Ever built a working RF noise source? - Page 1
Forum section: electronics / projects

author: chasxmd
author_rank: Contributor
timestamp: August 06, 2014, 04:08:07 am
content: I've built two RF noise sources compliments of "googled" schematics. Neither worked.. I poked around, tried to modify them, etc. Both worked using a diode in avalanche breakdown.Have you built a working RF noise source? How did you build it any gotchas? Got a link?Edit: <1GHz...Thanks,Charles, AC0GDiradan.com

author: free_electron
author_rank: Super Contributor
timestamp: August 06, 2014, 05:09:30 am
content: several. but i used a noise vacuum tube. special triode designed to create rf nose

author: ejeffrey
author_rank: Super Contributor
timestamp: August 06, 2014, 05:23:19 am
content: I have used a photodiode and LED as a noise source. I was only operating at around 10 MHz, but with the right diode you can go to 10 GHz. It was convenient for me at the time, but really an avalanche diode should work. Can you describe more about what didn't work?

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: August 06, 2014, 05:27:40 am
content: What do you mean by "not worked"? Was it generating wrong kind of noise? What kind of noise do you need? White noise? Pink noise? What schematics did you try exactly?

author: Richard Head
author_rank: Frequent Contributor
timestamp: August 06, 2014, 05:59:10 am
content: I've used a reverse biased B-C junction of a BJT on a couple of occasions and then amplified it. I found I could get a higher output from a B-C junction than a normal diode.My bandwidth requirement wasn't very wide though.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: August 06, 2014, 08:19:20 am
content: Wow it is very fascinating stuff! There appears to be a noise diode designed for every reasonable band:http://www.rf-microwave.com/en/shop/0/446-noise-generator-diodes/4953-NS303.html. Looks very similar to diode I found inside random number generator long time ago. 45 €/piece is kind of pricey howeverI think it make sense to buy one of those as broad range as possible and then add band pass filter on the output. It will depend on required bandwidth for noise however. Will narrower band noise diode generate higher bandwidth noise?

author: eurofox
author_rank: Unknown
timestamp: August 06, 2014, 09:41:31 am
content: Here you can buy a kit or parts.http://www.rf-microwave.com/en/shop/0/215-components-kits/2581-KIT-NS.html

author: chasxmd
author_rank: Contributor
timestamp: August 07, 2014, 02:17:39 am
content: Quote from: Alexei.Polkhanov on August 06, 2014, 08:19:20 amInteresting, thanks for the link! I'll check these out.

author: chasxmd
author_rank: Contributor
timestamp: August 07, 2014, 02:18:58 am
content: Quote from: eurofox on August 06, 2014, 09:41:31 amthank you, takes the fun out of building one myself but I'll throw this under the backup plan.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 07, 2014, 06:31:07 pm
content: Quote from: Richard Head on August 06, 2014, 05:59:10 amI've done the same thing with great results. Can't remember the device, but it was something common like a 2N2222 or 2N3906. The bandwidth was wide, as I was using it as a reference level for EMC tests.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: August 07, 2014, 09:05:47 pm
content: I am curious about this B-C junction method. How exactly do you build that? Do you leave the emitter floating? What voltage do you apply? It it in avalanche mode or something like that?

author: G0HZU
author_rank: Super Contributor
timestamp: August 07, 2014, 09:35:48 pm
content: I have built a couple of precision noise sources in the past.One I built many years ago is a high level noise source 200kHz to 180MHz at -86dBm/Hz. it is very flat with less than 0.5dBpkpk ripple in the noise level. It is very useful in lots of ways. Usually for annual health checking of my other test gear using various band limiting filters on its output.The other is a precision low level noise source covering 200kHz to 1300MHz. This also has about 0.5dB flatness across the full range but a much lower noise level of about -149dBm/Hz. It has very low VSWR in both hot/cold and I use it for amplifier noise figure testing.It actually works quite well to beyond 3GHz but the noise level starts to fall slightly above about 1500MHz.Both of them use proper 'noise' diodes that bias at about 28V dc.

author: rob77
author_rank: Super Contributor
timestamp: August 07, 2014, 09:51:34 pm
content: Quote from: Alexei.Polkhanov on August 07, 2014, 09:05:47 pmactually... +1i've done that with reverse biased C-E with a floating base - but it boils down to a B-E avalanche breakdown, because B-C is in forward when reverse biasing C-E with a floating base.the B-C junction has much higher breakdown voltage than the B-E (order of magnitude higher), so i'm curious what the circuit was.btw. some transistors are rather zenering than avalanche - so you need to find a noisy one

