To clarify what Steve said, this antenna is essentially a 5/8 over 5/8 antenna on 440, and a half wave antenna (electrically) on 2M. Both of these antennas are high impedance when end fed. The base "coil" is a matching network that steps up the impedance on both bands so that the 50 ohm coax will match the high impedance radiator. They work pretty well, with 2M performance approaching that of a similar HW mobile antenna, and the UHF part very close to that of a single band 440 antenna. That accounts for their popularity. Most people will never notice a degradation, although there is a slight amount, probably around a dB or so.
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