Broadband amplifier for White noise source? - Page 1
Forum section: electronics / rf-microwave

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 20, 2016, 04:40:11 pm
content: I bought a ham it up 1.3 upconverter, I mostly bought it because it has a built on RF white noise source which I have read works much better than any of the ebay sources. I thought about building one but the Ham it Up seemed to be a bargain since it is two devices in one.Anyways the noise source is pretty good although not linear, after UHF it starts dropping off slowly. So I have two reasons for amplification #1 I would like to get the thing working better up in the L and S bands, secondly I would like to be able to hook it up to an antenna and cause true interference for testing shielding etc. Before anyone gets up on there hi horse I am only talking about a few hundred milliwatts or even better 1 watt with attenuation to control the amount of crap it spews out. My house is also made of concrete so all my antennas really need to be outside (unless its a yagi pointed through window) to do anything, and I need wifi repeaters just to get decent signal 2 rooms away.I have never built an amplifier for a transmitter, most are based on certain bands or frequency so I haven't had much luck finding any schematics for something broadband. On the small scale would something like an MMIC work, I have some mar6, psa4-5043 which are both broadband mini circuits mmic's used in most SDR LNA's. I also have some mav-11's which mini circuits calls a monolithic amplifier, im not sure what that means but its noise floor is about 3db instead under 1db. The mar6 and psa4 are easy enough to use as far as building LNA's for reception... I have always been under the impression these are only to be used for RX only, after reading there data sheets I see nothing about that, nor does it say the mav11 can't be used for transmission....The reason I would like to get up to one watt is if I can is two fold, first like I said my house is an RF black hole and I want to test out some real world scenarios. Secondly at some point I would like to make a broadband amplifier that is more in the 25-50 watt range for a GNU radio controlled broadband transmitter, and im considering this a good first experimentation project.

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 21, 2016, 04:33:15 pm
content: Well im not to sure why no one answered this question but I found a few chips that can boost in to the few hundred milliwatt range, Im still confused if something like a mar 6 or mav 11 will work since the datasheet does not mention TX.I guess what confuses me is I have a Radio Shack HTA20 which is a 2m 30 watt power amp that has never been used. Is the ony thing that makes it a "2M' amp is the speed of the transistors and the filters? What would happen if one stripped the filters out and used it at 50mhz? Im not sure why it blow anything up as long as the impeadence matches and the transistors or fets switch fast enough.I would like to strip the filter out and use it as a broadband amp from HF to 2M or 70cm if that will work but I dont want to fry it either so if anyone could explain the details of why this may be a bad idea please do.

author: Yansi
author_rank: Super Contributor
timestamp: June 21, 2016, 05:08:23 pm
content: I'm not an RF expert though, but the datasheets clearly specifiey maximum output level in dBm and also the P1dB compression point. So what else would you need to use a MMIC as an output power stage?Here's a small comparison list. ERA5 gives the most power, almost 100mW.http://f5ad.free.fr/Docs_ATV/MMICs.pdfIf you need more power, just find more beefier gizmo, like CLY5:http://www.mouser.com/ds/2/412/CLY5-198574.pdfThat one kicks ass. 1W @1.8GHz.

author: rfeecs
author_rank: Frequent Contributor
timestamp: June 21, 2016, 05:27:58 pm
content: Quote from: rwgast_lowlevellogicdesin on June 21, 2016, 04:33:15 pmNo. So that is a 144-148 MHz 30 Watt amplifier. It will be designed specifically for that band. The matching networks will be narrow band. Removing the filters will not give you a broadband amplifier. Not to say for sure that you won't get some gain and output power at 50MHz, but most likely it will not work well out of the intended band of operation.MAR-6 and MAV-11 are darlington gain blocks. They are amplifiers, so yes they can be used to amplify power. But P1dB is very low, so you are not going to get much power. There are similar HBT gain blocks that can put out a little more. HMC475 can put out more than 100mW for example. These types of parts are made by Hittite (Analog Devices), Qorvo, Skyworks, etc. Available from major distributors.If you want to go higher power for a very broadband amp, you need higher voltage. So there are GaN parts, but you won't want to pay for them. A popular military application similar to yours is for jamming cell phones to prevent triggering "Improvised Explosive Devices."Note CLY5 from previous post is just a transistor, not a MMIC. It is unmatched. You have to design a matching network to get the performance quoted on the datasheet and you are back to a narrow band power amplifier.

