VHF antennas do not necessarily have more gain. In fact it's slightly easier to get more gain out of UHF antennas for technical reasons that I don't think you care about.
You cannot just pick up a random antenna like from your TV or your basement trash can and expect it to work properly. For every frequency range that you transmit on, you will need a different length antenna (matched to the proper frequency). An equation for antenna length is: 300=Frequency (in MHz) x Wavelength (in meters). You would then divide your wavelength by 4 if you want a quarter wave antenna, 8 if you want a 1/8th antenna etc.
I highly doubt your TV antenna will work unless it has been tuned to a frequency very close to what you want. Also, TV antennas are not designed to transmit signals (only receive) so it could be very sloppily matched and possibly destroy your radio if you try to put too much signal through it. I would strongly advise against it until you could give me more information on the antenna, what radio you have, what frequency you want to transmit on, and what radio service you are using.