Ever built a working RF noise source?

[chasxmd]

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, AC0GD
iradan.com

[free_electron]

several. but i used a noise vacuum tube. special triode designed to create rf nose

[ejeffrey]

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?

[Alexei.Polkhanov]

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?

[Richard Head]

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.

[Alexei.Polkhanov]

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 however 

I 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?

[eurofox]

Here you can buy a kit or parts.

http://www.rf-microwave.com/en/shop/0/215-components-kits/2581-KIT-NS.html

[chasxmd]

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 however 

I 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?

Interesting, thanks for the link! I'll check these out.

[chasxmd]

Here you can buy a kit or parts.

http://www.rf-microwave.com/en/shop/0/215-components-kits/2581-KIT-NS.html

thank you, takes the fun out of building one myself but I'll throw this under the backup plan.

[Conrad Hoffman]

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.

I'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.

[Alexei.Polkhanov]

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?

[G0HZU]

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.

[rob77]

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?

actually... +1

i'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

[Jay_Diddy_B]

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.html especially the articles listed in the description.

Also: http://www.noisecom.com/products/components/nc100-200-300-400-series-chips-and-diodes

Regards,

Jay_Diddy_B

[eurofox]

Special noise diodes:

http://www.rf-microwave.com/en/shop/0/446-noise-generator-diodes.html

[deano4265]

Some available on eBay at reasonable price http://www.ebay.com/itm/161382941660?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

[Fraser]

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 working  At $23 built and tested, they are pretty good value for money.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=231273984135

I 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

[Alexei.Polkhanov]

Some available on eBay at reasonable price http://www.ebay.com/itm/161382941660?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649

I don't know what is inside that unit but that blue anodized aluminum box is not an adequate RF enclosure by any means.

[Jay_Diddy_B]

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 this



This 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

[TurboTom]

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

[daqq]

Ever built a working RF noise source?

Sure I did - it was supposed to be an amplifier though... it was just noisy 

[LaserSteve]

You might want to look at this thread, too...

https://www.eevblog.com/forum/rf-microwave/russian-noise-diodetubes-anyone-use-these/

Steve

[Zero999]

Incandescent lamp + suitable amplifier.

[Alexei.Polkhanov]

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?

[jh15]

Imac, or Apple laptop power supply.