For the sake of audio
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PostPosted: Sun Feb 21, 2016 8:32 pm 

Joined: Mon Dec 13, 2004 3:29 pm
Posts: 4284
Location: Somewhere other than here.
"What does this have to do with audio?"

Nothing. Shut up and read.

A few days back, I was driving around, and saw a place called "XYZ Microwave", in some typical industrial park. Out of curiosity, I just had to stop in, and see what they were all about.

The sales engineer, that I talked to, was glad that someone stopped in, and knew what the stuff in the display case was, and did not ask if they fixed microwave ovens.

Well, there was one part I did not know. A cable had a connector that looked like an overgrown Type N connector. The thing that stood out was the center pin was not the typical pin. As opposed to the kind we see in BNCs and SMAs, the end was flat. This meant the mating connector also had a center pin with a flat end. The result is a broad contact area, as opposed to the usual male/female mating arrangement. They refer to this connector as a DIN connector. (How many different connectors are now known as "DIN"?)

This connector is now the standard, in cell phone world. And the reason is.......................

Passive Intermodulation Distortion.

Yes, those of us who work on stuff like this have long known the subtle diode effects, that can exist, is something that can cause problems, in certain situations. In this case, we are working with very low signal levels, over a very wide bandwidth, so there is enough energy that can cause this type of disturbance. No, I do not have any data on how much this lowers PIM, but there has to be enough to worry about, for this connector to the industry standard.

Yet, when someone claims they can hear a difference, between a clean and dirty RCA, the usual gang of suspects have a cow. While I personally do not claim to have heard this effect does not mean that it does not exist. Or that if it does exist, that it is audible. The fact someone claims they can hear it should give rise to curiosity. I thought that is how engineers think.

But, no, when it comes to audio, it is just audio, and we already know all there is to know about it. And there is no room for silliness, like this.


Audio is just audio, and everything is just "20 to 20". And why things like SPDIF cables give so many "experts" a cow.

It is just wire, right? And it only carries "20 to 20" data, so it only matters what it does at audio, right?

Well, no.

But, as I recently found out............

Someone asked someone that I know, who then told someone else that I know, who told someone else (and etc., etc.), about some stupid little cable, that we made, almost 25 years ago. Eventually, it got back to me.

Great. I was enjoying myself, not having to worry about any of the crap, any longer. But, no, folks still have to hound me, about this crap.

What is so hard to understand about a RF cable? How hard is it to understand that the TX, RX, and cable impedances should be matched? And just how hard is it to understand how a delay line works, even though I went out of my way, for over 20 years, to not point out a certain cable is a delay line?

How stupid are some of you people? Especially the ones with lots of education? It seems when it comes to audio that more book learnin' makes you more stupid.

Yes, I come from telecom, along with all of my weird friends, where conventional wisdom says that connectors do not matter, below 300 MHz. Too bad we all found out, decades ago, that connectors do matter. Impedance matters. Line length matters.

Maybe if the guy who designed SPDIF knew how it would be come to be used, he would have designed something where the clock could be better recovered, without all the jitter problems. But, as it was just intended as a test port, until the dorks in marketing got hold of it, that was not a consideration.

But, alas, that is not what we have to live with.

So, in this world that we have to live in.

In this world, we can use tricks, that have been known to an entire industry, long before any of us went to work in it. And one of those tricks is to use a pad, to get a better impedance match. Yet, when we mention this, we get tons of grief. Charlatans, who spent years saying we are lying and don't know what we are talking about, eventually try it, and find that they like it.

Then go on to use it, in their "products", and pretend they "invented" it. Jerks.

Of course, in between, they go on every forum they can find, and misrepresent what we said, making us look more stupid than we really are. (And we must be stupid, because we try to make a living, in audio, and none of us have fancy degrees.)

So, for the very last time...........

Pads do no lower jitter. Pads do prevent more jitter from being created, by a crappy impedance match. There is always going to be X amount of jitter created, just by the nature of the chain. We just found a way, without using any magic, to keep from generating more. Simple as that. End of story. Period. No more. Nada. Stop bothering us about it. (Either that, or I may have to no longer pay attention to buddies who have to tell me about this crap, every time someone gets their knickers in a knot.)

If the guys with lots of degrees can not figure this out, then they are not as smart as they think they are. To them, unless it appears in some peer-reviewed journal, it can not exist.

(Hate to tell them, I used to work on cutting-edge stuff, and none of it ever made its way into any journal. Period. We were too busy trying to make stuff work, to worry about telling everyone else what we were doing. Eventually, they would figure it out, on their own. Usually by buying the stuff we coerced various vendors to make, for us.)

