I've thought about putting on one of those shorty antennas, but the question always comes up. Are they that good? I've seen ones for $7, 12 and 24.
My first HHR I bought one off of EBay and it was a joke to install with the adapters that came with it. I didn't even try to see the reception from it. Sent it right back.
Don't know how to test signal strength of an antenna. The only test I can do is the strength of a radio station that is 50 miles from me. I live on Long Island and the station is from NYC.

 

I got mine from Stubby Antenna. I have this one. That was about 9 years ago. It does not pick up distant stations, but it's not terrible either. I live in a major metro area and don't listen to much local radio anyway. A couple of years ago it started to rust on the stem. One of these days I'll replace it.

 

With a shorter antenna, reception is a factor. But also your location to stations. Some stations for me are weak as is, shorty wouldn't work.

 

I know that your car body becomes part of your antenna. The windings of an OEN has X amount . This is where the quagmire comes in. Does a shorty one equal the OEM in windings ?

 

 

The length of an FM antenna is 1 meter. The height of the antenna is the determining factor, espcially with the built in amplifier. If you live in an area where 3 inches in height makes a difference in line-of-sight to the transmitting antenna it might make a difference.

Where did you hear anything about the car body being anything besides a ground plane?

 

It was something I read years ago. I took it as the ground plane made a bigger area for the antenna to get reception.
Some people have installed early Equinox antennas which are shorter and still had good reception.
Equinox is 11"
HHR is 16"
https://www.rockauto.com/en/moreinfo.php?pk=4684599&cc=1444478&jsn=591&jsn=591 &jsn=591
Rock Auto offers this also for the Equinox
https://www.rockauto.com/en/moreinfo.php?pk=4681644&cc=1444478&jsn=592&jsn=592
In the desription Of the second one from Rock Auto I take it as it's a power antenna , but I found a youtube of this part and it looks like it'e just a replacement mast.

 

The point I was trying to make is that the length of the wire not the length of the mast. If you can wrap a 1 meter wire around a 1 inch mast it would work.

 

That was my question before. "Does a shorty one equal the OEM in windings ?"

 

And answered in #6. The only difference the mast makes is elevation for line-of-site. Ground plane comes into the equation when they started making cars out of thinner gauge metal (mass).

The number of windings has nothing to do with it, just the length of the wire, it could be balled up as far as physics is concerned. ALL FM antennas are about 1 meter in length because that is the length of the radio wave it is designed to catch.