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Electronics => Projects, Designs, and Technical Stuff => Topic started by: Deactivated-1 on October 08, 2022, 11:27:22 pm

Title: Input and output impedance standards for video signals?
Post by: Deactivated-1 on October 08, 2022, 11:27:22 pm
Is the input impedance the standard for all analog and digital signals, 75 ohms?
what about the output impedance, is there a standard output impedance for video?
Title: Re: Input and output impedance standards for video signals?
Post by: boB on October 08, 2022, 11:30:40 pm

AFAIK, yes.  75 Ohms  for input and output on video.

Title: Re: Input and output impedance standards for video signals?
Post by: Benta on October 08, 2022, 11:37:49 pm
Yep, 75 ohms for output, input and cable. Professional video uses 75-ohm BNC connectors for RGB/Sync. Dunno what you mean by digital video in this context?
Title: Re: Input and output impedance standards for video signals?
Post by: Terry Bites on October 09, 2022, 11:14:02 am
A standard is a standard . 75R is used to get greater bandwith that a 50R will give. A 75R cable is lossier but has lower group delay. 50R is narrow band. An FM radio broadcast may have a bandwith of 200kHz. SD video will need 4.35MHz

Digital video uses 110R, often sent over 75R using a matching transformer. It's worth learning how to tell a 50R BNC from a 75R BNC, a subtle difference.

Pro analog audio uses 600R as do copper  telephone lines.

You dont need an emitter resistor to gnd if you DC couple. Send a current not a voltage. Just drive the line from the emitter via a 75R. .Avoid caps if you can. Sag and such.  Video line drivers are very low cost items, they abound in consumer video kit. EG THS7316DRG4

Title: Re: Input and output impedance standards for video signals?
Post by: Benta on October 09, 2022, 06:37:41 pm
Quote from: ELS122 on October 09, 2022, 12:49:33 am
I mean video standards such as HDMI as digital.
So why do you ask about analog video? Wasting our time for fun?
Title: Re: Input and output impedance standards for video signals?
Post by: NiHaoMike on October 10, 2022, 01:59:46 am
Almost every digital video standard uses differential pairs with about 100 ohms impedance, the biggest exception being SDI which was meant to run digital video over existing analog video cables.
Title: Re: Input and output impedance standards for video signals?
Post by: Terry Bites on October 11, 2022, 06:43:54 pm
www.maximintegrated.com/jp/design/technical-documents/tutorials/1/1184.html (http://www.maximintegrated.com/jp/design/technical-documents/tutorials/1/1184.html)

There is always the ITU, founded by Napoleon III.  www.itu.int (http://www.itu.int)  Still owned an operated by petty dictators I imagine. Actually they're decrepit bond villains but I'm splitting hairs.
ISO/IEC JTC 1/SC 29

You used to have have to include a picture of a young woman looking back over her shoulder to demonstate video standards.
Standards have improved and thankfully this is no longer a requirement.

Title: Re: Input and output impedance standards for video signals?
Post by: Datman on October 13, 2022, 02:21:34 pm
With 39 or 180 ohms to gnd, output impedance will surely be lower than 39+39 or 180+68 ohms!