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 07, 2014, 10:11:06 pm
content: Hi,Yes I have built a noise source. I built it to use with an HP 8970A Noise Figure Meter.I used a Noisecom NS302 noise diode. Here is the schematic:And the construction:You can see this work on a Spectrum analyzer, but the noise level is very low, and broadband. It was designed to be used in place of a (very expensive) HP 346C noise source. It has about 15dB more noise than a 50 Ohm resistor.There is some very useful information here:http://www.rf-microwave.com/en/shop/0/446-noise-generator-diodes/4952-NS301.htmlespecially the articles listed in the description.Also:http://www.noisecom.com/products/components/nc100-200-300-400-series-chips-and-diodesRegards,Jay_Diddy_B

author: eurofox
author_rank: Unknown
timestamp: August 07, 2014, 10:15:16 pm
content: Special noise diodes:http://www.rf-microwave.com/en/shop/0/446-noise-generator-diodes.html

author: deano4265
author_rank: Newbie
timestamp: August 07, 2014, 11:42:48 pm
content: Some available on eBay at reasonable pricehttp://www.ebay.com/itm/161382941660?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

author: Fraser
author_rank: Super Contributor
timestamp: August 08, 2014, 12:25:42 am
content: I have built some simple un-calibrated noise sources as a poor mans tracking generator replacement when building RF filters. I also purchased some ex-equipment Noisecom noise sources......excellent quality sources.More recently I stumbled upon some cheap noise sources from China. I bought a couple for interest. I know they are not as much fun as building your own but you may be able to learn from the design and get your own designs workingAt $23 built and tested, they are pretty good value for money.http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=231273984135I also bought a couple of the 138MHz to 4G4 RF signal sources and simple spectrum analyser units from the same seller.As a final comment....noise sources come in a variety of output levels. Some are designed for testing highly sensitive RF equipment with very low noise floors. Such a noise source would not drive a relatively insensitive receiver or spectrum analyser. Other designs provide much higher output levels but the challenge is getting a reasonably level output across wide frequencies using block amplification. MiniCircuits MMIC's do not have a flat frequency response. You will note that the Chinese design I detailed appears to use a diode producing noise that is driving a triple stage MMIC amplifier. This is not an uncommon approach and even Noisecom use similar in some of their units. For a very flat frequency response, it is often best to use a decent noise diode from Noisecom or similar, correctly bias it and do not use amplification ! You then get a very low level of noise but also a flatter frequency response.Also, be warned, trying to amplify wide band noise is not quite as simple as it may first appear. Slapping a few MMIC's on the output of a noise diode can easily lead to an overload condition in the latter MMIC stages if you overcook the gains. I had one MMIC getting very hot as a result of an experiment doing just such cascaded gain blocks. As Tektronix warn in their spectrum analyser manuals....when considering the overloading of the front end you must consider ALL signals within the equipment pass-band to be in play and additive in the overload calculations.Aurora

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: August 08, 2014, 03:22:13 am
content: Quote from: deano4265 on August 07, 2014, 11:42:48 pmI don't know what is inside that unit but that blue anodized aluminum box is not an adequate RF enclosure by any means.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 10, 2014, 07:57:08 pm
content: Hi group,In reading the thread, it is clear in my mind that there are two type of noise source that are being discussed here.1) One kind like thisThis is designed to put out a high amplitude noise signal that can be used in place of a tracking generator to make measurements on filters etc.2) There is a second kind, which are designed as low cost replacements for the HP346B/C like the one I made and this one:This only generate a very small amount noise, typical 15dB more noise than 50 Ohm resistor.If the original poster had built the second kind of noise source, he could very easily be fooled into thinking that it wasn't working.Here are some measurement on my noise source:In the first measurement I have the resolution bandwidth, RBW, set to 3MHz, remember noise amplitude is a function of square root of the bandwidth. I have set the video bandwidth, VBW, to 1kHz. I have set the span to 0 Hz. The center frequency is 200 MHz.The vertical is 2 dB division and the sweep is 10 seconds ( 1s/div). The attenuation has been set to 0dB.The Spectrum Analyzer is an HP8568A.I am turning the noise source on and off during the sweep. There is barely 0.4dB change in amplitude if the source is on.I then used this amplifier made by Avantek. The part number is hard to read, I think it is UTC5 -157H. It is marked 5 - 500MHz.I measured the gain of the amplifier in this set up:The attenuator was fed with the 200MHz -20dBm signal for the Spectrum Analyzer. With the attenuator set to 60dB, the Spectrum Analyzer showed:Therefore this amplifier has a gain of 60dB at 200 MHz.I then connected the noise source to the input of the amplifier. In this screen shot the upper trace is with the noise source on the lower trace is with the noise source off.In this configuration you can calculate the Noise Figure for the amplifier.I just wanted to show that with the second type of noise source, how small the signal is.Regards,Jay_Diddy_B

