The antenna is not (much) useable at any frequencies, but a rubber duck, basically an end fed dummy load that leaks a little, is more broadbanded than most people think.
You really need something like this
Seung SA2 Flexible Extended Range Antenna, Works for any hand held CB radio with a BNC connector, Improves signal, Flexible, Extends range (SA-2 SA 2 handheld SEUNGSA2 SEUNG-SA2)
Or better a telescopic ant like the cobra HA-TA or even better, one of the old radio shack center loaded telescopic, if you can find it.
The one they carry now is sold as a RX scanner antenna with TX on amateur bands with it lowered, but I suspect its the same thing I used to have.
A longer duck, like say 12 to 18 inches makes alot of difference as well.
BTW, running off the 9v battery pack, keys 3.8 watts according to my cheap power meter, at 27.185, at 25.615 was 3.4 watts and at 28.305 about 3.2. Its very broadbanded for what it is.
I used to have a 75-822 and a cobra hh-45, basically same radio. No TX at all below around 26.625, but would TX up to 28.305 with about 2 watts though