HF rf amplifier  circuit without balun core transformer  - Page 1
Forum section: electronics / rf-microwave

author: Dom13c
author_rank: Regular Contributor
timestamp: July 23, 2018, 07:21:38 pm
content: Is it possible to construct a rf hf amplifier circuit without a balun core transformer. If yes then please send me a circuit diagram of it. and if no then why? If anyone knows a possible cheap source of the balun core then let me know it.

author: innkeeper
author_rank: Unknown
timestamp: July 23, 2018, 07:32:15 pm
content: whats the required power output.. and I am assuming into 50 ohms in and out, correct?

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 23, 2018, 07:34:35 pm
content: you can take on the collector/drain side a RFC and couple out with a cap of appropriate rating; this is quite a sacrifice to a proper impedance matching, but for simplifing the circuit and low power it's working

author: bd139
author_rank: Super Contributor
timestamp: July 23, 2018, 08:11:40 pm
content: I just literally built one of those last night. HB9EVI’s approach works.Although you get bugger all power out. On 30m/10MHz I’m getting 1W for 3W in on a 2n3866. Matching is required if you want something better.Look for “oxo transmitter” on google images for the circuit. You can wind the collector coil on most ferrite cores usually with some experimentation.However you’re going to need a harmonic filter anyway...

author: David Hess
author_rank: Super Contributor
timestamp: July 24, 2018, 02:22:51 am
content: 20 to 50 watts is feasible that way. Over a relatively narrow bandwidth, the output LC coupling network can also perform an impedance transformation to help the situation.

author: Dom13c
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:33:51 am
content: Quote from: David Hess on July 24, 2018, 02:22:51 amCan you provide me some sort of circuit diagram for this, if possible??

author: Dom13c
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:43:31 am
content: Quote from: innkeeper on July 23, 2018, 07:32:15 pmOutput power has to be 10 watts. And yes, you are correct, it will be connected to 50 ohm in and out

author: xaxaxa
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:49:30 am
content: What frequency range are we talking about? Something that operates from 10MHz all the way to 30MHz will necessitate different techniques than something with 10% bandwidth at 27MHz...

author: Dom13c
author_rank: Regular Contributor
timestamp: July 24, 2018, 03:54:41 am
content: Quote from: xaxaxa on July 24, 2018, 03:49:30 amI'm trying to stay between 5-16 Mhz. Cause, the crystals that I've got lie between these values

author: Dom13c
author_rank: Regular Contributor
timestamp: July 24, 2018, 04:01:19 am
content: Quote from: bd139 on July 23, 2018, 08:11:40 pmThanks for the reference of oxo transmitter. I'll look for that. But the harmonic filter really sucks me for one reason. The lack of proper ferrite cores. Wondering how you get them!!

author: CJay
author_rank: Super Contributor
timestamp: July 24, 2018, 07:08:42 am
content: eBay, lots of online suppliers, radio clubs often have ferrites for sale, they're not hard to find and they're not expensive for the power levels you're talking about, they will make your life easier.Ditto RF amplifier schematics, many RF transistor datasheets have test circuits in them (RD06HHF1, 2SC1969, many of them are pretty much complete amplifiers...If you're still stuck, there are lots of transceiver schematics out there for commercial rigs that you could adapt to meet your needs, there are even kits out there, compllete with schematics.You're going to need a low pass filter, as already stated, you're also going to need to know a little about what type of amplifier you need and we can help a little more if you give us an idea what application you're aiming at?

author: David Hess
author_rank: Super Contributor
timestamp: July 24, 2018, 11:12:09 am
content: Quote from: Dom13c on July 24, 2018, 03:33:51 amAll of those old single transistor VHF kits work like this but the same idea applies to HF. VHF power amplifier modules are also configured this way.Nobody bothers with HF amplifiers like this anymore except at low power because covering more than one HF band requires tuning.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 24, 2018, 11:26:04 am
content: Quote from: Dom13c on July 24, 2018, 04:01:19 amfor the range of 10-15W and upto 16MHz you can get T50-2 powdered iron toroids, they are readily available from many sources and do the job; plan at least with a 5 pole tschebycheff 0,1dB filter and get some decent NP0 caps; ceramic should do for this power level

author: Dom13c
author_rank: Regular Contributor
timestamp: July 24, 2018, 01:50:01 pm
content: Quote from: CJay on July 24, 2018, 07:08:42 amI am aiming at linear power amplifier made with either IRF510 or BD139 . Can't afford to pay for those pricy rf transistors.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 24, 2018, 01:59:41 pm
content: For the very beginning, you can certainly use some of those classic transistors; the IRF510 is seen still quite often in RF amps anyway; but as a word of caution: the pricy RF transistors have their prices because of the favorable rf parameters, which you normally don't see on the first look; one big point are the intermodulation properties of a transistor, where a real rf component beats out the shit off the IRF510 and friends.It's an ever repeating issue among radio amateurs - on one side you want to construct for a bargain, but in the interest of everybody on the frequency, you have to take things like imd, harmonic suppression and phase noise into consideration - even though many amateurs give a literal shit about it.

