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Old 4th May 2003, 02:16 PM   #101
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Default Re: Late arrival, but still some things to say

[QUOTEBut if they are so hard to get, let me give you an idea, someone has talked about F-plugs.
They are very good, and they are 75 ohms.
What's more, the center pin is the cable's center pin.
----------------------------------------------
Yes, but they are the moct unreliable terminators I have come across. This applies to manufactured as well as home made versions (I am skilled). The centre pin looses contact with time because the design does not have the precision of 75Rs.
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Old 5th May 2003, 08:42 AM   #102
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Default Re: Re: Late arrival, but still some things to say

Quote:
Originally posted by Guido Tent


F plugs limit the variety of cables to be used (they require the - I think - 1 mm massive centre conductor.
Guido, it's not 1mm, it's less than that.
To me it seams more like 0.7 to 0.8mm.
Talking about massive, have you tried Supra Trico digital cable?
It's massive and it's excellent.
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Old 5th May 2003, 07:32 PM   #103
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Quote:
Originally posted by Pjotr


No, it comes from the radio electronics area. Mainly because vertical ground plane antennas were 50 ohms. The measurement industry has adopted it from this.

But if al this 75 ohm nick knack is a problem, why not use a 50 ohm system? 50 ohm drivers and receivers should be a snap for the serious DIY-selver.

But the F-connectors are a good solution. By using the accompanying 75 ohm cables you have also a low-cost low-loss high quality cable. It is available at any shop selling satellite-TV equipment.

Cheers
Hi,

Oh, that is very likely (you are probably older than I am)

They used N connectors in that application, not ?

I am not against 50 ohm, but the world has to turn (slightly....)

F connectors: The cables are OK, but not much variety in different brands.

all the best
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Old 6th May 2003, 02:43 AM   #104
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Default Main problem with Type F......

They are not designed for repeated insertion.

Jocko
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Old 6th May 2003, 11:04 AM   #105
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Default Re: Main problem with Type F......

Quote:
Originally posted by Jocko Homo
They are not designed for repeated insertion.

Jocko
Yes, but that is easilly solved in the female plug, you can adjust the contacts.
BNCs have that problem too, but it's more difficult to solve.
I had to remove the BNC female on my Audio Alchemy DDE v3.0 Dac, because of nasty interruptions in the sound.
The center contacts were relaxed...
And they get relaxed even without repeated insertion, as long as there's a plug connected.
I soldered Supra Trico cable directly on the Dac's circuit, where the BNC was.
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Old 8th May 2003, 07:06 PM   #106
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Quote:
Yes, but that is easilly solved in the female plug, you can adjust the contacts.
BNCs have that problem too, but it's more difficult to solve.
Iíve mounted several thousand BNCís and never encountered this problem. Anyway the 75 ohm BNCís have no isolation around the female contact so adjusting is easy. What is sometimes a problem is that the centre pin of the male contact can turn in the isolation. After many connects/disconnects the centre conductor of the coax will break from the pin due to turning when the centre conductor is made of stranded wire. With a solid centre conductor this is not a problem.

If you are looking for a really good 75 ohm connector that withstands many connects and disconnects go for LEMO. Not cheap but also not that expensive (app. $15)

http://www.lemo.com/
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File Type: jpg lemo coax-2.jpg (10.6 KB, 434 views)
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Old 8th May 2003, 08:56 PM   #107
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Smile Lemo

Quote:
Originally posted by Pjotr


Iíve mounted several thousand BNCís and never encountered this problem. Anyway the 75 ohm BNCís have no isolation around the female contact so adjusting is easy. What is sometimes a problem is that the centre pin of the male contact can turn in the isolation. After many connects/disconnects the centre conductor of the coax will break from the pin due to turning when the centre conductor is made of stranded wire. With a solid centre conductor this is not a problem.

If you are looking for a really good 75 ohm connector that withstands many connects and disconnects go for LEMO. Not cheap but also not that expensive (app. $15)

http://www.lemo.com/

Hi Pjotr,
Yes I concur, The Lemo system is the non-plus-ultra in connector sytems. But not universal.........
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Old 14th May 2003, 04:47 PM   #108
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BrianL,

The whole point of my original post was that if BNC's are good enough to be used in Digital HDTV facilites, then they are good enough for home digital audio. And that true 75 ohm connectors are not hard to aquire because they are widely used by the video industry.

You should note that all of my comments were in reference to Broadcast Video Production. I never tried to tell you what consumer products use.

If you have ever been to any facility that has to do with broadcast television, you will see hundreds or thousands of 75 ohm BNCs. They are not rare, they are easy to get. How do I know that they are true 75 ohm connectors? My co-workers test them using a TDR. They measure from 73 ohms to 76 ohms, we can even see the impedance changes caused by the dimples and weep holes on the center pin.

Where did I get the idea that baseband HDTV is 1.5 Giga Hertz? How about the specification from SMPTE, specifically SPMTE 292M, specs a bit rate of 1.485 Giga bits per second. That translates to a nominal bandwidth of 1.5 Giga Hertz, don't you agree?

Please read what I say and do not equate my comments about broadcast baseband HDTV to "the average PC monitor these days."

Here is some reference links for you:

The specs for an HDTV Video distribution amplifier.

http://www.nvision1.com/Prod/Process/SWB4211.asp

A good tutorial:

http://www.nvision1.com/Serv/RefLib/thebook2.pdf

And Belden's Cable Collage:

http://bwcecom.belden.com/college/college.htm

"Prepsterous!" No. Those are the facts and that is what I wrote.

Aud_Mot
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Old 14th May 2003, 05:27 PM   #109
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My co-workers test them using a TDR. They measure from 73 ohms to 76 ohms, we can even see the impedance changes caused by the dimples and weep holes on the center pin.

------------------------------------------------

Can you please explain what a TDR is, and the method of measurement?
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Old 14th May 2003, 09:28 PM   #110
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"Can you please explain what a TDR is, and the method of measurement?"

fmak,

TDR = Time Domain Reflectometry or Time Domain Reflectometer

Go to www.agilent.com, go to the search box, type in TDR and download Application Note AN1304 'Time Domain Reflectometry Theory'. I'm sure Tektronix have similar explanations.

James
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