I use the below antenna for receiving with a software defined radio USB dongle. Can the antenna also be used for transmitting, if I hook it up to an HT? I'm guessing the dipole antenna should be fine, but I don't know if the UHF loop would create a problem? More broadly, is every receiving antenna capable of being using to transmit?
Absolutely not. First of all, the 300 to 75 ohm balun (either inside this antenna if it is fed with only 75 ohm out, or the external one if 300 ohm out) will vaporize with even a couple hundred mW of power going through it. Second of all, the antenna is not going to be matched and is going to be a horrible SWR match which can fry the radio.
You will likely fry the radio and the antenna if you try to transmit into a pair of rabbit ears.