Analyser required suggestions and rev bias diode noise gen.

[Malcolm T]

In the process here of building a very simple spectrum analyser, and now need to download an audio spectrum analyser. I looked at Xanalyser but this requires what i think extra files or system to make it work ?. Is there another free for linux program that anyone can recommend that does not need extra programs to run or am i missing something ?.

Also any suggestions for a common diode for the noise generator , a general purpose NPN tranny works fine but any other suggestions please for diodes, has anyone else here built one ?.

Thanks.

[Terry_VK5TM]

Most any general purpose silicon diode will work for the noise generator, just play with the current through it to optimise the amount of noise it generates.

Even some zener diodes can get very noisy (but can also be a pain to set up).

Can't help with the software side of your Q.

[Radio Wrangler]

Zener diodes do indeed generate noise, but they tend to be rather high capacitance with big junction cross sectional areas to dissipate heat. The C spoils their HF noise output.

An old trick is to avalanche the base/emitter junction of an RF/microwave bipolar transistor. Keep the current low, else the part will fail.

There is an old HP journal on the development of the HP 346 family of noise sources which is quite informative. Noise/Com inc sold noise diodes on the open market. The HP dopdes had special processing with exceptionally strong doping in an area around the junction to discourage dopant migration. Some of the diodes in HP sources were made by Metellics inc. but I don't think they are catalogue items.

The HP N4000 series of 'smart' noise sources use the same diodes and RF structures as the 346 family did, with a few changes to dodge obsolete parts. The case is changes and an electronic calibration eeprom and digital thermometer are added for the smarts. These things are part of my past as a solo design project.

For diode mounting reasons, some of the sources have the diode mounted so that a negative voltage bias source is needed, and the pod includes a switched capacitor inverter to turn +28v into -28(ish) volts. Sounds bizarre, but it gave better bandwidth in the days of the 346 noise source, and the N4000 family follow it.

David

[Malcolm T]

Well, i will try a few diodes then .

[John_BS]

This works well.


John

[Malcolm T]

Thanks John , i have some diodes in my spares that look like a BAT17 glass package , hmmm.

[MrBungle]

If it’s one of the usual HF noise source designs don’t expect much flatness across the band. It’s better to use a tracking generator if you can. Saying that I managed to make useful measurements off a simple noise generator (LED + 2x 10dB 2n3866 stages) on HF. Output from my 7L12 via a low pass:



I don’t own this now. I found a NanoVNA more useful, more reliable and got less frowns from Mrs Bungle

[Malcolm T]

I looked at the Nano VNA , is that right 60 quid ?.

[MrBungle]

That's a bit expensive. I paid £36 for mine: https://www.ebay.co.uk/itm/323899986991

Look out for one with a battery, shielding and calibration bits mentioned and should be good.

[Malcolm T]

Thats mind blowing , Can it be run on linux . for a larger display ?.
Is it a direct order from China or are there stocks held in UK or europe ??.

[MrBungle]

Yes there's an application called NanoVNA-saver. Works on windows/mac/linux fine. I've tried it on CentOS 7 and use it on Windows 10 daily: https://github.com/mihtjel/nanovna-saver . Written in python. You just plug it in and point it at the correct virtual serial port and off it goes.

The one I ordered was drop shipped and took 3 working days to get here.

Absolutely amazing bit of kit

Action shot ... W7ZOI amplifier. This is connected to PC for remote control via NanoVNA saver



Resulting return loss and gain plot directly from NanoVNA saver:



It doesn't come with the blue case - I 3d printed that from a design online.

It will plot smith charts / SWR as well. I've used it for aligning filters and tuning up my 40m antenna so far with no problems. I had a RigExpert analyser but sold that pretty much straight away (and bought another oscilloscope that I didn't need )

[G0HZU_JMR]

has anyone else here built one ?

I've built a few over the years but these were designed as precision noise sources with a wide bandwidth, flat response and ultra low source VSWR in both on and off states. In every case I used a Noisecom diode as the initial noise source.

20 years ago it was possible to contact Noisecom and declare yourself as a radio ham and they would provide free samples of their noise diodes. I'm not sure that is possible today.