author: CJay
author_rank: Super Contributor
timestamp: June 21, 2016, 05:35:05 pm
content: Quote from: rwgast_lowlevellogicdesin on June 21, 2016, 04:33:15 pmNo reason you can't use a MAV11 for TX, it should do a few tens of milliwatts. There are better solutions, some easily available MMIC modules are good to 1W and you can use them push-pull into a broadband transformer.Stripping the filters out, not a great idea, they're usually designed to match the driver and load to the transistor, you're better redesigning them for 50MHz by the looks of it the HTA20 uses the PCB as an element of the filters so it'd take some effort.You'll also need to be sure it doesn't oscillate.Broadbanding it, not so easy, it may be better to build from scratch for the amount of effort it may take,Depent

author: Marco
author_rank: Super Contributor
timestamp: June 21, 2016, 06:18:54 pm
content: Not really DIY but BG7TBL has a 0.5W wideband amplifier on aliexpress&co (just search for wideband power amplifier and you can't miss it, class A so it has a big heatsink). Not sure which MMICs he used.Yansi, TriQuint hasnicer ones.

author: Yansi
author_rank: Super Contributor
timestamp: June 21, 2016, 06:24:28 pm
content: Thank you for tip Marco. The CLY5 is what I know from various HAM constructions from the 1296MHz and up bands.

author: rfeecs
author_rank: Frequent Contributor
timestamp: June 21, 2016, 06:49:17 pm
content: Quote from: rfeecs on June 21, 2016, 05:27:58 pmFor example, Marco's nicer one TriQuint(Qorvo) QPA2237, $130 from Mouser:http://www.mouser.com/ProductDetail/Qorvo/QPA2237/?qs=%2fha2pyFaduhaFdD1XZFo20c%252bH1FKAyj65XwuMp5ey0s%3dOr similar HMC1099, $104 from Digi-Key, but non-stocked:http://www.digikey.com/product-detail/en/analog-devices-inc/HMC1099LP5DE/1127-2867-ND/5268953If you really want 1W, one way would be NPTB00004A, $15 from Digi-Key. This is a GaN transistor. You would need to design a bias network (choke, bypass caps), bias at about 12V, and a lossy input match (2 resistors). That would give you gain and power from LF to beyond 2GHz. But with all the associated hassles of designing it and getting it to work without oscillating.

author: uncle_bob
author_rank: Unknown
timestamp: June 21, 2016, 11:47:43 pm
content: HiFor most people, what make noise sources useful is that they have an output noise density that is flat over a reasonable frequency band. You seem to be confusing frequency response and amplification. If you take a source that is down by 6 db at 400 MHz compared to 100 MHz, a simple amplifier will not help that at all. If you want a source that is flat to L band, it needs to start out flat to L band.Amplifying noise and not messing things up also depends a bit on what you expect in the time domain. A reasonable noise source will have a peak to average ratio in the 15 to 20 db range. To preserve this characteristic, your amplifier needs a compression point that is 15 to 20 db greater than the expected output power.If you actually are just trying to build a jammer ... there are other ways to do it.Bob

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 21, 2016, 11:51:07 pm
content: Ok thank you for the information, I am no RF expert either, im just learning and until now its mostly been on the RX side of things. Even if the mav and mar arent the best choice out there it's no huge issue. There very simple to use, just a 50 ohm line and power source with some BNC/SMA jacks and your ready to go, best of all I have them on hand!As far as the 2M amp goes I never planned on taking it apart I am just trying to figure out what makes it an amp for 2M and not some other frequency, that is if we were to take away the filters. I dont understand what is meant by the matching network is for 2M, I guess Im just assuming you bias the transistors and make sure everything is on 50ohm strip line and you should be able to amplify whatever frequency you want as long as the transistor can handle it. Is the problem the parrasitics on the PCB, is it some how designed to operate optimally 2M with out the inductance/capacitance of the traces screwing things up?Is it even possible to build or buy a broadband power amplifier? I mean like 30-100watts? My idea with the transmitter was GNURadio would handle everything so if your doing CW on HF it hits full power but if your doing some 2.4ghz work you set the amp down to a few hundred milliwatts. I am starting to thing an amplifier for this kind of genral use isn't possible to build and if there is something out there it's probably ridiculous expensive?

