Diy spdif cable. - Page 2 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 21st July 2004, 12:56 PM   #11
diyAudio Member
 
Join Date: Dec 2003
Location: Montreal
Quote:
Yes....if you are making your own.........you can make it anything that you want. As long as the TX, RXC, and cable impedances are all the same.
I though you could use any piece of crap(like I did, and there was no problem) to make one.
  Reply With Quote
Old 21st July 2004, 05:49 PM   #12
Giorgio is offline Giorgio  Italy
diyAudio Member
 
Join Date: Dec 2003
Location: Milan
Jocko,
You are right about antennas, I think that almost everyone knows that they are efficient only on a reduced band.

The MFJ-259, however, has a variable test oscillator and is able to measure complex impedence and SWR (and a lot of other related things) on a 1.7-170MHz range. Should be enough, in your view?

What I am not sure of, by the way, is if the SWR sensitivity is high enough. It is clear that 1 would be perfect, but what would be in your view an acceptable SWR, and on which range?

Many years ago, when I worked in telecom on baseband modems with biphase code the required bandwidth was considered twice the bitrate, but in my view this is ridiculously low, if we need precise edges. The eye pattern in fact was very rounded.

By the way, what TDR model have you? HP, isn't it?

Kind regards
Giorgio
  Reply With Quote
Old 21st July 2004, 11:30 PM   #13
Banned
 
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Default Correct-a-mundo......

As we say in Texas.

Yes, you would use an impeance bridge when measuring an antenna. And yes......I am old enough to remember the first MJF product..........along with the Omeag-T noise bridge. Almost went to work there after I moved to Texas.

However.........transmission lines are measured with TDRs, which are little more than a glorified step generator built into a very high speed 'scope. If you were stuck using an impedance bridge.......I would look to at least the seventh harmonic to see how low the rho (reflection coefficient) is.

On my fancy-schmancy SPDIF TX and RX boards.......the rho is around 0.02. Return loss greater than 30 dB, in other terms.

My TDR is an H-P......made in '63.....still working........bought military surplus......where it spent the first 30 years of its life at "Dickey Goober AFB", in Missouri.

Jocko
  Reply With Quote
Old 22nd July 2004, 07:21 AM   #14
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
Short question: anything wrong with F-type connectors/RG59 or 'sattelite' 75 ohm coax besides the not-so-reliable appearance if it's not going to be much fiddling around with it?
__________________
Deep down inside.
  Reply With Quote
Old 22nd July 2004, 08:19 AM   #15
Banned
 
Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Send a message via Yahoo to Elso Kwak
Red face F-Type connector

Quote:
Originally posted by lucpes
Short question: anything wrong with F-type connectors/RG59 or 'sattelite' 75 ohm coax besides the not-so-reliable appearance if it's not going to be much fiddling around with it?
Hi lucpes,
Yes they will work as my satelliete receiver is proving everyday.
The construction is sloppy as the center pin is the core of the cable and a pull on the cable will slip it out of the connector.
  Reply With Quote
Old 22nd July 2004, 07:59 PM   #16
Banned
 
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Not designed for repeated insertion/removal cycles.

Jocko
  Reply With Quote
Old 22nd July 2004, 11:38 PM   #17
diyAudio Member
 
CheffDeGaar's Avatar
 
Join Date: Feb 2003
Location: Safe and sound
Bas,

Elso's suggestion on TV/SAT cable works for me. But as our dear Jocko said, impedances must be matched all along the way, for start to end, including connectors. Making one's own SPDIF cable to achieve good performance doesn't make sense if you still use RCA connectors. IMHO, just begin to use 75 Ohms BNC connectors at both ends, and connect a 75 Ohms SAT cable between (Jocko prefers lengths > 1m, if I remember...) And make sure your TX and RX are 75 Ohms matched too (check the components on the PCBs). This includes replacing the existing input/output connectors on the equipments by 75 R BNC sockets. Once you have the BNC connectors, feel free to test any make of cable, provided its impedance is 75R... And keep the one you like the most.
If you want to be anal, get your hand on a 75R wideband reference load, calibrate your BNC-cable-BNC setup with the load, and TDR it...
But IMHO, your ears are your best measurement devices, and just try different existing cables. Of course you might want to diy one, but just keep in mind that you'll have to achieve a 75R impedance on a wide frequency range. You can find formulas on the web for various configurations of transmission lines, so take the configuration you find the most suitable for DIYing, and compute parametres to get the right impedance.

