
content: Unfortunately MRF300 comes in a thermally sucky package, don't try to dissipate more than 50W in it. For linear operation that means you are limited to about 50W of output per transistor (you will need to reduce supply voltage). My transistor of choice is always the MRFE6S9125N, it costs around $3 refurbished but it's difficult to obtain outside china. You need to solder it (and the pcb) to a copper plate, and mount the copper plate on a big heatsink with fan.

author: m3vuv
author_rank: Super Contributor
timestamp: June 07, 2020, 06:51:54 am
content: so have you a rectum paralizer to do any sort of testing for harmonics ?,or just plan on transmitting everywhere at once??

author: langwadt
author_rank: Super Contributor
timestamp: June 07, 2020, 10:49:43 am
content: Quote from: OwO on June 07, 2020, 04:38:27 am? MRF300 is 0.55C/W Rjc, MRFE6S9125N is 0.45C/W Rjc and it is a dual

author: aristarchus
author_rank: Regular Contributor
timestamp: June 07, 2020, 11:57:28 am
content: Hi,For a "beginning ham" as you say, you are already flirting with high power PAs and without mentioning anything about LPFs, IMHO this does not look good.Just my advice:Start with something at 70W to 100W, similar to this->https://www.aliexpress.com/af/minipa-hf.html?d=y&origin=n&SearchText=minipa+hfcombined with something like this->https://www.aliexpress.com/af/100W-low-pass-filter-LPF.html?d=y&origin=n&SearchText=100W+low+pass+filter+LPFDo not even consider a PA with IRF5xx.Just my 2c.

author: OwO
author_rank: Super Contributor
timestamp: June 07, 2020, 01:03:33 pm
content: Quote from: langwadt on June 07, 2020, 10:49:43 amRjc = junction tocase. The hard part is moving the heat from the transistor metal tab to the heatsink. The metal pad is tiny, so the only way you are going to get good enough heat transfer is if you solder it. If you mount the transistor directly to a heat sink with thermal paste, don't expect to safely dissipate much more than 50W. CPU dies are about the same size and they need a big heat spreader to transfer 100W. Also MRFE6S9125N is not a dual, it's a single transistor, but I would still limit power dissipation per transistor to < 100W. If you are going to solder the tab to a copper plate anyway, that removes the advantage of a TO-247 package so you might as well move to a real RF optimized package. MRF300 is very expensive for my tastes and the package it comes in is not an advantage for me.

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 01:22:58 pm
content: Quote from: OwO on June 07, 2020, 04:38:27 amI remember in the video the person said something about the efficiency being high, maybe 70 something percent? Looking at the device package the thermal solution, I could tell at the beginning would have to be very good. There doesnt seem to be enough surface area to absorb it away, fast enough, even with a monster heatsink, if the swr went high for very long.So would be wise to insert precisely flat, polished, large copper plate, definitely would need that copper heat spreader first, then some thermal grease only then aluminium. Still, the price is right. Its good to know that other alternatives exist and arent too epensive, to build ones-self. But I tend to agree, a very robust solid lower power amp will definitely be what I build first. I already have most of the parts I need to get started, besides the transistors themselves. Which makes the project a good one.@aristarchus - I'm not a ham yet, I dont even have any kind of HF radio yet, besides a receiver.But, don't worry, I promise you I wont run high power until I thourougly have thought throwugh the big picture - and wont unless I actually have a station that lets me use the power efficiently (directional antenna in particular) I will also have the best high pass filter I can build (what kind of caps would you use? Just generic high voltage ceramic caps? WIll need to ask some questions on that later) in the signal chain before I key the mike of any radio I have, also I plan to be fully equipped with a VNA to verify that my filters not only work but suppress out of band radiation hopefully well in excess of 60db down as per FCC regulations. I promise you, I will make absolutely sure before I even key the mike for the first time. On my honor.---You say "do not even consider a PA with IRFs, is that because the devices inherently produce signals that are dirty? This is important.It seems however that I wont need to use them, as there seem to be a bunch of other options. By building my own PA from a time proven design, I'd save so much money I could afford a better rig and amp. Also, I already have a bunch of parts and they arent doing me any good sitting unused.

