My little IN-13 Spectrum Analyser

[Paul Parry]

Hi All,

Rather than another clock ( not that I don't like making clocks! ) I thought I would have a go at a Nixie Spectrum Analyser.

Here's what I came up with. 18 channels and all analogue electronics. No DSP or FFT. 

Probably more work than needed on the supports for the IN-13's but that's me :)

https://www.youtube.com/watch?v=elgYdZZtmW8 

Cheers,

Paul

[gregebert]

Neat!

I'm surprised that the response on the IN-13's is pretty fast; I just assumed they were sluggish.

How much current did it take to get maximum-scale ? I can see from the video you get very close to the end.

When I did some bench testing on the ones I bought a few years ago, static testing above 3/4 scale often got weird behavior, such as lighting from the opposite end.

Did you ever encounter that ?

[threeneurons]

That's a beaut ! I have a current obsession with color organs. Going to make a couple with thyratrons. That plus neon, and my eyes definitely lit up !

IN-13's use 4.5mA max. x18 channels its 81mA, so its not really that bad.

What order filters ? Or trick it a little by upping the Q ?

[Nick]

Lovely as always, Paul.

Are you using a multiplexed switched capacitor filter like the ltc1059, or lots of distinct channels?

I only ask as I looked at something similar a couple of years ago - the traditional way was to use a whole bunch of individual discrete analogue bandpass filters. The approach I was looking at used a single switched capacitor filter that was analogue multiplexed across the bands I was interested in both in terms of the bandpass frequency and the output sample and hold. Used about 1/10th of the components.

Cheers

Nick

[John Smout]

> On 28 Feb 2018, at 01:26, Nick <gerbilp...@gmail.com> wrote:
>
> Lovely as always, Paul.
>
> Are you using a multiplexed switched capacitor filter like the ltc1059, or lots of distinct channels?

It’s lots of distinct channels - I laid out the PCB :)

John S

[Nick]

Top man as always, John!

Nice job, though - it looks quite beautiful. I'm wondering what folks' experience is with the lifespan of IN-13s?

Cheers

Nick

[Paul Parry]

Hi Nick,

I was quite surprised by the lifespan on the IN-13 tube.. someone did a forensic laboratory analysis https://www.saltechips.com/lab/the-shine-experiment/ and found if the tube was on continuously, it would take 14.7 years to reduce in brightness by 30% from new. 

The Issue with the IN-13 is they poison very quickly, if they display a static level for a week or so it is enough to poison them. However on the spectrum analyser they will never stay at a fixed point, so I'm not thinking that the lifespan is going to be much of an issue.

Cheers,

Paul

[Paul Parry]

Thank you, they take about 4mA for FSD, however they rarely need to go right to the top - a little reservoir capacitor helps.

The IN-13 has an extra lead, and has I guess like a pilot light at the bottom which helps the glow start at the right end. I've had a couple where the glow broke up, or did not reach the top of the tube, however you can burn them in just powered up for a couple of hours to fix that.

[Paul Parry]

No, current pull is not bad really, 125v and they are not all going to be lit all the time.

The filters are Fliege filters, seem to do the job ok.

[Jon D.]

I haven't done much of anything with filters, but isn't a Fliege filter a notch filter.  How did you turn it into a bandpass filter?  Apologies if this is a dumb question.

[Paul Parry]

It is indeed a notch filter, all that happens is that I get a DC level out of the filter, which then feeds into a comparator chain, which effectively inverts it. 

[Jon D.]

I like your description.  Inverting a DC level makes sense.  Then you have to have the inverted notch voltage drive your IN-13 to the max at the center frequency of the notch filter.  I suppose I was thinking too much about the frequency bandwidth of the bandpass.  18 somewhat narrow notches for the 18 audio channels up to 15KHz is probably a decent approximation for the audio range of frequencies.  The video looks great !!

Thanks.

[Robert L]

Hi Paul,

 

I've lost count of how many times I've viewed your video...

A very nice job indeed!

Best,

Bob L.