Just let your ears speak
__________________
/Cheff - Falling feels like flying, until you hit the ground
  Reply With Quote
Old 23rd July 2004, 12:35 AM   #18
diyAudio Member
 
Join Date: May 2002
Location: Plano , TX
Send a message via AIM to jewilson
CheffDeGaar,

My ears don't say anything but if they start Ií am going I'll have to see the doc about some better drugs....

Well, I do listen to Jocko when he talking about the SPDIF interface since he know what he's talking about. I know that difference his attention to detail has made in the sound of my systems. And round two is coming up....Right

Man, you don't have to be anal to test your designs with TDR or a spectrum analyzer. He know how to get the best results because he not guessing. Too much of this golden ear crap leads to poorly design equipment. Don't get me wrong, listening is the final proof. Having said that, if you don't know where to start, then you donít know where youíre going, then your lost.
__________________
Jim W.
  Reply With Quote
Old 23rd July 2004, 01:01 AM   #19
Banned
 
Join Date: Feb 2002
Location: As far from the NOSsers as possible
Default In theory.....

If all your impedances are amtched, then every cable should sound alike.

Ah....but we don't live in a perfect world.

As for the ears.....they tend to tell the truth, but we don't always know how to understand what it is telling us.

I think that I told this one before.....so I'll ty to be brief.

(Dragon Master ought to find this especially amusing.)

A big name audio guru from the West Coast made one of the silliest SPDIF cables that I have ever seen.

He could not understand how to make a proper build out resistor on th TX end, so he found out......by using his ears...that a 93 ohm cable sounded best. Lo and behold.......his ears then told him that it sounded better still with some goofy ham radio connector......also close to 93 ohms.

Because he was off by about 20 ohms too high on his TX impedance.

Too bad when you used in any other piece of gear that it sounded like dreck.

Only he wouldn't accept that, because:

It worked so well in his system.

True story.

Jocko
  Reply With Quote
Old 23rd July 2004, 11:36 AM   #20
Giorgio is offline Giorgio  Italy
diyAudio Member
 
Join Date: Dec 2003
Location: Milan
Default World is far from perfect...

In theory I pefectly agre, I have been up to few days ago a strong supporter of perfect 75 ohm alignment... Now I doubt of anything...

As per previois e-mail in same thread, at tnt-audio we have been testing a bunch (8) of digital cables, and the acustic tests results were perfectly aligned on various different systems and with different reviewers; by the way, I am told they are aligned with world consideration (I have stopped reading reviews.... unless I am very interested in the unit ;-))). The only problem is that if we assume that MFJ impedance measures are vaguely correct, the best wires from the sound point of view are at FAR, FAR away from 75ohm...

And I have definitely not only no explanation for this, but looking to the live SPDIF signal on my scope, the best cables seem to have the best signa form, which again maks sense but does not match with theory.

One explanation, in my view, could be in fact be that the terminations are not correct, but I have not checked yet...


br
Giorgio
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
SPDIF Audio Cable trunkmonkey Digital Line Level 13 26th February 2009 03:27 PM
spdif cable systemerror909 Digital Source 1 26th August 2008 05:15 PM
Adjustable spdif cable? smells like snake oil to me. OzMikeH Digital Source 10 8th February 2008 08:54 PM
Long cable length - SPDIF or analogue? johnm Digital Source 5 14th August 2007 09:17 PM


New To Site? Need Help?

All times are GMT. The time now is 02:54 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2