author: bd139
author_rank: Super Contributor
timestamp: July 24, 2018, 02:34:33 pm
content: <--- note username.Me or an IRF510 will get you a few watts. An IRF510 push-pull design with 24V supply can kick out quite a bit of power.Edit: As for "performance" as I'll group all the others in, yes. There are some properly nasty transmitters out there puking all over the airwaves. It's much safer for everyone if you stick to QRP power levels if you're homebrewing stuff and don't have a decent SA at hand.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 24, 2018, 02:39:20 pm
content: the IRF510 designs are not too bad if not driven too hardly at the limits; but nevertheless much more than max. -25dBc imd you don't get out of there, whereas many commercial amps don't exceed that mark either.

author: CJay
author_rank: Super Contributor
timestamp: July 24, 2018, 03:46:07 pm
content: Quote from: Dom13c on July 24, 2018, 01:50:01 pmI've played a bit with switching MOSFET RF amplifiers, they're fussy things if you push them and they let the magic smoke out at a microsecond's notice if you get it wrong.Sometimes they just let the smoke out for fun.They can be made stable and even made to work quite well, M0RZF.co.uk has some interesting information about them and how to use them.Personally, aiming for 10W would make me look for old CB transistors or something like a Mitsubishi RF FET, they're not expensive if you consider the simplicity and reliability, a genuine RD16HHF1 is £4...AMtools/spratreader on eBay is a reliable seller for ferrites,https://www.sdr-kits.net/RD16HHF1is a good source of genuine FETs

author: innkeeper
author_rank: Unknown
timestamp: July 24, 2018, 05:47:56 pm
content: this should suit your needs.you may need to adjust the pi input and output filters to suit the frequencies you want to use.schematic and circuit description here:http://users.belgacom.net/hamradio/schemas/RF_amplifier_15and17_meterband_10w_HFamp.htm

author: David Hess
author_rank: Super Contributor
timestamp: July 24, 2018, 06:00:36 pm
content: Ah, there you go; innkeeper's example is what I was thinking of.This is basically the same thing and what I was referring to. I have a 2 meter 25 watt amplifier which uses this configuration and it was common in kits. There is no reason it cannot be applied to HF but the bandwidth will be narrow especially with a high capacitance vertical power MOSFET but that is why there are tuning adjustments.http://users.cecs.anu.edu.au/~Gerard.Borg/engn4545_borg/VHFPA/2N7000/RFPAS_2N7000.html

author: Dom13c
author_rank: Regular Contributor
timestamp: July 25, 2018, 05:37:21 am
content: Quote from: HB9EVI on July 24, 2018, 01:59:41 pmyup. I know what you're talking about. those rf transistors have special built in circuit to enhance the performance. but paying that much doesn't make sense of for amature like me . BD139 and IRF 510 is more than enough for me

author: Dom13c
author_rank: Regular Contributor
timestamp: July 25, 2018, 07:26:50 am
content: Quote from: innkeeper on July 24, 2018, 05:47:56 pmThat's why I love you guys. you've git solutions to every problems. thanks to all of you

author: CJay
author_rank: Super Contributor
timestamp: July 25, 2018, 10:15:04 am
content: Worth noting that the design referenced is very similar to that of an awful of of CB 'burners' and that you're going to need to tinker with it to get a FET working in it (it can be done, I managed to get >35W @ 24V on 28MHz from a single FQP13N10 in a similar design before it grenaded).If you can track down an Eleflow RF transistor or even the EKL ERF2030, again, it'll make your life simpler as the venerable BD139 will not get you 10W output, but, they're 'special' RF transistors and cost way more.

