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.
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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.
[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.
Re: Main problem with Type F......
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.
Jocko Homo said:
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.
I’ve mounted several thousand BNC’s and never encountered this problem. Anyway the 75 ohm BNC’s 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/
Attachments
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
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
"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
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
A TDR will generate a display that allows you to see all the reflections along a transmission line. Reflections are caused by unmatched impedences.
Example: A transmission line that is made up of 2 lengths of cable (with BNCs on each end, 4 BNCs total) and the 2 cables are coupled together using a BNC barrel.
The TDR will allow you to see where (as in meters) the coupler is and at what points along the transmission line has a changing impedance.
If you had a cable buried, or run a long length, you could use the TDR to tell you that the cable had been crushed 137 meters down the cable.
If you had a BNC connector that was 50 ohm instead of 75 ohms, the TDR would raise a big red flag.
That is how I know that true 75 ohm BNCs exist and are made by many differnt companies.
Regards,
Aud_Mot
Example: A transmission line that is made up of 2 lengths of cable (with BNCs on each end, 4 BNCs total) and the 2 cables are coupled together using a BNC barrel.
The TDR will allow you to see where (as in meters) the coupler is and at what points along the transmission line has a changing impedance.
If you had a cable buried, or run a long length, you could use the TDR to tell you that the cable had been crushed 137 meters down the cable.
If you had a BNC connector that was 50 ohm instead of 75 ohms, the TDR would raise a big red flag.
That is how I know that true 75 ohm BNCs exist and are made by many differnt companies.
Regards,
Aud_Mot
I totally second Aud_Mot's comments along the way here...
It is quite strange though, that any commercial effort to use better connectors has resulted in even queerer products, like Lemo's CAMAC connectors or even worse, - on the optical side, the silly Toslink fibers, instead of quality ST or SC.....
There is also th epossibillity to avoid the"cumbersome" coaxials, as high quality optical transceivers and cables are rather cheap and easily available...
It is quite strange though, that any commercial effort to use better connectors has resulted in even queerer products, like Lemo's CAMAC connectors or even worse, - on the optical side, the silly Toslink fibers, instead of quality ST or SC.....
There is also th epossibillity to avoid the"cumbersome" coaxials, as high quality optical transceivers and cables are rather cheap and easily available...
I just asked VdH what it would cost to replace the RCA connectors on my Triaxial cable with these connectors:
I use one BNC to RCA converter since my Cambridge DAC has a gold plated BNC chasis part. For my new transport I'm still looking for a BNC chasis connector.
An externally hosted image should be here but it was not working when we last tested it.
I use one BNC to RCA converter since my Cambridge DAC has a gold plated BNC chasis part. For my new transport I'm still looking for a BNC chasis connector.
fmak said:
Hi Fred
I did TDR on the outpt of XO3, it is below -25 dB over 100 MHz so very close to 75 ohm, hence it shows reflectins on a 50 ohm system
The ripple is very likely caused by on chip crosstalk of the reclocker. What you proabbaly measure is about 100 or 200 mV amplitude.
Will consider picogates, les inductances, less groundbounce
all the best
--------------------------------------------------------------------------fmak said:Does anyone know of a source of gold plated 75R BNC Plugs and sockets please. Some plugs are sold by Supra but they look like 50R. I am mainly interested in sockets. Manufacturers have them but no one else seems to sell 'em.
Thank you for the many responses. I have finally found the answer ie Vampire 75R BNC at about $7 ea. They are one piece in the sense that the cable is directly soldered to the + and - contacts. Very good.
I don't like the Vampire sockets that much; they are pcb mounts and looks too much like 50R with a centre teflon block on the contact.
I have found that the simple way to modify 50R connectors is to remove and chop off a section of the centre pin insulator. This is all the difference there is in some makes of BNCs.
That depends upon the antenna!
A 1/2 lambda dipole is 75R, but a 1/4 Marconi (ground-plane) antenna is 1/2 this i.e. 37.5R
A 3/4 wave ground plane gets close to 50R, IIRC, but has a vertical beamwidth with multiple lobes, hence the radiating element is usually shortened to 5/8 wave and a matching element added to compensate.
Sorry - bit OT, I used to love designing antenna's ;-)
Andy.
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