author: bd139
author_rank: Super Contributor
timestamp: June 07, 2020, 01:31:34 pm
content: IRF parts are fine for HF stuff (<10MHz). You can get well within the harmonic requirements with a pretty dumb matching network / filter. They like to blow up if you run them into a mismatch but that mistake is only $0.50 a goI would build smaller amps and work up slowly:Buy safety glasses.Start with a 25W IRF510/IRF530 class C.Then work on a 50W IRF510/530 class C push pull.Then you know enough about how not to cost yourself $100 of transistors instantlyThen work on a 200W or so one with proper MRF parts.Depending on modulation requirements, big amplifiers might not be necessary. CW has approximately a 10dB gain in "effectiveness" so your 10W signal is the same as a 100W SSB signal really. FT8 even more!

author: paul002
author_rank: Regular Contributor
timestamp: June 07, 2020, 01:42:32 pm
content: I build one with irfn24 about 100watt works quite well on 12V Mosfets cost about 50 ct. Don't buy in china but at a trusted source, I made that mistake. Designed the PCB my self. Can share kicad files if people like. Also build a esp32 unit to measure SWR and power and controle the switchable LPF. The good thing is the IRFN24 works well on 12V

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 01:56:00 pm
content: The broadband device Joe was playing with looks much more useful if it can be used on both HF and VHF-UHF without producing unacceptable levels of harmonics, that would be worth spending more money on. I can make some kind of control/monitor ciruit to keep an eye on the PA, and it seems like energy well spent.I'd prefer soldering transistors, thats fine, whatever gives it the best contact. I have a number of miscellaneous largeish chunks of aluminium plus a bunch of old CPU fan heatsinks that are not being used. One is pretty large. Also have lots of PCB material and even some copper scraps that could be used, with my nibbling tool to make heat spreader.Quote from: OwO on June 07, 2020, 01:03:33 pmWhen you say "mounting" do you mean using a socket, and by "soldering" do you mean soldering the body to some metal, and soldering the legs?What I usually do with a power transistor is solder the legs and usually use a screw and a thin piece of insulation to mount the transistor to the heatsink. Usually with some thermal grease. But I can solder the body, if thats whats called for, I am set up to be able to do that.

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 02:00:31 pm
content: That looks very nice! On the additional board is that your switchable LPF filter board, and if so, what relays do you use?Yes, I would love to have the kicad files..Thank you!Quote from: paul002 on June 07, 2020, 01:42:32 pm

author: OwO
author_rank: Super Contributor
timestamp: June 07, 2020, 02:07:09 pm
content: Yes most RF transistors require soldering the body to a copper heat spreader. For that size a 2mm or 3mm thick, 7cm x 7cm copper plate is ideal (did simulations). For low ground inductance you might also want to solder the PCB ground plane to the heat spreader. At HF you can get away with not doing that, but at VHF/UHF it's a must.

author: paul002
author_rank: Regular Contributor
timestamp: June 07, 2020, 02:10:47 pm
content: here the kicad file, I also have some pcb's left. The relays are normal omron from aliexpress. I have a pcb for the esp32 on github. I use it also for VFO.https://github.com/paulh002/VFO-ESP32-Si5351I will also put the lpf on github later this week. The only problem I had was with the toroid cores. The chineese one are no good give to much insertion loss. Ordered some good ones now.

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 02:16:51 pm
content: When building LNAs I got a bit of advice from a friend that the single most important thing with LNAs was low ground inductance. And he was right.

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 02:27:03 pm
content: I use copper tape quite a bit for stuff like that now. (extending ground planes) Its quick and it works. But i worry about the adhesive drying out after a couple of years. And sometimes there isnt DC continuity when I think there should be. But for shielding and on Rf it works. (I make antennas out of it a lot.)Quote from: OwO on June 07, 2020, 02:07:09 pm

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 02:39:08 pm
content: Thank you forthe VFO circuit. I have a si5351 (adafruit version) and have only fooled around with it a tiny bit. My ultimate hope is to be able to use it with a signal derived from the 10MHz output from my GPSDO, (known stable good source.) To get an appropriate reference clock I'm hoping to use a PIC, I started on this project quite some time ago but have not had the time to finish the PIC part of it.have to investigate your circuit, it seems from looking at it I may have a good start on it already parts wise. I can probably print out the PCB from Kicad and etch it myself.Quote from: paul002 on June 07, 2020, 02:10:47 pm

author: paul002
author_rank: Regular Contributor
timestamp: June 07, 2020, 02:54:17 pm
content: There are two designs on github if you click on branches you can see a 2nd branch, I just received the pcb's for this version. This is a esp32 with 2x si5351 on the bord it self. Not using an adafruit expansion. The problem with these si5351 is crosstalk. It has 25 mhz xtals on board but you can remove them and use the gpsdo as clock. I don't know if you can use 10 Mhz direct and just adjust the pll. Would be great. Now I measure the error and correct it using small measurement software. I still need an GPSDO my self maybe build one.Quote from: cdev on June 07, 2020, 02:39:08 pm