I keep meaning to evaluate the lower cost options using RF BJTs but never get around to it. One advantage of the Noisecom diodes is that they seem to be surprisingly stable over temperature. I'm not sure the same will apply to other diodes or BJTs that can be used as low cost alternatives.

The other option is to buy a noise source ready made from ebay. These include a basic noise source diode and a few MMICs to boost the noise level. Some of the early versions had poor thermal management and a lumpy response but they may have improved since. I doubt the noise level will be very stable over time and temperature but this might not matter for casual use.

If you want something semi serious for RF work then I'd recommend you try and get a Noisecom diode or equivalent.

[Malcolm T]

Well thanks for the info . I like the 3d case Mr Bungle .
I will look out for Noisecom.

[G0HZU_JMR]

The advantage of the Noisecom diodes is that they produce a high level of noise for 'just' a diode. A typical Noisecom diode might produce 31dB ENR. This makes it easy to make a low level noise source for receiver testing because the diode can be followed by an attenuator and this will ensure low VSWR in both on and off states for maybe 10dB ENR.

If you just want lots of noise over several hundred MHz then the ebay noise source PCBs are probably the lowest cost option as the PCB will contain a noise source and several wideband MMIC amplifiers to boost the noise.

If you just want to generate noise over AF through to the SW bands then you could do it with salvaged parts with a regular BJT or one of the jellybean diodes already mentioned. This would cost virtually nothing to make and it might even be quite stable over temperature and time.

Nano VNA seconded (thirded?) you don't even need a PC and mine came with a rechargeable battery, open, short, load (50Ohm) plugs and a link lead. About 30 quid too.

[Terry_VK5TM]

Noisecom page for the Noise diode.

https://www.noisecom.com/products/co...ips-and-diodes

Not sure if they still do the "Ham Operator" deal, but be sure to be sitting down when you ask for the price on a noise diode

[Craig Sawyers]

Generating noise from a reverse biased diode in avalanche mode was invented and patented by my friend and mentor Gordon Edge (RIP) in 1961 while working at Pye. Attached.

Craig

[G0HZU_JMR]

My noise sources were made with the 'economy' NC501/2 range from Noisecom. However, this was way back in the 1990s so I'm not sure what they cost now. They may be quite expensive nowadays.

https://www.noisecom.com/products/co...s-bite-modules

All that is inside the TO8 metal can version that I used was a regular glass packaged (leaded) diode and a SMD cap and a small leaded resistor. I took one of mine apart to see if I could improve the frequency response by removing the innards and fitting them all as SMD to a PCB. This boosted the bandwidth for a flat response to well over 1GHz.

There were a few articles in VHFcomms that described noise diodes and here are a couple of them:

http://www.vhfcomm.co.uk/Noise%20diode.pdf

https://www.rf-microwave.com/app/res...Comm_NW303.pdf

Note that the technical description for ENR in the first article doesn't look right to me. But this doesn't really matter for higher ENR numbers like 31dB. The correct definition/calculation matters a lot more if the ENR is as low as 5.6dB for example.

[G0HZU_JMR]

Here's a nice article about noise figure measurement using the Y factor method and a noise source. It also gives the correct definition for ENR for a noise source. There are also some nice worked examples.

https://scdn.rohde-schwarz.com/ur/pw...oiseFigure.pdf

This stuff is only of interest if you want to use the noise source to measure receiver noise figure but it may still be of interest and it may make you want to make a suitable noise source for this kind of work. I have a semi automated setup for noise figure measurement using a PC and a screened enclosure (with internal LNA) and a spectrum analyser that uses equations taken from this article. I use my various noise sources with it and I get very good results.

[Radio Wrangler]

In 2000, Agilent needed AN57/2 the paper on noise figure accuracy re-writing. Firstly to bring it in line with the new Noise Figure Analyser family with its matching noise sources, and also because some underlying issues needed fixing.

The new version was written by an outside contractor... Ian, G3SEK. now GM3SEK.

AN57 has been redone again since then to push noise figure built into network and spectrum analysers, but those can't quite equal the performance of the NFA. So you may have to search around a bit. I think there's a copy or a link on Ian's site.

HP journal has an article on Howard Swain's HP 8970A and noise sources.

David