Why do modern RF Modulators require AC power?

[rpiguy9907]

So I have been sorting through a large lot of vintage computers I acquired and am tired of being unable to test for lack of an RF Modulator. I went to Walmart and all the RF Modulators require AC power? Why?

 

I never remember having to power up the RF modulator when I hooked my 2600 or C64 into the family television...

 

Are the new ones better?

Edited April 19, 2018 by rpiguy9907

[jjh76]

The built-in modulators on the 2600 and C64 get power from the mobo. The tv<>game switchboxes often used with these didn't need power because they just had a manual switch to physically change the connection from the console to the antenna. Other systems like the TI-99/4A that had an external automatic switching modulator do need power, but usually get it through one of the pins on the system's A/V port. And of course, the 4-port 5200 used the modulator itself as the power input for the system.

 

The generic composite to RF modulators you can get at Walmart or other stores use basically the same circuit, but need their own power because they have no way to get it from the machine itself.

 

One thing though - if the systems you are testing have a single RCA jack instead of the 2 (video + mono audio) or 3(video+stereo) used for composite out, then it probably has a built-in modulator, you just need an RCA to coax adapter to hook it up to the tv's antenna input:

 

https://www.amazon.com/RiteAV-Female-F-Type-Coax-Adapter/dp/B000V1O1LM

Edited April 19, 2018 by jjh76

[rpiguy9907]

Brilliant answer. Thank you!

[jjh76]

Oops, made a mistake there, the 4-port 5200 got it's power through an automatic switchbox, the actual modulator is inside the system.

[+OLD CS1]

Quick correction, the TI-99's modulator is not self-switching, or if there was a version of one it is not common. They require manual switching but derive power from the computer.

 

I think it is just a matter of convenience. A simple DC power supply is easy to derive from AC power with a few components and does not require any additional hardware external to the box, usually. I have seen some modulators which require a 9V or 12V external power supply.

[Osgeld]

yea its getting power from somewhere either from the device since the modulator is in the system like the second post stated or from an external source