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 05:39:06 pm
content: User @tvb has a set of PIC applications that can be written to inexpensive PIC microprocessors that can utilize what appears to be the uniquely synchronous nature of the PIC platform to allow various clocking related transformations to be accomplished with building blocks made from single PICs. His web site is leapsecond.com and he's also put the software (Called PicPet and PicDiv) for people to download there. It seems to me to be a good way to derive other clock rates in a verifiably stable way from a single known clock, also there are many other things they can do quite straightforwardly. The errors dont add up as they would with some other ways of getting similar outcomes.

author: cdev
author_rank: Super Contributor
timestamp: June 07, 2020, 05:42:03 pm
content: Do you sell your boards or have a web page where you describe your designs in more detail?I bought a TruePosition GPSDO telecom surplus, which is working out pretty well for me. There is a thread on this GPSDO which a bunch of people have now and a number of people, most notably @pigrew and @texaspyro have done a real lot to advance our knowledge on using them.. they have advanced features like learning to improve accuracy as the conditions for the oscillator change. I think it would be hard to match its value for money, even if I tried to build one myself. I think that soon I should also be able to use it to derive other frequencies in a pretty straightforward manner.Quote from: paul002 on June 07, 2020, 02:54:17 pm

author: paul002
author_rank: Regular Contributor
timestamp: June 08, 2020, 02:06:20 pm
content: I don't sell them (yet), I put the designs on github inclusive software. I think it is a bit to early to "sell" them. I am still testing it. But for people who want to experiment and share the results I share the pcb's designs and software on github. If people are in Europe I can send a board. (Post man in US must be rich because post tariffs over there is very high)

author: M0HZH
author_rank: Regular Contributor
timestamp: June 08, 2020, 03:55:21 pm
content: Quote from: OwO on June 07, 2020, 04:38:27 amI guarantee that the MRF300 package (TO-247-3) can handle many hundreds of watts and is not limiting performance. I've built many amplifiers with MRF300 and tested MRF300 in all conditions (including 200W+ watts thermal dissipation in long cycles) under thermal imaging, the package is good enough for the job as long as common sense thermal interfacing rules are applied (flat surfaces, even pressure, good quality TIM etc). The only challenge is the fact that there is only one bolt that holds it down and overtightening warps aluminium / copper; this is solved by either using a press-down clamp over the whole package with additional bolts, or (my recommended solution) by using liquid metal as a TIM; this offers lowest thermal and electrical resistance and the mounting pressure is not critical, but needs a copper heat spreader.Also, there are other devices in the TO-247-3 package designed for much higher power dissipation, with much lower Rth-j; see IXYS IXFK80N60 / IXFX80N60 for example.Quote from: cdev on June 06, 2020, 10:32:20 pmThat's my kit, I'm also offering a Low Pass Filter board as well as a Backpanel Unit with some accessories. A color touchscreen Control Unit is coming this month as well. If you have any questions, ask away./shameless plugGoing back to the main subject, if you just want to get on the air it's not economical in the long run to build stuff. It looks cheap now, buy you'll soon realize you want more features, QRP is frustrating as hell in this deep solar minimum we're going through, you will need some test equipment, you will break some stuff, you will make some bad choices and whatver you build won't have much market value if you want to upgrade later. Keeping an eye on eBay for a while, you'll be able to find a used Yaesu FT-747 / Kenwood TS-130S / Icom IC-730 for US$200, you'll get a solid 100W output radio with a good set of features for a beginner and it will keep its market value very well if you want to upgrade later.However.I started Amateur Radio by building my equipment (early days of SDR). It was a very long process that included a lot of reading and learning, testing and rebuilding, frustration and rewards. If you're looking to learn, understand what you're doing and enjoy this hobby to the fullest, definitely go this way, it will open up an entire world for you. This is what Amateur Radio is all about really, experimenting with radios stuff.

