I was wondering if it's possible to convert the signal from a standard coaxial tv jack, into hdmi, rca, or some other connection I could use with my receiver? Thanks

Yess.

That's the thing that the gubment is giving those $40 coupons out for so you can buy one when all the signals will be Hi Def after they convert all ther TV signals.

What can covert it and where can I buy it? can I make my own?

Oops sorry - that box converts digital to analog.

You need analog to digital like this -

http://cgi.ebay.com/Composite-Video-Analog-Audio-to-Digital-HDMI-Converter_W0QQitemZ370140885403QQcmdZViewItemQQims xZ20090107?IMSfp=TL090107146005r5682

http://tinyurl.com/939hrf

But all TV signal is scheduled to be converted to digital on 2/17/2009 so where will you get the analog TV signal?