FM/AM Tuner under around $500


I am looking to purchse a tuner but I do not really know the terminology involved or what the numbers associated with those words actually mean. If anybody can help on the following list it would be appreciated.

Selectivity:

Harmonic Distortion:

Separation:

S/N Ratio:

Capture Ratio:

Also if you have any product ideas for me to look and that as well ($500 range)
bianchi27
thanks for your input guys, very informative. I know I want to go digital and put tuning in stations above sound quality (although both are important). My main purpose is too get as many public radio stations as possible. There is great station about 45 mins to 1 hr from me but they have a weak signal.
Especially for the weak signal, getting a good directional FM antenna well above your roof--especially with a rotor, correctly aimed--this will make the most difference. Within the tuner, it's sensitivity that makes the most difference for far away stations. (lower number is better).

Best bang for the tuner buck, especially in distance reception would be a vintage tuner that has been modified, resulting in excellent sensitivity. Here is just one place to look:

http://www.antennaperformance.com/

....sell modded vintage tuners, giving you excellent reception for your $. They also sell high performance FM antennas.

I'm not associated. There are other people/companies, too. But my point is that restored & modified vintage would work best with your budget.
the analog transmissions are terrible in sa.the djs have to mush to play with..resulting in over modulation=distortion on fm. have called sabc a few times to tell them to lower it...works and back to distortion a few days later...gave up!
I use the digital transmissions like dmx on sat.take the analog output from the decoder to the amp...and wow...my hk sounds acceptable.picked up a fisher 77 retro tuner today, makes the hk tuner sound ugh.so another toy on top of the pile..and believe me it is so sensitive a one inch antenna pulls stereo 100%...now thats is something which i have to see with any avr.
radio has been my life since 14, crystal sets to the latest icoms, kenwoods..yaesu's etc.have around 7 transceivers and love hf, vhf, uhf and 27.555 with 100w pep on ssb with a processor is fun when the ionosphere opens up for us..