The only people who are impressed by articles, in peer-reviewed journals, are the same folks who are impressed by the number of degrees, that someone has. And a lot of those people, with the fancy degrees, are some of the DUMBEST people I have ever worked with.

Book smarts; yes. Make it work smarts; nope, total losers.

Well, that is about all I have to say, other than don't bother me about any of this.

I am not going to reply to any posts. But, feel free to discuss this. Just leave me out of this. And don't e-mail me. I am staying out of all of this.

Just remember the folks who say none of this matters are pretty much the same folks who say jitter doesn't matter, and clocks.......blah, blah, blah........................please, spare me. None of you people, save one, know what the hell you are talking about. And even he knows enough not to argue about clocks, with me.

Of course, he is probably smarter than I am, because he has worried about PIM, long before I did.

But, that is because he still has a job, and he better worry about it!

Oh, I just remembered! (Getting old stinks.)

One of things I talked about, with Mr. Microwave Sales Engineer, is the new connectors that are being used, for frequencies up to 110 GHz. (We both remembered the days when "they" were talking about 18 & 22 GHz, to be used for short hops, where you could not a fiber run.) (More irony, because after "we" invented fiber optics, we all got fired, and replaced with "fiber engineers". How they found fiber engineers was a mystery, since they did not exist, when "we" invented fiber optics.)

Anyway, a lot of these connectors are only good for a few uses, and they are toast. But they are really expensive! Sucks, when that happens. But, because of the laws of physics, they can not last long.

Then there are cheap-@$$ connectors, like U. fl., which are cheap, for other reasons. Yet, the same laws of physics apply, and are only good for a very limited number of insertions.

Yet some of you want to put them on your alleged "low jitter" clocks. Some of you should know better. Some of you are just idiots, but we already knew that.

Why the hell anyone would use a connector, designed for 2 GHz (or so), with a limited number of uses, is beyond me. Just remember that what looks like a solid conductor at 2 GHz looks like nothing, at 11 MHz.

Sure....................makes a lot of sense....................

Audio. Some of you guys.....................

Screw you guys, I'm going home.

It isn't personal.

Well, a few instances, yes, it is. Best you live nowhere close to Texas.


(Kindly disregard any typos and what not, that might have been missed. Caught a few. I am not inspired enough to go through all of this, to make sure it is 100% correct. After a certain age, you no longer give a crap about that stuff.)

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PostPosted: Tue Feb 23, 2016 1:25 pm 

Joined: Mon May 09, 2005 6:11 pm
Posts: 590
Location: Gran sasso
Apc 7 ?

I've just ordered a some from, they will be a perfect fit for my interconnects!!

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PostPosted: Tue Feb 23, 2016 6:09 pm 
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Joined: Thu Jul 26, 2007 5:45 pm
Posts: 1086

Jocko Homo wrote:
Screw you guys, I'm going home.

Have fun.

I recently got a 2.5GHz analyser with tracking generator for the lab (that was the test gear budget for this year, last year we blew it on 'scopes). Before that we were at 500MHz analogue and digital 'scopes.

Stuff I tested I had done before where I thought I understood how and stuff under 250MHz to measures generally peachy, but some stuff I tried "seat off pants", well, still not terrible, but had I been able to analyse my designs at that level I'd have done better. Worst, I first had to learn to get this bleedin thing to show a straight line in fixture for a loopback...

Ciao T

"For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." Richard Feynman

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PostPosted: Tue Feb 23, 2016 7:45 pm 

Joined: Mon Dec 13, 2004 3:29 pm
Posts: 4284
Location: Somewhere other than here.
OK, turns out I was not 100% correct.

The female connector center pin is not flat.

It is called a 7/16 DIN connector.


7/16 DIN connectors are used in antenna systems where there are multiple transmitters using the same antenna or where a base station antenna is co-located with a large number of other transmitting antennas... These connectors produce lower inter-modulation distortion products and thus are specified at busy RF sites and in almost all trunking systems where multiple transmitters share a common antenna. Note that an antenna rated for low passive inter-modulation (PIM) performance must be used along with these connectors. It defeats the purpose of designing a low PIM antenna system if regular N connectors or a non-PIM rated antenna are used.

None of this matters.................nothing to see here................move right along................bits are bits...............blah, blah.

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PostPosted: Tue Feb 23, 2016 8:38 pm 

Joined: Thu Dec 30, 2004 10:50 pm
Posts: 978
Location: Minnesota
Now I'm intrigued.

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PostPosted: Tue Mar 08, 2016 10:10 pm 

Joined: Fri Feb 25, 2005 2:26 am
Posts: 53
Location: il
great story. thanks jocko.

(another ex-telecom survivor)

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