author: bd139
author_rank: Super Contributor
timestamp: July 25, 2018, 10:26:21 am
content: I really need to look at specialist RF MOSFETs. I've been limping along with cheap crap for a while now. Fine for QRP stuff but I'm dying for more than 5W or so with current band conditions. I regularly blow the arse out of an IRF510 or two so this could get expensive.Also to note, the mythical properties of the original BD139 only apply to certain variants. Since Philips span off NXP they removed the fT from the datasheets. Not sure what silicon is in them but it's different and you'll be lucky if it does much at all as an RF PA. The ST branded units seem to follow the original devices and are 90% as good as the venerable 2n3866 up to about 20MHz but can shift a lot more power in that package. Also only £0.34 a go and quite difficult to blow up on a mismatch due to the high Vce.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: July 25, 2018, 10:40:20 am
content: A good BD139 is not really so easy to find anymore; I ordered some from aliexpress; just on the first look you could see what you got, the same they behaved in the circuit.on the other side, you can get some nice kits for 2m and 70cm doing 100W out of a used MRF186; sure, they are for higher frequencies and they already have a certain lifetime behind them when you get them, but for 30 bucks you get a nice PA doing it's job when you want to boost a qrp device. Before changing to the TS2000X, I used them on the FT736 and they worked well for quite a while

author: Dom13c
author_rank: Regular Contributor
timestamp: July 25, 2018, 10:43:22 am
content: Quote from: HB9EVI on July 24, 2018, 01:59:41 pmActually it is damn true. I just am trying to put together the whole thing as cheap as possible. So trying to avoid those rf buddies

author: Dom13c
author_rank: Regular Contributor
timestamp: July 25, 2018, 11:12:23 am
content: Quote from: CJay on July 25, 2018, 10:15:04 amActually , it's the cost of those rf buddies that sucks me. Otherwise they are way too better than the BD139 .

author: CJay
author_rank: Super Contributor
timestamp: July 25, 2018, 11:32:14 am
content: Agree, they're expensive, they have a load of advantages but you pay for them, the prices make my teeth itch, there must be decent bipolar parts out there somewhere, I don't think (for instance) Eleflow are manufacturing, I think they're rebadging, I could of course be wrong...

author: xaxaxa
author_rank: Regular Contributor
timestamp: July 26, 2018, 03:11:46 am
content: I don't know where you guys have been looking but "proper" RF transistors aren't expensive...MRFE6S9125N: $5 on taobao, 125W and operates from HF to VHFMRF5S9070N: $1 on taobao, $5 on aliexpress, 70W from HF to VHFMRFE6S9160: $12 on aliexpress, 160W from HF to VHFand many many more...These days a 2.4GHz 160W transistor costs $10 there isn't much reason to be using IRF510 or vintage bipolar parts...

author: CJay
author_rank: Super Contributor
timestamp: July 26, 2018, 06:14:12 am
content: Quote from: xaxaxa on July 26, 2018, 03:11:46 amI agree, you get a *lot* of transistor for the money, UHF cellphone station FETs are bargains these days but they're nowhere near as easy to work with as the parts we were discussing, the package is a PITA to work with as it's designed to be soldered down and there's a good amount of heat needed to do that, cell phone parts usually need 28V or higher which isn't common in a shack and they take some taming to keep them well behaved or you end up with a 70W UHF oscillator.They're also considerably more powerful than the OP needs and would be hard to get working well without ferrite impedance matching transformers.For those prices though, personally, I will order some just to have on the shelf so I can experiment at some future time.

author: bd139
author_rank: Super Contributor
timestamp: July 26, 2018, 07:02:02 am
content: Have to agree. One of my constraints is time and it’s very easy to whip out a mismatch smoked TO220 compared to proper RF transistors. Every PA design I have done has exploded at least twice. I thought I sucked but no this is apparently normal. Also the cheap switching FETs can be had for pocket money with free next day delivery here from reliable suppliers. $8 for 10x Vishay IRF510’s from RS. No slow boat, no risk of fakes or out of spec devices.Personally I’m trying to stay under 10W as that leads to manageable projects as well.

author: CJay
author_rank: Super Contributor
timestamp: July 26, 2018, 08:18:08 am
content: Quote from: bd139 on July 26, 2018, 07:02:02 amThe switching FETs have that disadvantage though, they aren't designed for linear operation so you're balancing on a knife edge where one slip will cut you, 'proper' RF parts are happier over a wide range of linear operation, swings n roundabouts, you pay extra for that and a datasheet that gives you that information whereas IRF, FQP etc switching FETs are best guess but dirt cheap so you can fry a few while you experiment (and I have, I've gone through a couple of dozen FQP13N10 devices while experimenting)There's a £12 70W MOSFET amplifier on it's way to me from China (ordered last week) to tinker with as wellIt's all fun and I'm trying to sort out a TaoBao account to get my hands on 20-30 of those dirt cheap 70W FETs so I can play some more.Maybe once I've tamed those I might have a go with the set of VRF2933 FETs I've been hanging onto for the last three or four years...