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 21, 2016, 11:55:12 pm
content: @Uncle_bobWell my source is pretty flat through UHF, I was thinking if I used an mmic and built a hi pass filter around 800mhz it will bring the l-band up in to the same region as the rest of the noise source. Like I also said I want to be able to use it as somewhat of a "jammer" but more of a very short range interference device to test shielding on devices.I would assume a jammer is as simple as picking a band and then getting an oscillator and amplifier meant for those frequencys.

author: uncle_bob
author_rank: Unknown
timestamp: June 21, 2016, 11:58:29 pm
content: Quote from: rwgast_lowlevellogicdesin on June 21, 2016, 11:55:12 pmHiIf you have good enough test gear and a lot of time, you can indeed design a very custom filter to reshape the noise. Unless it just happens to fall off at 6 db per decade for several decades, it's not going to be an easy fix.For the sort of testing you are talking about, a spectrum analyzer with a tracking generator is usually a better way to go.Bob

author: rfeecs
author_rank: Frequent Contributor
timestamp: June 22, 2016, 01:28:18 am
content: Quote from: rwgast_lowlevellogicdesin on June 21, 2016, 11:51:07 pmIt's possible to build a broadband power amplifier. These guys do them, for example:http://www.arworld.us/html/12300.aspYes, they are ridiculously expensive.Your SDR reminds me of the Joint Tactical Radio System:https://en.wikipedia.org/wiki/Joint_Tactical_Radio_SystemThe military's attempt to build one radio to replace virtually all the many and varied military radios. From 2MHz to 2GHz. Average cost per radio $37,700. But of course a military product will be insanely expensive.

author: Marco
author_rank: Super Contributor
timestamp: June 22, 2016, 03:58:11 am
content: Quote from: rwgast_lowlevellogicdesin on June 21, 2016, 11:51:07 pmHow much money do you want to spend? You can makewideband combinersto combine the power from those 100+$ MMICs. 4 QPA2237s would get you 30+ Watts.

author: uncle_bob
author_rank: Unknown
timestamp: June 22, 2016, 11:41:25 am
content: HiA SDR that directly covers a hundred MHz chunk of RF isn't to crazy on the receive side. If you start going past that, there are some significant performance trade off issues in addition to the cost.On the transmit side, you have things like spurs and harmonics that have legal limits on them. That gets you into bandpass filtering and switching those filters. There also are practical things like 12 amplifiers done as bandpass units are cheaper than one giant broadband super power unit.Can you do this? Sure you can. There are probably better ways to spend a the money (Buy a few BMW's ...).Bob

author: rwgast_lowlevellogicdesin
author_rank: Frequent Contributor
timestamp: June 22, 2016, 04:11:17 pm
content: Well your right sure I can, I am already doing it on RX, as far as using different antennas and band pass filters. What im actually doing is using a highly modified RTL Stick for now with a transverter. Well in reality its a homemade upconverter to cover 0-30mhz and a hacked up direct TV converter to get me up to 4 ghz. I will be using GaAs switches to switch in different filters and antennas. This will all be powered on a RasPi 3 and some micros connected to a UPS battery and a tracking solar panel. The RX will just be an SI5153 and PLL to get up to 4ghz hopefully connected to a mixer and the pi's audio out. I have a mountain as a back yard I am going to hike to the top and and put all this junk in a weather proof box then establish a wifi link to my house via cantannas. Then I will controll the whole thing via VNC (Virtual Desktop) from my house.Im trying to keep parts as few as possible. I want to make two trips up, one to make the antenna array and one to set the radio up. I guess for transmit beyond a few hundred milliwatts I will have to build ot buy a new amp and make another trip every time I want to find a band I want to experiment with as far as transmission. Im not a rag chewer but I know I at least want 2M for satcom along with 70cm and HF for data and CW later on. The thing is I know Im going to want to do RSSI/Beacon play in the ISM bands but I guess with proper ISM antennas I can get an mmic to work well if im using directional antennas from a hill? I cant do anything ridiculous and motorized up there without adding more power but I have been looking at beam forming as an option in some cases.From maybe 100ft over the twon (a basin/valley shape) at 315/434/915/2.4ghz a few hundred milliwats could get me a few miles of transmit coverage as long as its hi gain directional antennas? The basin is maybe 8-10 miles apart from my back yard to the mountain on the other side, how much TX power would it take to hit any spot in a 10 mile radius in the ISM bands?

