I screwed an Alta shorty onto the car at the dealership before I even signed the paperwork to take it home, and I've always had great reception.

 

Thank you Sowellman, that is what I thought, thanks for the confirmation! And I was thinking of the Alta 4" stubby

 

I have the longer of the Craven antennas. Out of curiosity I did a test. With my car parked in my drive in Carmel Valley, using a marginal radio station playing classical music (KBOQ) I tried the stock antenna, the Craven, and no antenna at all. I could hear no difference in the reception.

 

It WILL affect the AM stations, particularly the distant ones.

I'll say this though, the MINI antenna is the most amazing AM/FM antenna I've ever had on a car. OR, the HiFi radio has one of the best receiver circuits I've even seen. I get radio stations (AM: 1010 WINS, 660 The FAN, FM: 102.3 WBAB, ..) at my house which is very remote (120 miles) from the stations. I have NEVER picked up these stations from my house, and that includes my $5000 Denon receiver with a FM antenna on the roof of a 3 story house!!