author: bd139
author_rank: Super Contributor
timestamp: July 26, 2018, 08:33:05 am
content: Yes they are tetchy. I've got a hole in the wallpaper where a bit of MOSFET pinged off. I was being lazy as my current limited bench supply was being used to power the rig and connected my radio SMPS to it which promptly chucked 22A through it before it exploded.I might have a go with one of the Chinese kits. At that price it's no major loss if it turns out to be a turd.

author: Wirehead
author_rank: Regular Contributor
timestamp: July 26, 2018, 10:04:03 am
content: There are some beefy ones, which given proper cooling and a good power supply, will actually keep going until the insides splutter all over the place.. this was at 300W CW Carrier on 80m band...- simple switcher mosfetShorted out and sustained about 50A ..No smoke, just molten guts

author: CJay
author_rank: Super Contributor
timestamp: July 26, 2018, 10:48:26 am
content: Yeah, we used to have to chisel MOSFETs (IRFP450 I think) off heatsinks in Compaq 386S desktop power supplies, they spewed a jet of molten guts out through the tab, insulator and welded themselves to the heatsinks quite effectively, often leaving a hole right *through* the heatsink so even when you'd drilled out the weird rivets you couldn't get the damn things to move.I seem to remember it was usually the IRFP in the primary that was closest to the switching transformer...oops, the PSU seen in this video:

author: Dom13c
author_rank: Regular Contributor
timestamp: August 01, 2018, 10:32:40 am
content: Quote from: CJay on July 26, 2018, 06:14:12 amWell, I do agree with you. When it comes to buy rf transistors online, the problem of getting fake parts really sucks. And those matching transformers connected in circuit without proper measurements are nothing but an arrow thrown in the dark.

author: CJay
author_rank: Super Contributor
timestamp: August 01, 2018, 01:33:24 pm
content: I think you're overstating how difficult it is to make an impedance matching transformer, they're not difficult, especially for HF, the ratio is determined by the number of turns of wire, the impedance can be calculated fairly easily if you have the spec of the core, if you don't have the spec of the core then you can work it out with some wire, a calculator and an LCR meter, one of the cheap ATMega ones is good enough.

author: David Hess
author_rank: Super Contributor
timestamp: August 01, 2018, 01:53:15 pm
content: It also is not critical in the respect that you are not matching the output impedance of the power amplifier to the line or load; doing so would result in lower efficiency. This is why broadband power amplifiers get away with transformer turns ratios limited by construction. The turns ratio and supply voltage determine output power assuming that the output devices can support it. The design works backwards to the output devices.

author: Dom13c
author_rank: Regular Contributor
timestamp: August 05, 2018, 03:27:29 am
content: Quote from: CJay on August 01, 2018, 01:33:24 pmokay, I'll try it out the real problem arises when you dont have a lcr meter . the same is with me. It seems like I have to invest some bucks to buy one of them. cause the hobby I'm in definately needs one of them

author: Wolfgang
author_rank: Super Contributor
timestamp: August 05, 2018, 11:42:33 pm
content: Hi,if you want something transformerless you could go for a complementary amplifier.The web has some info from Chris Trask.http://home.earthlink.net/~christrask/Complementary%20Push-Pull%20Amplifiers.pdfI made one using 2N2905 and 2219 transistors, like that:https://electronicprojectsforfun.wordpress.com/rf-module-gallery/the-amplifier-module-gallery/a-complementary-hf-push-pull-amplifier/The frequency range is ca. 50MHz (-3dB) and you could extract 100mW output with a good linearity (38dBc). IP3 is 30dBm.Its linear and foolproof against output open, short or mismatch.

author: David Hess
author_rank: Super Contributor
timestamp: August 06, 2018, 04:02:07 am
content: Quote from: Wolfgang on August 05, 2018, 11:42:33 pmThe more things change, the more they stay the same. That design is very similar to simple high impedance active probes. Eventually they ended up with adiamond bufferoutput stage.The problem is that it is difficult to extract power from emitter follower outputs because their low impedance increase the effects of parasitic inductance. This is why higher power amplifiers also use higher voltages to allow higher impedance into the output transformer or network.QuoteThat design is very similar to the high voltage z-axis amplifier on a CRT oscilloscope.It does not help us here but very broadband push-pull power amplifiers for cable distribution use a push-pull stage driving a balun core transformer except that unlike a similar HF amplifier, the transistors are configured in common-base mode instead of common emitter. They made special transistors in the same packages with the base and emitter leads swapped just for these.One alternative I might consider is using multiple surface mount RF transistors in parallel in a more traditional circuit. It is too bad all of the inexpensive RF power transistors are gone.