author: cdev
author_rank: Super Contributor
timestamp: June 08, 2020, 05:20:37 pm
content: Hi,Thank you for all this info! I think that I am somewhere in the middle. I want to learn, but I also am trying to save money because thinking ahead, I know that I will do more experimenting if I KNOW that I can fix my own gear. Basically it comes down to that. If I buy a powerful amp and I'm not confident of my ability to maintain my antennas SWR under 2:1 max, I'll just run it derated all of the time, until thats fixed. Something like a PA, youre right, a kit probably would save money, plus the RF design is already "known to work" A VNA solves a lot of that problem but still, it may end up being trial and error until I know it inside and out. Which could be a while.here in the US, any working HF rig one finds on ebay is usually overpriced. That said, sometimes people looking for a long time luck out. But I have to say, the odds are higher than I'd like of getting somebody else's problem. Maybe things have changed now.I actually am one of the folks who would like to build stuff.. I'm not a masochist, nor am I really up to designing my own stuff at the rig level, but who knows, maybe someday, I certainly am up to putting a rig together from modular parts.What is "liquid metal" ? (as thermal interface material) Is it a brandname, like "Arctic Silver" or similar?Is the video accurate (as far as power needed and all the other stuff) How much does it cost?Quote from: M0HZH on June 08, 2020, 03:55:21 pm

author: M0HZH
author_rank: Regular Contributor
timestamp: June 08, 2020, 11:03:49 pm
content: The "liquid metal" I'm referring to is Galinstan, an alloy of tin, gallium and indium that is liquid at room temperature. It can be found under several brands, Thermal Grizzly Conductonaut and Coollaboratory Liquid Metal Pro being readily available for computer cooling. This is how it looks like when applied:Do not mistake it with Arctic Silver or any other product that has a metallic-sounding name.The video is accurate, although there were some developments since that video was shot.

author: langwadt
author_rank: Super Contributor
timestamp: June 08, 2020, 11:18:05 pm
content: Quote from: M0HZH on June 08, 2020, 11:03:49 pmtoo bad it eats aluminium

author: cdev
author_rank: Super Contributor
timestamp: June 09, 2020, 01:20:26 am
content: Its not dangerous to have around electronics?

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: June 09, 2020, 06:02:39 am
content: I believe it should be fine around copper, but aluminum can be a big issue. It will 'absorb' into aluminium and a number of other metals and make them very brittle. It can 'spread' through diffusion to any susceptible metal in contact with the originally contaminated metal (eg, a drop on an aluminum can will embrittle the entire can and any other cans that have metal-metal contact with it)

author: M0HZH
author_rank: Regular Contributor
timestamp: June 09, 2020, 08:12:01 am
content: The liquid metal surface tension characteristics allows it to "wet" other metals (transistor tab, copper heat spreader) very well and it wouldn't move afterwards; however, you need to make sure no stray tiny balls escape when applying.It is safe with copper / nickel but the gallium in the alloy will corrode aluminium.To avoid some of these downsides (which I think are outweighted by the advantages anyway) you can use indium pads, which are not easily accessible and quite expensive.

author: cdev
author_rank: Super Contributor
timestamp: June 09, 2020, 08:51:20 pm
content: what about plain old soldering, using leaded solder, digital hot plate up to around 1/2-2/3 of the temperature and then hot air with the right sized nozzle, no bigger, no smaller ?

author: M0HZH
author_rank: Regular Contributor
timestamp: June 10, 2020, 12:39:38 am
content: Can be done and is actually being done on some other high-power packages, but it's too much hassle to replace if the transistors fail.

author: galileo
author_rank: Contributor
timestamp: June 25, 2020, 01:57:09 am
content: Since this is basically a "cheapest radio for an electronics enthusiast" type of a questiona bit of a different answer: get a "hybrid rig". Old radios with tubes in the final amplifier section.All of them are 100W+, practically indestructible in high SWR conditions and as most of themare ~40 years old by now lots of stuff to fixGreat for learning, fairly easy to troubleshoot andfix. That's how I started a few years ago with a Yaesu FT-901DM and FT-102.

author: cdev
author_rank: Super Contributor
timestamp: June 25, 2020, 10:11:26 pm
content: Do you have any favorites? So far I havent been so lucky at finding radios that I think represent a low enough risk of dsappintment at a decent price.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 26, 2020, 01:55:55 am
content: Quote from: LaserSteve on June 26, 2020, 01:44:39 am

author: cdev
author_rank: Super Contributor
timestamp: June 26, 2020, 04:32:26 pm
content: Class C for 146+430 MHz?That sounds like a good beginners project if I can get it right.Quote from: bd139 on June 07, 2020, 01:31:34 pm

author: bd139
author_rank: Super Contributor
timestamp: June 26, 2020, 06:58:31 pm
content: Yeah that’d be fairly easy. Basically select a transistor and copy the PA transistor datasheet

author: cdev
author_rank: Super Contributor
timestamp: June 26, 2020, 08:16:01 pm
content: Sometimes transistors give up the ghost in a VERY short amount of time. So the idea of keeping them cheap in my first few projects makes a lot of sense to me.