I bought a 1/4 wave vertical at HRO today with a mag mount for the car. Yes, I should have got something with some gain instead, but I decided to go cheap. Eventually I'll buy a Diamond X-6000 for the receive antenna for the repeater, but not this week.
I hooked the transmitter up to the UHF antenna on the corner of the garage (A Diamond V2000, which has 8.4 dB gain on 430 MHz). I measured the transmitter as best I could on the SA and it seems to be generating about 5 dBm or so. With some feedline loss, I'll assume that the net gain of the antenna system is 8 dB, so that gives us a total of 13 dBm - 20 mW ERP.
I put the 1/4 wave vertical on the van, grabbed the 70 cm downconverter and the Insignia TV and went for a drive.... to the end of the block. Google Earth says that over flat ground, I got a maximum range of about 190 meters. I probably could have shouted that far.
So the distance record for amateur ATSC TV at the moment stands at just shy of two football fields.
The amplifier is coming.... someday....