6.5 for UHF and about 19.5 inches for an OK performing dual band VHF/UHF radio. Normally with a handheld radio the counterpoise (ground) is your own body as you are holding the HT. This is because ...

allows the pilot to use an existing VHF comm antenna with any hand-held VHF radio. According to EDMO, EXTenna Switch greatly extends the range and readability of most battery powered, hand-held ...