Lots of people have said that RTL-SDR dongles that they have been receiving don't have ESD protection diodes on the antenna inputs, which makes them susceptible to damage, particularly when you hook larger, gain antennas to them. I had read many notes about the EZTV645 that I bought which indicated didn't have the BAV99 diodes. I took it for granted that mine wouldn't. But today, I decided to lever it open (it's really easy, just stick a thumbnail underneath and pop it open). Here's what mine looked like inside:
The little protection diode is there, right below the antenna connector. Cool.
I did some other testing with the standard antenna, since I didn't have the appropriate adapter to really try it with anything else. It picks up fairly strong signals, like this recording I made of the nearby NOAA weather radio station on 162.425Mhz:
I did a few tests. I unscrewed the tiny antenna from its base, and.. the signal was about the same. That suggests to me that the feedline is probably just about as good an antenna as the "antenna" proper. I pondered for a moment, and then attached an 18" piece of wire to the base of the antenna mount. This should be about 1/4 wave at 162Mhz. The signal was about six db stronger, with fewer drop outs. Next project: to build some real antennas. High on my list are antennas for the 2M hand band, the 1090Mhz ADS-B aircraft telemetry band, and the 137MHz satellite transmissions. Stay tuned.