author: uncle_bob
author_rank: Unknown
timestamp: June 22, 2016, 11:05:56 pm
content: Quote from: rwgast_lowlevellogicdesin on June 22, 2016, 04:11:17 pmHiI believe you will find that most of the ISM bands have FCC limits on them. Often they are radiated limits rather than power.Bob

author: dmills
author_rank: Super Contributor
timestamp: June 24, 2016, 10:22:13 am
content: A note on power transistor matching:On the input side the power devices are usually either a few ohms in parallel with some annoying amount of cap (if a bipolar part) or a few ohms in series with a very annoying amount of cap if a mosfet, high power semis for HF use are never a broadband 50 ohm match.You CAN get transistors with an internal matching network, but they are inherently narrowband, they do however make matching easier, but are mostly a thing above 400MHz or so.Usually doing a broadband input match amounts to using a transformer to get from 50 ohms down to something lower (12.5 or 5.5 ohms are common because the winding ratios are easy), then using resistors to swamp the gate/base cap of the power device.A narrow band version will just use an L or Pi match in all probability (Inductor, often printed) and a cap with enough resistor to ensure stage stability, you can design these to be conjugate matches.On the output side, a narrow band design will be another L or Pi match and may try to conjugate the device drain impedance, while a wide band design will be a transformer with (usually) a shunt cap to make the load capacitive above the highest band of interest (Helps with stability).It is worth noting that a broadband stage does NOT conjugate match (Except possibly on the highest band) and likely does not have an output impedance of 50 ohms (It is actually often much closer to being a voltage source).I recommend a copy of "Experimental methods in RF design" as being your next book purchase.Regards, Dan.

author: Marco
author_rank: Super Contributor
timestamp: June 24, 2016, 10:53:42 am
content: All I got from that was "don't even try and let the MMIC designers worry about it"

author: chris_leyson
author_rank: Super Contributor
timestamp: June 24, 2016, 11:52:38 am
content: Quote.You also have to look at this from a frequency domain point of view . If you have a flat power spectral density then the PSD at any frequency will be proportional to the overall noise power and inversly proportional to theoverall noise bandwidth. You also have to allow for a peak to average ratio, PAPR, of 15 to 20dB for AWGN source. It's probably easier to generate a relatively narrow bandwith noise source and mix it to generate noise at the higher frequncies.In theory it is possible to generate a limited bandwidth noise souce with a flat PSD and only 6dB PAPR, in practice it would all depend on the linearity of the DAC used. Generating an FFT of a Golay Rudin Shapiro sequence is one method of getting 6dB PAPR. It might be worth looking up NPR, noise power ratio testing, see Analog devices app note MT-005.You might be better off using a swept source for interference measurement rather than a broadband noise source.

author: uncle_bob
author_rank: Unknown
timestamp: June 24, 2016, 01:10:34 pm
content: Quote from: chris_leyson on June 24, 2016, 11:52:38 amHiAs in, use a spectrum analyzer with a tracking generator !!!If the desire is to have a broad spectrum signal, the other way to do it is with an impulse. It is not a noise spectrum, but over a reasonable bandwidth you can have a fairly flat (and predictable) noise distribution. The whole "how to amplify it" thing is turned a bit on it's head when you go to an impulse.Bob

author: chris_leyson
author_rank: Super Contributor
timestamp: June 24, 2016, 01:49:16 pm
content: QuoteYep, that's the approach I would have used from the outset. I can foresee lots of difficulties in building a broadband power amplifier to amplify AWGN, flat frequency and phase, stabillity and then you need an additional 15 to 20dB headroom to cope with the peaks. I know it really doesn't help the OP but I just made a few suggestions for alternative approaches.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 24, 2016, 06:08:23 pm
content: Unless you want ultraflat response, a MMIC driving a discrete LDMOS might just get you there..BTW< MAV-11 is ancient , there are far better MMICs from Mini-Circuits, Sirenza, RFM, etc... (or whomever bought the line this month)Read reference two from this paper...http://www.w1ghz.org/small_proj/Simple_Broadband_Power_Amplifiers.pdfFYI:http://www.w1ghz.org/small_proj/ADL5324_Power_Amplifier.pdfMy version of the SBPA works well from 144 to 1.9 Ghz.. The LD-MOS cost 20$ from a Ham source...Steve