On Fri, Mar 17, 2006 at 10:13:59AM +0000, Dieter wrote:
>> Assuming for the moment that most video displays take 75 Ohm inputs,
>> does someone make 75-to-50 Ohm matching transformers for BNC?
>
>
>response down to DC, and transformers can't do that. Matching transformers
>are mostly RF devices, and good ones work well over a few octaves.
You don't need flat response down to DC - video is designed to be AC-coupled, which is why you have the back porch on the line synch signal for your black level clamp to find and clamp to the local 0V. TV line rate is 15kHz, which sets the lowest frequency where you need a flat resonse.
The transformers would want to be transmission line transformers. the last one I made was flat from 50kHz to 150MHz, but it was 1:1 . Getting a 75R to 50R matching transmission line transformer would be rather tricky. There is a technique for doing it, though I don't know what it is.
"The article was in HAM RADIO, January 1986 issue; it was called "Radio Frequency Broadband Transformer, Add fractional turns ratio techniques
to your impedance matching arsenal".
The Patent is number 4,839,616 January 13, 1989. "
Posted on rec.radio.amateur.homebrew in the thread Balun by will Herzog on Wed, Feb 25 1998 at 12:00 am
--
Bill Sloman, Nijmegen
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