[SBE] Video DA Help

[Stu Casteel]

sounds like you are on the right track - I don't have my part numbers handy 
but there used to be 8500 series DA's for pulse (sync, blanking etc) as 
opposed to video but for most applications a video DA should work for sync 
- but a common problem I've come across in situations like yours is where 
there is a double termination (or worse - I've seen BNC-T's used to split 
the signal)  - I'd look at the sync with a o-scope and verify that it has 
correct levels and is not otherwise distorted (60Hz hum, cross talk etc.)

ah, older plants - especially those with less than adequate documentation 
and revolving engineers...

At 22:51 27-11-07 -0500, you wrote:

>Not a trick question.

>

>Prior to me, when an STM-85N card failed, the sync for that equipment was 

>picked from something close via a loop through.

>

>We now have marginal sync in Master Control. I have bought another eight 

>Video DAs and a frame (EBay is good). I have ordered 1000 feet of cable. 

>When the cable arrives, All the equipment in Master Control will have a 

>sync line run directly to a DA port.

>

>I guess the STM-85N cards are a hold over from earlier equipment. They 

>appear to be a mini frame sync.

>

>When I asked this question of GVG, they would not answer directly. They 

>acknowledged that loop through equipment was fine, with the end of line 

>terminated. But they could not tell me what the maximum recommended 

>equipments was.

>

>To be safe, I have invested in the DAs and cable. Now to find the time to 

>run the cable and document the cable runs!

>

>At least we do have a set of drawings. They have been partially updated 

>with additions and deletions. Another project that I do not have time for, 

>verifying the drawings!

>

>We have 16 STN-85N cards that only the CB outputs are being used from. I 

>hope to get all of these out of the rack and replace them with 8500 series 

>DA cards. We have had two of these fail recently and I find others that 

>have problems. Most of the ones with problems have the far end of the 

>cable disconnected from the equipment and the cable terminated.

>

>The fun of working in an older plant.

>

>Thanks

>73

>Glenn

>

>

>

>At 10:21 PM 11/27/07, you wrote:

>>is this a trick question?

>>

>>the "proper" the answer is one - with a 75 ohm termination

>>

>>- there is no real limitation (within a facility) to how many devices you 

>>can daisy chain as long as each is a non terminating loop through as long 

>>as the final device has the 75 ohm termination

>>

>>prudent engineering design dictates that you limit the number of devices 

>>in such a daisy chain as removal of any device in the chain will affect 

>>all of the devices until properly terminated again (think service 

>>interrupting and how the GM feels about make goods)

>>

>>At 21:48 27-11-07 -0500, you wrote:

>>>We are using GVG 8500 series Video DAs to distribute sync. How many 

>>>devices can I safely deliver sync to from one port of a video DA?

>>>

>>>Thank You

>>>

>>>Glenn Little

>>>Assistant Chief Engineer

>>>WCIV TV/DT

>>>WB4UIV

>>>

>>>

>>>

>>>

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>

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