author: TurboTom
author_rank: Super Contributor
timestamp: September 12, 2016, 05:12:50 pm
content: Just out of curiosity and since there was a noise generator mentioned in the SSA3000X thread, I decided to experiment with a SPD-121M GaAs mixer diode that I´ve still got virtually hundreds of as a noise source in reverse breakdown mode.Guess what -- it worked even better than expected, see attached images. Since I´ve only got my Rigol DSA at work, I couldn´t check above 1.5GHz. But the noise level it produces without any amplification (except the SA´s internal 20dB PA, but that´s taken care of in the axis designation) and optimization is quite impressive. The yellow trace shows the noise output at approx. 1mA of current while the magenta trace was taken at 5mA. The cyan trace resembles the SA´s noise floor with the power to the noise generator turned off.I intend to design a PCB for this gadget and add two or three microwave gain blocks along with proper voltage / current regulation.Cheers,Thomas

author: daqq
author_rank: Super Contributor
timestamp: September 12, 2016, 05:40:39 pm
content: QuoteSure I did - it was supposed to be an amplifier though... it was just noisy

author: LaserSteve
author_rank: Super Contributor
timestamp: September 12, 2016, 06:21:30 pm
content: You might want to look at this thread, too...https://www.eevblog.com/forum/rf-microwave/russian-noise-diodetubes-anyone-use-these/Steve

author: Zero999
author_rank: Super Contributor
timestamp: September 12, 2016, 09:59:03 pm
content: Incandescent lamp + suitable amplifier.

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: September 12, 2016, 10:16:47 pm
content: Very recently I had an idea to try TVS diodes (connected in reverse) as noise source. I wonder if anyone tried that.I started wondering what those special "noise" diodes are. It appears that they are almost same as avalanche diodes with low threshold voltage. A was able to find avalanche diodes with 50V threshold on Digikey for example and decided what if I connect one in reverse to 50V bias, add resistor in series for current limiting and look if it can be used as good RF noise source. After that I realized that TVS diodes from Littlefuse may be another option?

author: jh15
author_rank: Frequent Contributor
timestamp: September 13, 2016, 02:42:15 am
content: Imac, or Apple laptop power supply.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 13, 2016, 06:50:55 am
content: Quote from: Hero999 on September 12, 2016, 09:59:03 pmStupid idea. But if it works, it ain't stupid.Seriously, though: a high temperature resistor is a good source of noise, and the only thing hotter than white-hot tungsten is UV-hot plasma. And, plasma being an electromagnetically active material, it can exhibit complex excitations and resonances with geometry of the apparatus (accidental cavities, stubs and whatnot).The only difficulty might be finding a bulb that matches well with its surroundings...We're looking at:https://www.google.com/search?q=sqrt%284+*+boltzmann+constant+*+2400+kelvin+*+50+ohms+*+1Hz%292.57 nV/rtHz is pretty low noise (most op-amps do considerably better..), but since we're contending with 0.9 nV/rtHz (50 ohms at 293K), it's not horrible. I mean, 9 dB must be good for something, right?A 50 ohm bulb might be 6.3V at 125mA, or 12.6V at 250mA. Not so hard to find, I think. Use a bias tee (L from +V, coupling C to load) to power it. (Note that the noise power is the same regardless of size, as long as the temperature is there -- so it's to your advantage to use as small a lamp as possible!)This looks reasonable:http://www.mouser.com/ProductDetail/JKL-Components/2203/?qs=sGAEpiMZZMtj1PWpWL2%252bvDwicDUvKr1eDUSCVRwqUUA%3dA bulb this small should be good into the GHz. The glass will give a somewhat lower impedance around the source, but that's probably an advantage given the wire leads, and wide spacing (twin-lead transmission line always has a highish impedance). Soldering it into a PCB, or poking it into PCB-mount sockets, should give reasonable SWR. (And you can even measure the SWR by transmitting into it! Just remember to do it while it's hot -- when unbiased and cold, it'll be a not-terrible short circuit instead!)If you want the second hottest noise source on the EEVBlog Forum, I suggest doing it.Tim

author: bson
author_rank: Unknown
timestamp: September 13, 2016, 07:09:52 am
content: Quote from: Alexei.Polkhanov on August 07, 2014, 09:05:47 pmAsk and ye shall receive. This pops up every so often.I put it on a small board with a THS3202DGN based wideband amplifier inside an EMI shield. Works great; the band is flat from DC out to about 500MHz, then the THS3202 ripples and falls off. (Like many CFB amplifiers it produces a single hump before hitting the wall. Mine is about +2dB, so no big deal and for frequency domain measurements it's easily normalized anyway.)What I find interesting is that some circuits that are very clean when swept show oddball wavy frequency response when hit with white noise. IMD is my guess.

author: LaserSteve
author_rank: Super Contributor
timestamp: September 13, 2016, 02:29:12 pm
content: Festoon lamps have been used as loads, power meters, and noise sources. Because they are cylindrical, its fairly easy to slip copper or brass tubing around them and make a coaxial device. The old RSGB UHF/VHF handbook has a few examples. I'm just not aware of it being carried out to 1 Ghz, although it is documented to high VHF. In the olden days, they were used as fairly accurate power meters. One lamp on DC, one lamp on RF, and mounted on either side of a oiled piece of paper. When the spot illumination was nearly equal, the RF power was close to its DC equivalent. I'm told this can hit accuracies of 2.5% or better with the human eye...Steve

author: jh15
author_rank: Frequent Contributor
timestamp: September 14, 2016, 05:23:08 am
content: I did the oiled paper photometry in high school physics in the '60s was precise. Then Polaroid, with the Swinger camera reminded me of it, comparing a grain of wheat bulb with the rangefinder view.Miss Dr. Land, he didn't seem evil like present companies. Always wanted to work for them, knew some, they loved it.He did hire the blind. If for profit or kindness, it was unique. Signted people would go nuts loading film in total darkness all day.

author: Timeok
author_rank: Contributor
timestamp: July 27, 2023, 12:16:26 pm
content: I made a series of noise sources using a BFR90A. The basic features are:Power supply: 28VFreq. 1MHz - 2GHzENR about 15dBFlatness +/- 0.6dBAnd most importantly, they are able to calibrate them individually.I have several prototypes and a final version.

author: ionospheric
author_rank: Newbie
timestamp: July 27, 2023, 05:03:34 pm
content: @Timeok Can you please share the schematic?Many thanks

author: jonpaul
author_rank: Super Contributor
timestamp: July 27, 2023, 06:42:22 pm
content: see Microwave Noise lamp:An ionized plasma emits a wideband noise sectra.For audio/LF we used GenRad noise gens with a Thyratron or noise diode (special Zener)The resistor thermal noise is calculated by the usual formula and depends on the Tdeg k and resistance only, very low in uV range ususally.Finally in 1970s Nat Semi made a rerpeating sequence (shift reg) noise source IC for hifi acoustic eq.Enjoy,j

author: iw5bsf
author_rank: Newbie
timestamp: August 24, 2023, 10:16:59 pm
content: hello i'm new in the forum i saw a great work i also have a noisecom diode anti-noise head to match the hp8970a but i can't set the parameters for the hp8970a could you give me some pointers thanksRobert

author: TimFox
author_rank: Super Contributor
timestamp: August 24, 2023, 10:43:41 pm
content: Has anyone tried using a 5722 vacuum diode?It is designed for use in "saturated" emission (not space-charge limited) so that the shot noise output can be computed directly from the DC plate current.I'm not sure how to optimize the connections to the filament/cathode; the plate goes to a 50 ohm load.The circuit in the data sheet (below) shows RFCs in the filament leads, but the three filament connections are bypassed to ground with 500 pF.If the cathode is supposed to be at AC ground, why are the RFCs needed?I thought it would be straightforward to regulate the emission by servoing the filament current, but I was hoping to use it a lower frequencies than the usual RF circuit.https://frank.pocnet.net/sheets/201/5/5722.pdf